Altered synthetic response of Campylobacter jejuni to cocultivation with human epithelial cells is associated with enhanced internalization

The Missing Pieces: The Role of Secretion Systems in Campylobacter jejuni Virulence

Campylobacter jejuni is likely the most common bacterial cause of gastroenteritis worldwide, responsible for millions of cases of inflammatory diarrhea characterized by severe abdominal cramps and blood in the stool. Further, C. jejuni infections are associated with post-infection sequelae in developed countries and malnutrition and growth-stunting in low- and middle-income countries. Despite the increasing prevalence of the disease, campylobacteriosis, and the recognition that this pathogen is a serious health threat, our understanding of C. jejuni pathogenesis remains incomplete. In this review, we focus on the Campylobacter secretion systems proposed to contribute to host-cell interactions and survival in the host. Moreover, we have applied a genomics approach to defining the structural and mechanistic features of C. jejuni type III, IV, and VI secretion systems. Special attention is focused on the flagellar type III secretion system and the prediction of putative effectors, given that the proteins exported via this system are essential for host cell invasion and the inflammatory response. We conclude that C. jejuni does not possess a type IV secretion system and relies on the type III and type VI secretion systems to establish a niche and potentiate disease.

Taking Control: Campylobacter jejuni Binding to Fibronectin Sets the Stage for Cellular Adherence and Invasion

Campylobacter jejuni, a foodborne pathogen, is one of the most common bacterial causes of gastroenteritis in the world. Undercooked poultry, raw (unpasteurized) dairy products, untreated water, and contaminated produce are the most common sources associated with infection. C. jejuni establishes a niche in the gut by adhering to and invading epithelial cells, which results in diarrhea with blood and mucus in the stool. The process of colonization is mediated, in part, by surface-exposed molecules (adhesins) that bind directly to host cell ligands or the extracellular matrix (ECM) surrounding cells. In this review, we introduce the known and putative adhesins of the foodborne pathogen C. jejuni. We then focus our discussion on two C. jejuni Microbial Surface Components Recognizing Adhesive Matrix Molecule(s) (MSCRAMMs), termed CadF and FlpA, which have been demonstrated to contribute to C. jejuni colonization and pathogenesis. In vitro studies have determined that these two surface-exposed proteins bind to the ECM glycoprotein fibronectin (FN). In vivo studies have shown that cadF and flpA mutants exhibit impaired colonization of chickens compared to the wild-type strain. Additional studies have revealed that CadF and FlpA stimulate epithelial cell signaling pathways necessary for cell invasion. Interestingly, CadF and FlpA have distinct FN-binding domains, suggesting that the functions of these proteins are non-redundant. In summary, the binding of FN by C. jejuni CadF and FlpA adhesins has been demonstrated to contribute to adherence, invasion, and cell signaling.

Molecular Dissection of the Campylobacter jejuni CadF and FlpA Virulence Proteins in Binding to Host Cell Fibronectin

Campylobacter jejuni, a zoonotic pathogen that frequently colonizes poultry, possesses two Microbial Surface Components Recognizing Adhesive Matrix Molecule(s) (MSCRAMMs) termed CadF and FlpA that bind to the glycoprotein fibronectin (FN). Previous to this study, it was not known whether the CadF and FlpA proteins were functionally redundant or if both were required to potentiate host cell binding and signaling processes. We addressed these questions by generating a complete repertoire of cadF and flpA mutants and complemented isolates, and performing multiple phenotypic assays. Both CadF and FlpA were found to be necessary for the maximal binding of C. jejuni to FN and to host cells. In addition, both CadF and FlpA are required for the delivery of the C. jejuni Cia effector proteins into the cytosol of host target cells, which in turn activates the MAPK signaling pathway (Erk 1/2) that is required for the C. jejuni invasion of host cells. These data demonstrate the non-redundant and bi-functional nature of these two C. jejuni FN-binding proteins. Taken together, the C. jejuni CadF and FlpA adhesins facilitate the binding of C. jejuni to the host cells, permit delivery of effector proteins into the cytosol of a host target cell, and aid in the rewiring of host cell signaling pathways to alter host cell behavior.

Campylobacter jejuni Demonstrates Conserved Proteomic and Transcriptomic Responses When Co-cultured With Human INT 407 and Caco-2 Epithelial Cells

Major foodborne bacterial pathogens, such as Campylobacter jejuni, have devised complex strategies to establish and foster intestinal infections. For more than two decades, researchers have used immortalized cell lines derived from human intestinal tissue to dissect C. jejuni-host cell interactions. Known from these studies is that C. jejuni virulence is multifactorial, requiring a coordinated response to produce virulence factors that facilitate host cell interactions. This study was initiated to identify C. jejuni proteins that contribute to adaptation to the host cell environment and cellular invasion. We demonstrated that C. jejuni responds to INT 407 and Caco-2 cells in a similar fashion at the cellular and molecular levels. Active protein synthesis was found to be required for C. jejuni to maximally invade these host cells. Proteomic and transcriptomic approaches were then used to define the protein and gene expression profiles of C. jejuni co-cultured with cells. By focusing on those genes showing increased expression by C. jejuni when co-cultured with epithelial cells, we discovered that C. jejuni quickly adapts to co-culture with epithelial cells by synthesizing gene products that enable it to acquire specific amino acids for growth, scavenge for inorganic molecules including iron, resist reactive oxygen/nitrogen species, and promote host cell interactions. Based on these findings, we selected a subset of the genes involved in chemotaxis and the regulation of flagellar assembly and generated C. jejuni deletion mutants for phenotypic analysis. Binding and internalization assays revealed significant differences in the interaction of C. jejuni chemotaxis and flagellar regulatory mutants. The identification of genes involved in C. jejuni adaptation to culture with host cells provides new insights into the infection process.

Methods to Study Campylobacter jejuni Adherence to and Invasion of Host Epithelial Cells

Measuring bacterial adherence and invasion of cells in vitro has enabled researchers to dissect the interactions of Campylobacter jejuni with eukaryotic cells. Numerous C. jejuni virulence determinants and host cell factors that contribute to the process of adherence, invasion, and immune modulation have been identified utilizing in vitro adherence and invasion assays. In this chapter, we describe the evaluation of C. jejuni adherence to and invasion of HeLa cells using the gentamicin-protection assay.

The Bacterial Species Campylobacter jejuni Induce Diverse Innate Immune Responses in Human and Avian Intestinal Epithelial Cells

Campylobacter remain the major cause of human gastroenteritis in the Developed World causing a significant burden to health services. Campylobacter are pathogens in humans and chickens, although differences in mechanistic understanding are incomplete, in part because phenotypic strain diversity creates inconsistent findings. Here, we took Campylobacter jejuni isolates (n = 100) from multi-locus sequence typed collections to assess their pathogenic diversity, through their inflammatory, cytotoxicity, adhesion, invasion and signaling responses in a high-throughput model using avian and human intestinal epithelial cells. C. jejuni induced IL-8 and CXCLi1/2 in human and avian epithelial cells, respectively, in a MAP kinase-dependent manner. In contrast, IL-10 responses in both cell types were PI 3-kinase/Akt-dependent. C. jejuni strains showed diverse levels of invasion with high invasion dependent on MAP kinase signaling in both cell lines. C. jejuni induced diverse cytotoxic responses in both cell lines with cdt-positive isolates showing significantly higher toxicity. Blockade of endocytic pathways suggested that invasion by C. jejuni was clathrin- and dynamin-dependent but caveolae- independent in both cells. In contrast, IL-8 (and CXCLi1/2) production was dependent on clathrin, dynamin, and caveolae. This study is important because of its scale, and the data produced, suggesting that avian and human epithelial cells use similar innate immune pathways where the magnitude of the response is determined by the phenotypic diversity of the Campylobacter species.

