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Ernst C, Andreassen PR, Giger GH, Nguyen BD, Gäbelein CG, Guillaume-Gentil O, Fattinger SA, Sellin ME, Hardt WD, Vorholt JA. Direct Salmonella injection into enteroid cells allows the study of host-pathogen interactions in the cytosol with high spatiotemporal resolution. PLoS Biol 2024; 22:e3002597. [PMID: 38684033 PMCID: PMC11057982 DOI: 10.1371/journal.pbio.3002597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 03/21/2024] [Indexed: 05/02/2024] Open
Abstract
Intestinal epithelial cells (IECs) play pivotal roles in nutrient uptake and in the protection against gut microorganisms. However, certain enteric pathogens, such as Salmonella enterica serovar Typhimurium (S. Tm), can invade IECs by employing flagella and type III secretion systems (T3SSs) with cognate effector proteins and exploit IECs as a replicative niche. Detection of flagella or T3SS proteins by IECs results in rapid host cell responses, i.e., the activation of inflammasomes. Here, we introduce a single-cell manipulation technology based on fluidic force microscopy (FluidFM) that enables direct bacteria delivery into the cytosol of single IECs within a murine enteroid monolayer. This approach allows to specifically study pathogen-host cell interactions in the cytosol uncoupled from preceding events such as docking, initiation of uptake, or vacuole escape. Consistent with current understanding, we show using a live-cell inflammasome reporter that exposure of the IEC cytosol to S. Tm induces NAIP/NLRC4 inflammasomes via its known ligands flagellin and T3SS rod and needle. Injected S. Tm mutants devoid of these invasion-relevant ligands were able to grow in the cytosol of IECs despite the absence of T3SS functions, suggesting that, in the absence of NAIP/NLRC4 inflammasome activation and the ensuing cell death, no effector-mediated host cell manipulation is required to render the epithelial cytosol growth-permissive for S. Tm. Overall, the experimental system to introduce S. Tm into single enteroid cells enables investigations into the molecular basis governing host-pathogen interactions in the cytosol with high spatiotemporal resolution.
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Affiliation(s)
- Chantal Ernst
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | | | - Gabriel H. Giger
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Bidong D. Nguyen
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | | | | | - Stefan A. Fattinger
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
- Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
| | - Mikael E. Sellin
- Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
| | - Wolf-Dietrich Hardt
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Julia A. Vorholt
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
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2
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Giraud E, Baucheron S, Foubert I, Doublet B, Nishino K, Cloeckaert A. Major primary bile salts repress Salmonella enterica serovar Typhimurium invasiveness partly via the efflux regulatory locus ramRA. Front Microbiol 2024; 15:1338261. [PMID: 38410385 PMCID: PMC10895713 DOI: 10.3389/fmicb.2024.1338261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 01/29/2024] [Indexed: 02/28/2024] Open
Abstract
Bile represses Salmonella enterica serovar Typhimurium (S. Typhimurium) intestinal cell invasion, but it remains unclear which bile components and mechanisms are implicated. Previous studies reported that bile inhibits the RamR binding to the ramA promoter, resulting in ramA increased transcription, and that ramA overexpression is associated to decreased expression of type III secretion system 1 (TTSS-1) invasion genes and to impaired intestinal cell invasiveness in S. Typhimurium. In this study, we assessed the possible involvement of the ramRA multidrug efflux regulatory locus and individual bile salts in the bile-mediated repression of S. Typhimurium invasion, using Caco-2 intestinal epithelial cells and S. Typhimurium strain ATCC 14028s. Our results indicate that (i) major primary bile salts, chenodeoxycholate and its conjugated-derivative salts, cholate, and deoxycholate, activate ramA transcription in a RamR-dependent manner, and (ii) it results in repression of hilA, encoding the master activator of TTSS-1 genes, and as a consequence in the repression of cellular invasiveness. On the other hand, crude ox bile extract and cholate were also shown to repress the transcription of hilA independently of RamR, and to inhibit cell invasion independently of ramRA. Altogether, these data suggest that bile-mediated repression of S. Typhimurium invasion occurs through pleiotropic effects involving partly ramRA, as well as other unknown regulatory pathways. Bile components other than the bile salts used in this study might also participate in this phenomenon.
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Affiliation(s)
| | | | | | | | - Kunihiko Nishino
- Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
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3
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Koczerka M, Lantier I, Morillon M, Deperne J, Clamagirand CD, Virlogeux-Payant I, Grépinet O. From intestine to beyond: Salmonella entry factors display distinct transcription pattern upon infection in murine models. Open Biol 2024; 14:230312. [PMID: 38228171 DOI: 10.1098/rsob.230312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 12/14/2023] [Indexed: 01/18/2024] Open
Abstract
The infectious process of bacteria of the genus Salmonella requires the finely regulated use of various virulence factors. Among them, the type 3 secretion system-1 (T3SS-1) and the Rck and PagN invasins are involved in the internalization of the pathogen within eukaryotic cells, but their precise role in the host and in the pathogenic process is still poorly understood. In this study, we aimed to determine the kinetics of expression of these entry factors in a typhoid fever-like and a gastroenteritis model in mice by in vivo imaging using bioluminescent Salmonella Typhimurium reporter strains carrying chromosomal transcriptional fusions. Only pagN and T3SS-1 transcription has been clearly identified. Independently of the pathological model, the caecum was identified as the main transcription site of both pagN and the T3SS-1-encoding gene both at early and late stages of the infection. An intense transcription of pagN was also observed in deep organs in the typhoid fever-like model, while that of T3SS-1 remained quite sporadic in these organs, and mainly focused on the intestine all along the infection. This work will help to understand the respective role of these entry factors at the cellular level in the pathogenesis of Salmonella in vivo.
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Affiliation(s)
| | | | - Marie Morillon
- INRAE, Université de Tours, ISP, 37380, Nouzilly, France
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4
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López-Yglesias AH, Lu CC, Lai MA, Quarles EK, Zhao X, Hajjar AM, Smith KD. FlgM is required to evade NLRC4-mediated host protection against flagellated Salmonella. Infect Immun 2023; 91:e0025523. [PMID: 37638725 PMCID: PMC10501211 DOI: 10.1128/iai.00255-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 07/07/2023] [Indexed: 08/29/2023] Open
Abstract
Salmonella enterica serovar Typhimurium is a leading cause of gastroenteritis worldwide and a deadly pathogen in children, immunocompromised patients, and the elderly. Salmonella induces innate immune responses through the NLRC4 inflammasome, which has been demonstrated to have distinct roles during systemic and mucosal detections of flagellin and non-flagellin molecules. We hypothesized that NLRC4 recognition of Salmonella flagellin is the dominant protective pathway during infection. To test this hypothesis, we used wild-type, flagellin-deficient, and flagellin-overproducing Salmonella to establish the role of flagellin in mediating NLRC4-dependent host resistance during systemic and mucosal infections in mice. We observed that during the systemic phase of infection, Salmonella efficiently evades NLRC4-mediated innate immunity. During mucosal Salmonella infection, flagellin recognition by the NLRC4 inflammasome pathway is the dominant mediator of protective innate immunity. Deletion of flgM results in constitutive expression of flagellin and severely limits systemic and mucosal Salmonella infections in an NLRC4 inflammasome-dependent manner. These data establish that recognition of Salmonella's flagellin by the NLRC4 inflammasome during mucosal infection is the dominant innate protective pathway for host resistance against the enteric pathogen and that FlgM-mediated evasion of the NLRC4 inflammasome enhances virulence and intestinal tissue destruction.
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Affiliation(s)
| | - Chun-Chi Lu
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, Washington, USA
| | - Marvin A. Lai
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, Washington, USA
| | - Ellen K. Quarles
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, Washington, USA
| | - Xiaodan Zhao
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, Washington, USA
| | - Adeline M. Hajjar
- Department of Comparative Medicine, University of Washington, Seattle, Washington, USA
| | - Kelly D. Smith
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, Washington, USA
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5
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Nava-Galeana J, Núñez C, Bustamante VH. Proteomic analysis reveals the global effect of the BarA/SirA-Csr regulatory cascade in Salmonella Typhimurium grown in conditions that favor the expression of invasion genes. J Proteomics 2023; 286:104960. [PMID: 37451358 DOI: 10.1016/j.jprot.2023.104960] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Accepted: 06/27/2023] [Indexed: 07/18/2023]
Abstract
In many bacteria, the BarA/SirA and Csr regulatory systems control expression of genes encoding a wide variety of cellular functions. The BarA/SirA two-component system induces the expression of CsrB and CsrC, two small non-coding RNAs that sequester CsrA, a protein that binds to target mRNAs and thus negatively or positively regulates their expression. BarA/SirA and CsrB/C induce expression of the Salmonella Pathogenicity Island 1 (SPI-1) genes required for Salmonella invasion of host cells. To further investigate the regulatory role of the BarA/SirA and Csr systems in Salmonella, we performed LC-MS/MS proteomic analysis using the WT S. Typhimurium strain and its derived ΔsirA and ΔcsrB ΔcsrC mutants grown in SPI-1-inducing conditions. The expression of 164 proteins with a wide diversity, or unknown, functions was significantly affected positively or negatively by the absence of SirA and/or CsrB/C. Interestingly, 19 proteins were identified as new targets for SirA-CsrB/C. Our results support that SirA and CsrB/C act in a cascade fashion to regulate gene expression in S. Typhimurium in the conditions tested. Notably, our results show that SirA-CsrB/C-CsrA controls expression of proteins required for the replication of Salmonella in the intestinal lumen, in an opposite way to its control exerted on the SPI-1 proteins. SIGNIFICANCE: The BarA/SirA and Csr global regulatory systems control a wide range of cellular processes, including the expression of virulence genes. For instance, in Salmonella, BarA/SirA and CsrB/C positively regulate expression of the SPI-1 genes, which are required for Salmonella invasion to host cells. In this study, by performing a proteomic analysis, we identified 164 proteins whose expression was positively or negatively controlled by SirA and CsrB/C in SPI-1-inducing conditions, including 19 new possible targets of these systems. Our results support the action of SirA and CsrB/C in a cascade fashion to control different cellular processes in Salmonella. Interestingly, our data indicate that SirA-CsrB/C-CsrA controls inversely the expression of proteins required for invasion of the intestinal epithelium and for replication in the intestinal lumen, which suggests a role for this regulatory cascade as a molecular switch for Salmonella virulence. Thus, our study further expands the insight into the regulatory mechanisms governing the virulence and physiology of an important pathogen.
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Affiliation(s)
- Jessica Nava-Galeana
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico
| | - Cinthia Núñez
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico
| | - Víctor H Bustamante
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico.
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6
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Fels U, Willems P, De Meyer M, Gevaert K, Van Damme P. Shift in vacuolar to cytosolic regime of infecting Salmonella from a dual proteome perspective. PLoS Pathog 2023; 19:e1011183. [PMID: 37535689 PMCID: PMC10426988 DOI: 10.1371/journal.ppat.1011183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 08/15/2023] [Accepted: 06/19/2023] [Indexed: 08/05/2023] Open
Abstract
By applying dual proteome profiling to Salmonella enterica serovar Typhimurium (S. Typhimurium) encounters with its epithelial host (here, S. Typhimurium infected human HeLa cells), a detailed interdependent and holistic proteomic perspective on host-pathogen interactions over the time course of infection was obtained. Data-independent acquisition (DIA)-based proteomics was found to outperform data-dependent acquisition (DDA) workflows, especially in identifying the downregulated bacterial proteome response during infection progression by permitting quantification of low abundant bacterial proteins at early times of infection when bacterial infection load is low. S. Typhimurium invasion and replication specific proteomic signatures in epithelial cells revealed interdependent host/pathogen specific responses besides pointing to putative novel infection markers and signalling responses, including regulated host proteins associated with Salmonella-modified membranes.
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Affiliation(s)
- Ursula Fels
- iRIP unit, Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Ghent, Belgium
- VIB-UGent Center for Medical Biotechnology, Ghent, Belgium
| | - Patrick Willems
- iRIP unit, Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Ghent, Belgium
| | - Margaux De Meyer
- iRIP unit, Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Ghent, Belgium
- VIB-UGent Center for Medical Biotechnology, Ghent, Belgium
| | - Kris Gevaert
- VIB-UGent Center for Medical Biotechnology, Ghent, Belgium
- Department of Biomolecular Medicine, Ghent University, Ghent, Belgium
| | - Petra Van Damme
- iRIP unit, Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Ghent, Belgium
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7
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Heyman O, Yehezkel D, Ciolli Mattioli C, Blumberger N, Rosenberg G, Solomon A, Hoffman D, Bossel Ben-Moshe N, Avraham R. Paired single-cell host profiling with multiplex-tagged bacterial mutants reveals intracellular virulence-immune networks. Proc Natl Acad Sci U S A 2023; 120:e2218812120. [PMID: 37399397 PMCID: PMC10334762 DOI: 10.1073/pnas.2218812120] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Accepted: 05/24/2023] [Indexed: 07/05/2023] Open
Abstract
Encounters between host cells and intracellular bacterial pathogens lead to complex phenotypes that determine the outcome of infection. Single-cell RNA sequencing (scRNA-seq) is increasingly used to study the host factors underlying diverse cellular phenotypes but has limited capacity to analyze the role of bacterial factors. Here, we developed scPAIR-seq, a single-cell approach to analyze infection with a pooled library of multiplex-tagged, barcoded bacterial mutants. Infected host cells and barcodes of intracellular bacterial mutants are both captured by scRNA-seq to functionally analyze mutant-dependent changes in host transcriptomes. We applied scPAIR-seq to macrophages infected with a library of Salmonella Typhimurium secretion system effector mutants. We analyzed redundancy between effectors and mutant-specific unique fingerprints and mapped the global virulence network of each individual effector by its impact on host immune pathways. ScPAIR-seq is a powerful tool to untangle bacterial virulence strategies and their complex interplay with host defense strategies that drive infection outcome.
