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Abstract
B cells have long been regarded as simple antibody production units, but are now becoming known as key players in both adaptive and innate immune responses. However, several bacteria, viruses and parasites have evolved the ability to manipulate B cell functions to modulate immune responses. Pathogens can affect B cells indirectly, by attacking innate immune cells and altering the cytokine environment, and can also target B cells directly, impairing B cell-mediated immune responses. In this Review, we provide a summary of recent advances in elucidating direct B cell-pathogen interactions and highlight how targeting this specific cell population benefits different pathogens.
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52
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Maier L, Diard M, Sellin ME, Chouffane ES, Trautwein-Weidner K, Periaswamy B, Slack E, Dolowschiak T, Stecher B, Loverdo C, Regoes RR, Hardt WD. Granulocytes impose a tight bottleneck upon the gut luminal pathogen population during Salmonella typhimurium colitis. PLoS Pathog 2014; 10:e1004557. [PMID: 25522364 PMCID: PMC4270771 DOI: 10.1371/journal.ppat.1004557] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 11/06/2014] [Indexed: 12/22/2022] Open
Abstract
Topological, chemical and immunological barriers are thought to limit infection by enteropathogenic bacteria. However, in many cases these barriers and their consequences for the infection process remain incompletely understood. Here, we employed a mouse model for Salmonella colitis and a mixed inoculum approach to identify barriers limiting the gut luminal pathogen population. Mice were infected via the oral route with wild type S. Typhimurium (S. Tm) and/or mixtures of phenotypically identical but differentially tagged S. Tm strains ("WITS", wild-type isogenic tagged strains), which can be individually tracked by quantitative real-time PCR. WITS dilution experiments identified a substantial loss in tag/genetic diversity within the gut luminal S. Tm population by days 2-4 post infection. The diversity-loss was not attributable to overgrowth by S. Tm mutants, but required inflammation, Gr-1+ cells (mainly neutrophilic granulocytes) and most likely NADPH-oxidase-mediated defense, but not iNOS. Mathematical modelling indicated that inflammation inflicts a bottleneck transiently restricting the gut luminal S. Tm population to approximately 6000 cells and plating experiments verified a transient, inflammation- and Gr-1+ cell-dependent dip in the gut luminal S. Tm population at day 2 post infection. We conclude that granulocytes, an important clinical hallmark of S. Tm-induced inflammation, impose a drastic bottleneck upon the pathogen population. This extends the current view of inflammation-fuelled gut-luminal Salmonella growth by establishing the host response in the intestinal lumen as a double-edged sword, fostering and diminishing colonization in a dynamic equilibrium. Our work identifies a potent immune defense against gut infection and reveals a potential Achilles' heel of the infection process which might be targeted for therapy.
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Affiliation(s)
- Lisa Maier
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
| | - Médéric Diard
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
| | - Mikael E. Sellin
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
| | - Elsa-Sarah Chouffane
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
| | | | - Balamurugan Periaswamy
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
| | - Emma Slack
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
| | - Tamas Dolowschiak
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
| | - Bärbel Stecher
- Max von Pettenkofer-Institut, München, Germany; German Center for Infection Research (DZIF), partner site Ludwig Maximilian University of Munich, Munich, Germany
| | - Claude Loverdo
- Eidgenössische Technische Hochschule Zürich, Institute of Integrative Biology, Zurich, Switzerland
| | - Roland R. Regoes
- Eidgenössische Technische Hochschule Zürich, Institute of Integrative Biology, Zurich, Switzerland
| | - Wolf-Dietrich Hardt
- Eidgenössische Technische Hochschule Zürich, Institute of Microbiology, Zurich, Switzerland
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53
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Abstract
UNLABELLED Neutrophils engulf and kill bacteria using oxidative and nonoxidative mechanisms. Despite robust antimicrobial activity, neutrophils are impaired in directing Salmonella clearance and harbor viable intracellular bacteria during early stages of infection that can subsequently escape to more-permissive cell types. The mechanisms accounting for this immune impairment are not understood. We report that Salmonella limits exposure to oxidative damage elicited by D-amino acid oxidase (DAO) in neutrophils by expressing an ABC importer specific for D-alanine, a DAO substrate found in peptidoglycan stem peptides. A Salmonella dalS mutant defective for D-alanine import was more susceptible to killing by DAO through exposure to greater oxidative stress during infection. This fitness defect was reversed by selective depletion of neutrophils or by inhibition of DAO in vivo with a small-molecule inhibitor. DalS-mediated subversion of neutrophil DAO is a novel host-pathogen interaction that enhances Salmonella survival during systemic infection. IMPORTANCE Neutrophils engulf Salmonella during early stages of infection, but bacterial killing is incomplete. Very little is known about how Salmonella survives in neutrophils to gain access to other cell types during infection. In this study, we show that D-amino acid oxidase (DAO) in neutrophils consumes D-alanine and that importing this substrate protects Salmonella from oxidative killing by neutrophil DAO. Loss of this importer results in increased bacterial killing in vitro, in neutrophils, and in a mouse model of infection, all phenotypes that are lost upon inhibition of DAO. These findings add mechanistic insight into a novel host-pathogen interaction that has consequences on infection outcome.
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54
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Merritt PM, Nero T, Bohman L, Felek S, Krukonis ES, Marketon MM. Yersinia pestis targets neutrophils via complement receptor 3. Cell Microbiol 2014; 17:666-87. [PMID: 25359083 DOI: 10.1111/cmi.12391] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2014] [Revised: 10/18/2014] [Accepted: 10/28/2014] [Indexed: 01/20/2023]
Abstract
Yersinia species display a tropism for lymphoid tissues during infection, and the bacteria select innate immune cells for delivery of cytotoxic effectors by the type III secretion system. Yet, the mechanism for target cell selection remains a mystery. Here we investigate the interaction of Yersinia pestis with murine splenocytes to identify factors that participate in the targeting process. We find that interactions with primary immune cells rely on multiple factors. First, the bacterial adhesin Ail is required for efficient targeting of neutrophils in vivo. However, Ail does not appear to directly mediate binding to a specific cell type. Instead, we find that host serum factors direct Y. pestis to specific innate immune cells, particularly neutrophils. Importantly, specificity towards neutrophils was increased in the absence of bacterial adhesins because of reduced targeting of other cell types, but this phenotype was only visible in the presence of mouse serum. Addition of antibodies against complement receptor 3 and CD14 blocked target cell selection, suggesting that a combination of host factors participate in steering bacteria towards neutrophils during plague infection.
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Affiliation(s)
- Peter M Merritt
- Department of Biology, Indiana University, Bloomington, IN, USA
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55
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Boumart Z, Velge P, Wiedemann A. Multiple invasion mechanisms and different intracellular Behaviors: a new vision ofSalmonella-host cell interaction. FEMS Microbiol Lett 2014; 361:1-7. [DOI: 10.1111/1574-6968.12614] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 09/16/2014] [Accepted: 09/27/2014] [Indexed: 12/20/2022] Open
Affiliation(s)
- Zineb Boumart
- Institut National de la Recherche Agronomique; UMR1282 Infectiologie et Santé Publique; Nouzilly France
- Université François Rabelais; UMR1282 Infectiologie et Santé Publique; Tours France
- Agence Nationale de Sécurité Sanitaire de l'alimentation; de l'environnement et du travail; Laboratoire de Ploufragan-Plouzané; Unité Hygiène et Qualité des Produits Avicoles et Porcins; Plouragan France
| | - Philippe Velge
- Institut National de la Recherche Agronomique; UMR1282 Infectiologie et Santé Publique; Nouzilly France
- Université François Rabelais; UMR1282 Infectiologie et Santé Publique; Tours France
| | - Agnès Wiedemann
- Institut National de la Recherche Agronomique; UMR1282 Infectiologie et Santé Publique; Nouzilly France
- Université François Rabelais; UMR1282 Infectiologie et Santé Publique; Tours France
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56
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Copenhaver AM, Casson CN, Nguyen HT, Fung TC, Duda MM, Roy CR, Shin S. Alveolar macrophages and neutrophils are the primary reservoirs for Legionella pneumophila and mediate cytosolic surveillance of type IV secretion. Infect Immun 2014; 82:4325-36. [PMID: 25092908 PMCID: PMC4187856 DOI: 10.1128/iai.01891-14] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 07/24/2014] [Indexed: 02/07/2023] Open
Abstract
Legionella pneumophila, an intracellular pathogen responsible for the severe pneumonia Legionnaires' disease, uses its dot/icm-encoded type IV secretion system (T4SS) to translocate effector proteins that promote its survival and replication into the host cell cytosol. However, by introducing bacterial products into the host cytosol, L. pneumophila also activates cytosolic immunosurveillance pathways, thereby triggering robust proinflammatory responses that mediate the control of infection. Thus, the pulmonary cell types that L. pneumophila infects not only may act as an intracellular niche that facilitates its pathogenesis but also may contribute to the immune response against L. pneumophila. The identity of these host cells remains poorly understood. Here, we developed a strain of L. pneumophila producing a fusion protein consisting of β-lactamase fused to the T4SS-translocated effector RalF, which allowed us to track cells injected by the T4SS. Our data reveal that alveolar macrophages and neutrophils both are the primary recipients of T4SS-translocated effectors and harbor viable L. pneumophila during pulmonary infection of mice. Moreover, both alveolar macrophages and neutrophils from infected mice produced tumor necrosis factor and interleukin-1α in response to T4SS-sufficient, but not T4SS-deficient, L. pneumophila. Collectively, our data suggest that alveolar macrophages and neutrophils are both an intracellular reservoir for L. pneumophila and a source of proinflammatory cytokines that contribute to the host immune response against L. pneumophila during pulmonary infection.
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Affiliation(s)
- Alan M Copenhaver
- Immunology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Cierra N Casson
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Hieu T Nguyen
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Thomas C Fung
- Immunology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Matthew M Duda
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Craig R Roy
- Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Sunny Shin
- Immunology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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57
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The neutrophil NLRC4 inflammasome selectively promotes IL-1β maturation without pyroptosis during acute Salmonella challenge. Cell Rep 2014; 8:570-82. [PMID: 25043180 DOI: 10.1016/j.celrep.2014.06.028] [Citation(s) in RCA: 308] [Impact Index Per Article: 30.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Revised: 06/01/2014] [Accepted: 06/18/2014] [Indexed: 12/19/2022] Open
Abstract
The macrophage NLRC4 inflammasome drives potent innate immune responses against Salmonella by eliciting caspase-1-dependent proinflammatory cytokine production (e.g., interleukin-1β [IL-1β]) and pyroptotic cell death. However, the potential contribution of other cell types to inflammasome-mediated host defense against Salmonella was unclear. Here, we demonstrate that neutrophils, typically viewed as cellular targets of IL-1β, themselves activate the NLRC4 inflammasome during acute Salmonella infection and are a major cell compartment for IL-1β production during acute peritoneal challenge in vivo. Importantly, unlike macrophages, neutrophils do not undergo pyroptosis upon NLRC4 inflammasome activation. The resistance of neutrophils to pyroptotic death is unique among inflammasome-signaling cells so far described and allows neutrophils to sustain IL-1β production at a site of infection without compromising the crucial inflammasome-independent antimicrobial effector functions that would be lost if neutrophils rapidly lysed upon caspase-1 activation. Inflammasome pathway modification in neutrophils thus maximizes host proinflammatory and antimicrobial responses during pathogen challenge.