Campylobacter-Acanthamoeba interactions

Campylobacter jejuni is a foodborne pathogen recognized as the major cause of human bacterial enteritis. Undercooked poultry products and contaminated water are considered as the most important sources of infection. Some studies suggest transmission and survival of this bacterial pathogen may be assisted by the free-living protozoa Acanthamoeba. The latter is known to play the role of a host for various pathogenic bacteria, protecting them from harsh environmental conditions. Importantly, there is a similarity between the mechanisms of bacterial survival within amoebae and macrophages, making the former a convenient tool for the investigation of the survival of pathogenic bacteria in the environment. However, the molecular mechanisms involved in the interaction between Campylobacter and Acanthamoeba are not well understood. Whilst some studies suggest the ability of C. jejuni to survive within the protozoa, the other reports support an extracellular mode of survival only. In this review, we focus on the studies investigating the interaction between Campylobacter and Acanthamoeba, address some reasons for the contradictory results, and discuss possible implications of these results for epidemiology. Additionally, as the molecular mechanisms involved remain unknown, we also suggest possible factors that may be involved in this process. Deciphering the molecular mechanisms of pathogen-protozoa interaction will assist in a better understanding of Campylobacter lifestyle and in the development of novel antibacterial drugs.

Reducing Campylobacter jejuni colonization of poultry via vaccination

Campylobacter jejuni is a leading bacterial cause of human gastrointestinal disease worldwide. While C. jejuni is a commensal organism in chickens, case-studies have demonstrated a link between infection with C. jejuni and the consumption of foods that have been cross-contaminated with raw or undercooked poultry. We hypothesized that vaccination of chickens with C. jejuni surface-exposed colonization proteins (SECPs) would reduce the ability of C. jejuni to colonize chickens, thereby reducing the contamination of poultry products at the retail level and potentially providing a safer food product for consumers. To test our hypothesis, we injected chickens with recombinant C. jejuni peptides from CadF, FlaA, FlpA, CmeC, and a CadF-FlaA-FlpA fusion protein. Seven days following challenge, chickens were necropsied and cecal contents were serially diluted and plated to determine the number of C. jejuni per gram of material. The sera from the chickens were also analyzed to determine the concentration and specificity of antibodies reactive against the C. jejuni SECPs. Vaccination of chickens with the CadF, FlaA, and FlpA peptides resulted in a reduction in the number of C. jejuni in the ceca compared to the non-vaccinated C. jejuni-challenged group. The greatest reduction in C. jejuni colonization was observed in chickens injected with the FlaA, FlpA, or CadF-FlaA-FlpA fusion proteins. Vaccination of chickens with different SECPs resulted in the production of C. jejuni-specific IgY antibodies. In summary, we show that the vaccination of poultry with individual C. jejuni SECPs or a combination of SECPs provides protection of chickens from C. jejuni colonization.

The focal complex of epithelial cells provides a signalling platform for interleukin-8 induction in response to bacterial pathogens

Bacterial pathogens can induce an inflammatory response from epithelial tissues due to secretion of the pro-inflammatory chemokine interleukin-8 (IL-8). Many bacterial pathogens manipulate components of the focal complex (FC) to induce signalling events in host cells. We examined the interaction of several bacterial pathogens with host cells, including Campylobacter jejuni, to determine if the FC is required for induction of chemokine signalling in response to bacterial pathogens. Our data indicate that secretion of IL-8 is triggered by C. jejuni, Helicobacter pylori and Salmonella enterica serovar Typhimurium in response to engagement of β1 integrins. Additionally, we found that the secretion of IL-8 from C. jejuni infected epithelial cells requires FAK, Src and paxillin, which in turn are necessary for Erk 1/2 recruitment and activation. Targeting the FC component paxillin with siRNA prevented IL-8 secretion from cells infected with several bacterial pathogens, including C. jejuni, Helicobacter pylori, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, Pseudomonas aeruginosa, and Vibrio parahaemolyticus. Our findings indicate that maximal IL-8 secretion from epithelial cells in response to bacterial infection is dependent on the FC. Based on the commonality of the host response to bacterial pathogens, we propose that the FC is a signalling platform for an epithelial cell response to pathogenic organisms.

Modification of intestinal microbiota and its consequences for innate immune response in the pathogenesis of campylobacteriosis

Campylobacter jejuni is the leading cause of bacterial food-borne gastroenteritis in the world, and thus one of the most important public health concerns. The initial stage in its pathogenesis after ingestion is to overcome colonization resistance that is maintained by the human intestinal microbiota. But how it overcomes colonization resistance is unknown. Recently developed humanized gnotobiotic mouse models have provided deeper insights into this initial stage and host's immune response. These studies have found that a fat-rich diet modifies the composition of the conventional intestinal microbiota by increasing the Firmicutes and Proteobacteria loads while reducing the Actinobacteria and Bacteroidetes loads creating an imbalance that exposes the intestinal epithelial cells to adherence. Upon adherence, deoxycholic acid stimulates C. jejuni to synthesize Campylobacter invasion antigens, which invade the epithelial cells. In response, NF- κ B triggers the maturation of dendritic cells. Chemokines produced by the activated dendritic cells initiate the clearance of C. jejuni cells by inducing the actions of neutrophils, B-lymphocytes, and various subsets of T-cells. This immune response causes inflammation. This review focuses on the progress that has been made on understanding the relationship between intestinal microbiota shift, establishment of C. jejuni infection, and consequent immune response.

Campylobacter jejuni actively invades the amoeba Acanthamoeba polyphaga and survives within non digestive vacuoles

The Gram-negative bacterium Campylobacter jejuni is able to enter, survive and multiply within the free living amoeba Acanthamoeba polyphaga, but the molecular mechanisms behind these events are still unclear. We have studied the uptake and intracellular trafficking of viable and heat killed bacterial cells of the C. jejuni strain 81–176 in A. polyphaga. We found that viable bacteria associated with a substantially higher proportion of Acanthamoeba trophozoites than heat killed bacteria. Furthermore, the kinetics of internalization, the total number of internalized bacteria as well as the intracellular localization of internalized C. jejuni were dramatically influenced by bacterial viability. Viable bacteria were internalized at a high rate already after 1 h of co-incubation and were observed in small vacuoles tightly surrounding the bacteria. In contrast, internalization of heat killed C. jejuni was low at early time points and did not peak until 96 h. These cells were gathered in large spacious vacuoles that were part of the degradative pathway as determined by the uptake of fluorescently labeled dextran. The amount of heat killed bacteria internalized by A. polyphaga did never reach the maximal amount of internalized viable bacteria. These results suggest that the uptake and intracellular survival of C. jejuni in A. polyphaga is bacterially induced.

Serine phosphorylation of cortactin is required for maximal host cell invasion by Campylobacter jejuni

BACKGROUND

Campylobacter jejuni causes acute disease characterized by severe diarrhea containing blood and leukocytes, fever, and abdominal cramping. Disease caused by C. jejuni is dependent on numerous bacterial and host factors. C. jejuni invasion of the intestinal epithelial cells is seen in both clinical samples and animal models indicating that host cell invasion is, in part, necessary for disease. C. jejuni utilizes a flagellar Type III Secretion System (T3SS) to deliver the Campylobacter invasion antigens (Cia) to host cells. The Cia proteins modulate host cell signaling leading to actin cytoskeleton rearrangement necessary for C. jejuni host cell invasion, and are required for the development of disease.