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Affiliation(s)
- Ori Heyman
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Dror Yehezkel
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Camilla Ciolli Mattioli
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Neta Blumberger
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Gili Rosenberg
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Aryeh Solomon
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Dotan Hoffman
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Noa Bossel Ben-Moshe
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
| | - Roi Avraham
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot7610001, Israel
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8
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Gül E, Enz U, Maurer L, Abi Younes A, Fattinger SA, Nguyen BD, Hausmann A, Furter M, Barthel M, Sellin ME, Hardt WD. Intraluminal neutrophils limit epithelium damage by reducing pathogen assault on intestinal epithelial cells during Salmonella gut infection. PLoS Pathog 2023; 19:e1011235. [PMID: 37384776 PMCID: PMC10337893 DOI: 10.1371/journal.ppat.1011235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 07/12/2023] [Accepted: 06/14/2023] [Indexed: 07/01/2023] Open
Abstract
Recruitment of neutrophils into and across the gut mucosa is a cardinal feature of intestinal inflammation in response to enteric infections. Previous work using the model pathogen Salmonella enterica serovar Typhimurium (S.Tm) established that invasion of intestinal epithelial cells by S.Tm leads to recruitment of neutrophils into the gut lumen, where they can reduce pathogen loads transiently. Notably, a fraction of the pathogen population can survive this defense, re-grow to high density, and continue triggering enteropathy. However, the functions of intraluminal neutrophils in the defense against enteric pathogens and their effects on preventing or aggravating epithelial damage are still not fully understood. Here, we address this question via neutrophil depletion in different mouse models of Salmonella colitis, which differ in their degree of enteropathy. In an antibiotic pretreated mouse model, neutrophil depletion by an anti-Ly6G antibody exacerbated epithelial damage. This could be linked to compromised neutrophil-mediated elimination and reduced physical blocking of the gut-luminal S.Tm population, such that the pathogen density remained high near the epithelial surface throughout the infection. Control infections with a ssaV mutant and gentamicin-mediated elimination of gut-luminal pathogens further supported that neutrophils are protecting the luminal surface of the gut epithelium. Neutrophil depletion in germ-free and gnotobiotic mice hinted that the microbiota can modulate the infection kinetics and ameliorate epithelium-disruptive enteropathy even in the absence of neutrophil-protection. Together, our data indicate that the well-known protective effect of the microbiota is augmented by intraluminal neutrophils. After antibiotic-mediated microbiota disruption, neutrophils are central for maintaining epithelial barrier integrity during acute Salmonella-induced gut inflammation, by limiting the sustained pathogen assault on the epithelium in a critical window of the infection.
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Affiliation(s)
- Ersin Gül
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Ursina Enz
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Luca Maurer
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Andrew Abi Younes
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Stefan A. Fattinger
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
- Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
| | - Bidong D. Nguyen
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Annika Hausmann
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
- reNEW – NNF Center for Stem Cell Medicine, University of Copenhagen, Denmark
| | - Markus Furter
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Manja Barthel
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Mikael E. Sellin
- Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
| | - Wolf-Dietrich Hardt
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland
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9
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Cruz E, Haeberle AL, Westerman TL, Durham ME, Suyemoto MM, Knodler LA, Elfenbein JR. Nonredundant Dimethyl Sulfoxide Reductases Influence Salmonella enterica Serotype Typhimurium Anaerobic Growth and Virulence. Infect Immun 2023; 91:e0057822. [PMID: 36722978 PMCID: PMC9933680 DOI: 10.1128/iai.00578-22] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 01/10/2023] [Indexed: 02/02/2023] Open
Abstract
Facultative anaerobic enteric pathogens can utilize a diverse array of alternate electron acceptors to support anaerobic metabolism and thrive in the hypoxic conditions within the mammalian gut. Dimethyl sulfoxide (DMSO) is produced by methionine catabolism and can act as an alternate electron acceptor to support anaerobic respiration. The DMSO reductase complex consists of three subunits, DmsA, DmsB, and DmsC, and allows bacteria to grow anaerobically with DMSO as an electron acceptor. The genomes of nontyphoidal Salmonella enterica encode three putative dmsABC operons, but the impact of the apparent genetic redundancy in DMSO reduction on the fitness of nontyphoidal S. enterica during infection remains unknown. We hypothesized that DMSO reduction would be needed for S. enterica serotype Typhimurium to colonize the mammalian gut. We demonstrate that an S. Typhimurium mutant with loss of function in all three putative DMSO reductases (ΔdmsA3) poorly colonizes the mammalian intestine when the microbiota is intact and when inflammation is absent. DMSO reduction enhances anaerobic growth through nonredundant contributions of two of the DMSO reductases. Furthermore, DMSO reduction influences virulence by increasing expression of the type 3 secretion system 2 and reducing expression of the type 3 secretion system 1. Collectively, our data demonstrate that the DMSO reductases of S. Typhimurium are functionally nonredundant and suggest DMSO is a physiologically relevant electron acceptor that supports S. enterica fitness in the gut.
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Affiliation(s)
- E. Cruz
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA
- Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, Wisconsin, USA
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - A. L. Haeberle
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA
| | - T. L. Westerman
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - M. E. Durham
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - M. M. Suyemoto
- Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - L. A. Knodler
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA
| | - J. R. Elfenbein
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
- Food Research Institute, University of Wisconsin-Madison, Madison, Wisconsin, USA
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10
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Abstract
The ability of bacteria to respond to changes in their environment is critical to their survival, allowing them to withstand stress, form complex communities, and induce virulence responses during host infection. A remarkable feature of many of these bacterial responses is that they are often variable across individual cells, despite occurring in an isogenic population exposed to a homogeneous environmental change, a phenomenon known as phenotypic heterogeneity. Phenotypic heterogeneity can enable bet-hedging or division of labor strategies that allow bacteria to survive fluctuating conditions. Investigating the significance of phenotypic heterogeneity in environmental transitions requires dynamic, single-cell data. Technical advances in quantitative single-cell measurements, imaging, and microfluidics have led to a surge of publications on this topic. Here, we review recent discoveries on single-cell bacterial responses to environmental transitions of various origins and complexities, from simple diauxic shifts to community behaviors in biofilm formation to virulence regulation during infection. We describe how these studies firmly establish that this form of heterogeneity is prevalent and a conserved mechanism by which bacteria cope with fluctuating conditions. We end with an outline of current challenges and future directions for the field. While it remains challenging to predict how an individual bacterium will respond to a given environmental input, we anticipate that capturing the dynamics of the process will begin to resolve this and facilitate rational perturbation of environmental responses for therapeutic and bioengineering purposes.
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11
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Park S, Jung B, Kim E, Yoon H, Hahn TW. Evaluation of Salmonella Typhimurium Lacking fruR, ssrAB, or hfq as a Prophylactic Vaccine against Salmonella Lethal Infection. Vaccines (Basel) 2022; 10:vaccines10091413. [PMID: 36146494 PMCID: PMC9506222 DOI: 10.3390/vaccines10091413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 08/23/2022] [Accepted: 08/23/2022] [Indexed: 11/16/2022] Open
Abstract
Non-typhoidal Salmonella (NTS) is one of the primary causes of foodborne gastroenteritis; occasionally, it causes invasive infection in humans. Because of its broad host range, covering diverse livestock species, foods of animal origin pose a critical threat of NTS contamination. However, there is currently no licensed vaccine against NTS infection. FruR, also known as Cra (catabolite repressor/activator), was initially identified as the transcriptional repressor of the fructose (fru) operon, and then found to activate or repress the transcription of many different genes associated with carbon and energy metabolism. In view of its role as a global regulator, we constructed a live attenuated vaccine candidate, ΔfruR, and evaluated its prophylactic effect against NTS infection in mice. A Salmonella Typhimurium mutant strain lacking fruR was defective in survival inside macrophages and exhibited attenuated virulence in infected mice. Immunization with the ΔfruR mutant stimulated the production of antibodies, including the IgG, IgM, and IgG subclasses, and afforded a protection of 100% to mice against the challenge of lethal infection with a virulent Salmonella strain. The prophylactic effect obtained after ΔfruR immunization was also validated by the absence of signs of hepatosplenomegaly, as these mice had comparable liver and spleen weights in comparison with healthy mice. These results suggest that the ΔfruR mutant strain can be further exploited as a promising vaccine candidate against Salmonella lethal infection.
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Affiliation(s)
- Soyeon Park
- Department of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University, Chuncheon 24341, Korea
| | - Bogyo Jung
- Department of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University, Chuncheon 24341, Korea
| | - Eunsuk Kim
- Department of Molecular Science and Technology, Ajou University, Suwon 16499, Korea
| | - Hyunjin Yoon
- Department of Molecular Science and Technology, Ajou University, Suwon 16499, Korea
- Correspondence: (H.Y.); (T.-W.H.)
| | - Tae-Wook Hahn
- Department of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University, Chuncheon 24341, Korea
- Correspondence: (H.Y.); (T.-W.H.)
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12
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Churchill MJ, Mitchell PS, Rauch I. Epithelial Pyroptosis in Host Defense. J Mol Biol 2022; 434:167278. [PMID: 34627788 PMCID: PMC10010195 DOI: 10.1016/j.jmb.2021.167278] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 09/17/2021] [Accepted: 09/25/2021] [Indexed: 12/28/2022]
Abstract
Pyroptosis is a lytic form of cell death that is executed by a family of pore-forming proteins called gasdermins (GSDMs). GSDMs are activated upon proteolysis by host proteases including the proinflammatory caspases downstream of inflammasome activation. In myeloid cells, GSDM pore formation serves two primary functions in host defense: the selective release of processed cytokines to initiate inflammatory responses, and cell death, which eliminates a replicative niche of the pathogen. Barrier epithelia also undergo pyroptosis. However, unique mechanisms are required for the removal of pyroptotic epithelial cells to maintain epithelial barrier integrity. In the following review, we discuss the role of epithelial inflammasomes and pyroptosis in host defense against pathogens. We use the well-established role of inflammasomes in intestinal epithelia to highlight principles of epithelial pyroptosis in host defense of barrier tissues, and discuss how these principles might be shared or distinctive across other epithelial sites.
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Affiliation(s)
- Madeline J Churchill
- Department of Molecular Microbiology & Immunology, Oregon Health and Science University, Portland, OR, USA
| | | | - Isabella Rauch
- Department of Molecular Microbiology & Immunology, Oregon Health and Science University, Portland, OR, USA.
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13
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Nozaki K, Li L, Miao EA. Innate Sensors Trigger Regulated Cell Death to Combat Intracellular Infection. Annu Rev Immunol 2022; 40:469-498. [PMID: 35138947 PMCID: PMC9614550 DOI: 10.1146/annurev-immunol-101320-011235] [Citation(s) in RCA: 59] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Intracellular pathogens pose a significant threat to animals. In defense, innate immune sensors attempt to detect these pathogens using pattern recognition receptors that either directly detect microbial molecules or indirectly detect their pathogenic activity. These sensors trigger different forms of regulated cell death, including pyroptosis, apoptosis, and necroptosis, which eliminate the infected host cell niche while simultaneously promoting beneficial immune responses. These defenses force intracellular pathogens to evolve strategies to minimize or completely evade the sensors. In this review, we discuss recent advances in our understanding of the cytosolic pattern recognition receptors that drive cell death, including NLRP1, NLRP3, NLRP6, NLRP9, NLRC4, AIM2, IFI16, and ZBP1. Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Kengo Nozaki
- Department of Immunology and Department of Molecular Genetics and Microbiology, Duke University, Durham, North Carolina, USA;
| | - Lupeng Li
- Department of Immunology and Department of Molecular Genetics and Microbiology, Duke University, Durham, North Carolina, USA; .,Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Edward A Miao
- Department of Immunology and Department of Molecular Genetics and Microbiology, Duke University, Durham, North Carolina, USA;
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14
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Fang Z, Méresse S. Endomembrane remodeling and dynamics in Salmonella infection. MICROBIAL CELL (GRAZ, AUSTRIA) 2022; 9:24-41. [PMID: 35127930 PMCID: PMC8796136 DOI: 10.15698/mic2022.02.769] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 12/08/2021] [Accepted: 12/10/2021] [Indexed: 11/13/2022]
Abstract
Salmonellae are bacteria that cause moderate to severe infections in humans, depending on the strain and the immune status of the infected host. These pathogens have the particularity of residing in the cells of the infected host. They are usually found in a vacuolar compartment that the bacteria shape with the help of effector proteins. Following invasion of a eukaryotic cell, the bacterial vacuole undergoes maturation characterized by changes in localization, composition and morphology. In particular, membrane tubules stretching over the microtubule cytoskeleton are formed from the bacterial vacuole. Although these tubules do not occur in all infected cells, they are functionally important and promote intracellular replication. This review focuses on the role and significance of membrane compartment remodeling observed in infected cells and the bacterial and host cell pathways involved.