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58
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Campbell-Valois FX, Sansonetti PJ. Tracking bacterial pathogens with genetically-encoded reporters. FEBS Lett 2014; 588:2428-36. [PMID: 24859085 DOI: 10.1016/j.febslet.2014.05.022] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Accepted: 05/12/2014] [Indexed: 11/15/2022]
Abstract
During the infectious process, bacterial pathogens are subject to changes in environmental conditions such as nutrient availability, immune response challenges, bacterial density and physical contacts with targeted host cells. These conditions occur in the colonized organs, in diverse regions within infected tissues or even at the subcellular level for intracellular pathogens. Integration of environmental cues leads to measurable biological responses in the bacterium required for adaptation. Recent progress in technology enabled the study of bacterial adaptation in situ using genetically encoded reporters that allow single cell analysis or whole body imaging based on fluorescent proteins, alternative fluorescent assays or luciferases. This review presents a historical perspective and technical details on the methods used to develop transcriptional reporters, protein-protein interaction assays and secretion detection assays to study pathogenic bacteria adaptation in situ. Finally, studies published in the last 5 years on gram positive and gram negative bacterial adaptation to the host during infection are discussed. However, the methods described here could easily be extended to study complex microbial communities within host tissue and in the environment.
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Affiliation(s)
- F-X Campbell-Valois
- Institut Pasteur, Unité de Pathogénie Microbienne Moléculaire, 25-28 rue du Docteur-Roux, 75724 Paris, France; INSERM, U786, 75015 Paris, France
| | - Philippe J Sansonetti
- Institut Pasteur, Unité de Pathogénie Microbienne Moléculaire, 25-28 rue du Docteur-Roux, 75724 Paris, France; INSERM, U786, 75015 Paris, France; Collège de France, Chaire de Microbiologie et Maladies infectieuses, 11 Place Marcelin Berthelot, 75005 Paris, France.
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59
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CD11b+ Ly6Chi Ly6G- immature myeloid cells recruited in response to Salmonella enterica serovar Typhimurium infection exhibit protective and immunosuppressive properties. Infect Immun 2014; 82:2606-14. [PMID: 24711563 DOI: 10.1128/iai.01590-13] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Immature myeloid cells in bone marrow are a heterogeneous population of cells that, under normal conditions, provide tissues with protective cell types such as granulocytes and macrophages. Under certain pathological conditions, myeloid cell homeostasis is altered and immature forms of these cells appear in tissues. Murine immature myeloid cells that express CD11b and Ly6C or Ly6G (two isoforms of Gr-1) have been associated with immunosuppression in cancer (in the form of myeloid-derived suppressor cells) and, more recently, infection. Here, we found that CD11b(+) Ly6C(hi) Ly6G(-) and CD11b(+) Ly6C(int) Ly6G(+) cells accumulated and persisted in tissues of mice infected with Salmonella enterica serovar Typhimurium (S. Typhimurium). Recruitment of CD11b(+) Ly6C(hi) Ly6G(-) but not CD11b(+) Ly6C(int) Ly6G(+) cells from bone marrow into infected tissues depended on chemokine receptor CCR2. The CD11b(+) Ly6C(hi) Ly6G(-) cells exhibited a mononuclear morphology, whereas the CD11b(+) Ly6C(int) Ly6G(+) cells exhibited a polymorphonuclear or band-shaped nuclear morphology. The CD11b(+) Ly6C(hi) Ly6G(-) cells differentiated into macrophage-like cells following ex vivo culture and could present antigen to T cells in vitro. However, significant proliferation of T cells was observed only when the ability of the CD11b(+) Ly6C(hi) Ly6G(-) cells to produce nitric oxide was blocked. CD11b(+) Ly6C(hi) Ly6G(-) cells recruited in response to S. Typhimurium infection could also present antigen to T cells in vivo, but increasing their numbers by adoptive transfer did not cause a corresponding increase in T cell response. Thus, CD11b(+) Ly6C(hi) Ly6G(-) immature myeloid cells recruited in response to S. Typhimurium infection exhibit protective and immunosuppressive properties that may influence the outcome of infection.
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60
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Spatial segregation of virulence gene expression during acute enteric infection with Salmonella enterica serovar Typhimurium. mBio 2014; 5:e00946-13. [PMID: 24496791 PMCID: PMC3950517 DOI: 10.1128/mbio.00946-13] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
To establish a replicative niche during its infectious cycle between the intestinal lumen and tissue, the enteric pathogen Salmonella enterica serovar Typhimurium requires numerous virulence genes, including genes for two type III secretion systems (T3SS) and their cognate effectors. To better understand the host-pathogen relationship, including early infection dynamics and induction kinetics of the bacterial virulence program in the context of a natural host, we monitored the subcellular localization and temporal expression of T3SS-1 and T3SS-2 using fluorescent single-cell reporters in a bovine, ligated ileal loop model of infection. We observed that the majority of bacteria at 2 h postinfection are flagellated, express T3SS-1 but not T3SS-2, and are associated with the epithelium or with extruding enterocytes. In epithelial cells, S. Typhimurium cells were surrounded by intact vacuolar membranes or present within membrane-compromised vacuoles that typically contained numerous vesicular structures. By 8 h postinfection, T3SS-2-expressing bacteria were detected in the lamina propria and in the underlying mucosa, while T3SS-1-expressing bacteria were in the lumen. Our work identifies for the first time the temporal and spatial regulation of T3SS-1 and -2 expression during an enteric infection in a natural host and provides further support for the concept of cytosolic S. Typhimurium in extruding epithelium as a mechanism for reseeding the lumen. The pathogenic bacterium Salmonella enterica serovar Typhimurium invades and persists within host cells using distinct sets of virulence genes. Genes from Salmonella pathogenicity island 1 (SPI-1) are used to initiate contact and facilitate uptake into nonphagocytic host cells, while genes within SPI-2 allow the pathogen to colonize host cells. While many studies have identified bacterial virulence determinants in animal models of infection, very few have focused on virulence gene expression at the single-cell level during an in vivo infection. To better understand when and where bacterial virulence factors are expressed during an acute enteric infection of a natural host, we infected bovine jejunal-ileal loops with S. Typhimurium cells harboring fluorescent transcriptional reporters for SPI-1 and -2 (PinvF and PssaG, respectively). After a prescribed time of infection, tissue and luminal fluid were collected and analyzed by microscopy. During early infection (≤2 h), bacteria within both intact and compromised membrane-bound vacuoles were observed within the epithelium, with the majority expressing SPI-1. As the infection progressed, S. Typhimurium displayed differential expression of the SPI-1 and SPI-2 regulons, with the majority of tissue-associated bacteria expressing SPI-2 and the majority of lumen-associated bacteria expressing SPI-1. This underscores the finding that Salmonella virulence gene expression changes as the pathogen transitions from one anatomical location to the next.
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61
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Structure of an SspH1-PKN1 complex reveals the basis for host substrate recognition and mechanism of activation for a bacterial E3 ubiquitin ligase. Mol Cell Biol 2013; 34:362-73. [PMID: 24248594 DOI: 10.1128/mcb.01360-13] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
IpaH proteins are bacterium-specific E3 enzymes that function as type three secretion system (T3SS) effectors in Salmonella, Shigella, and other Gram-negative bacteria. IpaH enzymes recruit host substrates for ubiquitination via a leucine-rich repeat (LRR) domain, which can inhibit the catalytic domain in the absence of substrate. The basis for substrate recognition and the alleviation of autoinhibition upon substrate binding is unknown. Here, we report the X-ray structure of Salmonella SspH1 in complex with human PKN1. The LRR domain of SspH1 interacts specifically with the HR1b coiled-coil subdomain of PKN1 in a manner that sterically displaces the catalytic domain from the LRR domain, thereby activating catalytic function. SspH1 catalyzes the ubiquitination and proteasome-dependent degradation of PKN1 in cells, which attenuates androgen receptor responsiveness but not NF-κB activity. These regulatory features are conserved in other IpaH-substrate interactions. Our results explain the mechanism whereby substrate recognition and enzyme autoregulation are coupled in this class of bacterial ubiquitin ligases.
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62
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Ahmad I, Wigren E, Le Guyon S, Vekkeli S, Blanka A, El Mouali Y, Anwar N, Chuah ML, Lünsdorf H, Frank R, Rhen M, Liang ZX, Lindqvist Y, Römling U. The EAL-like protein STM1697 regulates virulence phenotypes, motility and biofilm formation in Salmonella typhimurium. Mol Microbiol 2013; 90:1216-32. [PMID: 24127899 DOI: 10.1111/mmi.12428] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/09/2013] [Indexed: 11/30/2022]
Abstract
The ubiquitous second messenger c-di-GMP regulates the switching of bacterial lifestyles from motility to sessility and acute to chronic virulence to adjust bacterial fitness to altered environmental conditions. Conventionally, EAL proteins being c-di-GMP phosphodiesterases promote motility and acute virulence phenotypes such as invasion into epithelial cells and inhibit biofilm formation. We report here that in contradiction, the EAL-like protein STM1697 of Salmonella typhimurium suppresses motility, invasion into HT-29 epithelial cell line and secretion of the type three secretion system 1 effector protein SipA, whereas it promotes rdar biofilm formation and CsgD expression. STM1697 can, however, functionally replace the EAL-like protein STM1344 and vice versa, whereby both proteins neither degrade nor bind c-di-GMP. Like STM1344, STM1697 suppresses the transcription of class 2 and class 3 flagella regulon genes by binding to FlhD, a component of the master regulator of the flagella regulon FlhD4 C2 and act additively under numerous conditions. Interestingly, the interaction interface of STM1697 with FlhD2 is distinct from its paralogue STM1344. We predict that the stand alone EAL domain proteins STM1697 and STM1344 belong to a subclass of EAL domain proteins in S. typhimurium, which are all involved in motility, biofilm and virulence regulation through interaction with proteins that regulate flagella function.