RESULTS

This study was based on the hypothesis that the C. jejuni CiaD effector protein mediates Erk 1/2 dependent cytoskeleton rearrangement. We showed that CiaD was required for the maximal phosphorylation of Erk 1/2 by performing an immunoblot with a p-Erk 1/2 specific antibody and that Erk 1/2 participates in C. jejuni invasion of host cells by performing the gentamicin protection assay in the presence and absence of the PD98059 (a potent inhibitor of Erk 1/2 activation). CiaD was also found to be required for the maximal phosphorylation of cortactin S405 and S418, as judged by immunoblot analysis. The response of human INT 407 epithelial cells to infection with C. jejuni was evaluated by confocal microscopy and scanning electron microscopy to determine the extent of membrane ruffling. This analysis revealed that CiaD, Erk 1/2, and cortactin participate in C. jejuni-induced membrane ruffling. Finally, cortactin and N-WASP were found to be involved in C. jejuni invasion of host cells using siRNA to N-WASP, and siRNA to cortactin, coupled with the gentamicin protection assay.

CONCLUSION

We conclude that CiaD is involved in the activation of Erk 1/2 and that activated Erk 1/2 facilitates C. jejuni invasion by phosphorylation of cortactin on serine 405 and 418. This is the first time that cortactin and N-WASP have been shown to be involved in C. jejuni invasion of host cells. These data also provide a mechanistic basis for the requirement of Erk 1/2 in C. jejuni-mediated cytoskeletal rearrangement.

The Campylobacter jejuni CiaD effector protein activates MAP kinase signaling pathways and is required for the development of disease

Background

Enteric pathogens utilize a distinct set of proteins to modulate host cell signaling events that promote host cell invasion, induction of the inflammatory response, and intracellular survival. Human infection with Campylobacter jejuni, the causative agent of campylobacteriosis, is characterized by diarrhea containing blood and leukocytes. The clinical presentation of acute disease, which is consistent with cellular invasion, requires the delivery of the Campylobacter invasion antigens (Cia) to the cytosol of host cells via a flagellar Type III Secretion System (T3SS). We identified a novel T3SS effector protein, which we termed CiaD that is exported from the C. jejuni flagellum and delivered to the cytosol of host cells.

Results

We show that the host cell kinases p38 and Erk 1/2 are activated by CiaD, resulting in the secretion of interleukin-8 (IL-8) from host cells. Additional experiments revealed that CiaD-mediated activation of p38 and Erk 1/2 are required for maximal invasion of host cells by C. jejuni. CiaD contributes to disease, as evidenced by infection of IL-10 knockout mice. Noteworthy is that CiaD contains a Mitogen-activated protein (MAP) kinase-docking site that is found within effector proteins produced by other enteric pathogens. These findings indicate that C. jejuni activates the MAP kinase signaling pathways Erk 1/2 and p38 to promote cellular invasion and the release of the IL-8 pro-inflammatory chemokine.

Conclusions

The identification of a novel T3SS effector protein from C. jejuni significantly expands the knowledge of virulence proteins associated with C. jejuni pathogenesis and provides greater insight into the mechanism utilized by C. jejuni to invade host cells.

The fibronectin-binding motif within FlpA facilitates Campylobacter jejuni adherence to host cell and activation of host cell signaling

Campylobacter jejuni is a gram-negative, curved and rod-shaped bacterium that causes human gastroenteritis. Acute disease is associated with C. jejuni invasion of the intestinal epithelium. Epithelial cells infected with C. jejuni strains containing mutations in the FlpA and CadF fibronectin (Fn)-binding proteins exhibit reduced invasion of host cells and a C. jejuni CadF FlpA double mutant is impaired in the activation of epidermal growth factor receptor (EGFR) and Rho GTPase Rac1. Although these observations establish a role for Fn-binding proteins during C. jejuni invasion, their mechanistic contributions to invasion-associated signaling are unclear. We examined FlpA, a C. jejuni Fn-binding protein composed of three FNIII-like repeats D1, D2 and D3, to identify the interactions required for cellular adherence on pathogen-induced host cell signaling. We report that FlpA binds the Fn gelatin-binding domain via a motif within the D2 repeat. Epithelial cells infected with a flpA mutant exhibited decreased Rac1 activation and reduced membrane ruffling that coincided with impaired delivery of the secreted Cia proteins and reduced cell association. Phosphorylation of the Erk1/2 kinase, a downstream effector of EGFR signaling, was specifically associated with FlpA-mediated activation of β₁-integrin and EGFR signaling. In vivo experiments revealed that FlpA is necessary for C. jejuni disease based on bacterial dissemination to the spleen of IL-10^−/− germ-free mice. Thus, a novel Fn-binding motif within FlpA potentiates activation of Erk1/2 signaling via β₁-integrin during C. jejuni infection.

Role of motAB in adherence and internalization in polarized Caco-2 cells and in cecal colonization of Campylobacter jejuni

Campylobacter jejuni, a gram-negative motile bacterium commonly found in the chicken gastrointestinal tract, is one of the leading causes of bacterial gastroenteritis in humans worldwide. An intact and functional flagellum is important for C. jejuni virulence and colonization. To understand the role of C. jejuni motility in adherence and internalization in polarized Caco-2 cells and in cecal colonization of chickens we constructed a C. jejuni NCTC11168 V1 deltamotAB mutant. The motAB genes code for the flagellar motor, which enables the rotation of the flagellum. The nonmotile deltamotAB mutant expressed a full-length flagellum, which allowed us to differentiate between the roles of full-length flagella and motility in the ability of C. jejuni to colonize. To study the adherence and invasion abilities of the C. jejuni deltamotAB mutant we chose to use polarized Caco-2 cells, which are thought to be more representative of in vivo intestinal cell architecture and function. Although the C. jejuni deltamotAB mutant adhered significantly better than the wild type to the Caco-2 cells, we observed a significant reduction in the ability to invade the cells. In this study we obtained evidence that the flagellar rotation triggers C. jejuni invasion into polarized Caco-2 cells and we believe that C. jejuni is propelled into the cell with a drill-like rotation. The deltamotAB mutant was also tested for its colonization potential in a 1-day-old chicken model. The nonmotile C. jejuni deltamotAB mutant was not able to colonize any birds at days 3 and 7, suggesting that motility is essential for C. jejuni colonization.

The Campylobacter jejuni CiaC virulence protein is secreted from the flagellum and delivered to the cytosol of host cells

Campylobacter jejuni is a leading cause of bacterial gastroenteritis worldwide. Acute C. jejuni-mediated disease (campylobacteriosis) involves C. jejuni invasion of host epithelial cells using adhesins (e.g., CadF and FlpA) and secreted proteins [e.g., the Campylobacter invasion antigens (Cia)]. The genes encoding the Cia proteins are up-regulated upon co-culture of C. jejuni with epithelial cells. One of the Cia proteins, CiaC, is required for maximal invasion of host cells by C. jejuni. Previous work has also revealed that CiaC is, in part, responsible for host cell cytoskeletal rearrangements that result in membrane ruffling. This study was performed to test the hypothesis that CiaC is delivered to the cytosol of host cells. To detect the delivery of CiaC into cultured epithelial cells, we used the adenylate cyclase domain (ACD) of Bordetella pertussis CyaA as a reporter. In this study, we found that export and delivery of the C. jejuni Cia proteins into human INT 407 epithelial cells required a functional flagellar hook complex composed of FlgE, FlgK, and FlgL. Assays performed with bacterial culture supernatants supported the hypothesis that CiaC delivery requires bacteria-host cell contact. We also found that CiaC was delivered to host cells by cell-associated (bound) bacteria, as judged by experiments performed with inhibitors that specifically target the cell signaling pathways utilized by C. jejuni for cell invasion. Interestingly, the C. jejuni flgL mutant, which is incapable of exporting and delivering the Cia proteins, did not induce INT 407 cell membrane ruffles. Complementation of the flgL mutant with plasmid-encoded flgL restored the motility and membrane ruffling. These data support the hypothesis that the C. jejuni Cia proteins, which are exported from the flagellum, are delivered to the cytosol of host cells.