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Affiliation(s)
- Ziyan Fang
- Aix Marseille University, CNRS, INSERM, CIML, Marseille, France
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15
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Bonfim-Melo A, Noordstra I, Gupta S, Chan AH, Jones MJK, Schroder K, Yap AS. Rapid lamellipodial responses by neighbor cells drive epithelial sealing in response to pyroptotic cell death. Cell Rep 2022; 38:110316. [PMID: 35108534 DOI: 10.1016/j.celrep.2022.110316] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 12/08/2021] [Accepted: 01/07/2022] [Indexed: 11/28/2022] Open
Abstract
Cell injury poses a substantial challenge for epithelia homeostasis. Several cellular processes preserve epithelial barriers in response to apoptosis, but less is known about other forms of cell death, such as pyroptosis. Here we use an inducible caspase-1 system to analyze how colon epithelial monolayers respond to pyroptosis. We confirm that sporadic pyroptotic cells are physically eliminated from confluent monolayers by apical extrusion. This is accompanied by a transient defect in barrier function at the site of the pyroptotic cells. By visualizing cell shape changes and traction patterns in combination with cytoskeletal inhibitors, we show that rapid lamellipodial responses in the neighbor cells are responsible for correcting the leakage and resealing the barrier. Cell contractility is not required for this resealing response, in contrast to the response to apoptosis. Therefore, pyroptosis elicits a distinct homeostatic response from the epithelium that is driven by the stimulation of lamellipodia in neighbor cells.
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Affiliation(s)
- Alexis Bonfim-Melo
- Division of Cell and Developmental Biology, The University of Queensland, St. Lucia, QLD 4072, Australia; The University of Queensland Diamantina Institute, Faculty of Medicine, The University of Queensland, Brisbane, QLD 4102, Australia.
| | - Ivar Noordstra
- Division of Cell and Developmental Biology, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Shafali Gupta
- Division of Cell and Developmental Biology, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Amy H Chan
- Division of Cell and Developmental Biology, The University of Queensland, St. Lucia, QLD 4072, Australia; Centre for Inflammatory Disease Research, Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Mathew J K Jones
- The University of Queensland Diamantina Institute, Faculty of Medicine, The University of Queensland, Brisbane, QLD 4102, Australia
| | - Kate Schroder
- Division of Cell and Developmental Biology, The University of Queensland, St. Lucia, QLD 4072, Australia; Centre for Inflammatory Disease Research, Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Alpha S Yap
- Division of Cell and Developmental Biology, The University of Queensland, St. Lucia, QLD 4072, Australia; Centre for Inflammatory Disease Research, Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia.
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16
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Peptidoglycan editing in non-proliferating intracellular Salmonella as source of interference with immune signaling. PLoS Pathog 2022; 18:e1010241. [PMID: 35077524 PMCID: PMC8815878 DOI: 10.1371/journal.ppat.1010241] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 02/04/2022] [Accepted: 01/01/2022] [Indexed: 02/07/2023] Open
Abstract
Salmonella enterica causes intracellular infections that can be limited to the intestine or spread to deeper tissues. In most cases, intracellular bacteria show moderate growth. How these bacteria face host defenses that recognize peptidoglycan, is poorly understood. Here, we report a high-resolution structural analysis of the minute amounts of peptidoglycan purified from S. enterica serovar Typhimurium (S. Typhimurium) infecting fibroblasts, a cell type in which this pathogen undergoes moderate growth and persists for days intracellularly. The peptidoglycan of these non-proliferating bacteria contains atypical crosslinked muropeptides with stem peptides trimmed at the L-alanine-D-glutamic acid-(γ) or D-glutamic acid-(γ)-meso-diaminopimelic acid motifs, both sensed by intracellular immune receptors. This peptidoglycan has a reduced glycan chain average length and ~30% increase in the L,D-crosslink, a type of bridge shared by all the atypical crosslinked muropeptides identified. The L,D-transpeptidases LdtD (YcbB) and LdtE (YnhG) are responsible for the formation of these L,D-bridges in the peptidoglycan of intracellular bacteria. We also identified in a fraction of muropeptides an unprecedented modification in the peptidoglycan of intracellular S. Typhimurium consisting of the amino alcohol alaninol replacing the terminal (fourth) D-alanine. Alaninol was still detectable in the peptidoglycan of a double mutant lacking LdtD and LdtE, thereby ruling out the contribution of these enzymes to this chemical modification. Remarkably, all multiple mutants tested lacking candidate enzymes that either trim stem peptides or form the L,D-bridges retain the capacity to modify the terminal D-alanine to alaninol and all attenuate NF-κB nuclear translocation. These data inferred a potential role of alaninol-containing muropeptides in attenuating pro-inflammatory signaling, which was confirmed with a synthetic tetrapeptide bearing such amino alcohol. We suggest that the modification of D-alanine to alaninol in the peptidoglycan of non-proliferating intracellular S. Typhimurium is an editing process exploited by this pathogen to evade immune recognition inside host cells. The peptidoglycan, built as a giant polymer of glycan chains crosslinked with short peptides, is essential for cell shape and survival in most bacteria. Its unique chemistry is recognized by innate immune receptors, thereby enabling neutralization of invading microbes. A striking feature of the peptidoglycan is its constant remodeling by a plethora of endogenous enzymes. In addition, some bacterial pathogens introduce structural modifications that interfere with immune recognition. These modifications have been characterized in pathogens mostly in laboratory nutrient media. Whether facultative intracellular pathogens modify peptidoglycan structure inside host cells, was unknown. The work presented here shows that non-proliferating Salmonella enterica serovar Typhimurium remodels the peptidoglycan structure in response to intracellular cues and that some of these modifications involve unprecedented changes as the presence of an amino alcohol that hampers activation of the master immune regulator NF-κB. Peptidoglycan editing might therefore empower persistence of bacterial pathogens in the intracellular niche.
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17
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Xu J, Wang J, Liu A, Zhang Y, Gao X. Structural and Functional Analysis of SsaV Cytoplasmic Domain and Variable Linker States in the Context of the InvA-SsaV Chimeric Protein. Microbiol Spectr 2021; 9:e0125121. [PMID: 34851139 PMCID: PMC8635156 DOI: 10.1128/spectrum.01251-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Accepted: 11/05/2021] [Indexed: 11/20/2022] Open
Abstract
The type III secretion (T3S) injectisome is a syringe-like protein-delivery nanomachine widely utilized by Gram-negative bacteria. It can deliver effector proteins directly from bacteria into eukaryotic host cells, which is crucial for the bacterial-host interaction. Intracellular pathogen Salmonella enterica serovar Typhimurium encodes two sets of T3S injectisomes from Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2), which are critical for its host invasion and intracellular survival, respectively. The inner membrane export gate protein, SctV (InvA in SPI-1 and SsaV in SPI-2), is the largest component of the injectisome and is essential for assembly and function of T3SS. Here, we report the 2.11 Å cryo-EM structure of the SsaV cytoplasmic domain (SsaVC) in the context of a full-length SctV chimera consisting of the transmembrane region of InvA, the linker of SsaV (SsaVL) and SsaVC. The structural analysis shows that SsaVC exists in a semi-open state and SsaVL exhibits two major orientations, implying a highly dynamic process of SsaV for the substrate selection and secretion in a full-length context. A biochemical assay indicates that SsaVL plays an essential role in maintaining the nonameric state of SsaV. This study offers near atomic-level insights into how SsaVC and SsaVL facilitate the assembly and function of SsaV and may lead to the development of potential anti-virulence therapeutics against T3SS-mediated bacterial infection. IMPORTANCE Type III secretion system (T3SS) is a multicomponent nanomachine and a critical virulence factor for a wide range of Gram-negative bacterial pathogens. It can deliver numbers of effectors into the host cell to facilitate the bacterial host infection. Export gate protein SctV, as one of the engines of T3SS, is at the center of T3SS assembly and function. In this study, we show the high-resolution atomic structure of the cytosolic domain of SctV in the nonameric state with variable linker conformations. Our first observation of conformational changes of the linker region of SctV and the semi-open state of the cytosolic domain of SctV in the full-length context further support that the substrate selection and secretion process of SctV is highly dynamic. These findings have important implications for the development of therapeutic strategies targeting SctV to combat T3SS-mediated bacterial infection.
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Affiliation(s)
- Jinghua Xu
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Jiuqing Wang
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Aijun Liu
- Shanghai Fifth People's Hospital and Shanghai Key Laboratory of Medical Epigenetics, International Co-laboratory of Medical Epigenetics and Metabolism (Ministry of Science and Technology), Institutes of Biomedical Sciences, Fudan University, Shanghai, China
| | - Yanqing Zhang
- Shanghai Fifth People's Hospital and Shanghai Key Laboratory of Medical Epigenetics, International Co-laboratory of Medical Epigenetics and Metabolism (Ministry of Science and Technology), Institutes of Biomedical Sciences, Fudan University, Shanghai, China
| | - Xiang Gao
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
- School of Life Sciences, Shandong University, Qingdao, China
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18
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Fattinger SA, Sellin ME, Hardt WD. Salmonella effector driven invasion of the gut epithelium: breaking in and setting the house on fire. Curr Opin Microbiol 2021; 64:9-18. [PMID: 34492596 DOI: 10.1016/j.mib.2021.08.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 08/10/2021] [Accepted: 08/17/2021] [Indexed: 12/15/2022]
Abstract
Salmonella Typhimurium (S.Tm) is a major cause of diarrheal disease. The invasion into intestinal epithelial cells (IECs) is a central step in the infection cycle. It is associated with gut inflammation and thought to benefit S.Tm proliferation also in the intestinal lumen. Importantly, it is still not entirely clear how inflammation is elicited and to which extent it links to IEC invasion efficiency in vivo. In this review, we summarize recent findings explaining IEC invasion by type-three-secretion-system-1 (TTSS-1) effector proteins and discuss their effects on invasion and gut inflammation. In non-polarized tissue culture cells, the TTSS-1 effectors (mainly SopB/E/E2) elicit large membrane ruffles fueling cooperative invasion, and can directly trigger pro-inflammatory signaling. By contrast, in the murine gut, we observe discreet-invasion (mainly via the TTSS-1 effector SipA) and a prominent pro-inflammatory role of the host?"s epithelial inflammasome(s), which sense pathogen associated molecular patterns (PAMPs). We discuss why it has remained a major challenge to tease apart direct and indirect inflammatory effects of TTSS-1 effectors and explain why further research will be needed to fully determine their inflammation-modulating role(s).
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Affiliation(s)
- Stefan A Fattinger
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland; Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.
| | - Mikael E Sellin
- Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.
| | - Wolf-Dietrich Hardt
- Institute of Microbiology, Department of Biology, ETH Zurich, Zurich, Switzerland.
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19
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Powers TR, Haeberle AL, Predeus AV, Hammarlöf DL, Cundiff JA, Saldaña-Ahuactzi Z, Hokamp K, Hinton JCD, Knodler LA. Intracellular niche-specific profiling reveals transcriptional adaptations required for the cytosolic lifestyle of Salmonella enterica. PLoS Pathog 2021; 17:e1009280. [PMID: 34460873 PMCID: PMC8432900 DOI: 10.1371/journal.ppat.1009280] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 09/10/2021] [Accepted: 08/06/2021] [Indexed: 11/18/2022] Open
Abstract
Salmonella enterica serovar Typhimurium (S. Typhimurium) is a zoonotic pathogen that causes diarrheal disease in humans and animals. During salmonellosis, S. Typhimurium colonizes epithelial cells lining the gastrointestinal tract. S. Typhimurium has an unusual lifestyle in epithelial cells that begins within an endocytic-derived Salmonella-containing vacuole (SCV), followed by escape into the cytosol, epithelial cell lysis and bacterial release. The cytosol is a more permissive environment than the SCV and supports rapid bacterial growth. The physicochemical conditions encountered by S. Typhimurium within the epithelial cytosol, and the bacterial genes required for cytosolic colonization, remain largely unknown. Here we have exploited the parallel colonization strategies of S. Typhimurium in epithelial cells to decipher the two niche-specific bacterial virulence programs. By combining a population-based RNA-seq approach with single-cell microscopic analysis, we identified bacterial genes with cytosol-induced or vacuole-induced expression signatures. Using these genes as environmental biosensors, we defined that Salmonella is exposed to oxidative stress and iron and manganese deprivation in the cytosol and zinc and magnesium deprivation in the SCV. Furthermore, iron availability was critical for optimal S. Typhimurium replication in the cytosol, as well as entC, fepB, soxS, mntH and sitA. Virulence genes that are typically associated with extracellular bacteria, namely Salmonella pathogenicity island 1 (SPI1) and SPI4, showed increased expression in the cytosol compared to vacuole. Our study reveals that the cytosolic and vacuolar S. Typhimurium virulence gene programs are unique to, and tailored for, residence within distinct intracellular compartments. This archetypical vacuole-adapted pathogen therefore requires extensive transcriptional reprogramming to successfully colonize the mammalian cytosol.