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Affiliation(s)
- Irfan Ahmad
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, 17177, Stockholm, Sweden
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63
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Mastroeni P, Grant A. Dynamics of spread of Salmonella enterica in the systemic compartment. Microbes Infect 2013; 15:849-57. [PMID: 24183878 DOI: 10.1016/j.micinf.2013.10.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 10/09/2013] [Indexed: 12/21/2022]
Abstract
Traditional microbiological and immunological tools, combined with modern imaging, and molecular and mathematical approaches, have revealed the dispersive nature of Salmonella infections. Bacterial escape from infected cells, spread in the tissues and attempts to restrain this process by the host give rise to fascinating scenarios that underpin the pathogenesis of salmonelloses.
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Affiliation(s)
- Pietro Mastroeni
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, United Kingdom.
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64
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Pechous RD, Sivaraman V, Price PA, Stasulli NM, Goldman WE. Early host cell targets of Yersinia pestis during primary pneumonic plague. PLoS Pathog 2013; 9:e1003679. [PMID: 24098126 PMCID: PMC3789773 DOI: 10.1371/journal.ppat.1003679] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2013] [Accepted: 08/20/2013] [Indexed: 01/14/2023] Open
Abstract
Inhalation of Yersinia pestis causes primary pneumonic plague, a highly lethal syndrome with mortality rates approaching 100%. Pneumonic plague progression is biphasic, with an initial pre-inflammatory phase facilitating bacterial growth in the absence of host inflammation, followed by a pro-inflammatory phase marked by extensive neutrophil influx, an inflammatory cytokine storm, and severe tissue destruction. Using a FRET-based probe to quantitate injection of effector proteins by the Y. pestis type III secretion system, we show that these bacteria target alveolar macrophages early during infection of mice, followed by a switch in host cell preference to neutrophils. We also demonstrate that neutrophil influx is unable to limit bacterial growth in the lung and is ultimately responsible for the severe inflammation during the lethal pro-inflammatory phase. Inhalation of the bacterium Yersinia pestis results in primary pneumonic plague, a severe necrotizing pneumonia with mortality rates approaching 100% in the absence of timely antibiotic administration. Despite the notoriety of Y. pestis as a potential biological weapon and its well-established pandemic potential, very little is known regarding early host-pathogen interactions that lead to the progression of pulmonary infection. Y. pestis harbors a type III secretion system (T3SS) for delivery of Yersinia outer protein (Yop) effectors into host cells, an early and essential step in pathogenesis. In the work presented here, we identify the host cell targets of Y. pestis Yop secretion in the lung. We show that Y. pestis initially targets alveolar macrophages, followed by a shift in host cell preference to neutrophils. Through cellular depletion studies, we demonstrate that Y. pestis is highly resistant to macrophage- and neutrophil-mediated clearance, and that the accumulation of neutrophils in the lung is responsible for the severe necrotizing pneumonia that develops during the pro-inflammatory phase of pneumonic plague.
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Affiliation(s)
- Roger D. Pechous
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Vijay Sivaraman
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Paul A. Price
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Nikolas M. Stasulli
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - William E. Goldman
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- * E-mail:
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65
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Kidwai AS, Mushamiri I, Niemann GS, Brown RN, Adkins JN, Heffron F. Diverse secreted effectors are required for Salmonella persistence in a mouse infection model. PLoS One 2013; 8:e70753. [PMID: 23950998 PMCID: PMC3741292 DOI: 10.1371/journal.pone.0070753] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2013] [Accepted: 06/26/2013] [Indexed: 01/08/2023] Open
Abstract
Salmonella enterica serovar Typhimurium causes typhoid-like disease in mice and is a model of typhoid fever in humans. One of the hallmarks of typhoid is persistence, the ability of the bacteria to survive in the host weeks after infection. Virulence factors called effectors facilitate this process by direct transfer to the cytoplasm of infected cells thereby subverting cellular processes. Secretion of effectors to the cell cytoplasm takes place through multiple routes, including two separate type III secretion (T3SS) apparati as well as outer membrane vesicles. The two T3SS are encoded on separate pathogenicity islands, SPI-1 and -2, with SPI-1 more strongly associated with the intestinal phase of infection, and SPI-2 with the systemic phase. Both T3SS are required for persistence, but the effectors required have not been systematically evaluated. In this study, mutations in 48 described effectors were tested for persistence. We replaced each effector with a specific DNA barcode sequence by allelic exchange and co-infected with a wild-type reference to calculate the ratio of wild-type parent to mutant at different times after infection. The competitive index (CI) was determined by quantitative PCR in which primers that correspond to the barcode were used for amplification. Mutations in all but seven effectors reduced persistence demonstrating that most effectors were required. One exception was CigR, a recently discovered effector that is widely conserved throughout enteric bacteria. Deletion of cigR increased lethality, suggesting that it may be an anti-virulence factor. The fact that almost all Salmonella effectors are required for persistence argues against redundant functions. This is different from effector repertoires in other intracellular pathogens such as Legionella.
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Affiliation(s)
- Afshan S. Kidwai
- Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Ivy Mushamiri
- Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon, United States of America
| | - George S. Niemann
- Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Roslyn N. Brown
- Center for Bioproducts and Bioenergy, Washington State University, Richland, Washington, United States of America
| | - Joshua N. Adkins
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, United States of America
| | - Fred Heffron
- Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon, United States of America
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Odendall C, Rolhion N, Förster A, Poh J, Lamont DJ, Liu M, Freemont PS, Catling AD, Holden DW. The Salmonella kinase SteC targets the MAP kinase MEK to regulate the host actin cytoskeleton. Cell Host Microbe 2013; 12:657-68. [PMID: 23159055 PMCID: PMC3510437 DOI: 10.1016/j.chom.2012.09.011] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 07/27/2012] [Accepted: 09/25/2012] [Indexed: 01/09/2023]
Abstract
After host cell entry, Salmonella replicate in membrane-bound compartments, which accumulate a dense meshwork of F-actin through the kinase activity of the Salmonella SPI-2 type III secretion effector SteC. We find that SteC promotes actin cytoskeleton reorganization by activating a signaling pathway involving the MAP kinases MEK and ERK, myosin light chain kinase (MLCK) and Myosin IIB. Specifically, SteC phosphorylates MEK directly on serine 200 (S200), a previously unstudied phosphorylation site. S200 phosphorylation is predicted to displace a negative regulatory helix causing autophosphorylation on the known MEK activatory residues, S218 and S222. In support of this, substitution of S200 with alanine prevented phosphorylation on S218 and S222, and phosphomimetic mutations of S200 stimulated phosphorylation of these residues. Both steC-null and kinase-deficient mutant strains displayed enhanced replication in infected cells, suggesting that SteC manipulates the actin cytoskeleton to restrain bacterial growth, thereby regulating virulence.
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Affiliation(s)
- Charlotte Odendall
- Section of Microbiology, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London SW7 2AZ, UK
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67
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Moest TP, Méresse S. Salmonella T3SSs: successful mission of the secret(ion) agents. Curr Opin Microbiol 2013; 16:38-44. [DOI: 10.1016/j.mib.2012.11.006] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 11/15/2012] [Accepted: 11/26/2012] [Indexed: 10/27/2022]
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Sharma N, Akhade AS, Qadri A. Sphingosine-1-phosphate suppresses TLR-induced CXCL8 secretion from human T cells. J Leukoc Biol 2013; 93:521-8. [PMID: 23345392 DOI: 10.1189/jlb.0712328] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
T cells produce a number of cytokines and chemokines upon stimulation with TLR agonists in the presence or absence of TCR signals. Here, we show that secretion of neutrophil chemoattractant CXCL8 from human T cell line Jurkat in response to stimulation with TLR agonists is reduced when cell stimulation is carried out in presence of serum. Serum does not, however, inhibit TCR-activated secretion of CXCL8 nor does it down-regulate TLR-costimulated IL-2 secretion from activated T cells. The molecule that can mimic the ability to bring about suppression in CXCL8 from TLR-activated T cells is serum-borne bioactive lipid, S1P. Serum and S1P-mediated inhibition require intracellular calcium. S1P also suppresses CXCL8 secretion from peripheral blood-derived human T cells activated ex vivo with various TLR ligands. Our findings reveal a previously unrecognized role for S1P in regulating TLR-induced CXCL8 secretion from human T cells.
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69
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Perez-Lopez A, Rosales-Reyes R, Alpuche-Aranda CM, Ortiz-Navarrete V. Salmonella downregulates Nod-like receptor family CARD domain containing protein 4 expression to promote its survival in B cells by preventing inflammasome activation and cell death. THE JOURNAL OF IMMUNOLOGY 2013; 190:1201-9. [PMID: 23284055 DOI: 10.4049/jimmunol.1200415] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Salmonella infects and survives within B cells, but the mechanism used by the bacterium to promote its survival in these cells is unknown. In macrophages, flagellin secreted by Salmonella activates the Nod-like receptor (NLR) family CARD domain containing protein 4 (NLRC4) inflammasome, leading to the production of IL-1β and pyroptosis of infected cells. In this study, we demonstrated that the NLRC4 inflammasome is functional in B cells; however, in Salmonella-infected B cells, IL-1β secretion is prevented through the downregulation of NLRC4 expression. A functional Salmonella pathogenicity island 1 type III secretion system appears to be required for this process. Furthermore, infection induces Yap phosphorylation and promotes the interaction of Yap with Hck, thus preventing the transcriptional activation of NLRC4. The ability of Salmonella to inhibit IL-1β production also prevents B cell death; thus, B cells represent an ideal niche in which Salmonella resides, thereby promoting its persistence and dissemination.