Host epithelial cell invasion by Campylobacter jejuni: trigger or zipper mechanism?

Campylobacter jejuni, a spiral-shaped Gram-negative pathogen, is a highly frequent cause of gastrointestinal foodborne illness in humans worldwide. Clinical outcome of C. jejuni infections ranges from mild to severe diarrheal disease, and some other complications including reactive arthritis and Guillain–Barré syndrome. This review article highlights various C. jejuni pathogenicity factors, host cell determinants, and proposed signaling mechanisms involved in human host cell invasion and their potential role in the development of C. jejuni-mediated disease. A model is presented which outlines the various important interactions of C. jejuni with the intestinal epithelium, and we discuss the pro’s and con’s for the “zipper” over the “trigger” mechanism of invasion. Future work should clarify the contradictory role of some previously identified factors, and should identify and characterize novel virulence determinants, which are crucial to provide fresh insights into the diversity of strategies employed by this pathogen to cause disease.

Genotypic and phenotypic properties of cattle-associated Campylobacter and their implications to public health in the USA

Since cattle are a major source of food and the cattle industry engages people from farms to processing plants and meat markets, it is conceivable that beef-products contaminated with Campylobacter spp. would pose a significant public health concern. To better understand the epidemiology of cattle-associated Campylobacter spp. in the USA, we characterized the prevalence, genotypic and phenotypic properties of these pathogens. Campylobacter were detected in 181 (19.2%) out of 944 fecal samples. Specifically, 71 C. jejuni, 132 C. coli, and 10 other Campylobacter spp. were identified. The prevalence of Campylobacter varied regionally and was significantly (P<0.05) higher in fecal samples collected from the South (32.8%) as compared to those from the North (14.8%), Midwest (15.83%), and East (12%). Pulsed Field Gel Electrophoresis (PFGE) analysis showed that C. jejuni and C. coli isolates were genotypically diverse and certain genotypes were shared across two or more of the geographic locations. In addition, 13 new C. jejuni and two C. coli sequence types (STs) were detected by Multi Locus Sequence Typing (MLST). C. jejuni associated with clinically human health important sequence type, ST-61 which was not previously reported in the USA, was identified in the present study. Most frequently observed clonal complexes (CC) were CC ST-21, CC ST-42, and CC ST-61, which are also common in humans. Further, the cattle associated C. jejuni strains showed varying invasion and intracellular survival capacity; however, C. coli strains showed a lower invasion and intracellular survival potential compared to C. jejuni strains. Furthermore, many cattle associated Campylobacter isolates showed resistance to several antimicrobials including ciprofloxacin, erythromycin, and gentamicin. Taken together, our results highlight the importance of cattle as a potential reservoir for clinically important Campylobacter.

HtrA chaperone activity contributes to host cell binding in Campylobacter jejuni

Background

Acute gastroenteritis caused by the food-borne pathogen Campylobacter jejuni is associated with attachment of bacteria to the intestinal epithelium and subsequent invasion of epithelial cells. In C. jejuni, the periplasmic protein HtrA is required for efficient binding to epithelial cells. HtrA has both protease and chaperone activity, and is important for virulence of several bacterial pathogens.

Results

The aim of this study was to determine the role of the dual activities of HtrA in host cell interaction of C. jejuni by comparing an htrA mutant lacking protease activity, but retaining chaperone activity, with a ΔhtrA mutant and the wild type strain. Binding of C. jejuni to both epithelial cells and macrophages was facilitated mainly by HtrA chaperone activity that may be involved in folding of outer membrane adhesins. In contrast, HtrA protease activity played only a minor role in interaction with host cells.

Conclusion

We show that HtrA protease and chaperone activities contribute differently to C. jejuni's interaction with mammalian host cells, with the chaperone activity playing the major role in host cell binding.

Physiological characterization of Campylobacter jejuni under cold stresses conditions: its potential for public threat

Campylobacter jejuni is the major cause of human gastroenteritis worldwide. Under stress conditions, C. jejuni can enter a viable but non-culturable (VBNC) state. We found that the C. jejuni was able to enter a VBNC state by prolonged incubation at 4°C. The standard isolation methods using pre-enrichment steps in Bolton broth or Preston broth could not detect the VBNC cells in spiked chicken meat. The transcription levels of virulence-associated genes (flaA, flaB, cadF, ciaB, cdtA, cdtB and cdtC) were expressed in VBNC cells but in low levels. The VBNC cells retained the ability to invade Caco-2 human intestinal epithelial cells in vitro. In most cases, VBNC cells failed to resuscitate in Caco-2 cells, but in some experiments, they formed colonies after co-incubation with host cells. Collectively, C. jejuni enters into a VBNC state at 4°C and the VBNC C. jejuni remains virulent which may possibly lead to disease in humans. C. jejuni in VBNC state is a potential concern for food safety.

Campylobacter jejuni survival within human epithelial cells is enhanced by the secreted protein CiaI

Although it is known that Campylobacter jejuni invade the cells that line the human intestinal tract, the bacterial proteins that enable this pathogen to survive within Campylobacter-containing vacuoles (CCV) have not been identified. Here, we describe the identification and characterization of a protein that we termed CiaI for Campylobacter invasion antigen involved in intracellular survival. We show that CiaI harbours an amino-terminal type III secretion sequence and is secreted from C. jejuni through the flagellar type III secretion system. In addition, the ciaI mutant was impaired in intracellular survival when compared with a wild-type strain, as judged by the gentamicin-protection assay. Fluorescence microscopy examination of epithelial cells infected with the C. jejuni ciaI mutant revealed that the CCV were more frequently co-localized with Cathepsin D (a lysosomal marker) than the CCV in cells infected with a C. jejuni wild-type strain. Ectopic expression of CiaI-GFP in epithelial cells yielded a punctate phenotype not observed with the other C. jejuni genes, and this phenotype was abolished by mutation of a dileucine motif located in the carboxy-terminus of the protein. Based on the data, we conclude that CiaI contributes to the ability of C. jejuni to survive within epithelial cells.

Identification of Campylobacter jejuni genes involved in its interaction with epithelial cells

Campylobacter jejuni is the leading cause of infectious gastroenteritis in industrialized nations. Its ability to enter and survive within nonphagocytic cells is thought to be very important for pathogenesis. However, little is known about the C. jejuni determinants that mediate these processes. Through an extensive transposon mutagenesis screen, we have identified several loci that are required for C. jejuni efficient entry and survival within epithelial cells. Among these loci, insertional mutations in aspA, aspB, and sodB resulted in drastic reduction in C. jejuni entry and/or survival within host cells and a severe defect in colonization in an animal model. The implications of these findings for the understanding of C. jejuni-host cell interactions are discussed.

An overview of methods used to clarify pathogenesis mechanisms of Campylobacter jejuni

Thermotolerant campylobacters are the most frequent cause of bacterial infection of the lower intestine worldwide. The mechanism of pathogenesis of Campylobacter jejuni comprises four main stages: adhesion to intestinal cells, colonization of the digestive tract, invasion of targeted cells, and toxin production. In response to the high number of cases of human campylobacteriosis, various virulence study models are available according to the virulence stage being analyzed. The aim of this review is to compare the different study models used to look at human disease. Molecular biology tools used to identify genes or proteins involved in virulence mechanisms are also summarized. Despite high cost and limited availability, animal models are frequently used to study digestive disease, in particular to analyze the colonization stage. Eukaryotic cell cultures have been developed because of fewer restrictions on their use and the lower cost of these cultures compared with animal models, and this ex vivo approach makes it possible to mimic the bacterial cell-host interactions observed in natural disease cases. Models are complemented by molecular biology tools, especially mutagenesis and DNA microarray methods to identify putative virulence genes or proteins and permit their characterization. No current model seems to be ideal for studying the complete range of C. jejuni virulence. However, the models available deal with different aspects of the complex pathogenic mechanisms particular to this bacterium.