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Affiliation(s)
- TuShun R. Powers
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Amanda L. Haeberle
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Alexander V. Predeus
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Disa L. Hammarlöf
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Jennifer A. Cundiff
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Zeus Saldaña-Ahuactzi
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Karsten Hokamp
- Smurfit Institute of Genetics, School of Genetics and Microbiology, Trinity College Dublin, Dublin, Ireland
| | - Jay C. D. Hinton
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Leigh A. Knodler
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
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Graef FA, Celiberto LS, Allaire JM, Kuan MTY, Bosman ES, Crowley SM, Yang H, Chan JH, Stahl M, Yu H, Quin C, Gibson DL, Verdu EF, Jacobson K, Vallance BA. Fasting increases microbiome-based colonization resistance and reduces host inflammatory responses during an enteric bacterial infection. PLoS Pathog 2021; 17:e1009719. [PMID: 34352037 PMCID: PMC8341583 DOI: 10.1371/journal.ppat.1009719] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 06/15/2021] [Indexed: 01/04/2023] Open
Abstract
Reducing food intake is a common host response to infection, yet it remains unclear whether fasting is detrimental or beneficial to an infected host. Despite the gastrointestinal tract being the primary site of nutrient uptake and a common route for infection, studies have yet to examine how fasting alters the host's response to an enteric infection. To test this, mice were fasted before and during oral infection with the invasive bacterium Salmonella enterica serovar Typhimurium. Fasting dramatically interrupted infection and subsequent gastroenteritis by suppressing Salmonella's SPI-1 virulence program, preventing invasion of the gut epithelium. Virulence suppression depended on the gut microbiota, as Salmonella's invasion of the epithelium proceeded in fasting gnotobiotic mice. Despite Salmonella's restored virulence within the intestines of gnotobiotic mice, fasting downregulated pro-inflammatory signaling, greatly reducing intestinal pathology. Our study highlights how food intake controls the complex relationship between host, pathogen and gut microbiota during an enteric infection.
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Affiliation(s)
- Franziska A. Graef
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Larissa S. Celiberto
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Joannie M. Allaire
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Mimi T. Y. Kuan
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Else S. Bosman
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Shauna M. Crowley
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Hyungjun Yang
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Justin H. Chan
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Martin Stahl
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Hongbing Yu
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Candice Quin
- Department of Biology, University of British Columbia, Kelowna, British Columbia, Canada
| | - Deanna L. Gibson
- Department of Biology, University of British Columbia, Kelowna, British Columbia, Canada
| | - Elena F. Verdu
- Farncombe Institute, McMaster University, Hamilton, Ontario, Canada
| | - Kevan Jacobson
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Bruce A. Vallance
- Department of Pediatrics, BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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21
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Pérez-Morales D, Nava-Galeana J, Rosales-Reyes R, Teehan P, Yakhnin H, Melchy-Pérez EI, Rosenstein Y, De la Cruz MA, Babitzke P, Bustamante VH. An incoherent feedforward loop formed by SirA/BarA, HilE and HilD is involved in controlling the growth cost of virulence factor expression by Salmonella Typhimurium. PLoS Pathog 2021; 17:e1009630. [PMID: 34048498 PMCID: PMC8192010 DOI: 10.1371/journal.ppat.1009630] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 06/10/2021] [Accepted: 05/10/2021] [Indexed: 12/02/2022] Open
Abstract
An intricate regulatory network controls the expression of Salmonella virulence genes. The transcriptional regulator HilD plays a central role in this network by controlling the expression of tens of genes mainly required for intestinal colonization. Accordingly, the expression/activity of HilD is highly regulated by multiple factors, such as the SirA/BarA two-component system and the Hcp-like protein HilE. SirA/BarA positively regulates translation of hilD mRNA through a regulatory cascade involving the small RNAs CsrB and CsrC, and the RNA-binding protein CsrA, whereas HilE inhibits HilD activity by protein-protein interaction. In this study, we show that SirA/BarA also positively regulates translation of hilE mRNA through the same mentioned regulatory cascade. Thus, our results reveal a paradoxical regulation exerted by SirA/BarA-Csr on HilD, which involves simultaneous opposite effects, direct positive control and indirect negative control through HilE. This kind of regulation is called an incoherent type-1 feedforward loop (I1-FFL), which is a motif present in certain regulatory networks and represents a complex biological problem to decipher. Interestingly, our results, together with those from a previous study, indicate that HilE, the repressor component of the I1-FFL reported here (I1-FFLSirA/BarA-HilE-HilD), is required to reduce the growth cost imposed by the expression of the genes regulated by HilD. Moreover, we and others found that HilE is necessary for successful intestinal colonization by Salmonella. Thus, these findings support that I1-FFLSirA/BarA-HilE-HilD cooperates to control the precise amount and activity of HilD, for an appropriate balance between the growth cost and the virulence benefit generated by the expression of the genes induced by this regulator. I1-FFLSirA/BarA-HilE-HilD represents a complex regulatory I1-FFL that involves multiple regulators acting at distinct levels of gene expression, as well as showing different connections to the rest of the regulatory network governing Salmonella virulence. To infect the intestine of a broad range of hosts, including humans, Salmonella is required to express a large number of genes encoding different cellular functions, which imposes a growth penalty. Thus, Salmonella has developed complex regulatory mechanisms that control the expression of virulence genes. Here we identified a novel and sophisticated regulatory mechanism that is involved in the fine-tuned control of the expression level and activity of the transcriptional regulator HilD, for the appropriate balance between the growth cost and the virulence benefit generated by the expression of tens of Salmonella genes. This mechanism forms an incoherent type-1 feedforward loop (I1-FFL), which involves paradoxical regulation; that is, a regulatory factor exerting simultaneous opposite control (positive and negative) on another factor. I1-FFLs are present in regulatory networks of diverse organisms, from bacteria to humans, and represent a complex biological problem to decipher. Interestingly, the I1-FFL reported here is integrated by ancestral regulators and by regulators that Salmonella has acquired during evolution. Thus, our findings reveal a novel I1-FFL of bacteria, which is involved in virulence. Moreover, our results illustrate the integration of ancestral and acquired factors into a regulatory motif, which can lead to the expansion of regulatory networks.
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Affiliation(s)
- Deyanira Pérez-Morales
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
- Consejo Nacional de Ciencia y Tecnología, Ciudad de México, México
| | - Jessica Nava-Galeana
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Roberto Rosales-Reyes
- Unidad de Investigación en Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Paige Teehan
- Department of Biochemistry and Molecular Biology, Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Helen Yakhnin
- Department of Biochemistry and Molecular Biology, Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Erika I. Melchy-Pérez
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Yvonne Rosenstein
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Miguel A. De la Cruz
- Unidad de Investigación Médica en Enfermedades Infecciosas y Parasitarias, Hospital de Pediatría, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Ciudad de México, México
| | - Paul Babitzke
- Department of Biochemistry and Molecular Biology, Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Víctor H. Bustamante
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
- * E-mail:
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Chong A, Cooper KG, Kari L, Nilsson OR, Hillman C, Fleming BA, Wang Q, Nair V, Steele-Mortimer O. Cytosolic replication in epithelial cells fuels intestinal expansion and chronic fecal shedding of Salmonella Typhimurium. Cell Host Microbe 2021; 29:1177-1185.e6. [PMID: 34043959 DOI: 10.1016/j.chom.2021.04.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 03/30/2021] [Accepted: 04/29/2021] [Indexed: 12/20/2022]
Abstract
Persistent and intermittent fecal shedding, hallmarks of Salmonella infections, are important for fecal-oral transmission. In the intestine, Salmonella enterica serovar Typhimurium (STm) actively invades intestinal epithelial cells (IECs) and survives in the Salmonella-containing vacuole (SCV) and the cell cytosol. Cytosolic STm replicate rapidly, express invasion factors, and induce extrusion of infected epithelial cells into the intestinal lumen. Here, we engineered STm that self-destruct in the cytosol (STmCytoKill), but replicates normally in the SCV, to examine the role of cytosolic STm in infection. Intestinal expansion and fecal shedding of STmCytoKill are impaired in mouse models of infection. We propose a model whereby repeated rounds of invasion, cytosolic replication, and release of invasive STm from extruded IECs fuels the high luminal density required for fecal shedding.
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Affiliation(s)
- Audrey Chong
- Laboratory of Bacteriology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
| | - Kendal G Cooper
- Laboratory of Bacteriology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
| | - Laszlo Kari
- Laboratory of Bacteriology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
| | - Olof R Nilsson
- Laboratory of Bacteriology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
| | - Chad Hillman
- Laboratory of Bacteriology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
| | - Brittany A Fleming
- Laboratory of Bacteriology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
| | - Qinlu Wang
- Bioinformatics and Computational Biosciences Branch, Office of Cyber Infrastructure and Computational Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20894, USA
| | - Vinod Nair
- Research Technologies Branch, Rocky Mountain Laboratories, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
| | - Olivia Steele-Mortimer
- Laboratory of Bacteriology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA.
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Salmonella enterica Serovar Typhimurium SPI-1 and SPI-2 Shape the Global Transcriptional Landscape in a Human Intestinal Organoid Model System. mBio 2021; 12:mBio.00399-21. [PMID: 34006652 PMCID: PMC8262845 DOI: 10.1128/mbio.00399-21] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The intestinal epithelium is a primary interface for engagement of the host response by foodborne pathogens, like Salmonella enterica Typhimurium. While the interaction of S Typhimurium with the mammalian host has been well studied in transformed epithelial cell lines or in the complex intestinal environment in vivo, few tractable models recapitulate key features of the intestine. Human intestinal organoids (HIOs) contain a polarized epithelium with functionally differentiated cell subtypes, including enterocytes and goblet cells and a supporting mesenchymal cell layer. HIOs contain luminal space that supports bacterial replication, are more amenable to experimental manipulation than animals and are more reflective of physiological host responses. Here, we use the HIO model to define host transcriptional responses to S Typhimurium infection, also determining host pathways dependent on Salmonella pathogenicity island-1 (SPI-1)- and -2 (SPI-2)-encoded type 3 secretion systems (T3SS). Consistent with prior findings, we find that S Typhimurium strongly stimulates proinflammatory gene expression. Infection-induced cytokine gene expression was rapid, transient, and largely independent of SPI-1 T3SS-mediated invasion, likely due to continued luminal stimulation. Notably, S Typhimurium infection led to significant downregulation of host genes associated with cell cycle and DNA repair, leading to a reduction in cellular proliferation, dependent on SPI-1 and SPI-2 T3SS. The transcriptional profile of cell cycle-associated target genes implicates multiple miRNAs as mediators of S Typhimurium-dependent cell cycle suppression. These findings from Salmonella-infected HIOs delineate common and distinct contributions of SPI-1 and SPI-2 T3SSs in inducing early host responses during enteric infection and reinforce host cell proliferation as a process targeted by Salmonella IMPORTANCE Salmonella enterica serovar Typhimurium (S Typhimurium) causes a significant health burden worldwide, yet host responses to initial stages of intestinal infection remain poorly understood. Due to differences in infection outcome between mice and humans, physiological human host responses driven by major virulence determinants of Salmonella have been more challenging to evaluate. Here, we use the three-dimensional human intestinal organoid model to define early responses to infection with wild-type S Typhimurium and mutants defective in the SPI-1 or SPI-2 type-3 secretion systems. While both secretion system mutants show defects in mouse models of oral Salmonella infection, the specific contributions of each secretion system are less well understood. We show that S Typhimurium upregulates proinflammatory pathways independently of either secretion system, while the downregulation of the host cell cycle pathways relies on both SPI-1 and SPI-2. These findings lay the groundwork for future studies investigating how SPI-1- and SPI-2-driven host responses affect infection outcome and show the potential of this model to study host-pathogen interactions with other serovars to understand how initial interactions with the intestinal epithelium may affect pathogenesis.
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Interactions between Salmonella and host macrophages - Dissecting NF-κB signaling pathway responses. Microb Pathog 2021; 154:104846. [PMID: 33711426 DOI: 10.1016/j.micpath.2021.104846] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 12/18/2020] [Accepted: 02/22/2021] [Indexed: 01/07/2023]
Abstract
Salmonella not only invades host cells, but also replicates intracellularly to cause a range of diseases, including gastroenteritis and systemic infections such as typhoid fever. The body's first line of defense against pathogens is the innate immune response system that can protect against Salmonella invasion and replication. Nuclear factor κB (NF-κB) is an important transcriptional regulator that plays an important role in host inflammatory responses to pathogens. Both the canonical and non-canonical NF-κB signaling pathways are activated by Salmonella in many different ways through its virulence factors, leading to the release of inflammatory factors and the activation of inflammatory responses in mammalian hosts. Equally, Salmonella, as an enteropathogen, has accordingly evolved strategies to disturb NF-κB activation, such as secreting some effector proteins by type III secretion systems as well as inducing host cells to express NF-κB pathway inhibitors, allowing it to colonize and persistently infect the hosts. This review focuses on how Salmonella activates NF-κB signaling pathway and the strategies used by Salmonella to interfere with the NF-κB pathway activation.