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Affiliation(s)
- Araceli Perez-Lopez
- Departamento de Biomedicina Molecular, Centro de Investigación y Estudios Avanzados del Instituto Politecnico Nacional, Mexico City CP 07360, México
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70
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García-Pérez BE, De la Cruz-López JJ, Castañeda-Sánchez JI, Muñóz-Duarte AR, Hernández-Pérez AD, Villegas-Castrejón H, García-Latorre E, Caamal-Ley A, Luna-Herrera J. Macropinocytosis is responsible for the uptake of pathogenic and non-pathogenic mycobacteria by B lymphocytes (Raji cells). BMC Microbiol 2012; 12:246. [PMID: 23113903 PMCID: PMC3559283 DOI: 10.1186/1471-2180-12-246] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Accepted: 10/12/2012] [Indexed: 12/18/2022] Open
Abstract
Background The classical roles of B cells include the production of antibodies and cytokines and the generation of immunological memory, these being key factors in the adaptive immune response. However, their role in innate immunity is currently being recognised. Traditionally, B cells have been considered non-phagocytic cells; therefore, the uptake of bacteria by B cells is not extensively documented. In this study, we analysed some of the features of non-specific bacterial uptake by B lymphocytes from the Raji cell line. In our model, B cells were infected with Mycobacterium tuberculosis (MTB), Mycobacterium smegmatis (MSM), and Salmonella typhimurium (ST). Results Our observations revealed that the Raji B cells were readily infected by the three bacteria that were studied. All of the infections induced changes in the cellular membrane during bacterial internalisation. M. smegmatis and S. typhimurium were able to induce important membrane changes that were characterised by abundant filopodia and lamellipodia formation. These membrane changes were driven by actin cytoskeletal rearrangements. The intracellular growth of these bacteria was also controlled by B cells. M. tuberculosis infection also induced actin rearrangement-driven membrane changes; however, the B cells were not able to control this infection. The phorbol 12-myristate 13-acetate (PMA) treatment of B cells induced filopodia and lamellipodia formation, the production of spacious vacuoles (macropinosomes), and the fluid-phase uptake that is characteristic of macropinocytosis. S. typhimurium infection induced the highest fluid-phase uptake, although both mycobacteria also induced fluid uptake. A macropinocytosis inhibitor such as amiloride was used and abolished the bacterial uptake and the fluid-phase uptake that is triggered during the bacterial infection. Conclusions Raji B cells can internalise S. typhimurium and mycobacteria through an active process, such as macropinocytosis, although the resolution of the infection depends on factors that are inherent in the virulence of each pathogen.
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Affiliation(s)
- Blanca Estela García-Pérez
- Immunology Department, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D,F, México
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71
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Koshy AA, Dietrich HK, Christian DA, Melehani JH, Shastri AJ, Hunter CA, Boothroyd JC. Toxoplasma co-opts host cells it does not invade. PLoS Pathog 2012; 8:e1002825. [PMID: 22910631 PMCID: PMC3406079 DOI: 10.1371/journal.ppat.1002825] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 06/12/2012] [Indexed: 11/18/2022] Open
Abstract
Like many intracellular microbes, the protozoan parasite Toxoplasma gondii injects effector proteins into cells it invades. One group of these effector proteins is injected from specialized organelles called the rhoptries, which have previously been described to discharge their contents only during successful invasion of a host cell. In this report, using several reporter systems, we show that in vitro the parasite injects rhoptry proteins into cells it does not productively invade and that the rhoptry effector proteins can manipulate the uninfected cell in a similar manner to infected cells. In addition, as one of the reporter systems uses a rhoptry:Cre recombinase fusion protein, we show that in Cre-reporter mice infected with an encysting Toxoplasma-Cre strain, uninfected-injected cells, which could be derived from aborted invasion or cell-intrinsic killing after invasion, are actually more common than infected-injected cells, especially in the mouse brain, where Toxoplasma encysts and persists. This phenomenon has important implications for how Toxoplasma globally affects its host and opens a new avenue for how other intracellular microbes may similarly manipulate the host environment at large.
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Affiliation(s)
- Anita A. Koshy
- Department of Medicine (Infectious Disease), Stanford University School of Medicine, Stanford, California, United States of America
- Department of Neurology, Stanford University School of Medicine, Stanford, California, United States of America
| | - Hans K. Dietrich
- Department of Medicine (Infectious Disease), Stanford University School of Medicine, Stanford, California, United States of America
| | - David A. Christian
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Jason H. Melehani
- Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California, United States of America
| | - Anjali J. Shastri
- Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California, United States of America
| | - Christopher A. Hunter
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - John C. Boothroyd
- Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail:
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72
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Garai P, Gnanadhas DP, Chakravortty D. Salmonella enterica serovars Typhimurium and Typhi as model organisms: revealing paradigm of host-pathogen interactions. Virulence 2012; 3:377-88. [PMID: 22722237 PMCID: PMC3478240 DOI: 10.4161/viru.21087] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The lifestyle of intracellular pathogens has always questioned the skill of a microbiologist in the context of finding the permanent cure to the diseases caused by them. The best tool utilized by these pathogens is their ability to reside inside the host cell, which enables them to easily bypass the humoral immunity of the host, such as the complement system. They further escape from the intracellular immunity, such as lysosome and inflammasome, mostly by forming a protective vacuole-bound niche derived from the host itself. Some of the most dreadful diseases are caused by these vacuolar pathogens, for example, tuberculosis by Mycobacterium or typhoid fever by Salmonella. To deal with such successful pathogens therapeutically, the knowledge of a host-pathogen interaction system becomes primarily essential, which further depends on the use of a model system. A well characterized pathogen, namely Salmonella, suits the role of a model for this purpose, which can infect a wide array of hosts causing a variety of diseases. This review focuses on various such aspects of research on Salmonella which are useful for studying the pathogenesis of other intracellular pathogens.
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Affiliation(s)
- Preeti Garai
- Department of Microbiology and Cell Biology, Centre for Infectious Disease Research and Biosafety Laboratories, Indian Institute of Science, Bangalore, India
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73
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van der Heijden J, Finlay BB. Type III effector-mediated processes in Salmonella infection. Future Microbiol 2012; 7:685-703. [DOI: 10.2217/fmb.12.49] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Salmonella is one of the most successful bacterial pathogens that infect humans in both developed and developing countries. In order to cause infection, Salmonella uses type III secretion systems to inject bacterial effector proteins into host cells. In the age of antibiotic resistance, researchers have been looking for new strategies to reduce Salmonella infection. To understand infection and to analyze type III secretion as a potential therapeutic target, research has focused on identification of effectors, characterization of effector functions and how they contribute to disease. Many effector-mediated processes have been identified that contribute to infection but thus far no specific treatment has been found. In this perspective we discuss our current understanding of effector-mediated processes and discuss new techniques and approaches that may help us to find a solution to this worldwide problem.
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Affiliation(s)
- Joris van der Heijden
- Michael Smith Laboratories, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
- Department of Microbiology & Immunology, University of British Columbia, Vancouver, BC, Canada
| | - B Brett Finlay
- Department of Biochemistry & Molecular Biology, University of British Columbia, Vancouver, BC, Canada
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74
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Loetscher Y, Wieser A, Lengefeld J, Kaiser P, Schubert S, Heikenwalder M, Hardt WD, Stecher B. Salmonella transiently reside in luminal neutrophils in the inflamed gut. PLoS One 2012; 7:e34812. [PMID: 22493718 PMCID: PMC3321032 DOI: 10.1371/journal.pone.0034812] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Accepted: 03/05/2012] [Indexed: 01/03/2023] Open
Abstract
BACKGROUND Enteric pathogens need to grow efficiently in the gut lumen in order to cause disease and ensure transmission. The interior of the gut forms a complex environment comprising the mucosal surface area and the inner gut lumen with epithelial cell debris and food particles. Recruitment of neutrophils to the intestinal lumen is a hallmark of non-typhoidal Salmonella enterica infections in humans. Here, we analyzed the interaction of gut luminal neutrophils with S. enterica serovar Typhimurium (S. Tm) in a mouse colitis model. RESULTS Upon S. Tm(wt) infection, neutrophils transmigrate across the mucosa into the intestinal lumen. We detected a majority of pathogens associated with luminal neutrophils 20 hours after infection. Neutrophils are viable and actively engulf S. Tm, as demonstrated by live microscopy. Using S. Tm mutant strains defective in tissue invasion we show that pathogens are mostly taken up in the gut lumen at the epithelial barrier by luminal neutrophils. In these luminal neutrophils, S. Tm induces expression of genes typically required for its intracellular lifestyle such as siderophore production iroBCDE and the Salmonella pathogenicity island 2 encoded type three secretion system (TTSS-2). This shows that S. Tm at least transiently survives and responds to engulfment by gut luminal neutrophils. Gentamicin protection experiments suggest that the life-span of luminal neutrophils is limited and that S. Tm is subsequently released into the gut lumen. This "fast cycling" through the intracellular compartment of gut luminal neutrophils would explain the high fraction of TTSS-2 and iroBCDE expressing intra- and extracellular bacteria in the lumen of the infected gut. CONCLUSION In conclusion, live neutrophils recruited during acute S. Tm colitis engulf pathogens in the gut lumen and may thus actively engage in shaping the environment of pathogens and commensals in the inflamed gut.
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Affiliation(s)
| | - Andreas Wieser
- Max von Pettenkofer Insititute, Ludwig Maximilians University Munich, Munich, Germany
| | | | - Patrick Kaiser
- Institute of Microbiology, ETH Zürich, Zürich, Switzerland
| | - Sören Schubert
- Max von Pettenkofer Insititute, Ludwig Maximilians University Munich, Munich, Germany
| | - Mathias Heikenwalder
- Institute for Virology, Technical University Munich/Helmholtz Center Munich, Munich, Germany
| | | | - Bärbel Stecher
- Institute of Microbiology, ETH Zürich, Zürich, Switzerland
- Max von Pettenkofer Insititute, Ludwig Maximilians University Munich, Munich, Germany
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Rosales-Reyes R, Pérez-López A, Sánchez-Gómez C, Hernández-Mote RR, Castro-Eguiluz D, Ortiz-Navarrete V, Alpuche-Aranda CM. Salmonella infects B cells by macropinocytosis and formation of spacious phagosomes but does not induce pyroptosis in favor of its survival. Microb Pathog 2012; 52:367-74. [PMID: 22475626 DOI: 10.1016/j.micpath.2012.03.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 03/12/2012] [Accepted: 03/15/2012] [Indexed: 11/26/2022]
Abstract
We have previously reported that Salmonella infects B cells and survives within endosomal-lysosomal compartments. However, the mechanisms used by Salmonella to enter B cells remain unknown. In this study, we have shown that Salmonella induces its own entry by the induction of localized ruffling, macropinocytosis, and spacious phagosome formation. These events were associated with the rearrangement of actin and microtubule networks. The Salmonella pathogenesis island 1 (SPI-1) was necessary to invade B cells. In contrast to macrophages, B cells were highly resistant to cell death induced by Salmonella. These data demonstrate the ability of Salmonella to infect these non-professional phagocytic cells, where the bacterium can find an ideal intracellular niche to support persistence and the possible dissemination of infection.