Cloning, sequencing and expression of full-length Campylobacter invasion antigen B gene operon from Campylobacter lari

A novel PCR primer pair for amplification of full-length cia B gene from thermophilic campylobacters, generated an amplicon of approximately 2.2 kilo base pairs (kbp) with all 18 isolates (n = 7 for urease-negative (UN) C. lari; n = 9 urease-positive thermophilic Campylobacter (UPTC); n = 1 C. jejuni; n = 1 C. coli). The putative open reading frame (ORF) of the cia B from C. lari isolates consisted of 1,833 bp similarly, but differing from those of C. jejuni and C. coli isolates. The putative promoter structures consisting of a semi-conserved T -rich sequence and a consensus sequence at the -10 region were identified upstream of the putative ORF in all the C. lari isolates. A start codon ATG and a probable ribosome binding site were also identified in all the isolates. In addition, two distinctly different and taxon (UN C. lari and UPTC) dependent hypothetically intrinsic rho -independent transcriptional terminators for the cia B were identified to occur within the C. lari. Reverse transcription-PCR analysis identified the transcription of cia B gene in the C. lari cells. The neighbor joining tree suggested that the nucleotide sequence information of the cia B had molecular discrimination efficacy among UN C. lari, UPTC, C. jejuni and C. coli organisms.

Identification of a Campylobacter jejuni-secreted protein required for maximal invasion of host cells

The food-borne pathogen Campylobacter jejuni is dependent on a functional flagellum for motility and the export of virulence proteins that promote maximal host cell invasion. Both the flagellar and non-flagellar proteins exported via the flagellar type III secretion system contain a sequence within the amino-terminus that directs their export from the bacterial cell. Accordingly, we developed a genetic screen to identify C. jejuni genes that encode a type III secretion amino-terminal sequence that utilizes the flagellar type III secretion system of Yersinia enterocolitica and a phospholipase reporter (yplA). We screened a library of 321 C. jejuni genes and identified proteins with putative type III secretion amino-terminal sequences. One gene identified by the screen was Cj1242. We generated a mutation in Cj1242, and performed growth rate, motility, secretion and INT 407 cell adherence and internalization assays. The C. jejuni Cj1242 mutant was not altered in growth rate or motility when compared with the wild-type strain, but displayed an altered secretion profile and a reduction in host cell internalization. Based on the phenotype of the C. jejuni Cj1242 mutant, we designated the protein Campylobacter invasion antigen C (CiaC). Collectively, our findings indicate that CiaC is a potentially important virulence factor.

Campylobacter proteomics: guidelines, challenges and future perspectives

Campylobacter species are a major cause of disease in mammalian systems. The most common human etiological agent within this genus is Campylobacter jejuni - the leading cause of bacterial gastroenteritis in the developed world. While this organism has been extensively studied at the cellular level, and the genome sequences of several strains have now been elucidated, little is known regarding the role of individual proteins in virulence processes, such as adhesion, colonization and toxicity towards host cells. Proteomics encompasses the global analysis of proteins at the organism level. The technologies included under this term have now started to be utilized for understanding how Campylobacter species respond to changes in the environment, with an emphasis on the human host, as well as to map subcellular locations of proteins, in particular those that are surface-associated. C. jejuni is also of great significance as, unlike most other bacteria, it is able to post-translationally modify its proteins. The analysis of such proteins represents a major challenge in understanding this organism at the proteomic and cellular levels. This review will examine the state-of-the-art in Campylobacter proteomics, as well as provide insights into strategies that need to be undertaken to provide a comprehensive understanding of this organism at the molecular and functional level.

Campylobacter jejuni cocultured with epithelial cells reduces surface capsular polysaccharide expression

The host cell environment can alter bacterial pathogenicity. We employed a combination of cellular and molecular techniques to study the expression of Campylobacter jejuni polysaccharides cocultured with HCT-8 epithelial cells. After two passages, the amount of membrane-bound high-molecular-weight polysaccharide was considerably reduced. Microarray profiling confirmed significant downregulation of capsular polysaccharide (CPS) locus genes. Experiments using conditioned media showed that sugar depletion occurred only when the bacterial and epithelial cells were cocultured. CPS depletion occurred when C. jejuni organisms were exposed to conditioned media from a different C. jejuni strain but not when exposed to conditioned media from other bacterial species. Proteinase K or heat treatment of conditioned media under coculture conditions abrogated the effect on the sugars, as did formaldehyde fixation and cycloheximide treatment of host cells or chloramphenicol treatment of the bacteria. However, sugar depletion was not affected in flagellar export (fliQ) and quorum-sensing (luxS) gene mutants. Passaged C. jejuni showed reduced invasiveness and increased serum sensitivity in vitro. C. jejuni alters its surface polysaccharides when cocultured with epithelial cells, suggesting the existence of a cross talk mechanism that modulates CPS expression during infection.

Culture of Campylobacter jejuni with sodium deoxycholate induces virulence gene expression

Campylobacter jejuni, a spiral-shaped gram-negative bacterium, is a leading bacterial cause of human food-borne illness. Acute disease is associated with C. jejuni invasion of the intestinal epithelium. Further, maximal host cell invasion requires the secretion of proteins termed Campylobacter invasion antigens (Cia). As bile acids are known to alter the pathogenic behavior of other gastrointestinal pathogens, we hypothesized that the virulence potential of Campylobacter may be triggered by the bile acid deoxycholate (DOC). In support of this hypothesis, culturing C. jejuni with a physiologically relevant concentration of DOC significantly altered the kinetics of cell invasion, as shown by gentamicin protection assays. In contrast to C. jejuni harvested from Mueller-Hinton (MH) agar plates, C. jejuni harvested from MH agar plates supplemented with DOC secreted the Cia proteins, as judged by metabolic labeling experiments. DOC was also found to induce the expression of the ciaB gene, as determined by beta-galactosidase reporter, real-time reverse transcription-PCR, and microarray analyses. Microarray analysis further revealed that DOC induced the expression of virulence genes (ciaB, cmeABC, dccR, and tlyA). In summary, we demonstrated that it is possible to enhance the pathogenic behavior of C. jejuni by modifying the culture conditions. These results provide a foundation for identifying genes expressed by C. jejuni in response to in vivo-like culture conditions.

Influence of Campylobacter jejuni fliA, rpoN and flgK genes on colonization of the chicken gut

Campylobacter jejuni, a commensal Gram-negative motile bacterium commonly found in chickens is a frequent cause of human gastrointestinal infections. The polar flagellum of C. jejuni is an important virulence and colonization factor, providing motility to the cell as well as a type III secretion function. The flagellar biosynthesis genes fliA (sigma28) and rpoN (sigma54) of C. jejuni regulate a large number of genes involved in motility, protein secretion and invasion, which have been shown to be important factors for the virulence of this organism. To understand the role of the flagellar sigma factors, sigma28 and sigma54, in regulating colonization of the chicken intestinal tract, we assessed fliA and rpoN mutants of C. jejuni NCTC11168 for their ability to secrete Cia proteins and to adhere to and invade Hela cells. The mutants were also tested for their in vivo colonization potential in a chicken model with two different challenge doses. The fliA mutant showed reduced motility (25% that of the wild type) but secreted Cia proteins, yet it did not colonize the chicken cecum. The rpoN mutant cells lacked the spiral shape of C. jejuni and motility was reduced to 10% of the wild-type. The rpoN mutant did not secrete any Cia proteins but RT-PCR analysis showed the presence of ciaB mRNA, indicating that ciaB gene expression was independent of sigma54. Not surprisingly, the colonization defects of both fliA and rpoN mutants were more severe than the flgK mutant. We also demonstrated that FlgK, the hook filament junction protein of C. jejuni, is required for assembly of the flagellar secretory apparatus and an flgK mutant of C. jejuni expressing only the hook showed diminished motility and was completely attenuated for cecal colonization in chickens.