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High-Definition DIC Imaging Uncovers Transient Stages of Pathogen Infection Cycles on the Surface of Human Adult Stem Cell-Derived Intestinal Epithelium. mBio 2021; 13:e0002222. [PMID: 35100876 PMCID: PMC8805028 DOI: 10.1128/mbio.00022-22] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Interactions between individual pathogenic microbes and host tissues involve fast and dynamic processes that ultimately impact the outcome of infection. Using live-cell microscopy, these dynamics can be visualized to study, e.g., microbe motility, binding and invasion of host cells, and intrahost-cell survival. Such methodology typically employs confocal imaging of fluorescent tags in tumor-derived cell line infections on glass. This allows high-definition imaging but poorly reflects the host tissue's physiological architecture and may result in artifacts. We developed a method for live-cell imaging of microbial infection dynamics on human adult stem cell-derived intestinal epithelial cell (IEC) layers. These IEC layers are grown in apical imaging chambers, optimized for physiological cell arrangement and fast, but gentle, differential interference contrast (DIC) imaging. This allows subsecond visualization of both microbial and epithelial surface ultrastructure at high resolution without using fluorescent reporters. We employed this technology to probe the behavior of two model pathogens, Salmonella enterica serovar Typhimurium and Giardia intestinalis, at the intestinal epithelial surface. Our results reveal pathogen-specific swimming patterns on the epithelium and show that Salmonella lingers on the IEC surface for prolonged periods before host cell invasion, while Giardia uses circular swimming with intermittent attachments to scout for stable adhesion sites. The method even permits tracking of individual Giardia flagella, demonstrating that active flagellar beating and attachment to the IEC surface are not mutually exclusive. This work describes a generalizable and relatively inexpensive approach to resolving dynamic pathogen-IEC layer interactions, applicable even to genetically nontractable microorganisms. IMPORTANCE Knowledge of dynamic niche-specific interactions between single microbes and host cells is essential to understand infectious disease progression. However, advances in this field have been hampered by the inherent conflict between the technical requirements for high-resolution live-cell imaging on the one hand and conditions that best mimic physiological infection niche parameters on the other. Toward bridging this divide, we present a methodology for differential interference contrast (DIC) imaging of pathogen interactions at the apical surface of enteroid-derived intestinal epithelia, providing both high spatial and temporal resolution. This alleviates the need for fluorescent reporters in live-cell imaging and provides dynamic information about microbe interactions with a nontransformed, confluent, polarized, and microvilliated human gut epithelium. Using this methodology, we uncover previously unrecognized stages of Salmonella and Giardia infection cycles at the epithelial surface.
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Cooper KG, Chong A, Kari L, Jeffrey B, Starr T, Martens C, McClurg M, Posada VR, Laughlin RC, Whitfield-Cargile C, Garry Adams L, Bryan LK, Little SV, Krath M, Lawhon SD, Steele-Mortimer O. Regulatory protein HilD stimulates Salmonella Typhimurium invasiveness by promoting smooth swimming via the methyl-accepting chemotaxis protein McpC. Nat Commun 2021; 12:348. [PMID: 33441540 PMCID: PMC7806825 DOI: 10.1038/s41467-020-20558-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 11/27/2020] [Indexed: 12/31/2022] Open
Abstract
In the enteric pathogen Salmonella enterica serovar Typhimurium, invasion and motility are coordinated by the master regulator HilD, which induces expression of the type III secretion system 1 (T3SS1) and motility genes. Methyl-accepting chemotaxis proteins (MCPs) detect specific ligands and control the direction of the flagellar motor, promoting tumbling and changes in direction (if a repellent is detected) or smooth swimming (in the presence of an attractant). Here, we show that HilD induces smooth swimming by upregulating an uncharacterized MCP (McpC), and this is important for invasion of epithelial cells. Remarkably, in vitro assays show that McpC can suppress tumbling and increase smooth swimming in the absence of exogenous ligands. Expression of mcpC is repressed by the universal regulator H-NS, which can be displaced by HilD. Our results highlight the importance of smooth swimming for Salmonella Typhimurium invasiveness and indicate that McpC can act via a ligand-independent mechanism when incorporated into the chemotactic receptor array.
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Affiliation(s)
- Kendal G Cooper
- Laboratory of Bacteriology, Rocky Mountain Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, 59840, USA
| | - Audrey Chong
- Laboratory of Bacteriology, Rocky Mountain Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, 59840, USA
| | - Laszlo Kari
- Laboratory of Bacteriology, Rocky Mountain Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, 59840, USA
| | - Brendan Jeffrey
- NIAID Bioinformatics and Computational Biosciences Branch, Rocky Mountain Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, 59840, USA
| | - Tregei Starr
- Laboratory of Bacteriology, Rocky Mountain Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, 59840, USA
- GlaxoSmithKline, Hamilton, MT, 59840, USA
| | - Craig Martens
- NIAID RML Research Technologies Section, Genomics Unit, Rocky Mountain Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, 59840, USA
| | - Molly McClurg
- Department of Biological and Health Sciences, Texas A&M University-Kingsville, Kingsville, TX, 78363, USA
| | - Victoria R Posada
- Department of Biological and Health Sciences, Texas A&M University-Kingsville, Kingsville, TX, 78363, USA
| | - Richard C Laughlin
- Department of Biological and Health Sciences, Texas A&M University-Kingsville, Kingsville, TX, 78363, USA
| | - Canaan Whitfield-Cargile
- Department of Veterinary Large Animal Clinical Sciences, Texas A&M College of Veterinary Medicine and Biomedical Sciences, College Station, TX, 77843, USA
| | - L Garry Adams
- Department of Veterinary Pathobiology, Texas A&M College of Veterinary Medicine and Biomedical Sciences, College Station, TX, 77843, USA
| | - Laura K Bryan
- Department of Veterinary Pathobiology, Texas A&M College of Veterinary Medicine and Biomedical Sciences, College Station, TX, 77843, USA
| | - Sara V Little
- Department of Veterinary Pathobiology, Texas A&M College of Veterinary Medicine and Biomedical Sciences, College Station, TX, 77843, USA
| | - Mary Krath
- Department of Veterinary Pathobiology, Texas A&M College of Veterinary Medicine and Biomedical Sciences, College Station, TX, 77843, USA
| | - Sara D Lawhon
- Department of Veterinary Pathobiology, Texas A&M College of Veterinary Medicine and Biomedical Sciences, College Station, TX, 77843, USA
| | - Olivia Steele-Mortimer
- Laboratory of Bacteriology, Rocky Mountain Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, 59840, USA.
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Salmonella enterica Serovar Typhimurium Exploits Cycling through Epithelial Cells To Colonize Human and Murine Enteroids. mBio 2021; 12:mBio.02684-20. [PMID: 33436434 PMCID: PMC7844539 DOI: 10.1128/mbio.02684-20] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Enterobacterial pathogens infect the gut by a multistep process, resulting in colonization of both the lumen and the mucosal epithelium. Due to experimental constraints, it remains challenging to address how luminal and epithelium-lodged pathogen populations cross-feed each other in vivo Enteroids are cultured three-dimensional miniature intestinal organs with a single layer of primary intestinal epithelial cells (IECs) surrounding a central lumen. They offer new opportunities to study enterobacterial infection under near-physiological conditions, at a temporal and spatial resolution not attainable in animal models, but remain poorly explored in this context. We employed microinjection, time-lapse microscopy, bacterial genetics, and barcoded consortium infections to describe the complete infection cycle of Salmonella enterica serovar Typhimurium in both human and murine enteroids. Flagellar motility and type III secretion system 1 (TTSS-1) promoted Salmonella Typhimurium targeting of the intraepithelial compartment and breaching of the epithelial barrier. Strikingly, however, TTSS-1 also potently boosted colonization of the enteroid lumen. By tracing the infection over time, we identified a cycle(s) of TTSS-1-driven IEC invasion, intraepithelial replication, and reemergence through infected IEC expulsion as a key mechanism for Salmonella Typhimurium luminal colonization. These findings suggest a positive feed-forward loop, through which IEC invasion by planktonic bacteria fuels further luminal population expansion, thereby ensuring efficient colonization of both the intraepithelial and luminal niches.IMPORTANCE Pathogenic gut bacteria are common causes of intestinal disease. Enteroids-cultured three-dimensional replicas of the mammalian gut-offer an emerging model system to study disease mechanisms under conditions that recapitulate key features of the intestinal tract. In this study, we describe the full life cycle of the prototype gut pathogen Salmonella enterica serovar Typhimurium within human and mouse enteroids. We map the consecutive steps and define the bacterial virulence factors that drive colonization of luminal and epithelial compartments, as well as breaching of the epithelial barrier. Strikingly, our work reveals how bacterial colonization of the epithelium potently fuels expansion also in the luminal compartment, through a mechanism involving the death and expulsion of bacterium-infected epithelial cells. These findings have repercussions for our understanding of the Salmonella infection cycle. Moreover, our work provides a comprehensive foundation for the use of microinjected enteroids to model gut bacterial diseases.
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RIPK3-Dependent Recruitment of Low-Inflammatory Myeloid Cells Does Not Protect from Systemic Salmonella Infection. mBio 2020; 11:mBio.02588-20. [PMID: 33024046 PMCID: PMC7542371 DOI: 10.1128/mbio.02588-20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Macrophages employ multiple strategies to limit pathogen infection. For example, macrophages may undergo regulated cell death, including RIPK3-dependent necroptosis, as a means of combatting intracellular bacterial pathogens. However, bacteria have evolved mechanisms to evade or exploit immune responses. Salmonella is an intracellular pathogen that avoids and manipulates immune detection within macrophages. We examined the contribution of RIPK3 to Salmonella-induced macrophage death. Our findings indicate that noninvasive Salmonella does not naturally induce necroptosis, but it does so when caspases are inhibited. Moreover, RIPK3 induction (following caspase inhibition) does not impact host survival following Salmonella systemic infection. Finally, our data show that RIPK3 induction results in recruitment of low-inflammatory myeloid cells, which was unexpected, as necroptosis is typically described as highly inflammatory. Collectively, these data improve our understanding of pathogen-macrophage interactions, including outcomes of regulated cell death during infection in vivo, and reveal a potential new role for RIPK3 in resolving inflammation. Regulated macrophage death has emerged as an important mechanism to defend against intracellular pathogens. However, the importance and consequences of macrophage death during bacterial infection are poorly resolved. This is especially true for the recently described RIPK3-dependent lytic cell death, termed necroptosis. Salmonella enterica serovar Typhimurium is an intracellular pathogen that precisely regulates virulence expression within macrophages to evade and manipulate immune responses, which is a key factor in its ability to cause severe systemic infections. We combined genetic and pharmacological approaches to examine the importance of RIPK3 for S. Typhimurium-induced macrophage death using conditions that recapitulate bacterial gene expression during systemic infection in vivo. Our findings indicate that noninvasive S. Typhimurium does not naturally induce macrophage necroptosis but does so in the presence of pan-caspase inhibition. Moreover, our data suggest that RIPK3 induction (following caspase inhibition) does not impact host survival following S. Typhimurium infection, which differs from previous findings based on inert lipopolysaccharide (LPS) injections. Finally, although necroptosis is typically characterized as highly inflammatory, our data suggest that RIPK3 skews the peritoneal myeloid population away from an inflammatory profile to that of a classically noninflammatory profile. Collectively, these data improve our understanding of S. Typhimurium-macrophage interactions, highlight the possibility that purified bacterial components may not accurately recapitulate the complexity of host-pathogen interactions, and reveal a potential and unexpected role for RIPK3 in resolving inflammation.
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Salmonella enterica Infection of Murine and Human Enteroid-Derived Monolayers Elicits Differential Activation of Epithelium-Intrinsic Inflammasomes. Infect Immun 2020; 88:IAI.00017-20. [PMID: 32284374 DOI: 10.1128/iai.00017-20] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 04/06/2020] [Indexed: 02/07/2023] Open
Abstract
Recent studies have determined that inflammasome signaling plays an important role in driving intestinal epithelial cell (IEC) responses to bacterial infections, such as Salmonella enterica serovar Typhimurium. There are two primary inflammasome pathways, canonical (involving caspase-1) and noncanonical (involving caspase-4 and -5 in humans and caspase-11 in mice). Prior studies identified the canonical inflammasome as the major pathway leading to interleukin-18 (IL-18) release and restriction of S Typhimurium replication in the mouse cecum. In contrast, the human C2Bbe1 colorectal carcinoma cell line expresses little caspase-1 but instead utilizes caspase-4 to respond to S Typhimurium infection. Intestinal enteroid culture has enabled long-term propagation of untransformed IECs from multiple species, including mouse and human. Capitalizing on this technology, we used a genetic approach to directly compare the relative importance of different inflammatory caspases in untransformed mouse and human IECs and transformed human IECs upon S Typhimurium infection in vitro We show that caspase-1 is important for restricting intracellular S Typhimurium replication and initiating IL-18 secretion in mouse IECs but is dispensable in human IECs. In contrast, restriction of intracellular S Typhimurium and production of IL-18 are dependent on caspase-4 in both transformed and untransformed human IECs. Notably, cytosolic replication in untransformed cells from both species was less pronounced than in transformed human cells, suggesting that transformation may impact additional pathways that restrict S Typhimurium replication. Taken together, these data highlight the differences between mouse and human IECs and the utility of studying transformed and untransformed cells in parallel.