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Affiliation(s)
- Roberto Rosales-Reyes
- Laboratorio de Infectología, Microbiología e Inmunología Clínicas, Departamento de Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico
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Lee SJ, Liang L, Juarez S, Nanton MR, Gondwe EN, Msefula CL, Kayala MA, Necchi F, Heath JN, Hart P, Tsolis RM, Heyderman RS, MacLennan CA, Felgner PL, Davies DH, McSorley SJ. Identification of a common immune signature in murine and human systemic Salmonellosis. Proc Natl Acad Sci U S A 2012; 109:4998-5003. [PMID: 22331879 PMCID: PMC3324033 DOI: 10.1073/pnas.1111413109] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Despite the importance of Salmonella infections in human and animal health, the target antigens of Salmonella-specific immunity remain poorly defined. We have previously shown evidence for antibody-mediating protection against invasive Salmonellosis in mice and African children. To generate an overview of antibody targeting in systemic Salmonellosis, a Salmonella proteomic array containing over 2,700 proteins was constructed and probed with immune sera from Salmonella-infected mice and humans. Analysis of multiple inbred mouse strains identified 117 antigens recognized by systemic antibody responses in murine Salmonellosis. Importantly, many of these antigens were independently identified as target antigens using sera from Malawian children with Salmonella bacteremia, validating the study of the murine model. Furthermore, vaccination with SseB, the most prominent antigenic target in Malawian children, provided mice with significant protection against Salmonella infection. Together, these data uncover an overlapping immune signature of disseminated Salmonellosis in mice and humans and provide a foundation for the generation of a protective subunit vaccine.
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Affiliation(s)
- Seung-Joo Lee
- Center for Comparative Medicine, Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, and
| | - Li Liang
- Department of Medicine, University of California, Irvine, CA 92697
| | - Silvia Juarez
- Department of Medicine, University of California, Irvine, CA 92697
| | - Minelva R. Nanton
- Center for Comparative Medicine, Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, and
| | - Esther N. Gondwe
- Malawi-Liverpool-Wellcome Trust Clinical Research Program, College of Medicine, University of Malawi, PO Box 30096, Chichiri, Blantyre 3, Malawi
| | - Chisomo L. Msefula
- Malawi-Liverpool-Wellcome Trust Clinical Research Program, College of Medicine, University of Malawi, PO Box 30096, Chichiri, Blantyre 3, Malawi
| | - Matthew A. Kayala
- Institute for Genomics and Bioinformatics, University of California, Irvine, CA 92067
| | - Francesca Necchi
- Novartis Vaccines Institute for Global Health, 53100 Siena, Italy
- Medical Research Council Centre for Immune Regulation, School of Immunity and Infection, College of Medicine and Dental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom; and
| | - Jennifer N. Heath
- Medical Research Council Centre for Immune Regulation, School of Immunity and Infection, College of Medicine and Dental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom; and
| | - Peter Hart
- Novartis Vaccines Institute for Global Health, 53100 Siena, Italy
- Medical Research Council Centre for Immune Regulation, School of Immunity and Infection, College of Medicine and Dental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom; and
| | - Renée M. Tsolis
- Department of Medical Microbiology and Immunology, School of Medicine, University of California, Davis, CA 95616
| | - Robert S. Heyderman
- Malawi-Liverpool-Wellcome Trust Clinical Research Program, College of Medicine, University of Malawi, PO Box 30096, Chichiri, Blantyre 3, Malawi
- Liverpool School of Tropical Medicine, University of Liverpool, Liverpool L3 5QA, United Kingdom
| | - Calman A. MacLennan
- Malawi-Liverpool-Wellcome Trust Clinical Research Program, College of Medicine, University of Malawi, PO Box 30096, Chichiri, Blantyre 3, Malawi
- Novartis Vaccines Institute for Global Health, 53100 Siena, Italy
- Medical Research Council Centre for Immune Regulation, School of Immunity and Infection, College of Medicine and Dental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom; and
| | | | - D. Huw Davies
- Department of Medicine, University of California, Irvine, CA 92697
| | - Stephen J. McSorley
- Center for Comparative Medicine, Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, and
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Ahmad I, Lamprokostopoulou A, Le Guyon S, Streck E, Barthel M, Peters V, Hardt WD, Römling U. Complex c-di-GMP signaling networks mediate transition between virulence properties and biofilm formation in Salmonella enterica serovar Typhimurium. PLoS One 2011; 6:e28351. [PMID: 22164276 PMCID: PMC3229569 DOI: 10.1371/journal.pone.0028351] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Accepted: 11/07/2011] [Indexed: 11/21/2022] Open
Abstract
Upon Salmonella enterica serovar Typhimurium infection of the gut, an early line of defense is the gastrointestinal epithelium which senses the pathogen and intrusion along the epithelial barrier is one of the first events towards disease. Recently, we showed that high intracellular amounts of the secondary messenger c-di-GMP in S. typhimurium inhibited invasion and abolished induction of a pro-inflammatory immune response in the colonic epithelial cell line HT-29 suggesting regulation of transition between biofilm formation and virulence by c-di-GMP in the intestine. Here we show that highly complex c-di-GMP signaling networks consisting of distinct groups of c-di-GMP synthesizing and degrading proteins modulate the virulence phenotypes invasion, IL-8 production and in vivo colonization in the streptomycin-treated mouse model implying a spatial and timely modulation of virulence properties in S. typhimurium by c-di-GMP signaling. Inhibition of the invasion and IL-8 induction phenotype by c-di-GMP (partially) requires the major biofilm activator CsgD and/or BcsA, the synthase for the extracellular matrix component cellulose. Inhibition of the invasion phenotype is associated with inhibition of secretion of the type three secretion system effector protein SipA, which requires c-di-GMP metabolizing proteins, but not their catalytic activity. Our findings show that c-di-GMP signaling is at least equally important in the regulation of Salmonella-host interaction as in the regulation of biofilm formation at ambient temperature.
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Affiliation(s)
- Irfan Ahmad
- Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institutet, Stockholm, Sweden
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Bouabe H, Liu Y, Moser M, Bösl MR, Heesemann J. Novel highly sensitive IL-10-beta-lactamase reporter mouse reveals cells of the innate immune system as a substantial source of IL-10 in vivo. THE JOURNAL OF IMMUNOLOGY 2011; 187:3165-76. [PMID: 21844394 DOI: 10.4049/jimmunol.1101477] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
In this study, we report on a novel, highly sensitive IL-10 reporter mouse based on the reporter enzyme β-lactamase and the fluorescence resonance energy transfer substrate coumarin-cephalosporin-fluorescein (4). In contrast to an IL-10 reporter mouse model that we generated by using enhanced GFP as reporter and allowed tracking IL-10 expression only in T cells, the IL-10-β-lactamase reporter (ITIB) mouse enables us to easily analyze and quantify IL-10 production at the single-cell level in all myeloid and lymphoid cell types. Furthermore, the ITIB mouse allows studying of the kinetics of IL-10 expression on a single-cell basis and provides a valuable tool for in vivo screening of cell type-specific IL-10-modulating drugs. Remarkably, the ITIB mouse revealed that, although a significant portion of each myeloid and lymphoid cell type produces IL-10, macrophages represent the major IL-10 producer population in several organs of naive mice. Moreover, using the examples of bacterial infection and transplantable skin melanoma models, we demonstrate the exceptional applicability of the ITIB mouse for the identification of IL-10-producing cells during immune responses in vivo. In this study, we identified tumor-infiltrating F4/80(+) macrophages as the major source for IL-10 in B16-F10 melanoma in vivo. During systemic infection with Yersinia enterocolitica, although the proportion of IL-10(+) cells increased in each myeloid and lymphoid cell type population, infiltrating CD11b(+)Ly6G(+) neutrophils represent a majority among IL-10-producing cells at the site of infection. We conclude that cells of the innate immune system that are involved in immune homeostasis or immune responses are substantial sources of IL-10.
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Affiliation(s)
- Hicham Bouabe
- Department of Bacteriology, Max von Pettenkofer Institute, Munich 80336, Germany.
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79
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Yoon H, Ansong C, McDermott JE, Gritsenko M, Smith RD, Heffron F, Adkins JN. Systems analysis of multiple regulator perturbations allows discovery of virulence factors in Salmonella. BMC SYSTEMS BIOLOGY 2011; 5:100. [PMID: 21711513 PMCID: PMC3213010 DOI: 10.1186/1752-0509-5-100] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Accepted: 06/28/2011] [Indexed: 01/16/2023]
Abstract
Background Systemic bacterial infections are highly regulated and complex processes that are orchestrated by numerous virulence factors. Genes that are coordinately controlled by the set of regulators required for systemic infection are potentially required for pathogenicity. Results In this study we present a systems biology approach in which sample-matched multi-omic measurements of fourteen virulence-essential regulator mutants were coupled with computational network analysis to efficiently identify Salmonella virulence factors. Immunoblot experiments verified network-predicted virulence factors and a subset was determined to be secreted into the host cytoplasm, suggesting that they are virulence factors directly interacting with host cellular components. Two of these, SrfN and PagK2, were required for full mouse virulence and were shown to be translocated independent of either of the type III secretion systems in Salmonella or the type III injectisome-related flagellar mechanism. Conclusions Integrating multi-omic datasets from Salmonella mutants lacking virulence regulators not only identified novel virulence factors but also defined a new class of translocated effectors involved in pathogenesis. The success of this strategy at discovery of known and novel virulence factors suggests that the approach may have applicability for other bacterial pathogens.
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Affiliation(s)
- Hyunjin Yoon
- Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon 97239, USA
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80
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Malik-Kale P, Jolly CE, Lathrop S, Winfree S, Luterbach C, Steele-Mortimer O. Salmonella - at home in the host cell. Front Microbiol 2011; 2:125. [PMID: 21687432 PMCID: PMC3109617 DOI: 10.3389/fmicb.2011.00125] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Accepted: 05/19/2011] [Indexed: 11/16/2022] Open
Abstract
The Gram-negative bacterium Salmonella enterica has developed an array of sophisticated tools to manipulate the host cell and establish an intracellular niche, for successful propagation as a facultative intracellular pathogen. While Salmonella exerts diverse effects on its host cell, only the cell biology of the classic “trigger”-mediated invasion process and the subsequent development of the Salmonella-containing vacuole have been investigated extensively. These processes are dependent on cohorts of effector proteins translocated into host cells by two type III secretion systems (T3SS), although T3SS-independent mechanisms of entry may be important for invasion of certain host cell types. Recent studies into the intracellular lifestyle of Salmonella have provided new insights into the mechanisms used by this pathogen to modulate its intracellular environment. Here we discuss current knowledge of Salmonella-host interactions including invasion and establishment of an intracellular niche within the host.