A major role for intestinal epithelial nucleotide oligomerization domain 1 (NOD1) in eliciting host bactericidal immune responses to Campylobacter jejuni

Campylobacter jejuni is the foremost cause of bacterial-induced diarrhoeal disease worldwide. Although it is well established that C. jejuni infection of intestinal epithelia triggers host innate immune responses, the mechanism(s) involved remain poorly defined. Innate immunity can be initiated by families of structurally related pattern-recognition receptors (PRRs) that recognize specific microbial signature motifs. Here, we demonstrated maximal induction of epithelial innate responses during infection with live C. jejuni cells. In contrast when intestinal epithelial cells (IECs) were exposed to paraformaldehyde-fixed bacteria, host responses were minimal and a marked reduction in the number of intracellular bacteria was noted in parallel. These findings suggested a role for intracellular host-C. jejuni interactions in eliciting early innate immunity. We therefore investigated the potential involvement of a family of intracellular, cytoplasmic PRRs, the nucleotide-binding oligomerization domain (NOD) proteins in C. jejuni recognition. We identified NOD1, but not NOD2, as a major PRR for C. jejuni in IEC. We also found that targeting intestinal epithelial NOD1 with small interfering RNA resulted in an increase in number of intracellular C. jejuni, thus highlighting a critical role for NOD1-mediated antimicrobial defence mechanism(s) in combating this infection at the gastrointestinal mucosal surface.

Characterization of genetically matched isolates of Campylobacter jejuni reveals that mutations in genes involved in flagellar biosynthesis alter the organism's virulence potential

Phenotypic and genotypic evidence suggests that not all Campylobacter jejuni isolates are pathogenic for humans. We hypothesized that differences in gene content or gene expression alter the degree of pathogenicity of C. jejuni isolates. A C. jejuni isolate (Turkey) recovered from a turkey and a second C. jejuni isolate (CS) recovered from a chicken differed in their degrees of in vitro and in vivo virulence. The C. jejuni Turkey isolate invaded INT 407 human epithelial cells and secreted the Cia (Campylobacter invasion antigen) proteins, while the C. jejuni CS isolate was noninvasive for human epithelial cells and did not secrete the Cia proteins. Newborn piglets inoculated with the C. jejuni Turkey isolate developed more severe clinical signs of campylobacteriosis than piglets inoculated with the C. jejuni CS isolate. Additional work revealed that flagellin was not expressed in the C. jejuni CS isolate. Microarray and real-time reverse transcription-PCR analyses revealed that all flagellar class II genes were significantly downregulated in the C. jejuni CS isolate compared to the C. jejuni Turkey isolate. Finally, nucleotide sequencing of the flgR gene revealed the presence of a single residue that was different in the FlgR proteins of the C. jejuni Turkey and CS isolates. Complementation of the C. jejuni CS isolate with a wild-type copy of the flgR gene restored the isolate's motility. Collectively, these findings support the hypothesis that critical differences in gene content or gene expression can alter the pathogenic potential of C. jejuni isolates.

Campylobacter jejuni strains compete for colonization in broiler chicks

Campylobacter jejuni isolates possess multiple adhesive proteins termed adhesins, which promote the organism's attachment to epithelial cells. Based on the proposal that one or more adhesins are shared among C. jejuni isolates, we hypothesized that C. jejuni strains would compete for intestinal and cecal colonization in broiler chicks. To test this hypothesis, we selected two C. jejuni strains with unique SmaI pulsed-field gel electrophoresis macrorestriction profiles and generated one nalidixic acid-resistant strain (the F38011 Nal(r) strain) and one streptomycin-resistant strain (the 02-833L Str(r) strain). In vitro binding assays revealed that the C. jejuni F38011 Nal(r) and 02-833L Str(r) strains adhered to LMH chicken hepatocellular carcinoma epithelial cells and that neither strain influenced the binding potential of the other strain at low inoculation doses. However, an increase in the dose of the C. jejuni 02-833L Str(r) strain relative to that of the C. jejuni F38011 Nal(r) strain competitively inhibited the binding of the C. jejuni F38011 Nal(r) strain to LMH cells in a dose-dependent fashion. Similarly, the C. jejuni 02-833L Str(r) strain was found to significantly reduce the efficiency of intestinal and cecal colonization by the C. jejuni F38011 Nal(r) strain in broiler chickens. Based on the number of bacteria recovered from the ceca, the maximum number of bacteria that can colonize the digestive tracts of chickens may be limited by host constraints. Collectively, these data support the hypothesis that C. jejuni strains compete for colonization in chicks and suggest that it may be possible to design novel intervention strategies for reducing the level at which C. jejuni colonizes the cecum.

Correlation Between In Vitro Secretion of Virulence-Associated Proteins of Campylobacter jejuni and Colonization of Chickens

The mechanisms used by Campylobacter jejuni to colonize the (chicken) intestinal tract have not been defined. In this study, we obtained evidence that in the presence of chicken serum and mucus, C. jejuni secreted proteins that may play a role in the colonization of chicken gut (Campylobacter invasion antigen = Cia). C. jejuni strains NCTC11168V1 and 81-176, as well as an NCTC11168V1 flaA mutant, were found to colonize intestinal tract and secrete proteins in the presence of chicken mucus, chicken serum, or fetal bovine serum in cell culture-conditioned medium. C. jejuni strain NCTC11168V26, which was observed to be a poor colonizer compared with the other C. jejuni isolates, did not secrete Cia proteins. Secreted proteins were also recognized by Western immunoblot using sera from birds that had been colonized by C. jejuni. These data suggest that C. jejuni secretes Cia proteins during colonization of chicken gut and that these Cia proteins play an important role in colonization.

The Campylobacter jejuni stringent response controls specific stress survival and virulence-associated phenotypes

Campylobacter jejuni is a highly prevalent food-borne pathogen that causes diarrhoeal disease in humans. A natural zoonotic, it must overcome significant stresses both in vivo and during transmission despite the absence of several traditional stress response genes. Although relatively little is understood about its mechanisms of pathogenesis, its ability to interact with and invade human intestinal epithelial cells closely correlates with virulence. A C. jejuni microarray-based screen revealed that several known virulence genes and several uncharacterized genes, including spoT, were rapidly upregulated during infection of human epithelial cells. spoT and its homologue relA have been shown in other bacteria to regulate the stringent response, an important stress response that to date had not been demonstrated for C. jejuni or any other epsilon-proteobacteria. We have found that C. jejuni mounts a stringent response that is regulated by spoT. Detailed analyses of a C. jejuni delta spoT mutant revealed that the stringent response is required for several specific stress, transmission and antibiotic resistance-related phenotypes. These include stationary phase survival, growth and survival under low CO2/high O2 conditions, and rifampicin resistance. A secondary suppressor strain that specifically rescues the low CO2 growth defect of the delta spoT mutant was also isolated. The stringent response additionally proved to be required for the virulence-related phenotypes of adherence, invasion, and intracellular survival in two human epithelial cell culture models of infection; spoT is the first C. jejuni gene shown to participate in longer term survival in epithelial cells. Microarray analyses comparing wild-type to the delta spoT mutant also revealed a strong correlation between gene expression profiles and phenotype differences observed. Together, these data demonstrate a critical role for the C. jejuni stringent response in multiple aspects of C. jejuni biology and pathogenesis and, further, may lend novel insight into unexplored features of the stringent response in other prokaryotic organisms.

