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Fisher DJ, Beare PA. Recent advances in genetic systems in obligate intracellular human-pathogenic bacteria. Front Cell Infect Microbiol 2023; 13:1202245. [PMID: 37404720 PMCID: PMC10315504 DOI: 10.3389/fcimb.2023.1202245] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Accepted: 05/22/2023] [Indexed: 07/06/2023] Open
Abstract
The ability to genetically manipulate a pathogen is fundamental to discovering factors governing host-pathogen interactions at the molecular level and is critical for devising treatment and prevention strategies. While the genetic "toolbox" for many important bacterial pathogens is extensive, approaches for modifying obligate intracellular bacterial pathogens were classically limited due in part to the uniqueness of their obligatory lifestyles. Many researchers have confronted these challenges over the past two and a half decades leading to the development of multiple approaches to construct plasmid-bearing recombinant strains and chromosomal gene inactivation and deletion mutants, along with gene-silencing methods enabling the study of essential genes. This review will highlight seminal genetic achievements and recent developments (past 5 years) for Anaplasma spp., Rickettsia spp., Chlamydia spp., and Coxiella burnetii including progress being made for the still intractable Orientia tsutsugamushi. Alongside commentary of the strengths and weaknesses of the various approaches, future research directions will be discussed to include methods for C. burnetii that should have utility in the other obligate intracellular bacteria. Collectively, the future appears bright for unraveling the molecular pathogenic mechanisms of these significant pathogens.
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Affiliation(s)
- Derek J. Fisher
- School of Biological Sciences, Southern Illinois University, Carbondale, IL, United States
| | - Paul A. Beare
- Rocky Mountain Laboratory, National Institute of Health, Hamilton, MT, United States
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Bui DC, Luo T, McBride JW. Type 1 secretion system and effectors in Rickettsiales. Front Cell Infect Microbiol 2023; 13:1175688. [PMID: 37256108 PMCID: PMC10225607 DOI: 10.3389/fcimb.2023.1175688] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 05/02/2023] [Indexed: 06/01/2023] Open
Abstract
Obligate intracellular bacteria in the order Rickettsiales are transmitted by arthropod vectors and cause life-threatening infections in humans and animals. While both type 1 and type 4 secretion systems (T1SS and T4SS) have been identified in this group, the most extensive studies of Rickettsiales T1SS and associated effectors have been performed in Ehrlichia. These studies have uncovered important roles for the T1SS effectors in pathobiology and immunity. To evade innate immune responses and promote intracellular survival, Ehrlichia and other related obligate pathogens secrete multiple T1SS effectors which interact with a diverse network of host targets associated with essential cellular processes. T1SS effectors have multiple functional activities during infection including acting as nucleomodulins and ligand mimetics that activate evolutionarily conserved cellular signaling pathways. In Ehrlichia, an array of newly defined major immunoreactive proteins have been identified that are predicted as T1SS substrates and have conformation-dependent antibody epitopes. These findings highlight the underappreciated and largely uncharacterized roles of T1SS effector proteins in pathobiology and immunity. This review summarizes current knowledge regarding roles of T1SS effectors in Rickettsiales members during infection and explores newly identified immunoreactive proteins as potential T1SS substrates and targets of a protective host immune response.
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Affiliation(s)
- Duc-Cuong Bui
- Department of Pathology, University of Texas Medical Branch, Galveston, TX, United States
| | - Tian Luo
- Department of Pathology, University of Texas Medical Branch, Galveston, TX, United States
| | - Jere W. McBride
- Department of Pathology, University of Texas Medical Branch, Galveston, TX, United States
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX, United States
- Center for Biodefense and Emerging Infectious Diseases, University of Texas Medical Branch, Galveston, TX, United States
- Sealy Institute for Vaccine Sciences, University of Texas Medical Branch, Galveston, TX, United States
- Institute for Human Infections and Immunity, University of Texas Medical Branch, Galveston, TX, United States
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3
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Hunt JR, Carlyon JA. Analysis of Orientia tsutsugamushi promoter activity. Pathog Dis 2021; 79:6369350. [PMID: 34515306 DOI: 10.1093/femspd/ftab044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Accepted: 09/10/2021] [Indexed: 02/07/2023] Open
Abstract
Orientia tsutsugamushi is an obligate intracellular bacterium that causes scrub typhus, a potentially fatal rickettsiosis, and for which no genetic tools exist. Critical to addressing this technical gap is to identify promoters for driving expression of antibiotic resistance and fluorescence reporter genes in O. tsutsugamushi. Such promoters would need to be highly conserved among strains, expressed throughout infection, and exhibit strong activity. We examined the untranslated regions upstream of O. tsutsugamushi genes encoding outer membrane protein A (ompA), 22-kDa type-specific antigen (tsa22) and tsa56. The bacterium transcribed all three during infection of monocytic, endothelial and epithelial cells. Examination of the upstream noncoding regions revealed putative ribosome binding sites, one set of predicted -10 and -35 sequences for ompA and two sets of -10 and -35 sequences for tsa22 and tsa56. Comparison of these regions among geographically diverse O. tsutsugamushi patient isolates revealed nucleotide identities ranging from 84.8 to 100.0%. Upon examination of the candidates for the ability to drive green fluorescence protein expression in Escherichia coli, varying activities were observed with one of the tsa22 promoters being the strongest. Identification and validation of O. tsutsugamushi promoters is an initial key step toward genetically manipulating this important pathogen.