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Affiliation(s)
- Preeti Malik-Kale
- Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, National Institutes of Allergy and Infectious Disease, National Institute of Health Hamilton, MT, USA
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81
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McDermott JE, Yoon H, Nakayasu ES, Metz TO, Hyduke DR, Kidwai AS, Palsson BO, Adkins JN, Heffron F. Technologies and approaches to elucidate and model the virulence program of salmonella. Front Microbiol 2011; 2:121. [PMID: 21687430 PMCID: PMC3108385 DOI: 10.3389/fmicb.2011.00121] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Accepted: 05/15/2011] [Indexed: 11/13/2022] Open
Abstract
Salmonella is a primary cause of enteric diseases in a variety of animals. During its evolution into a pathogenic bacterium, Salmonella acquired an elaborate regulatory network that responds to multiple environmental stimuli within host animals and integrates them resulting in fine regulation of the virulence program. The coordinated action by this regulatory network involves numerous virulence regulators, necessitating genome-wide profiling analysis to assess and combine efforts from multiple regulons. In this review we discuss recent high-throughput analytic approaches used to understand the regulatory network of Salmonella that controls virulence processes. Application of high-throughput analyses have generated large amounts of data and necessitated the development of computational approaches for data integration. Therefore, we also cover computer-aided network analyses to infer regulatory networks, and demonstrate how genome-scale data can be used to construct regulatory and metabolic systems models of Salmonella pathogenesis. Genes that are coordinately controlled by multiple virulence regulators under infectious conditions are more likely to be important for pathogenesis. Thus, reconstructing the global regulatory network during infection or, at the very least, under conditions that mimic the host cellular environment not only provides a bird's eye view of Salmonella survival strategy in response to hostile host environments but also serves as an efficient means to identify novel virulence factors that are essential for Salmonella to accomplish systemic infection in the host.
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Affiliation(s)
- Jason E. McDermott
- Computational Biology and Bioinformatics Group, Pacific Northwest National LaboratoryRichland, WA, USA
| | - Hyunjin Yoon
- Department of Molecular Microbiology and Immunology, Oregon Health and Sciences UniversityPortland, OR, USA
| | - Ernesto S. Nakayasu
- Biological Separations and Mass Spectroscopy Group, Pacific Northwest National LaboratoryRichland WA, USA
| | - Thomas O. Metz
- Biological Separations and Mass Spectroscopy Group, Pacific Northwest National LaboratoryRichland WA, USA
| | - Daniel R. Hyduke
- Systems Biology, University of California San DiegoSan Diego, CA, USA
| | - Afshan S. Kidwai
- Department of Molecular Microbiology and Immunology, Oregon Health and Sciences UniversityPortland, OR, USA
| | | | - Joshua N. Adkins
- Biological Separations and Mass Spectroscopy Group, Pacific Northwest National LaboratoryRichland WA, USA
| | - Fred Heffron
- Department of Molecular Microbiology and Immunology, Oregon Health and Sciences UniversityPortland, OR, USA
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82
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Stepanova H, Volf J, Malcova M, Matiasovic J, Faldyna M, Rychlik I. Association of attenuated mutants of Salmonella enterica serovar Enteritidis with porcine peripheral blood leukocytes. FEMS Microbiol Lett 2011; 321:37-42. [PMID: 21569080 DOI: 10.1111/j.1574-6968.2011.02305.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
In this study, we were interested in the association of attenuated mutants of Salmonella enterica serovar Enteritidis with subpopulations of porcine white blood cells (WBC). The mutants included those with inactivated aroA, phoP, rfaL, rfaG, rfaC and fliC genes and a mutant with five major pathogenicity islands removed (ΔSPI1-5 mutant). Using flow cytometry, we did not observe any difference in the interactions of the wild-type S. Enteritidis, aroA and phoP mutants with WBC. ΔSPI1-5 and fliC mutants had a minor defect in their association with granulocytes and monocytes, but not with T- or B-lymphocytes. All three rfa mutants associated with granulocytes, monocytes and B-lymphocytes more than the wild-type S. Enteritidis did. Electron microscopy confirmed that the association correlated with the intracellular presence of S. Enteritidis and that the Salmonella-containing vacuole in the WBC infected with the rfa mutants, unlike all other strains, did not develop into a spacious phagosome. Intact lipopolysaccharide, but not the type III secretion system encoded by SPI-1, SPI-2 or the flagellar operon, is important for the initial interaction of S. Enteritidis with porcine leukocytes. This information can be used for the design of live Salmonella vaccines preferentially targeting particular cell types including cancer or tumor cells.
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83
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Discovery of Salmonella virulence factors translocated via outer membrane vesicles to murine macrophages. Infect Immun 2011; 79:2182-92. [PMID: 21464085 DOI: 10.1128/iai.01277-10] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Typhimurium, an intracellular pathogen and leading cause of food-borne illness, encodes a plethora of virulence effectors. Salmonella virulence factors are translocated into host cells and manipulate host cellular activities, providing a more hospitable environment for bacterial proliferation. In this study, we report a new set of virulence factors that is translocated into the host cytoplasm via bacterial outer membrane vesicles (OMV). PagK (or PagK1), PagJ, and STM2585A (or PagK2) are small proteins composed of ∼70 amino acids and have high sequence homology to each other (>85% identity). Salmonella lacking all three homologues was attenuated for virulence in a mouse infection model, suggesting at least partial functional redundancy among the homologues. While each homologue was translocated into the macrophage cytoplasm, their translocation was independent of all three Salmonella gene-encoded type III secretion systems (T3SSs)-Salmonella pathogenicity island 1 (SPI-1) T3SS, SPI-2 T3SS, and the flagellar system. Selected methods, including direct microscopy, demonstrated that the PagK-homologous proteins were secreted through OMV, which were enriched with lipopolysaccharide (LPS) and outer membrane proteins. Vesicles produced by intracellular bacteria also contained lysosome-associated membrane protein 1 (LAMP1), suggesting the possibility of OMV convergence with host cellular components during intracellular trafficking. This study identified novel Salmonella virulence factors secreted via OMV and demonstrated that OMV can function as a vehicle to transfer virulence determinants to the cytoplasm of the infected host cell.
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84
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Aussel L, Zhao W, Hébrard M, Guilhon AA, Viala JPM, Henri S, Chasson L, Gorvel JP, Barras F, Méresse S. Salmonella detoxifying enzymes are sufficient to cope with the host oxidative burst. Mol Microbiol 2011; 80:628-40. [PMID: 21362067 DOI: 10.1111/j.1365-2958.2011.07611.x] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The oxidative burst produced by the NADPH oxidase (Phox) is an essential weapon used by host cells to eradicate engulfed pathogens. In Salmonella typhimurium, oxidative stress resistance has been previously proposed to be mediated by the pathogenicity island 2 type III secretion system (T3SS-2), periplasmic superoxide dismutases and cytoplasmic catalases/peroxidases. Here, we fused an OxyR-dependent promoter to the gfp to build the ahpC-gfp transcriptional fusion. This reporter was used to monitor hydrogen peroxide levels as sensed by Salmonella during the course of an infection. We showed that the expression of this fusion was under the exclusive control of reactive oxygen species produced by the host. The ahpC-gfp expression was noticeably modified in the absence of bacterial periplasmic superoxide dismutases or cytoplasmic catalases/peroxidases. Surprisingly, inactivation of the T3SS-2 had no effect on the ahpC-gfp expression. All together, these results led to a model in which Salmonella resistance relies on its arsenal of detoxifying enzymes to cope with Phox-mediated oxidative stress.
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Affiliation(s)
- Laurent Aussel
- Laboratoire de Chimie Bactérienne - Institut de Microbiologie de la Méditerranée - IFR 88, UPR 9043 du CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
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85
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Dissemination of persistent intestinal bacteria via the mesenteric lymph nodes causes typhoid relapse. Infect Immun 2011; 79:1479-88. [PMID: 21263018 DOI: 10.1128/iai.01033-10] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Enteric pathogens can cause relapsing infections in a proportion of treated patients, but greater understanding of this phenomenon is hindered by the lack of appropriate animal models. We report here a robust animal model of relapsing primary typhoid that initiates after apparently successful antibiotic treatment of susceptible mice. Four days of enrofloxacin treatment were sufficient to reduce bacterial loads below detectable levels in all major organs, and mice appeared otherwise healthy. However, any interruption of further antibiotic therapy allowed renewed fecal shedding and renewed bacterial growth in systemic tissues to occur, and mice eventually succumbed to relapsing infection. In vivo imaging of luminescent Salmonella identified the mesenteric lymph nodes (MLNs) as a major reservoir of relapsing infection. A magnetic-bead enrichment strategy isolated MLN-resident CD11b(+) Gr-1(-) monocytes associated with low numbers of persistent Salmonella. However, the removal of MLNs increased the severity of typhoid relapse, demonstrating that this organ serves as a protective filter to restrain the dissemination of bacteria during antibiotic therapy. Together, these data describe a robust animal model of typhoid relapse and identify an important intestinal phagocyte subset involved in protection against the systemic spread of enteric infection.
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86
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Abstract
The last decade has witnessed increasing research on dissemination of bacterial pathogens in their hosts and on the processes that underlie bacterial spread and growth during organ colonization. Here, we discuss work on the mouse model of human typhoid fever caused by Salmonella enterica serovar Typhimurium. This has revealed the use of several routes of systemic dissemination that result in colonization and growth within the spleen and liver, the major sites of bacterial proliferation. We also highlight techniques that enable in vivo analysis of the infecting population at the spatiotemporal and single cell levels. These approaches have provided more detailed insights into the events underlying the dynamics of Salmonella replication, spread and clearance within host organs and tissues.
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Affiliation(s)
- Kathryn G Watson
- Centre for Molecular Microbiology and Infection, Imperial College London, Armstrong Road, London SW7 2AZ, UK
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87
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Autenrieth SE, Linzer TR, Hiller C, Keller B, Warnke P, Köberle M, Bohn E, Biedermann T, Bühring HJ, Hämmerling GJ, Rammensee HG, Autenrieth IB. Immune evasion by Yersinia enterocolitica: differential targeting of dendritic cell subpopulations in vivo. PLoS Pathog 2010; 6:e1001212. [PMID: 21124820 PMCID: PMC2991265 DOI: 10.1371/journal.ppat.1001212] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2010] [Accepted: 10/27/2010] [Indexed: 11/18/2022] Open
Abstract
CD4(+) T cells are essential for the control of Yersinia enterocolitica (Ye) infection in mice. Ye can inhibit dendritic cell (DC) antigen uptake and degradation, maturation and subsequently T-cell activation in vitro. Here we investigated the effects of Ye infection on splenic DCs and T-cell proliferation in an experimental mouse infection model. We found that OVA-specific CD4(+) T cells had a reduced potential to proliferate when stimulated with OVA after infection with Ye compared to control mice. Additionally, proliferation of OVA-specific CD4(+) T cells was markedly reduced when cultured with splenic CD8α(+) DCs from Ye infected mice in the presence of OVA. In contrast, T-cell proliferation was not impaired in cultures with CD4(+) or CD4(-)CD8α(-) DCs isolated from Ye infected mice. However, OVA uptake and degradation as well as cytokine production were impaired in CD8α(+) DCs, but not in CD4(+) and CD4(-)CD8α(-) DCs after Ye infection. Pathogenicity factors (Yops) from Ye were most frequently injected into CD8α(+) DCs, resulting in less MHC class II and CD86 expression than on non-injected CD8α(+) DCs. Three days post infection with Ye the number of splenic CD8α(+) and CD4(+) DCs was reduced by 50% and 90%, respectively. The decreased number of DC subsets, which was dependent on TLR4 and TRIF signaling, was the result of a faster proliferation and suppressed de novo DC generation. Together, we show that Ye infection negatively regulates the stimulatory capacity of some but not all splenic DC subpopulations in vivo. This leads to differential antigen uptake and degradation, cytokine production, cell loss, and cell death rates in various DC subpopulations. The data suggest that these effects might be caused directly by injection of Yops into DCs and indirectly by affecting the homeostasis of CD4(+) and CD8α(+) DCs. These events may contribute to reduced T-cell proliferation and immune evasion of Ye.