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Synergistic Effect of Eugenol and Probiotic Lactobacillus Plantarum Zs2058 Against Salmonella Infection in C57bl/6 Mice. Nutrients 2020; 12:nu12061611. [PMID: 32486242 PMCID: PMC7352263 DOI: 10.3390/nu12061611] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 05/24/2020] [Accepted: 05/27/2020] [Indexed: 12/13/2022] Open
Abstract
Previously, we showed the preventive effects of Lactobacillus plantarum ZS2058 (ZS2058) on Salmonella infection in murine models. In this work, we found that eugenol has a selective antibacterial effect, which inhibited Salmonella more than probiotics ZS2058 in vitro. It suggested a synergistic effect of them beyond their individual anti-Salmonella activity. We verified the conjecture in murine models. The results showed that the combination of ZS2058 and eugenol (CLPZE) significantly increased (p = 0.026) the survival rate of Salmonella-infected mice from 60% to 80% and the effect of CLPZE on preventing Salmonella-infection was 2-fold that of ZS2058 alone and 6-fold that of eugenol alone. CLPZE had a synergistic effect on inhibiting ST growth (the coefficient drug interaction ((CDI) = 0.829), reducing its invasiveness (CDI = 0.373) and downregulating virulence genes’ expression in vitro. CLPZE helped the host form a healthier gut ecosystem. CLPZE also elicited a stronger and earlier immune response to systemic infection. In conclusion, these obtained results suggest that ZS2058 and eugenol have a synergistic effect on preventing Salmonella infection and open new perspectives in the strategies of controlling the prevalence of Salmonella by combination of probiotics and functional food components.
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Crowley SM, Han X, Allaire JM, Stahl M, Rauch I, Knodler LA, Vallance BA. Intestinal restriction of Salmonella Typhimurium requires caspase-1 and caspase-11 epithelial intrinsic inflammasomes. PLoS Pathog 2020; 16:e1008498. [PMID: 32282854 PMCID: PMC7179941 DOI: 10.1371/journal.ppat.1008498] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2019] [Revised: 04/23/2020] [Accepted: 03/25/2020] [Indexed: 12/22/2022] Open
Abstract
We investigated the role of the inflammasome effector caspases-1 and -11 during Salmonella enterica serovar Typhimurium infection of murine intestinal epithelial cells (IECs). Salmonella burdens were significantly greater in the intestines of caspase-1/11 deficient (Casp1/11−/−), Casp1−/− and Casp11−/− mice, as compared to wildtype mice. To determine if this reflected IEC-intrinsic inflammasomes, enteroid monolayers were derived and infected with Salmonella. Casp11−/− and wildtype monolayers responded similarly, whereas Casp1−/− and Casp1/11−/− monolayers carried significantly increased intracellular burdens, concomitant with marked decreases in IEC shedding and death. Pretreatment with IFN-γ to mimic inflammation increased caspase-11 levels and IEC death, and reduced Salmonella burdens in Casp1−/− monolayers, while high intracellular burdens and limited cell shedding persisted in Casp1/11−/− monolayers. Thus caspase-1 regulates inflammasome responses in IECs at baseline, while proinflammatory activation of IECs reveals a compensatory role for caspase-11. These results demonstrate the importance of IEC-intrinsic canonical and non-canonical inflammasomes in host defense against Salmonella. Intestinal epithelial cells (IECs) are located at the interface between the gut lumen and the mucosal immune system and form the first layer of defense against the invasive enteric pathogen Salmonella enterica serovar Typhimurium. To prevent Salmonella, and other pathogens from establishing a foothold in the gut, the host mobilizes the inflammasome to selectively eject infected/compromised IECs from the epithelial layer into the intestinal lumen. This involves the activation of the inflammatory caspases; caspase-1 and -11. The individual contributions of each caspase to intestinal host defense, as well as the importance of IEC-intrinsic inflammasomes have not been previously defined, due to the lack of Casp1−/− mice as well as appropriate IEC-intrinsic defense models. Here, we determined that both caspases contribute to controlling Salmonella pathogen burdens and IEC shedding in the mouse intestine. Caspase-1 appears to play a larger role at baseline since caspase-11 expression must be first induced through proinflammatory signalling. Our data also highlights that IEC-intrinsic caspase activation is sufficient for infection-induced cell shedding and that the intestinal epithelium is a key site for inflammasome-mediated immune defense.
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Affiliation(s)
- Shauna M Crowley
- Department of Pediatrics, BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Xiao Han
- Department of Pediatrics, BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Joannie M Allaire
- Department of Pediatrics, BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Martin Stahl
- Department of Pediatrics, BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - Isabella Rauch
- Department of Medical Microbiology & Immunology, School of Medicine, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Leigh A Knodler
- Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Bruce A Vallance
- Department of Pediatrics, BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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Type III Secretion Effectors with Arginine N-Glycosyltransferase Activity. Microorganisms 2020; 8:microorganisms8030357. [PMID: 32131463 PMCID: PMC7142665 DOI: 10.3390/microorganisms8030357] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 02/27/2020] [Accepted: 02/29/2020] [Indexed: 01/31/2023] Open
Abstract
Type III secretion systems are used by many Gram-negative bacterial pathogens to inject proteins, known as effectors, into the cytosol of host cells. These virulence factors interfere with a diverse array of host signal transduction pathways and cellular processes. Many effectors have catalytic activities to promote post-translational modifications of host proteins. This review focuses on a family of effectors with glycosyltransferase activity that catalyze addition of N-acetyl-d-glucosamine to specific arginine residues in target proteins, leading to reduced NF-κB pathway activation and impaired host cell death. This family includes NleB from Citrobacter rodentium, NleB1 and NleB2 from enteropathogenic and enterohemorrhagic Escherichia coli, and SseK1, SseK2, and SseK3 from Salmonella enterica. First, we place these effectors in the general framework of the glycosyltransferase superfamily and in the particular context of the role of glycosylation in bacterial pathogenesis. Then, we provide detailed information about currently known members of this family, their role in virulence, and their targets.
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Intestinal epithelial NAIP/NLRC4 restricts systemic dissemination of the adapted pathogen Salmonella Typhimurium due to site-specific bacterial PAMP expression. Mucosal Immunol 2020; 13:530-544. [PMID: 31953493 PMCID: PMC7181392 DOI: 10.1038/s41385-019-0247-0] [Citation(s) in RCA: 80] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 11/18/2019] [Accepted: 12/10/2019] [Indexed: 02/07/2023]
Abstract
Inflammasomes can prevent systemic dissemination of enteropathogenic bacteria. As adapted pathogens including Salmonella Typhimurium (S. Tm) have evolved evasion strategies, it has remained unclear when and where inflammasomes restrict their dissemination. Bacterial population dynamics establish that the NAIP/NLRC4 inflammasome specifically restricts S. Tm migration from the gut to draining lymph nodes. This is solely attributable to NAIP/NLRC4 within intestinal epithelial cells (IECs), while S. Tm evades restriction by phagocyte NAIP/NLRC4. NLRP3 and Caspase-11 also fail to restrict S. Tm mucosa traversal, migration to lymph nodes, and systemic pathogen growth. The ability of IECs (not phagocytes) to mount a NAIP/NLRC4 defense in vivo is explained by particularly high NAIP/NLRC4 expression in IECs and the necessity for epithelium-invading S. Tm to express the NAIP1-6 ligands-flagella and type-III-secretion-system-1. Imaging reveals both ligands to be promptly downregulated following IEC-traversal. These results highlight the importance of intestinal epithelial NAIP/NLRC4 in blocking bacterial dissemination in vivo, and explain why this constitutes a uniquely evasion-proof defense against the adapted enteropathogen S. Tm.
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Autophagy Induction by a Small Molecule Inhibits Salmonella Survival in Macrophages and Mice. Antimicrob Agents Chemother 2019:AAC.01536-19. [PMID: 31591121 PMCID: PMC6879225 DOI: 10.1128/aac.01536-19] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Salmonella enterica is a natural bacterial pathogen of humans and animals that causes systemic infection or gastroenteritis. During systemic infection, Salmonella generally resides within professional phagocytes, typically macrophages, whereas gastroenteritis is caused by infection of epithelial cells. We are only beginning to understand which host pathways contribute to Salmonella survival in particular cell types. Salmonella enterica is a natural bacterial pathogen of humans and animals that causes systemic infection or gastroenteritis. During systemic infection, Salmonella generally resides within professional phagocytes, typically macrophages, whereas gastroenteritis is caused by infection of epithelial cells. We are only beginning to understand which host pathways contribute to Salmonella survival in particular cell types. We therefore sought to identify compounds that perturb Salmonella-host interactions using a chemical genetics approach. We found one small molecule, D61, that reduces Salmonella load in cell line and primary macrophages but has no effect on Salmonella growth in epithelial cells or rich medium. We determined that in macrophages, D61 induces LC3II, a marker of the autophagy pathway, and promotes aggregation of LC3II near Salmonella. We found that D61 antibacterial activity depends on the VPS34 complex and on ATG5. D61 also reduced Salmonella load in the spleens and livers of infected mice. Lastly, we demonstrate that D61 antibacterial activity in macrophages is synergistic with the antibiotic chloramphenicol but that this synergy is largely independent of the known autophagy-stimulating activity of chloramphenicol. Thus, a small molecule has antibacterial activity specifically in macrophages and mice based on the promotion of bacterial degradation by autophagy. These observations demonstrate the potential therapeutic utility of stimulating autophagy in cells and animals to curb infection.
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The Small RNA PinT Contributes to PhoP-Mediated Regulation of the Salmonella Pathogenicity Island 1 Type III Secretion System in Salmonella enterica Serovar Typhimurium. J Bacteriol 2019; 201:JB.00312-19. [PMID: 31262841 DOI: 10.1128/jb.00312-19] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 06/26/2019] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Typhimurium induces inflammatory diarrhea and bacterial uptake into intestinal epithelial cells using the Salmonella pathogenicity island 1 (SPI1) type III secretion system (T3SS). HilA activates transcription of the SPI1 structural components and effector proteins. Expression of hilA is activated by HilD, HilC, and RtsA, which act in a complex feed-forward regulatory loop. Many environmental signals and other regulators are integrated into this regulatory loop, primarily via HilD. After the invasion of Salmonella into host intestinal epithelial cells or during systemic replication in macrophages, the SPI T3SS is no longer required or expressed. We have shown that the two-component regulatory system PhoPQ, required for intracellular survival, represses the SPI1 T3SS mostly by controlling the transcription of hilA and hilD Here we show that PinT, one of the PhoPQ-regulated small RNAs (sRNAs), contributes to this regulation by repressing hilA and rtsA translation. PinT base pairs with both the hilA and rtsA mRNAs, resulting in translational inhibition of hilA, but also induces degradation of the rts transcript. PinT also indirectly represses expression of FliZ, a posttranslational regulator of HilD, and directly represses translation of ssrB, encoding the primary regulator of the SPI2 T3SS. Our in vivo mouse competition assays support the concept that PinT controls a series of virulence genes at the posttranscriptional level in order to adapt Salmonella from the invasion stage to intracellular survival.IMPORTANCE Salmonella is one of the most important food-borne pathogens, infecting over one million people in the United States every year. These bacteria use a needle-like device to interact with intestinal epithelial cells, leading to invasion of the cells and induction of inflammatory diarrhea. A complex regulatory network controls expression of the invasion system in response to numerous environmental signals. Here we explore the molecular mechanisms by which the small RNA PinT contributes to this regulation, facilitating inactivation of the system after invasion. PinT controls several important virulence systems in Salmonella, tuning the transition between different stages of infection.
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HilD induces expression of a novel Salmonella Typhimurium invasion factor, YobH, through a regulatory cascade involving SprB. Sci Rep 2019; 9:12725. [PMID: 31484980 PMCID: PMC6726612 DOI: 10.1038/s41598-019-49192-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 08/20/2019] [Indexed: 12/27/2022] Open
Abstract
HilD is an AraC-like transcriptional regulator encoded in the Salmonella pathogenicity island 1 (SPI-1), which actives transcription of many genes within and outside SPI-1 that are mainly required for invasion of Salmonella into host cells. HilD controls expression of target genes directly or by acting through distinct regulators; three different regulatory cascades headed by HilD have been described to date. Here, by analyzing the effect of HilD on the yobH gene in Salmonella enterica serovar Typhimurium (S. Typhimurium), we further define an additional regulatory cascade mediated by HilD, which was revealed by previous genome-wide analyses. In this regulatory cascade, HilD acts through SprB, a LuxR-like regulator encoded in SPI-1, to induce expression of virulence genes. Our data show that HilD induces expression of sprB by directly counteracting H-NS-mediated repression on the promoter region upstream of this gene. Then, SprB directly activates expression of several genes including yobH, slrP and ugtL. Interestingly, we found that YobH, a protein of only 79 amino acids, is required for invasion of S. Typhimurium into HeLa cells and mouse macrophages. Thus, our results reveal a novel S. Typhimurium invasion factor and provide more evidence supporting the HilD-SprB regulatory cascade.