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Affiliation(s)
- Jason R Hunt
- Department of Microbiology and Immunology, Virginia Commonwealth University (VCU) Medical Center, School of Medicine, VCU, Richmond, VA 23298, USA
| | - Jason A Carlyon
- Department of Microbiology and Immunology, Virginia Commonwealth University (VCU) Medical Center, School of Medicine, VCU, Richmond, VA 23298, USA
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Functional Characterization of Multiple Ehrlichia chaffeensis Sodium (Cation)/Proton Antiporter Genes Involved in the Bacterial pH Homeostasis. Int J Mol Sci 2021; 22:ijms22168420. [PMID: 34445146 PMCID: PMC8395091 DOI: 10.3390/ijms22168420] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 07/30/2021] [Accepted: 08/02/2021] [Indexed: 11/16/2022] Open
Abstract
Ehrlichia chaffeensis causes human monocytic ehrlichiosis. Little is known about how this and other related tick-borne rickettsia pathogens maintain pH homeostasis in acidified phagosomes and the extracellular milieu. The membrane-bound sodium (cation)/proton antiporters are found in a wide range of organisms aiding pH homeostasis. We recently reported a mutation in an antiporter gene of E. chaffeensis (ECH_0379) which causes bacterial in vivo attenuation. The E. chaffeensis genome contains 10 protein coding sequences encoding for predicted antiporters. We report here that nine of these genes are transcribed during the bacterial growth in macrophages and tick cells. All E. chaffeensis antiporter genes functionally complemented antiporter deficient Escherichia coli. Antiporter activity for all predicted E. chaffeensis genes was observed at pH 5.5, while gene products of ECH_0179 and ECH_0379 were also active at pH 8.0, and ECH_0179 protein was complemented at pH 7.0. The antiporter activity was independently verified for the ECH_0379 protein by proteoliposome diffusion analysis. This is the first description of antiporters in E. chaffeensis and demonstrates that the pathogen contains multiple antiporters with varying biological functions, which are likely important for the pH homeostasis of the pathogen’s replicating and infectious forms.
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Wang Y, Nair ADS, Alhassan A, Jaworski DC, Liu H, Trinkl K, Hove P, Ganta CK, Burkhardt N, Munderloh UG, Ganta RR. Multiple Ehrlichia chaffeensis Genes Critical for Its Persistent Infection in a Vertebrate Host Are Identified by Random Mutagenesis Coupled with In Vivo Infection Assessment. Infect Immun 2020; 88:e00316-20. [PMID: 32747600 PMCID: PMC7504954 DOI: 10.1128/iai.00316-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 07/23/2020] [Indexed: 12/14/2022] Open
Abstract
Ehrlichia chaffeensis, a tick-transmitted obligate intracellular rickettsial agent, causes human monocytic ehrlichiosis. In recent reports, we described substantial advances in developing random and targeted gene disruption methods to investigate the functions of E. chaffeensis genes. We reported earlier that the Himar1 transposon-based random mutagenesis is a valuable tool in defining E. chaffeensis genes critical for its persistent growth in vivo in reservoir and incidental hosts. The method also aided in extending studies focused on vaccine development and immunity. Here, we describe the generation and mapping of 55 new mutations. To define the critical nature of the bacterial genes, infection experiments were carried out in the canine host with pools of mutant organisms. Infection evaluation in the physiologically relevant host by molecular assays and by xenodiagnoses allowed the identification of many proteins critical for the pathogen's persistent in vivo growth. Genes encoding proteins involved in biotin biosynthesis, protein synthesis and fatty acid biosynthesis, DNA repair, electron transfer, and a component of a multidrug resistance (MDR) efflux pump were concluded to be essential for the pathogen's in vivo growth. Three known immunodominant membrane proteins, i.e., two 28-kDa outer membrane proteins (P28/OMP) and a 120-kDa surface protein, were also recognized as necessary for the pathogen's obligate intracellular life cycle. The discovery of many E. chaffeensis proteins crucial for its continuous in vivo growth will serve as a major resource for investigations aimed at defining pathogenesis and developing novel therapeutics for this and related pathogens of the rickettsial family Anaplasmataceae.