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Affiliation(s)
- Stella E Autenrieth
- Interfakultäres Institut für Zellbiologie, Universität Tübingen, Tübingen, Germany.
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88
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Quantitative PCR-based competitive index for high-throughput screening of Salmonella virulence factors. Infect Immun 2010; 79:360-8. [PMID: 21041489 DOI: 10.1128/iai.00873-10] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Salmonella enterica serovar Typhimurium is an intracellular pathogen and a main cause of food-borne illness. In this study, a quantitative PCR (qPCR)-based competitive index (CI) method was developed to simultaneously compare the growth of multiple Salmonella strains. This method was applied to a mixture of 17 Salmonella mutants lacking regulator genes, and their survival ratios were compared based on expression of natural resistance-associated macrophage protein 1 (Nramp1). Nramp1, as a major host innate immune component, controls the intracellular replication of pathogens. Deletion strains containing unique DNA barcodes in place of regulator genes were mixed with the parental control, and the bacteria were inoculated into congenic mice differing only at Nramp1. Most of the deletion strains were outcompeted by wild-type bacteria in either mouse strain, and the lack of Nramp1 didn't increase the tested strain/parent control replication ratios. When the same collection of mutants was tested in congenic mouse-derived primary macrophages, a major Nramp1-expressing cell type, six strains (ΔhimD, ΔphoP/phoQ, ΔrpoE, ΔrpoS, ΔompR/envZ, and Δhfq strains) grew better in Nramp1(-/-) than in Nramp1(+/+) macrophages, suggesting that these six regulators may play roles in overcoming Nramp1-mediated bactericidal activity in primary macrophages. The discrepancy in survival of macrophages and that of mice suggests either that there are differences in macrophage populations or that other cell types expressing Nramp1 control Salmonella proliferation in the host. The method described allows competitive infection analysis to be carried out on complex mixtures of bacteria and provides high reproducibility from independent biological replicates.
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89
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Discovery of novel secreted virulence factors from Salmonella enterica serovar Typhimurium by proteomic analysis of culture supernatants. Infect Immun 2010; 79:33-43. [PMID: 20974834 DOI: 10.1128/iai.00771-10] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Typhimurium is a leading cause of acute gastroenteritis throughout the world. This pathogen has two type III secretion systems (TTSS) encoded in Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) that deliver virulence factors (effectors) to the host cell cytoplasm and are required for virulence. While many effectors have been identified and at least partially characterized, the full repertoire of effectors has not been catalogued. In this proteomic study, we identified effector proteins secreted into defined minimal medium designed to induce expression of the SPI-2 TTSS and its effectors. We compared the secretomes of the parent strain to those of strains missing essential (ssaK::cat) or regulatory (ΔssaL) components of the SPI-2 TTSS. We identified 20 known SPI-2 effectors. Excluding the translocon components SseBCD, all SPI-2 effectors were biased for identification in the ΔssaL mutant, substantiating the regulatory role of SsaL in TTS. To identify novel effector proteins, we coupled our secretome data with a machine learning algorithm (SIEVE, SVM-based identification and evaluation of virulence effectors) and selected 12 candidate proteins for further characterization. Using CyaA' reporter fusions, we identified six novel type III effectors and two additional proteins that were secreted into J774 macrophages independently of a TTSS. To assess their roles in virulence, we constructed nonpolar deletions and performed a competitive index analysis from intraperitoneally infected 129/SvJ mice. Six mutants were significantly attenuated for spleen colonization. Our results also suggest that non-type III secretion mechanisms are required for full Salmonella virulence.
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90
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Abstract
The pattern recognition molecules Nod1 and Nod2 play important roles in intestinal homeostasis; however, how these proteins impact on the development of inflammation during bacterial colitis has not been examined. In the streptomycin-treated mouse model of Salmonella colitis, we found that mice deficient for both Nod1 and Nod2 had attenuated inflammatory pathology, reduced levels of inflammatory cytokines, and increased colonization of the mucosal tissue. Nod1 and Nod2 from both hematopoietic and nonhematopoietic sources contributed to the pathology, and all phenotypes were recapitulated in mice deficient for the signaling adaptor protein Rip2. However, the influence of Rip2 was strictly dependent on infection conditions that favored expression of the Salmonella pathogenicity island 2 (SPI-2) type III secretion system (TTSS), as Rip2 was dispensable for inflammation when mice were infected with bacteria grown under conditions that promoted expression of the SPI-1 TTSS. Thus, Nod1 and Nod2 can modulate inflammation and mediate efficient clearance of bacteria from the mucosal tissue during Salmonella colitis, but their role is dependent on the expression of the SPI-2 TTSS.
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91
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Role of two-component sensory systems of Salmonella enterica serovar Dublin in the pathogenesis of systemic salmonellosis in cattle. Microbiology (Reading) 2010; 156:3108-3122. [DOI: 10.1099/mic.0.041830-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Salmonella enterica serovar Dublin (S. Dublin) is associated with enteritis, typhoid and abortion in cattle. Infections are acquired by the oral route, and the bacteria transit through varied anatomical and cellular niches to elicit systemic disease. S. Dublin must therefore sense and respond to diverse extrinsic stimuli to control gene expression in a spatial and temporal manner. Two-component systems (TCSs) play key roles in such processes, and typically contain a membrane-associated sensor kinase (SK) that modifies a cognate response regulator. Analysis of the genome sequence of S. Dublin identified 31 conserved SK genes. Each SK gene was separately disrupted by lambda Red recombinase-mediated insertion of transposons harbouring unique sequence tags. Calves were challenged with a pool of the mutants together with control strains of defined virulence by the oral and intravenous routes. Quantification of tagged mutants in output pools derived from various tissues and cannulated lymphatic vessels allowed the assignment of spatial roles for each SK following oral inoculation or when the intestinal barrier was bypassed by intravenous delivery. Mutant phenotypes were also assigned in cultured intestinal epithelial cells. Mutants with insertions in barA, envZ, phoQ, ssrA or qseC were significantly negatively selected at all enteric and systemic sites sampled after oral dosing. Mutants lacking baeS, dpiB or citA were negatively selected at some but not all sites. After intravenous inoculation, only barA and phoQ mutants were significantly under-represented at systemic sites. The novel role of baeS in intestinal colonization was confirmed by oral co-infection studies, with a mutant exhibiting modest but significant attenuation at a number of enteric sites. This is the first systematic analysis of the role of all Salmonella TCSs in a highly relevant model of enteric fever. Spatial roles were assigned to eight S. Dublin SKs, but most were not essential for intestinal or systemic infection of the target host.
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92
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Dumont A, Boucrot E, Drevensek S, Daire V, Gorvel JP, Poüs C, Holden DW, Méresse S. SKIP, the host target of the Salmonella virulence factor SifA, promotes kinesin-1-dependent vacuolar membrane exchanges. Traffic 2010; 11:899-911. [PMID: 20406420 DOI: 10.1111/j.1600-0854.2010.01069.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In Salmonella-infected cells, the bacterial effector SifA forms a functional complex with the eukaryotic protein SKIP (SifA and kinesin-interacting protein). The lack of either partner has important consequences on the intracellular fate and on the virulence of this pathogen. In addition to SifA, SKIP binds the microtubule-based motor kinesin-1. Yet the absence of SifA or SKIP results in an unusual accumulation of kinesin-1 on the bacterial vacuolar membrane. To understand this apparent contradiction, we investigated the interaction between SKIP and kinesin-1 and the function of this complex. We show that the C-terminal RUN (RPIP8, UNC-14 and NESCA) domain of SKIP interacted specifically with the tetratricopeptide repeat (TPR) domain of the kinesin light chain. Overexpression of SKIP induced a microtubule- and kinesin-1-dependent anterograde movement of late endosomal/lysosomal compartments. In infected cells, SifA contributed to the fission of vesicles from the bacterial vacuole and the SifA/SKIP complex was required for the formation and/or the anterograde transport of kinesin-1-enriched vesicles. These observations reflect the role of SKIP as a linker and/or an activator for kinesin-1.
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Affiliation(s)
- Audrey Dumont
- Centre d'Immunologie de Marseille-Luminy, CNRS UMR 6102, INSERM U631, Université de la Méditerranée, Parc Scientifique de Luminy, Case 906-13288 Marseille Cedex 9, France
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93
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Karasova D, Sebkova A, Havlickova H, Sisak F, Volf J, Faldyna M, Ondrackova P, Kummer V, Rychlik I. Influence of 5 major Salmonella pathogenicity islands on NK cell depletion in mice infected with Salmonella enterica serovar Enteritidis. BMC Microbiol 2010; 10:75. [PMID: 20226037 PMCID: PMC2848020 DOI: 10.1186/1471-2180-10-75] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Accepted: 03/12/2010] [Indexed: 11/10/2022] Open
Abstract
Background In this study we were interested in the colonisation and early immune response of Balb/C mice to infection with Salmonella Enteritidis and isogenic pathogenicity island free mutants. Results The virulence of S. Enteritidis for Balb/C mice was exclusively dependent on intact SPI-2. Infections with any of the mutants harbouring SPI-2 (including the mutant in which we left only SPI-2 but removed SPI-1, SPI-3, SPI-4 and SPI-5) resulted in fatalities, liver injures and NK cell depletion from the spleen. The infection was of minimal influence on counts of splenic CD4 CD8 T lymphocytes and γδ T-lymphocytes although a reduced ability of splenic lymphocytes to respond to non-specific mitogens indicated general immunosuppression in mice infected with SPI-2 positive S. Enteritidis mutants. Further investigations showed that NK cells were depleted also in blood but not in the caecal lamina propria. However, NK cell depletion was not directly associated with the presence of SPI-2 and was rather an indicator of virulence or avirulence of a particular mutant because the depletion was not observed in mice infected with other attenuated mutants such as lon and rfaL. Conclusions The virulence of S. Enteritidis for Balb/C mice is exclusively dependent on the presence of SPI-2 in its genome, and a major hallmark of the infection in terms of early changes in lymphocyte populations is the depletion of NK cells in spleen and blood. The decrease of NK cells in circulation can be used as a marker of attenuation of S. Enteritidis mutants for Balb/C mice.