Identification of a fibronectin-binding domain within the Campylobacter jejuni CadF protein

The binding of Campylobacter jejuni to fibronectin (Fn), a component of the extracellular matrix, is mediated by a 37 kDa outer membrane protein termed CadF for Campylobacter adhesion to Fn. Previous studies have indicated that C. jejuni binds to Fn on the basolateral surface of T84 human colonic cells. To further characterize the interaction of the CadF protein with Fn, enzyme-linked immunosorbent assays were performed to identify the Fn-binding domain (Fn-BD). Using overlapping 30-mer and 16-mer peptides derived from translated cadF nucleotide sequence, maximal Fn-binding activity was localized to four amino acids (AA 134-137) consisting of the residues phenylalanine-arginine-leucine-serine (FRLS). A mouse alpha-CadF peptide polyclonal antibody (M alpha-CadF peptide pAb) was generated using FRLS containing peptides and found to react with viable C. jejuni as judged by indirect fluorescent microscopy, suggesting that the FRLS residues are surface-exposed. Binding of CadF to purified Fn and INT 407 human epithelial cells was significantly inhibited with peptides containing the Fn-BD. Moreover, a CadF recombinant variant protein, in which the Phe-Arg-Leu residues (CadF AA 134-136) were altered to Ala-Ala-Gly, exhibited a 91% decrease in Fn-binding activity as compared with the wild-type CadF protein. Collectively, these data indicate that the FRLS residues (CadF AA 134-137) of the C. jejuni CadF protein possess Fn-binding activity.

Secretion of virulence proteins from Campylobacter jejuni is dependent on a functional flagellar export apparatus

Campylobacter jejuni, a gram-negative motile bacterium, secretes a set of proteins termed the Campylobacter invasion antigens (Cia proteins). The purpose of this study was to determine whether the flagellar apparatus serves as the export apparatus for the Cia proteins. Mutations were generated in five genes encoding three structural components of the flagella, the flagellar basal body (flgB and flgC), hook (flgE2), and filament (flaA and flaB) genes, as well as in genes whose products are essential for flagellar protein export (flhB and fliI). While mutations that affected filament assembly were found to be nonmotile (Mot-) and did not secrete Cia proteins (S-), a flaA (flaB+) filament mutant was found to be nonmotile but Cia protein secretion competent (Mot-, S+). Complementation of a flaA flaB double mutant with a shuttle plasmid harboring either the flaA or flaB gene restored Cia protein secretion, suggesting that Cia export requires at least one of the two filament proteins. Infection of INT 407 human intestinal cells with the C. jejuni mutants revealed that maximal invasion of the epithelial cells required motile bacteria that are secretion competent. Collectively, these data suggest that the C. jejuni Cia proteins are secreted from the flagellar export apparatus.

The biology of the post-genomic era: the proteomics

The complete identification of coding sequences in a number of species has led to announce the beginning of the post-genomic era, new tools have become available to study complex phenomena in biological systems. Rapid advances in genomic sequencing and bioinformatics have established the field of genomics to investigate thousands genes' activity through mRNA display. However, recent studies have demonstrated a lack of correlation between the transcriptional profiles and the actual protein levels in cells, so investigation of the expressed part of the genome is also required to link genomic data to biological function. It is possible that evolutional development occured by increasing complexity of regulation processes at the level of RNA and protein molecules instead of simple increase in gene number, so investigation of proteins and protein complexes became important fields of our post-genomic era. High-resolution two-dimensional gels combined with sensitive mass spectrometry can reveal virtually all proteins present in cells opening new insights into functions of cells, tissues and whole organisms.

Proteomics of bacterial pathogens

The rapid growth of proteomics that has been built upon the available bacterial genome sequences has opened provided new approaches to the analysis of bacterial functional genomics. In the study of pathogenic bacteria the combined technologies of genomics, proteomics and bioinformatics has provided valuable tools for the study of complex phenomena determined by the action of multiple gene sets. The review considers some of the recent developments in the establishment of proteomic databases as well as attempts to define pathogenic determinants at the level of the proteome for some of the major human pathogens. Proteomics can also provide practical applications through the identification of immunogenic proteins that may be potential vaccine targets as well as in extending our understanding of antibiotic action. There is little doubt that proteomics has provided us with new and valuable information on bacterial pathogens and will continue to be an important source of information in the coming years.

Fibronectin-facilitated invasion of T84 eukaryotic cells by Campylobacter jejuni occurs preferentially at the basolateral cell surface

Previous studies have indicated that the ability to bind to fibronectin is a key feature in successful cell invasion by Campylobacter jejuni. Given the spatial distribution of fibronectin and the architecture of the epithelium, this suggests the possibility that C. jejuni cell invasion might preferentially occur at the basolateral cell surface. To test this hypothesis, we examined the interaction of C. jejuni with T84 human colonic cells. When grown under the appropriate conditions, T84 cells form a polarized cell monolayer. C. jejuni translocation of a T84 cell monolayer appeared to occur via a paracellular (extracellular) route as opposed to a transcellular (intracellular) route based on the finding that a C. jejuni noninvasive mutant translocated as efficiently as its isogenic parent. Additional studies revealed that two distinct C. jejuni wild-type isolates could compete with one another for host cell receptors, whereas a C. jejuni fibronectin-binding-deficient mutant could not compete with a wild-type isolate for host cell receptors. Further, C. jejuni adherence and internalization were significantly inhibited by antifibronectin antibodies but only when cells were first treated with EGTA to expose basolateral cell surfaces. Together, these results support the theory that C. jejuni invasion occurs preferentially at the basolateral surface of eukaryotic cells.

Campylobacter fetus adheres to and enters INT 407 cells

Campylobacter fetus is a Gram-negative bacterial pathogen of humans and ungulates and is normally transmitted via ingestion of contaminated food or water with infection resulting in mild to severe enteritis. However, despite clinical evidence that C. fetus infection often involves transient bacteremic states from which systemic infection may develop and the frequent isolation of C. fetus from extra-intestinal sites, this organism displays very poor invasiveness in in vitro models of infection. In this study, immunofluorescence microscopy and gentamicin protection assays were used to investigate the ability of six clinical isolates and one reference strain of C. fetus to adhere to and invade the human intestinal epithelial cell line, INT 407. During an initial 4-h infection period, all C. fetus strains were detected intracellularly using both techniques, though adherence and internalization levels were very low when determined from gentamicin protection assays. Microscopy results indicated that during a 4-h infection period, four of the five clinical strains tested were adherent to 41.3-87.3% of INT 407 cells observed and that 25.2-34.6% of INT 407 cells contained intracellular C. fetus. The C. fetus reference strain displayed the lowest levels of adherence and internalization. A modified infection assay revealed that C. fetus adherence did not necessarily culminate in internalization. Despite the large percentage of INT 407 cells with adherent bacteria, the percentage of INT 407 cells with intracellular bacteria remained unchanged when incubation was extended from 4 h to 20 h. However, microscopy of INT 407 cells 24 h postinfection (p.i.) revealed that infected host cells contained clusters of densely packed C. fetus cells. Gentamicin protection assays revealed that intracellular C. fetus cells were not only viable 24 h p.i. but also that C. fetus had increased in number approximately three- to fourfold between 4 and 24 h p.i., indicative of intracellular replication. Investigation of the role of the host cell cytoskeleton revealed that pretreatment of host cells with cytochalasin D, colchicine, vinblastine, taxol, or dimethyl sulfoxide (DMSO) did not impact upon C. fetus adherence or internalization of INT 407 cells. Microscopy indicated neither rearrangement nor colocalization of either microtubules or microfilaments in INT 407 cells in response to C. fetus adherence or internalization. Together, these data indicate that clinical isolates of C. fetus are capable of adhering, entering, and surviving within the nonphagocytic epithelial cell line, INT 407.