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Affiliation(s)
- Ying Wang
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Arathy D S Nair
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Andy Alhassan
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
- Department of Pathobiology, School of Veterinary Medicine, St. George's University, West Indies, Grenada
| | - Deborah C Jaworski
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Huitao Liu
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Kathleen Trinkl
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Paidashe Hove
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
- Department of Pathobiology, School of Veterinary Medicine, St. George's University, West Indies, Grenada
| | - Charan K Ganta
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Nicole Burkhardt
- Department of Entomology, University of Minnesota, St. Paul, Minnesota, USA
| | - Ulrike G Munderloh
- Department of Entomology, University of Minnesota, St. Paul, Minnesota, USA
| | - Roman R Ganta
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
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Liu H, Ganta RR. Sequence Determinants Spanning -10 Motif and Spacer Region Implicated in Unique Ehrlichia chaffeensis Sigma 32-Dependent Promoter Activity of dnaK Gene. Front Microbiol 2019; 10:1772. [PMID: 31428069 PMCID: PMC6687850 DOI: 10.3389/fmicb.2019.01772] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 07/18/2019] [Indexed: 11/21/2022] Open
Abstract
Ehrlichia chaffeensis is an obligate intracellular tick-borne bacterium that causes human monocytic ehrlichiosis. Studying Ehrlichia gene regulation is challenge, as this and related rickettsiales lack natural plasmids and mutagenesis experiments are of a limited scope. E. chaffeensis contains only two sigma factors, σ32 and σ70. We previously developed Escherichia coli surrogate system to study transcriptional regulation from RNA polymerase (RNAP) containing Ehrlichia σ32 or σ70. We reported that RNAP binding motifs of E. chaffeensis genes recognized by σ32 or σ70 share extensive homology and that transcription may be initiated by either one of the sigma factors, although transcriptional efficiencies differ. In the current study, we investigated mapping the E. chaffeensis dnaK gene promoter using the pathogen σ32 expressed in E. coli lacking its native σ32. The E. coli surrogate system and our previously described in vitro transcription system aided in defining the unique −10 motif and spacer sequence of the dnaK promoter. We also mapped σ32 amino acids/domains engaged in its promoter regulation in E. chaffeensis. The data reported in this study demonstrate that the −10 and −35 motifs and spacer sequence located between the two motifs of dnaK promoter are critical for the RNAP function. Further, we mapped the importance of all six nucleotide positions of the −10 motif and identified critical determinants within it. In addition, we reported that the lack of C-rich sequence upstream to the −10 motif is unique in driving the pathogen-specific transcription by its σ32 from dnaK gene promoter. This is the first study in defining an E. chaffeensis σ32-dependent promoter and it offers insights about how this and other related rickettsial pathogens regulate stress response genes.