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Chong A, Starr T, Finn CE, Steele-Mortimer O. A role for the Salmonella Type III Secretion System 1 in bacterial adaptation to the cytosol of epithelial cells. Mol Microbiol 2019; 112:1270-1283. [PMID: 31370104 DOI: 10.1111/mmi.14361] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/29/2019] [Indexed: 12/15/2022]
Abstract
Salmonella enterica serovar Typhimurium is a facultative intracellular pathogen that invades the intestinal epithelium. Following invasion of epithelial cells, Salmonella survives and replicates within two distinct intracellular niches. While all of the bacteria are initially taken up into a membrane bound vacuole, the Salmonella-containing vacuole or SCV, a significant proportion of them promptly escape into the cytosol. Cytosolic Salmonella replicates more rapidly compared to the vacuolar population, although the reasons for this are not well understood. SipA, a multi-function effector protein, has been shown to affect intracellular replication and is secreted by cytosolic Salmonella via the invasion-associated Type III Secretion System 1 (T3SS1). Here, we have used a multipronged microscopy approach to show that SipA does not affect bacterial replication rates per se, but rather mediates intra-cytosolic survival and/or initiation of replication following bacterial egress from the SCV. Altogether, our findings reveal an important role for SipA in the early survival of cytosolic Salmonella.
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Affiliation(s)
- Audrey Chong
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
| | - Tregei Starr
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
| | - Ciaran E Finn
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
| | - Olivia Steele-Mortimer
- Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
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PhoP-Mediated Repression of the SPI1 Type 3 Secretion System in Salmonella enterica Serovar Typhimurium. J Bacteriol 2019; 201:JB.00264-19. [PMID: 31182495 DOI: 10.1128/jb.00264-19] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 05/31/2019] [Indexed: 12/13/2022] Open
Abstract
Salmonella must rapidly adapt to various niches in the host during infection. Relevant virulence factors must be appropriately induced, and systems that are detrimental in a particular environment must be turned off. Salmonella infects intestinal epithelial cells using a type 3 secretion system (T3SS) encoded on Salmonella pathogenicity island 1 (SPI1). The system is controlled by three AraC-like regulators, HilD, HilC, and RtsA, which form a complex feed-forward loop to activate expression of hilA, encoding the main transcriptional regulator of T3SS structural genes. This system is tightly regulated, with many of the activating signals acting at the level of hilD translation or HilD protein activity. Once inside the phagosomes of epithelial cells, or in macrophages during systemic stages of disease, the SPI1 T3SS is no longer required or expressed. Here, we show that the PhoPQ two-component system, critical for intracellular survival, appears to be the primary mechanism by which Salmonella shuts down the SPI1 T3SS. PhoP negatively regulates hilA through multiple distinct mechanisms: direct transcriptional repression of the hilA promoter, indirect transcriptional repression of both the hilD and rtsA promoters, and activation of the small RNA (sRNA) PinT. Genetic analyses and electrophoretic mobility shift assays suggest that PhoP specifically binds the hilA promoter to block binding of activators HilD, HilC, and RtsA as a mechanism of repression.IMPORTANCE Salmonella is one of the most common foodborne pathogens, causing an estimated 1.2 million illnesses per year in the United States. A key step in infection is the activation of the bacterial invasion machinery, which induces uptake of the bacterium into epithelial cells and leads to induction of inflammatory diarrhea. Upon entering the vacuolar compartments of host cells, Salmonella senses an environmental transition and represses the invasion machinery with a two-component system relevant for survival within the vacuole. This adaptation to specific host niches is an important example of how signals are integrated for survival of the pathogen.
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Barcoded Consortium Infections Resolve Cell Type-Dependent Salmonella enterica Serovar Typhimurium Entry Mechanisms. mBio 2019; 10:mBio.00603-19. [PMID: 31113898 PMCID: PMC6529635 DOI: 10.1128/mbio.00603-19] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Salmonella enterica serovar Typhimurium (S.Tm) is a widespread and broad-host-spectrum enteropathogen with the capacity to invade diverse cell types. Still, the molecular basis for the host cell invasion process has largely been inferred from studies of a few selected cell lines. Our work resolves the mechanisms that Salmonellae employ to invade prototypical host cell types, i.e., human epithelial, monocyte, and macrophage cells, at a previously unattainable level of temporal and quantitative precision. This highlights efficient bacterium-driven entry into innate immune cells and uncovers a type III secretion system effector module that dominates active bacterial invasion of not only epithelial cells but also monocytes and macrophages. The results are derived from a generalizable method, where we combine barcoding of the bacterial chromosome with mixed consortium infections of cultured host cells. The application of this methodology across bacterial species and infection models will provide a scalable means to address host-pathogen interactions in diverse contexts. Bacterial host cell invasion mechanisms depend on the bacterium’s virulence factors and the properties of the target cell. The enteropathogen Salmonella enterica serovar Typhimurium (S.Tm) invades epithelial cell types in the gut mucosa and a variety of immune cell types at later infection stages. The molecular mechanism(s) of host cell entry has, however, been studied predominantly in epithelial cell lines. S.Tm uses a type three secretion system (TTSS-1) to translocate effectors into the host cell cytosol, thereby sparking actin ruffle-dependent entry. The ruffles also fuel cooperative invasion by bystander bacteria. In addition, several TTSS-1-independent entry mechanisms exist, involving alternative S.Tm virulence factors, or the passive uptake of bacteria by phagocytosis. However, it remains ill-defined how S.Tm invasion mechanisms vary between host cells. Here, we developed an internally controlled and scalable method to map S.Tm invasion mechanisms across host cell types and conditions. The method relies on host cell infections with consortia of chromosomally tagged wild-type and mutant S.Tm strains, where the abundance of each strain can be quantified by qPCR or amplicon sequencing. Using this methodology, we quantified cooccurring TTSS-1-dependent, cooperative, and TTSS-1-independent invasion events in epithelial, monocyte, and macrophage cells. We found S.Tm invasion of epithelial cells and monocytes to proceed by a similar MOI-dependent mix of TTSS-1-dependent and cooperative mechanisms. TTSS-1-independent entry was more frequent in macrophages. Still, TTSS-1-dependent invasion dominated during the first minutes of interaction also with this cell type. Finally, the combined action of the SopB/SopE/SopE2 effectors was sufficient to explain TTSS-1-dependent invasion across both epithelial and phagocytic cells.
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Lv Q, Chu X, Yao X, Ma K, Zhang Y, Deng X. Inhibition of the type III secretion system by syringaldehyde protects mice from Salmonella enterica serovar Typhimurium. J Cell Mol Med 2019; 23:4679-4688. [PMID: 31066220 PMCID: PMC6584516 DOI: 10.1111/jcmm.14354] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 03/20/2019] [Accepted: 04/10/2019] [Indexed: 11/28/2022] Open
Abstract
The invasiveness of Salmonella enterica serovar Typhimurium (S. Typhimurium) is closely associated with the Salmonella pathogenicity island (SPI)‐encoded type Ⅲ secretion system (T3SS), which can directly inject a series of effector proteins into eukaryotic cells to enable bacterial infection. In this study, syringaldehyde was identified as an effective inhibitor of the S. Typhimurium T3SS using an effector protein‐lactamase fusion reporter system. Syringaldehyde treatment could inhibit the expression of important effector proteins (SipA, SipB and SipC) at a concentration of 0.18 mM without affecting bacterial growth. Additionally, significant inhibition of bacterial invasion and cellular injury was observed following the syringaldehyde treatment in the co‐infection system of HeLa cells and S. Typhimurium. Furthermore, treatment with syringaldehyde provided systemic protection to mice infected with S. Typhimurium, reducing mortality (40.00%) and bacterial loads and relieving caecal damage and systemic inflammation. The results presented in this study indicate that syringaldehyde significantly affects T3SS activity and is a potential leading compound for treating S. Typhimurium infections.
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Affiliation(s)
- Qianghua Lv
- Department of Respiratory Medicine, First Hospital, Jilin University, Changchun, China.,Key Laboratory of Zoonosis Research, Ministry of Education, College of Veterinary Medicine, Institute of Zoonosis, Jilin University, Changchun, China
| | - Xiao Chu
- Department of Respiratory Medicine, First Hospital, Jilin University, Changchun, China.,Key Laboratory of Zoonosis Research, Ministry of Education, College of Veterinary Medicine, Institute of Zoonosis, Jilin University, Changchun, China
| | - Xinyu Yao
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Veterinary Medicine, Institute of Zoonosis, Jilin University, Changchun, China
| | - Kelong Ma
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Veterinary Medicine, Institute of Zoonosis, Jilin University, Changchun, China
| | - Yong Zhang
- Department of Respiratory Medicine, First Hospital, Jilin University, Changchun, China
| | - Xuming Deng
- Department of Respiratory Medicine, First Hospital, Jilin University, Changchun, China.,Key Laboratory of Zoonosis Research, Ministry of Education, College of Veterinary Medicine, Institute of Zoonosis, Jilin University, Changchun, China
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The Interplay between Salmonella enterica Serovar Typhimurium and the Intestinal Mucosa during Oral Infection. Microbiol Spectr 2019; 7. [PMID: 30953432 DOI: 10.1128/microbiolspec.bai-0004-2019] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Bacterial infection results in a dynamic interplay between the pathogen and its host. The underlying interactions are multilayered, and the cellular responses are modulated by the local environment. The intestine is a particularly interesting tissue regarding host-pathogen interaction. It is densely colonized by commensal microbes and a portal of entry for ingested pathogens. This necessitates constant monitoring of microbial stimuli in order to maintain homeostasis during encounters with benign microbiota and to trigger immune defenses in response to bacterial pathogens. Homeostasis is maintained by physical barriers (the mucus layer and epithelium), chemical defenses (antimicrobial peptides), and innate immune responses (NLRC4 inflammasome), which keep the bacteria from reaching the sterile lamina propria. Intestinal pathogens represent potent experimental tools to probe these barriers and decipher how pathogens can circumvent them. The streptomycin mouse model of oral Salmonella enterica serovar Typhimurium infection provides a well-characterized, robust experimental system for such studies. Strikingly, each stage of the gut tissue infection poses a different set of challenges to the pathogen and requires tight control of virulence factor expression, host response modulation, and cooperation between phenotypic subpopulations. Therefore, successful infection of the intestinal tissue relies on a delicate and dynamic balance between responses of the pathogen and its host. These mechanisms can be deciphered to their full extent only in realistic in vivo infection models.
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Passaris I, Cambré A, Govers SK, Aertsen A. Bimodal Expression of the Salmonella Typhimurium spv Operon. Genetics 2018; 210:621-635. [PMID: 30143595 PMCID: PMC6216589 DOI: 10.1534/genetics.118.300822] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 08/14/2018] [Indexed: 02/03/2023] Open
Abstract
The well-studied spv operon of Salmonellatyphimurium is important for causing full virulence in mice and both the regulation and function of the Spv proteins have been characterized extensively over the past several decades. Using quantitative single-cell fluorescence microscopy, we demonstrate the spv regulon to display a bimodal expression pattern that originates in the bimodal expression of the SpvR activator. The spv expression pattern is influenced by growth conditions and the specific Styphimurium strain used, but does not require Salmonella-specific virulence regulators. By monitoring real-time promoter kinetics, we reveal that SpvA has the ability to impart negative feedback on spvABCD expression without affecting spvR expression. Together, our data suggest that the SpvA protein counteracts the positive feedback loop imposed by SpvR, and could thus be responsible for dampening spvABCD expression and coordinating virulence protein production in time. The results presented here yield new insights in the intriguing regulation of the spv operon and adds this operon to the growing list of virulence factors exhibiting marked expression heterogeneity in Styphimurium.
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Affiliation(s)
- Ioannis Passaris
- Department of Microbial and Molecular Systems (MS), Katholieke Universiteit Leuven, 3001 Leuven, Belgium
| | - Alexander Cambré
- Department of Microbial and Molecular Systems (MS), Katholieke Universiteit Leuven, 3001 Leuven, Belgium
| | - Sander K Govers
- Department of Microbial and Molecular Systems (MS), Katholieke Universiteit Leuven, 3001 Leuven, Belgium
| | - Abram Aertsen
- Department of Microbial and Molecular Systems (MS), Katholieke Universiteit Leuven, 3001 Leuven, Belgium
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Westerman TL, Bogomolnaya L, Andrews-Polymenis HL, Sheats MK, Elfenbein JR. The Salmonella type-3 secretion system-1 and flagellar motility influence the neutrophil respiratory burst. PLoS One 2018; 13:e0203698. [PMID: 30204776 PMCID: PMC6133356 DOI: 10.1371/journal.pone.0203698] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Accepted: 08/24/2018] [Indexed: 11/28/2022] Open
Abstract
Neutrophils are innate immune response cells designed to kill invading microorganisms. One of the mechanisms neutrophils use to kill bacteria is generation of damaging reactive oxygen species (ROS) via the respiratory burst. However, during enteric salmonellosis, neutrophil-derived ROS actually facilitates Salmonella expansion and survival in the gut. This seeming paradox led us to hypothesize that Salmonella may possess mechanisms to influence the neutrophil respiratory burst. In this work, we used an in vitro Salmonella-neutrophil co-culture model to examine the impact of enteric infection relevant virulence factors on the respiratory burst of human neutrophils. We report that neutrophils primed with granulocyte-macrophage colony stimulating factor and suspended in serum containing complement produce a robust respiratory burst when stimulated with viable STm. The magnitude of the respiratory burst increases when STm are grown under conditions to induce the expression of the type-3 secretion system-1. STm mutants lacking the type-3 secretion system-1 induce less neutrophil ROS than the virulent WT. In addition, we demonstrate that flagellar motility is a significant agonist of the neutrophil respiratory burst. Together our data demonstrate that both the type-3 secretion system-1 and flagellar motility, which are established virulence factors in enteric salmonellosis, also appear to directly influence the magnitude of the neutrophil respiratory burst in response to STm in vitro.