Campylobacter jejuni--microtubule-dependent invasion

Campylobacter jejuni is the leading bacterial cause of food-borne illness worldwide and a major cause of Guillain-Barré paralysis. Recent molecular and cellular studies of one well-characterized C. jejuni strain have begun to unravel the details of an unusual microtubule-dependent (actin-filament-independent) gut-invasion mechanism, through which at least some C. jejuni initiate disease. Although responsible for causing a human dysenteric syndrome remarkably similar to that triggered by Shigella spp., current evidence suggests that C. jejuni use some markedly different molecular mechanisms of pathogenesis compared with shigellae.

Detection on surfaces and in Caco-2 cells of Campylobacter jejuni cells transformed with new gfp, yfp, and cfp marker plasmids

We have developed two sets of Campylobacter shuttle vectors containing either the gfp (green fluorescent protein), yfp (yellow fluorescent protein), or cfp (cyan fluorescent protein) reporter gene. In one set, the reporter gene is fused to a consensus Campylobacter promoter sequence (P(c)). The other set contains a pUC18 multicloning site upstream of the reporter gene, allowing the construction of transcriptional fusions using known promoters or random genomic fragments. C. jejuni cells transformed with the P(c) fusion plasmids are strongly fluorescent and easily visualized on chicken skin, on plant tissue, and within infected Caco-2 cells. In each C. jejuni strain tested, these plasmids were maintained over several passages in the absence of antibiotic selection. Also, in many C. jejuni strains, >91% of the cells transformed with the P(c) fusion plasmids remained fluorescent after several days. Experiments with yellow fluorescent and cyan fluorescent C. jejuni transformants suggest that aggregates containing two or more strains of C. jejuni may be present in an enrichment broth culture. Colonies arising from these aggregates would be heterologous in nature; therefore, isolation of a pure culture of C. jejuni, by selecting single colonies, from an environmental sample may not always yield a single strain.

Detection and characterization of autoagglutination activity by Campylobacter jejuni

In several gram-negative bacterial pathogens, autoagglutination (AAG) activity is a marker for interaction with host cells and virulence. Campylobacter jejuni strains also show AAG, but this property varies considerably among strains. To examine the characteristics of C. jejuni AAG, we developed a quantitative in vitro assay. For strain 81-176, which shows high AAG, activity was optimal for cells grown for < or = 24 h, was independent of growth temperature, and was best measured for cells suspended in phosphate-buffered saline at 25 degrees C for 24 h. AAG activity was heat labile and was abolished by pronase or acid-glycine (pH 2.2) treatment but not by lipase, DNase, or sodium metaperiodate. Strain 4182 has low AAG activity, but extraction with water increased AAG, suggesting the loss of an inhibitor. Strain 6960 has weak AAG with no effect due to water extraction. Our study with clinical isolates suggests that C. jejuni strains may be grouped into three AAG phenotypes. A variant derived from strain 81116 that is flagellate but immotile showed the strong AAG exhibited by the parent strain, suggesting that motility per se is not necessary for the AAG activity. AAG correlated with both bacterial hydrophobicity and adherence to INT407 cells. Mutants which lack flagella (flaA, flaB, and flbA) or common cell surface antigen (peb1A) were constructed in strain 81-176 by natural transformation-mediated allelic exchange. Both AAG activity and bacterial hydrophobicity were abolished in the aflagellate mutants but not the peb1A mutant. In total, these findings indicate that C. jejuni AAG is highly associated with flagellar expression.

Identification of proteins required for the internalization of Campylobacter jejuni into cultured mammalian cells

Clinical and in vitro experimental data suggest that invasion of intestinal epithelial cells is an essential step in the pathogenesis of Campylobacter jejuni-mediated enteritis. However, the molecular mechanism of C. jejuni internalization remains poorly defined. The goal of this study was to identify a gene that encodes a protein required for the internalization of C. jejuni into host cells. A C. jejuni gene, designated ciaB, was identified upon immunoscreening C. jejuni genomic DNA-phage libraries with an antiserum generated against C. jejuni co-cultivated with INT 407 cells. The C. jejuni ciaB gene encodes a protein of 610 amino acids with a calculated molecular mass of 73,154 Da. The deduced amino acid sequence of the CiaB protein shares similarity with type III secreted proteins, associated with invasion of host cells, from other more extensively characterized bacterial pathogens. In vitro binding and internalization assays revealed that the binding of C. jejuni ciaB null mutants was indistinguishable from that of the parental isolate, whereas a significant reduction was noted in internalization. Immunoblot analysis using an anti-CiaB specific antibody revealed that CiaB is secreted into the supernatant fluids upon co-cultivation of C. jejuni with INT 407 cell conditioned medium. Metabolic labeling experiments revealed that at least eight C. jejuni proteins, ranging in size from 12.8 to 108 kDa, are secreted into the culture medium. C. jejuni ciaB null mutants were deficient in the secretion of all proteins, indicating that CiaB is required for the secretion process. Identification of the C. jejuni ciaB gene represents a significant advance in understanding the molecular mechanism of C. jejuni internalization.

Secretion of Campylobacter jejuni Cia proteins is contact dependent

Campylobacter jejuni is a common cause of human gastrointestinal disease worldwide. Despite the prevalence of C. jejuni infections, the mechanisms of C. jejuni pathogenesis remain ill-defined. Invasion of the cells lining the intestinal tract is hypothesized to be essential for the development of C. jejuni-mediated enteritis. Recent studies in our laboratory have revealed that C. jejuni secrete proteins, termed Cia for Campylobacter invasion antigens, upon incubation with human intestinal cells. A mutation in one of the genes encoding a secreted protein resulted in an invasion-deficient phenotype. The purpose of this study was to identify a component capable of stimulating the synthesis and secretion of the Cia proteins from C. jejuni. Here, we report that these processes can be induced upon incubating C. jejuni in medium supplemented with fetal bovine serum. The synthesis and secretion of the Cia proteins were not affected by heat-treatment of the fetal bovine serum, indicating that the stimulating molecule in serum is heat stable. The stimulatory molecule was not unique to fetal bovine serum as sera from other sources including human, pig, sheep, goat, rabbit, mouse, and chicken also induced the synthesis and release of the Cia proteins. These findings indicate that the synthesis and secretion of the Cia proteins can be induced in a cell-free system by incubating C. jejuni in serum-supplemented tissue culture medium.

Proteomics in medical microbiology

The techniques of proteomics (high resolution two-dimensional electrophoresis and protein characterisation) are widely used for microbiological research to analyse global protein synthesis as an indicator of gene expression. The rapid progress in microbial proteomics has been achieved through the wide availability of whole genome sequences for a number of bacterial groups. Beyond providing a basic understanding of microbial gene expression, proteomics has also played a role in medical areas of microbiology. Progress has been made in the use of the techniques for investigating the epidemiology and taxonomy of human microbial pathogens, the identification of novel pathogenic mechanisms and the analysis of drug resistance. In each of these areas, proteomics has provided new insights that complement genomic-based investigations. This review describes the current progress in these research fields and highlights some of the technical challenges existing for the application of proteomics in medical microbiology. The latter concern the analysis of genetically heterogeneous bacterial populations and the integration of the proteomic and genomic data for these bacteria. The characterisation of the proteomes of bacterial pathogens growing in their natural hosts remains a future challenge.

Pathophysiology of Campylobacter jejuni infections of humans

Campylobacter jejuni and closely related organisms are major causes of human bacterial enteritis. These infections can lead to extraintestinal disease and severe long-term complications. Of these, neurological damage, apparently due to the immune response of the host, is the most striking. This review examines current knowledge of the pathophysiology of the organism. Diversity of C. jejuni isolates in genotypic and phenotypic characteristics now is recognized and clinically relevant examples are presented. Expected future directions are outlined.