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Affiliation(s)
- Huitao Liu
- Center of Excellence for Vector-Borne Diseases, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
| | - Roman R Ganta
- Center of Excellence for Vector-Borne Diseases, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
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Oliva Chávez AS, Herron MJ, Nelson CM, Felsheim RF, Oliver JD, Burkhardt NY, Kurtti TJ, Munderloh UG. Mutational analysis of gene function in the Anaplasmataceae: Challenges and perspectives. Ticks Tick Borne Dis 2018; 10:482-494. [PMID: 30466964 DOI: 10.1016/j.ttbdis.2018.11.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Revised: 08/13/2018] [Accepted: 11/09/2018] [Indexed: 01/10/2023]
Abstract
Mutational analysis is an efficient approach to identifying microbial gene function. Until recently, lack of an effective tool for Anaplasmataceae yielding reproducible results has created an obstacle to functional genomics, because surrogate systems, e.g., ectopic gene expression and analysis in E. coli, may not provide accurate answers. We chose to focus on a method for high-throughput generation of mutants via random mutagenesis as opposed to targeted gene inactivation. In our search for a suitable mutagenesis tool, we considered attributes of the Himar1 transposase system, i.e., random insertion into AT dinucleotide sites, which are abundant in Anaplasmataceae, and lack of requirement for specific host factors. We chose the Anaplasma marginale tr promoter, and the clinically irrelevant antibiotic spectinomycin for selection, and in addition successfully implemented non-antibiotic selection using an herbicide resistance gene. These constructs function reasonably well in Anaplasma phagocytophilum harvested from human promyelocyte HL-60 cells or Ixodes scapularis tick cells. We describe protocols developed in our laboratory, and discuss what likely makes them successful. What makes Anaplasmataceae electroporation competent is unknown and manipulating electroporation conditions has not improved mutational efficiency. A concerted effort is needed to resolve remaining problems that are inherent to the obligate intracellular bacteria. Finally, using this approach, we describe the discovery and characterization of a putative secreted effector necessary for Ap survival in HL-60 cells.
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Affiliation(s)
- Adela S Oliva Chávez
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA.
| | - Michael J Herron
- Department of Entomology, University of Minnesota, St. Paul, MN, USA
| | - Curtis M Nelson
- Department of Entomology, University of Minnesota, St. Paul, MN, USA
| | | | - Jonathan D Oliver
- School of Public Health, Division of Environmental Health Sciences, University of Minnesota, Minneapolis, MN, USA
| | | | - Timothy J Kurtti
- Department of Entomology, University of Minnesota, St. Paul, MN, USA
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Nguyen Trong TP, Wang J, Majzoub-Altweck M, Fell S, Straubinger RK. Recovering host cell-free Anaplasma phagocytophilum from HL-60 cells by using rock tumbler grit in comparison to the syringe lysis method. Ticks Tick Borne Dis 2018; 10:280-285. [PMID: 30455057 DOI: 10.1016/j.ttbdis.2018.11.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 10/26/2018] [Accepted: 11/08/2018] [Indexed: 12/25/2022]
Abstract
Anaplasma phagocytophilum (Ap) is a tick-transmitted obligate intracellular bacterium and the causative agent of the granulocytic anaplasmosis in various species of domestic animals and in humans. During intracellular development Ap transforms from a dense-cored cell form into a reticulate cell form and vice versa. For isolation of intracellular bacteria, a range of different purification methods is used. However, unlike other Gram-negative bacteria Ap is considered to be sensitive to mechanical stress and osmolarity changes. An updated semi-purification method using rock tumbler grit is introduced here to increase the outcome of bacteria and to facilitate the procedure of host cell lysis. The objective of this study was to evaluate the structural integrity and infectivity of Ap after lysis of the host cells using rock tumbler grit and to compare the outcome to that of the frequently used method, syringe lysis. Human promyelocytic leukemia cell lines (HL-60) were infected with Ap and following host cell-free bacteria were assessed by transmission electron microscopy. The outcome of the different purification methods was compared using live/dead-staining based on immunofluorescence to count the number of viable bacteria and real-time PCR to compare the amount of DNA. Subsequently the isolated bacteria were tested to infect naive cell cultures. We observed that both Ap dense-cored cells and reticulate cells are preserved intact after the application of rock tumbler grit. The number of viable, host cell-free bacteria was higher by factor 1.7-2.4 compared to the syringe lysis protocol. Quantitative analysis based on real-time PCR showed an increase of bacterial DNA up to 1.6-2.9 times higher using the rock tumbler grit protocol. Bacteria released from the same number of infected host cells were used for new infections. Flow cytometric analysis of the cell cultures confirmed that the number of Ap organisms recovered by using the rock tumbler grit protocol resulted in higher infection rates than the number of Ap organisms recovered by using syringe lysis protocol. Our observations indicate that the rock tumbler grit protocol can be applied as a safe, robust and convenient method to recover Ap compared to syringe lysis.