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Affiliation(s)
- Daniela Karasova
- Veterinary Research Institute, Hudcova 70, 62100 Brno, Czech Republic
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94
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Durand EA, Maldonado-Arocho FJ, Castillo C, Walsh RL, Mecsas J. The presence of professional phagocytes dictates the number of host cells targeted for Yop translocation during infection. Cell Microbiol 2010; 12:1064-82. [PMID: 20148898 DOI: 10.1111/j.1462-5822.2010.01451.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Type III secretion systems deliver effector proteins from Gram-negative bacterial pathogens into host cells, where they disarm host defences, allowing the pathogens to establish infection. Although Yersinia pseudotuberculosis delivers its effector proteins, called Yops, into numerous cell types grown in culture, we show that during infection Y. pseudotuberculosis selectively targets Yops to professional phagocytes in Peyer's patches, mesenteric lymph nodes and spleen, although it colocalizes with B and T cells as well as professional phagocytes. Strikingly, in the absence of neutrophils, the number of cells with translocated Yops was significantly reduced although the bacterial loads were similar, indicating that Y. pseudotuberculosis did not arbitrarily deliver Yops to the available cells. Using isolated splenocytes, selective binding and selective targeting to professional phagocytes when bacteria were limiting was also observed, indicating that tissue architecture was not required for the tropism for professional phagocytes. In isolated splenocytes, YadA and Invasin increased the number of all cells types with translocated Yops, but professional phagocytes were still preferentially translocated with Yops in the absence of these adhesins. Together these results indicate that Y. pseudotuberculosis discriminates among cells it encounters during infection and selectively delivers Yops to phagocytes while refraining from translocation to other cell types.
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Affiliation(s)
- Enrique A Durand
- Department of Molecular Biology and Microbiology, Tufts University, Boston MA 02111, USA
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95
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Valdez Y, Ferreira RBR, Finlay BB. Molecular mechanisms of Salmonella virulence and host resistance. Curr Top Microbiol Immunol 2010; 337:93-127. [PMID: 19812981 DOI: 10.1007/978-3-642-01846-6_4] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Salmonella species can cause typhoid fever and gastroenteritis in humans and pose a global threat to human health. In order to establish a successful infection, Salmonella utilize a large number of genes encoding a variety of virulence factors. Different animal models of infection have been used to better understand the mechanisms underlying each disease including cattle, rodents, and nematodes. To date, a number of different bacterial virulence factors have been identified using such animal models, most of which are secreted by two type three secretion systems (T3SS) encoded within Salmonella pathogenicity islands (SPI) 1 and 2. These proteins alter various host cell pathways, facilitating the invasion of epithelial cells during infection, as well as the survival and replication of Salmonella inside phagocytic cells. On the other hand, host genetics and resistance also play a role in the susceptibility to Salmonella infection. The natural resistance-associated macrophage protein 1 (Nramp1), for example, is critical for host defense, since mice lacking Nramp1 fail to control bacterial replication and succumb to low doses of S. Typhimurium. In this chapter, we analyze the different pathogen and host factors that play a role in the dynamic interaction between Salmonella and its host and their impact on disease.
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Affiliation(s)
- Yanet Valdez
- Department of Microbiology and Immunology, Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada
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96
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Silva MT. When two is better than one: macrophages and neutrophils work in concert in innate immunity as complementary and cooperative partners of a myeloid phagocyte system. J Leukoc Biol 2010; 87:93-106. [PMID: 20052802 DOI: 10.1189/jlb.0809549] [Citation(s) in RCA: 210] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The antimicrobial effector activity of phagocytes is crucial in the host innate defense against infection, and the classic view is that the phagocytes operating against intracellular and extracellular microbial pathogens are,respectively, macrophages and neutrophils. As a result of the common origin of the two phagocytes, they share several functionalities, including avid phagocytosis,similar kinetic behavior under inflammatory/infectious conditions, and antimicrobial and immunomodulatory activities. However, consequent to specialization during their differentiation, macrophages and neutrophils acquire distinctive, complementary features that originate different levels of antimicrobial capacities and cytotoxicity and different tissue localization and lifespan.This review highlights data suggesting the perspective that the combination of overlapping and complementary characteristics of the two professional phagocytes promotes their cooperative participation as effectors and modulators in innate immunity against infection and as orchestrators of adaptive immunity. In the concerted activities operating in antimicrobial innate immunity, macrophages and neutrophils are not able to replace each other. The common and complementary developmental,kinetic, and functional properties of neutrophils and macrophages make them the effector arms of a myeloid phagocyte system that groups neutrophils with members of the old mononuclear phagocyte system. The use by mammals of a system with two dedicated phagocytic cells working cooperatively represents an advantageous innate immune attack strategy that allows the efficient and safe use of powerful but dangerous microbicidal molecules.This crucial strategy is a target of key virulence mechanisms of successful pathogens.
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Affiliation(s)
- Manuel T Silva
- Instituto de Biologia Molecular e Celular, Rua do Campo Alegre 823, Porto, Portugal.
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Pseudomonas aeruginosa cytotoxin ExoU is injected into phagocytic cells during acute pneumonia. Infect Immun 2010; 78:1447-56. [PMID: 20100855 DOI: 10.1128/iai.01134-09] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
ExoU, a cytotoxin translocated into host cells via the type III secretion system of Pseudomonas aeruginosa, is associated with increased mortality and disease severity. We previously showed that impairment of recruited phagocytic cells allowed survival of ExoU-secreting P. aeruginosa in the lung. Here we analyzed types of cells injected with ExoU in vivo using translational fusions of ExoU with a beta-lactamase reporter (ExoU-Bla). Cells injected with ExoU-Bla were detectable in vitro but not in vivo, presumably due to the rapid cytotoxicity induced by the toxin. Therefore, we used a noncytotoxic ExoU variant, designated ExoU(S142A)-Bla, to analyze injection in vivo. We determined that phagocytic cells in the lung were frequently injected with ExoU(S142A). Early during infection, resident macrophages constituted the majority of cells into which ExoU was injected, but neutrophils and monocytes became the predominant types of cells into which ExoU was injected upon recruitment into the lung. We observed a modest preference for injection into neutrophils over injection into other cell types, but in general the repertoire of injected immune cells reflected the relative abundance of these cells in the lung. Our results indicate that phagocytic cells in the lung are injected with ExoU and support the hypothesis that ExoU-mediated impairment of phagocytes has a role in the pathogenesis of pneumonia caused by P. aeruginosa.
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98
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Abstract
Bacterial pathogens must overcome a range of challenges during the process of infecting their host. The ability of a pathogen to sense and respond appropriately to changes in host environment is vital if the pathogen is to succeed. Mammalian defense strategies include the use of barriers like skin and epithelial surfaces, the production of a chemical arsenal, such as stomach acid and reactive oxygen and nitrogen species, and a highly coordinated cellular and humoral immune response. Salmonella serovars are significant human and animal pathogens which have evolved several mechanisms to overcome mammalian host defense. Here we focus on the interplay which occurs between Salmonella and the host during the infection process, with particular emphasis on the complex bacterial response to reactive nitrogen species produced by the host. We discuss recent advances in our understanding of the key mechanisms which confer bacterial resistance to nitrogen species, which in response to nitric oxide include the flavohemoglobin, HmpA, the flavorubredoxin, NorV, and the cytochrome c nitrite reductase, NrfA, whilst in response to nitrate include a repertoire of nitrate reductases. Elucidating the precise role of different aspects of microbial physiology, nitrogen metabolism, and detoxification during infection will provide valuable insight into novel opportunities and potential targets for the development of therapeutic approaches.
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Enninga J, Rosenshine I. Imaging the assembly, structure and activity of type III secretion systems. Cell Microbiol 2009; 11:1462-70. [PMID: 19622097 DOI: 10.1111/j.1462-5822.2009.01360.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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100
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Kint G, Sonck KA, Schoofs G, De Coster D, Vanderleyden J, De Keersmaecker SC. 2D proteome analysis initiates new insights on the Salmonella Typhimurium LuxS protein. BMC Microbiol 2009; 9:198. [PMID: 19754952 PMCID: PMC2761396 DOI: 10.1186/1471-2180-9-198] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Accepted: 09/15/2009] [Indexed: 12/31/2022] Open
Abstract
Background Quorum sensing is a term describing a bacterial communication system mediated by the production and recognition of small signaling molecules. The LuxS enzyme, catalyzing the synthesis of AI-2, is conserved in a wide diversity of bacteria. AI-2 has therefore been suggested as an interspecies quorum sensing signal. To investigate the role of endogenous AI-2 in protein expression of the Gram-negative pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium), we performed a 2D-DIGE proteomics experiment comparing total protein extract of wildtype S. Typhimurium with that of a luxS mutant, unable to produce AI-2. Results Differential proteome analysis of wildtype S. Typhimurium versus a luxS mutant revealed relatively few changes beyond the known effect on phase 2 flagellin. However, two highly differentially expressed protein spots with similar molecular weight but differing isoelectric point, were identified as LuxS whereas the S. Typhimurium genome contains only one luxS gene. This observation was further explored and we show that the S. Typhimurium LuxS protein can undergo posttranslational modification at a catalytic cysteine residue. Additionally, by constructing LuxS-βla and LuxS-PhoA fusion proteins, we demonstrate that S. Typhimurium LuxS can substitute the cognate signal peptide sequences of β-lactamase and alkaline phosphatase for translocation across the cytoplasmic membrane in S. Typhimurium. This was further confirmed by fractionation of S. Typhimurium protein extracts, followed by Western blot analysis. Conclusion 2D-DIGE analysis of a luxS mutant vs. wildtype Salmonella Typhimurium did not reveal new insights into the role of AI-2/LuxS in Salmonella as only a small amount of proteins were differentially expressed. However, subsequent in depth analysis of the LuxS protein itself revealed two interesting features: posttranslational modification and potential translocation across the cytoplasmic membrane. As the S. Typhimurium LuxS protein does not contain obvious signal motifs, it is speculated that LuxS is a new member of so called moonlighting proteins. These observations might have consequences in future studies on AI-2 quorum signaling in S. Typhimurium.
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Affiliation(s)
- Gwendoline Kint
- Centre of Microbial and Plant Genetics, K, U, Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
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