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Affiliation(s)
- Trina L. Westerman
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, United States of America
| | - Lydia Bogomolnaya
- Department of Microbial Pathogenesis and Immunology, College of Medicine, Texas A&M University, Bryan, TX, United States of America
- Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russia
| | - Helene L. Andrews-Polymenis
- Department of Microbial Pathogenesis and Immunology, College of Medicine, Texas A&M University, Bryan, TX, United States of America
| | - M. Katherine Sheats
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, United States of America
| | - Johanna R. Elfenbein
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, United States of America
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Basic Processes in Salmonella-Host Interactions: Within-Host Evolution and the Transmission of the Virulent Genotype. Microbiol Spectr 2018; 5. [PMID: 28884670 DOI: 10.1128/microbiolspec.mtbp-0012-2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Transmission and virulence are central aspects of pathogen evolution. However, in many cases their interconnection has proven difficult to assess by experimentation. Here we discuss recent advances from a mouse model for Salmonella diarrhea. Mouse models mimic the enhanced susceptibility of antibiotic-treated individuals to nontyphoidal salmonellosis. In streptomycin-pretreated mice, Salmonella enterica subspecies 1 serovar Typhimurium efficiently colonizes the gut lumen and elicits pronounced enteropathy. In the host's gut, S. Typhimurium forms two subpopulations that cooperate to elicit disease and optimize transmission. The disease-causing subpopulation expresses a set of dedicated virulence factors (the type 3 secretion system 1 [TTSS-1]) that drive gut tissue invasion. The virulence factor expression is "costly" by retarding the growth rate and exposing the pathogen to innate immune defenses within the gut tissue. These costs are compensated by the gut inflammation (a "public good") that is induced by the invading subpopulation. The inflamed gut lumen fuels S. Typhimurium growth, in particular that of the TTSS-1 "off" subpopulation. The latter grows up to very high densities and promotes transmission. Thus, both phenotypes cooperate to elicit disease and ensure transmission. This system has provided an experimental framework for studying within-host evolution of pathogen virulence, how cooperative virulence is stabilized, and how environmental changes (e.g., antibiotic therapy) affect the transmission of the virulent genotype.
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The Ethanolamine Permease EutH Promotes Vacuole Adaptation of Salmonella enterica and Listeria monocytogenes during Macrophage Infection. Infect Immun 2018. [PMID: 29531136 DOI: 10.1128/iai.00172-18] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Ethanolamine is a ubiquitous and essential molecule within a host. Significantly, bacterial pathogens exploit ethanolamine during infection to promote growth and regulate virulence. The ethanolamine permease EutH is dispensable for growth in vitro under standard conditions, whereas EutH is required for ethanolamine utilization at low pH. These findings suggested a model in which EutH facilitates diffusion of ethanolamine into the bacterial cell in acidic environments. To date, the ecological significance of this model has not been thoroughly investigated, and the importance of EutH to bacterial growth under physiologically relevant conditions is not known. During infection, immune cells internalize invading bacteria within an acidic, nutrient-depleted vacuole called the phagosome. Here, we investigated the hypothesis that EutH promotes bacterial survival following phagocytosis. Our findings indicate that EutH is important for survival and replication of the facultative intracellular pathogens Salmonella enterica serovar Typhimurium and Listeria monocytogenes during prolonged or transient exposure to the phagosome, respectively. Furthermore, in agreement with EutH being important in the acidic environment, neutralization of the vacuole abolished the requirement for EutH. Significantly, consistent with a role for EutH in promoting intramacrophage survival, EutH was not required during S Typhimurium local intestinal infection but specifically conferred an advantage upon dissemination to peripheral organs. These findings reveal a physiologically relevant and conserved role for EutH in spatiotemporal niche adaptation during infection.
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46
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HilD and PhoP independently regulate the expression of grhD1, a novel gene required for Salmonella Typhimurium invasion of host cells. Sci Rep 2018; 8:4841. [PMID: 29555922 PMCID: PMC5859253 DOI: 10.1038/s41598-018-23068-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 03/06/2018] [Indexed: 01/28/2023] Open
Abstract
When Salmonella is grown in the nutrient-rich lysogeny broth (LB), the AraC-like transcriptional regulator HilD positively controls the expression of genes required for Salmonella invasion of host cells, such as the Salmonella pathogenicity island 1 (SPI-1) genes. However, in minimal media, the two-component system PhoP/Q activates the expression of genes necessary for Salmonella replication inside host cells, such as the SPI-2 genes. Recently, we found that the SL1344_1872 hypothetical gene, located in a S. Typhimurium genomic island, is co-expressed with the SPI-1 genes. In this study we demonstrate that HilD induces indirectly the expression of SL1344_1872 when S. Typhimurium is grown in LB; therefore, we named SL1344_1872 as grhD1 for gene regulated by HilD. Furthermore, we found that PhoP positively controls the expression of grhD1, independently of HilD, when S. Typhimurium is grown in LB or N-minimal medium. Moreover, we demonstrate that the grhD1 gene is required for the invasion of S. Typhimurium into epithelial cells, macrophages and fibroblasts, as well as for the intestinal inflammatory response caused by S. Typhimurium in mice. Thus, our results reveal a novel virulence factor of Salmonella, whose expression is positively and independently controlled by the HilD and PhoP transcriptional regulators.
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Zhang K, Riba A, Nietschke M, Torow N, Repnik U, Pütz A, Fulde M, Dupont A, Hensel M, Hornef M. Minimal SPI1-T3SS effector requirement for Salmonella enterocyte invasion and intracellular proliferation in vivo. PLoS Pathog 2018. [PMID: 29522566 PMCID: PMC5862521 DOI: 10.1371/journal.ppat.1006925] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Effector molecules translocated by the Salmonella pathogenicity island (SPI)1-encoded type 3 secretion system (T3SS) critically contribute to the pathogenesis of human Salmonella infection. They facilitate internalization by non-phagocytic enterocytes rendering the intestinal epithelium an entry site for infection. Their function in vivo has remained ill-defined due to the lack of a suitable animal model that allows visualization of intraepithelial Salmonella. Here, we took advantage of our novel neonatal mouse model and analyzed various bacterial mutants and reporter strains as well as gene deficient mice. Our results demonstrate the critical but redundant role of SopE2 and SipA for enterocyte invasion, prerequisite for transcriptional stimulation and mucosal translocation in vivo. In contrast, the generation of a replicative intraepithelial endosomal compartment required the cooperative action of SipA and SopE2 or SipA and SopB but was independent of SopA or host MyD88 signaling. Intraepithelial growth had no critical influence on systemic spread. Our results define the role of SPI1-T3SS effector molecules during enterocyte invasion and intraepithelial proliferation in vivo providing novel insight in the early course of Salmonella infection. Non-typhoidal Salmonella represent a major causative agent of gastroenteritis worldwide. Hallmark of the pathogenesis is their ability to actively invade the intestinal epithelium by virtue of their type 3 secretion system that delivers bacterial virulence factors directly into the host cell cytosol. The role of these virulence factors during enterocyte entry and intraepithelial growth has only been investigated in vitro since the previously established in vivo models in small animals did not allow visualization of intraepithelial Salmonella. However, immortalized cell lines lack the overlaying mucus layer, final cell lineage differentiation, apical-basolateral polarization as well as continuous migration along the crypt villus axis and thus the role of virulence factors during the Salmonella infection in vivo has remained largely undefined. Here, we took advantage of our novel neonatal mouse infection model and for the first time systematically analyzed the importance of Salmonella virulence factors for enterocyte invasion and intraepithelial growth.
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Affiliation(s)
- Kaiyi Zhang
- Institute of Medical Microbiology, RWTH University Hospital, Aachen, Germany
| | - Ambre Riba
- Institute of Medical Microbiology, RWTH University Hospital, Aachen, Germany
| | - Monika Nietschke
- Division of Microbiology, University of Osnabrück, Osnabrück, Germany
| | - Natalia Torow
- Institute of Medical Microbiology, RWTH University Hospital, Aachen, Germany
| | - Urska Repnik
- Department of Biosciences, University of Oslo, Oslo, Norway
| | - Andreas Pütz
- Institute of Medical Microbiology, RWTH University Hospital, Aachen, Germany
| | - Marcus Fulde
- Institute of Microbiology and Epizootics, Freie Universität Berlin, Berlin, Germany
| | - Aline Dupont
- Institute of Medical Microbiology, RWTH University Hospital, Aachen, Germany
| | - Michael Hensel
- Division of Microbiology, University of Osnabrück, Osnabrück, Germany
| | - Mathias Hornef
- Institute of Medical Microbiology, RWTH University Hospital, Aachen, Germany
- * E-mail:
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48
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Consequences of Epithelial Inflammasome Activation by Bacterial Pathogens. J Mol Biol 2018; 430:193-206. [DOI: 10.1016/j.jmb.2017.03.031] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 03/17/2017] [Accepted: 03/19/2017] [Indexed: 01/02/2023]
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49
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Ben Rejeb S, Lereclus D, Slamti L. Analysis of abrB Expression during the Infectious Cycle of Bacillus thuringiensis Reveals Population Heterogeneity. Front Microbiol 2017; 8:2471. [PMID: 29312181 PMCID: PMC5732988 DOI: 10.3389/fmicb.2017.02471] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 11/28/2017] [Indexed: 11/19/2022] Open
Abstract
Using the model host/pathogen pair Galleria mellonella/Bacillus thuringiensis, we have shown that these bacteria could kill their insect host, survive in its cadaver and form spores by sequentially activating virulence, necrotrophism and sporulation genes. However, the population isolated from the cadavers was heterogeneous, including non-sporulating cells in an unknown physiological state. To characterize these bacteria, we used a transcriptional fusion between the promoter of a gene expressed during early exponential growth (abrB) and a reporter gene encoding a destabilized version of GFP, in combination with a fluorescent reporter of the necrotrophic state. The composition of the bacterial population during infection was then analyzed by flow cytometry. We showed that the PabrB promoter was activated in the population that had turned on the necrotrophic reporter, suggesting a re-entry into vegetative growth. Strikingly, the cells that did not go through the necrotrophic state did not activate the PabrB promoter and appear as a dormant subpopulation. We propose a new model describing the B. thuringiensis cell types during infection.
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Affiliation(s)
- Samia Ben Rejeb
- Micalis Institute, Institut National de la Recherche Agronomique, AgroParisTech, Université Paris-Saclay, Jouy-en-Josas, France
| | - Didier Lereclus
- Micalis Institute, Institut National de la Recherche Agronomique, AgroParisTech, Université Paris-Saclay, Jouy-en-Josas, France
| | - Leyla Slamti
- Micalis Institute, Institut National de la Recherche Agronomique, AgroParisTech, Université Paris-Saclay, Jouy-en-Josas, France
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50
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Castanheira S, García-Del Portillo F. Salmonella Populations inside Host Cells. Front Cell Infect Microbiol 2017; 7:432. [PMID: 29046870 PMCID: PMC5632677 DOI: 10.3389/fcimb.2017.00432] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 09/20/2017] [Indexed: 11/13/2022] Open
Abstract
Bacteria of the Salmonella genus cause diseases ranging from gastroenteritis to life-threatening typhoid fever and are among the most successful intracellular pathogens known. After the invasion of the eukaryotic cell, Salmonella exhibits contrasting lifestyles with different replication rates and subcellular locations. Although Salmonella hyper-replicates in the cytosol of certain host cell types, most invading bacteria remain within vacuoles in which the pathogen proliferates at moderate rates or persists in a dormant-like state. Remarkably, these cytosolic and intra-vacuolar intracellular lifestyles are not mutually exclusive and can co-exist in the same infected host cell. The mechanisms that direct the invading bacterium to follow the cytosolic or intra-vacuolar “pathway” remain poorly understood. In vitro studies show predominance of either the cytosolic or the intra-vacuolar population depending on the host cell type invaded by the pathogen. The host and pathogen factors controlling phagosomal membrane integrity and, as consequence, the egress into the cytosol, are intensively investigated. Other aspects of major interest are the host defenses that may affect differentially the cytosolic and intra-vacuolar populations and the strategies used by the pathogen to circumvent these attacks. Here, we summarize current knowledge about these Salmonella intracellular subpopulations and discuss how they emerge during the interaction of this pathogen with the eukaryotic cell.
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Affiliation(s)
- Sónia Castanheira
- Laboratory of Intracellular Bacterial Pathogens, Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas (CNB-CSIC), Madrid, Spain
| | - Francisco García-Del Portillo
- Laboratory of Intracellular Bacterial Pathogens, Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas (CNB-CSIC), Madrid, Spain
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