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Affiliation(s)
- Thu Phong Nguyen Trong
- Institute for Infectious Diseases and Zoonoses, Department of Veterinary Sciences, Faculty of Veterinary Medicine, LMU Munich, Veterinaerstr. 13, 80539, Munich, Germany.
| | - Jinyong Wang
- Department of Microbiology & Immunology Chicago Medical School Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road 2-407, North Chicago, IL, 60064, USA.
| | - Monir Majzoub-Altweck
- Institute of Veterinary Pathology, Center for Clinical Veterinary Medicine Faculty of Veterinary Medicine, LMU Munich, Veterinaerstr. 13, 80539, Munich, Germany.
| | - Shari Fell
- Institute for Infectious Diseases and Zoonoses, Department of Veterinary Sciences, Faculty of Veterinary Medicine, LMU Munich, Veterinaerstr. 13, 80539, Munich, Germany.
| | - Reinhard K Straubinger
- Institute for Infectious Diseases and Zoonoses, Department of Veterinary Sciences, Faculty of Veterinary Medicine, LMU Munich, Veterinaerstr. 13, 80539, Munich, Germany.
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McGill JL, Wang Y, Ganta CK, Boorgula GDY, Ganta RR. Antigen-Specific CD4 +CD8 + Double-Positive T Cells Are Increased in the Blood and Spleen During Ehrlichia chaffeensis Infection in the Canine Host. Front Immunol 2018; 9:1585. [PMID: 30050533 PMCID: PMC6050357 DOI: 10.3389/fimmu.2018.01585] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Accepted: 06/26/2018] [Indexed: 12/11/2022] Open
Abstract
Ehrlichia chaffeensis is an obligate intracellular bacterium belonging to the order, Rickettsiales and is a frequent cause of severe and fatal tick-borne infection in people in North America. The reservoir host for E. chaffeensis is the white-tailed deer, while humans and dogs are regarded as common incidental hosts. In dogs, we and others have shown that E. chaffeensis establishes a chronic infection that persists for several weeks to months, while promoting the development of Th1 and Th17 cellular responses and pathogen-specific humoral immunity. We demonstrate here that vaccination with a live, attenuated clone of E. chaffeensis bearing a targeted mutation in the Ech_0230 gene neither promotes the development of long-lived cellular or humoral immunity, nor confers protection against secondary wild-type E. chaffeensis challenge. In dogs, a population of mature CD4+CD8+ double-positive (DP) T cells exists in the periphery that shares similarities with the DP T cell populations that have been described in humans and swine. Little is known about the function of these cells, particularly in the context of infectious diseases. Here, we demonstrate that canine DP T cells expand significantly in response to E. chaffeensis infection. Using in vitro antigen recall assays, we further demonstrate that canine DP T cells undergo clonal expansion, produce IFNγ and IL-17, and upregulate expression of granzyme B and granulysin. Together, our results demonstrate that DP T cells accumulate in the host during E. chaffeensis infection, and suggest that alternative lymphocyte populations may participate in the immune response to tick-borne infections in the incidental host.
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Affiliation(s)
- Jodi L. McGill
- Department of Veterinary Microbiology and Preventative Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, United States
| | - Ying Wang
- Center of Excellence for Vector-Borne Diseases, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
| | - Chanran K. Ganta
- Center of Excellence for Vector-Borne Diseases, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
| | - Gunavanthi D. Y. Boorgula
- Center of Excellence for Vector-Borne Diseases, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
| | - Roman R. Ganta
- Center of Excellence for Vector-Borne Diseases, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
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Protein and DNA synthesis demonstrated in cell-free Ehrlichia chaffeensis organisms in axenic medium. Sci Rep 2018; 8:9293. [PMID: 29915240 PMCID: PMC6006305 DOI: 10.1038/s41598-018-27574-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Accepted: 05/30/2018] [Indexed: 01/23/2023] Open
Abstract
Ehrlichia chaffeensis, a tick-transmitted rickettsial bacterium, is the causative agent of human monocytic ehrlichiosis. Biochemical characterization of this and other related Rickettsiales remains a major challenge, as they require a host cell for their replication. We investigated the use of an axenic medium for E. chaffeensis growth, assessed by protein and DNA synthesis, in the absence of a host cell. E. chaffeensis organisms harvested from in vitro cultures grown in a vertebrate cell line were fractionated into infectious dense-core cells (DC) and the non-infectious replicating form, known as reticulate cells (RC) by renografin density gradient centrifugation and incubated in the axenic medium containing amino acids, nucleotides, and different energy sources. Bacterial protein and DNA synthesis were observed in RCs in response to glucose-6-phosphate, although adenosine triphosphate, alpha-ketoglutarate or sodium acetate supported protein synthesis. The biosynthetic activity could not be detected in DCs in the axenic medium. While the data demonstrate de novo protein and DNA synthesis under axenic conditions for E. chaffeensis RCs, additional modifications are required in order to establish conditions that support bacterial replication, and transition to DCs.
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