Campylobacter jejuni activates mitogen-activated protein kinases in Caco-2 cell monolayers and in vitro infected primary human colonic tissue

Oncogenic potential of Campylobacter infection in the gastrointestinal tract: narrative review

BACKGROUND

Campylobacter jejuni is the leading cause of zoonotic gastroenteritis. The other emerging group of Campylobacters spp. are part of human oral commensal, represented by C. concisus (CC), which has been recently linked to non-oral conditions. Although long-term gastrointestinal (GI) complications from these two groups of Campylobacters have been previously reviewed individually, overall impact of Campylobacter infection on GI carcinogenesis and their inflammatory precursor lesions has not been assessed collectively.

AIMS

To evaluate the available evidence concerning the association between Campylobacter infection/colonization and inflammatory bowel disease (IBD), reflux esophagitis/metaplasia colorectal cancer (CRC) and esophageal cancer (EC).

METHODS

We performed a comprehensive literature search of PubMed for relevant original publications and systematic reviews/meta-analyses of epidemiological and clinical studies. In addition, we gathered additional information concerning microbiological data, animal models and mechanistic data from in vitro studies.

RESULTS

Both retrospective and prospective studies on IBD showed relatively consistent increased risk associated with Campylobacter infection. Despite lack of supporting prospective studies, retrospective studies based on tissue/fecal microbiome revealed consistent enrichment of Campylobacter in CRC samples. Studies on EC precursor lesions (esophagitis and metaplasia) were generally supportive for the association with Campylobacter, while inconsistent observations on EC. Studies on both IBD and EC precursors suggested the predominant role of CC, but studies on CRC were not informative of species.

CONCLUSIONS

There is sufficient evidence calling for concerted effort in unveiling direct and indirect connection of this organism to colorectal and esophageal cancer in humans.

Campylobacter jejuni: targeting host cells, adhesion, invasion, and survival

Campylobacter jejuni, causing strong enteritis, is an unusual bacterium with numerous peculiarities. Chemotactically controlled motility in viscous milieu allows targeted navigation to intestinal mucus and colonization. By phase variation, quorum sensing, extensive O-and N-glycosylation and use of the flagellum as type-3-secretion system C. jejuni adapts effectively to environmental conditions. C. jejuni utilizes proteases to open cell-cell junctions and subsequently transmigrates paracellularly. Fibronectin at the basolateral side of polarized epithelial cells serves as binding site for adhesins CadF and FlpA, leading to intracellular signaling, which again triggers membrane ruffling and reduced host cell migration by focal adhesion. Cell contacts of C. jejuni results in its secretion of invasion antigens, which induce membrane ruffling by paxillin-independent pathway. In addition to fibronectin-binding proteins, other adhesins with other target structures and lectins and their corresponding sugar structures are involved in host-pathogen interaction. Invasion into the intestinal epithelial cell depends on host cell structures. Fibronectin, clathrin, and dynein influence cytoskeletal restructuring, endocytosis, and vesicular transport, through different mechanisms. C. jejuni can persist over a 72-h period in the cell. Campylobacter-containing vacuoles, avoid fusion with lysosomes and enter the perinuclear space via dynein, inducing signaling pathways. Secretion of cytolethal distending toxin directs the cell into programmed cell death, including the pyroptotic release of proinflammatory substances from the destroyed cell compartments. The immune system reacts with an inflammatory cascade by participation of numerous immune cells. The development of autoantibodies, directed not only against lipooligosaccharides, but also against endogenous gangliosides, triggers autoimmune diseases. Lesions of the epithelium result in loss of electrolytes, water, and blood, leading to diarrhea, which flushes out mucus containing C. jejuni. Together with the response of the immune system, this limits infection time. Based on the structural interactions between host cell and bacterium, the numerous virulence mechanisms, signaling, and effects that characterize the infection process of C. jejuni, a wide variety of targets for attenuation of the pathogen can be characterized. The review summarizes strategies of C. jejuni for host-pathogen interaction and should stimulate innovative research towards improved definition of targets for future drug development. KEY POINTS: • Bacterial adhesion of Campylobacter to host cells and invasion into host cells are strictly coordinated processes, which can serve as targets to prevent infection. • Reaction and signalling of host cell depend on the cell type. • Campylobacter virulence factors can be used as targets for development of antivirulence drug compounds.

Akkermansia and its metabolites play key roles in the treatment of campylobacteriosis in mice

Introduction

Campylobacter jejuni (C. jejuni) is a common food-borne bacterial pathogen that can use the host's innate immune response to induce the development of colitis. There has been some research on the role of normal intestinal flora in C. jejuni-induced colitis, but the mechanisms that play a central role in resistance to C. jejuni infection have not been explored.

Methods

We treated Campylobacter jejuni-infected mice with fecal microbiota transplantation (FMT), oral butyric acid and deoxycholic acid in a controlled trial and analyzed the possible mechanisms of treatment by a combination of chromatography, immunohistochemistry, fluorescence in situ hybridization, 16s rRNA gene, proteomics and western blot techniques.

Results

We first investigated the therapeutic effect of FMT on C. jejuni infection. The results showed that FMT significantly reduced the inflammatory response and blocked the invasion of C.jejuni into the colonic tissue. We observed a significant increase in the abundance of Akkermansia in the colon of mice after FMT, as well as a significant increase in the levels of butyric acid and deoxycholic acid. We next demonstrated that oral administration of sodium butyrate or deoxycholic acid had a similar therapeutic effect. Further proteomic analysis showed that C.jejuni induced colitis mainly through activation of the PI3K-AKT signaling pathway and MAPK signaling pathway, whereas Akkermansia, the core flora of FMT, and the gut microbial metabolites butyric acid and deoxycholic acid both inhibited these signaling pathways to counteract the infection of C. jejuni and alleviate colitis. Finally, we verified the above idea by in vitro cellular assays. In conclusion, FMT is highly effective in the treatment of colitis caused by C. jejuni, with which Akkermansia and butyric and deoxycholic acids are closely associated.The present study demonstrates that Akkermansia and butyric and deoxycholic acids are effective in the treatment of colitis caused by C. jejuni.

Discussion

This is the first time that Akkermansia has been found to be effective in fighting pathogens, which provides new ideas and insights into the use of FMT to alleviate colitis caused by C. jejuni and Akkermansia as a treatment for intestinal sexually transmitted diseases caused by various pathogens.

Campylobacter jejuni Triggers Signaling through Host Cell Focal Adhesions To Inhibit Cell Motility

Campylobacter jejuni is a major foodborne pathogen that exploits the focal adhesions of intestinal cells to promote invasion and cause severe gastritis. Focal adhesions are multiprotein complexes involved in bidirectional signaling between the actin cytoskeleton and the extracellular matrix. We investigated the dynamics of focal adhesion structure and function in C. jejuni-infected cells using a comprehensive set of approaches, including confocal microscopy of live and fixed cells, immunoblotting, and superresolution interferometric photoactivated localization microscopy (iPALM). We found that C. jejuni infection of epithelial cells results in increased focal adhesion size and altered topology. These changes resulted in a persistent modulatory effect on the host cell focal adhesion, evidenced by an increase in cell adhesion strength, a decrease in individual cell motility, and a reduction in collective cell migration. We discovered that C. jejuni infection causes an increase in phosphorylation of paxillin and an alteration of paxillin turnover at the focal adhesion, which together represent a potential mechanistic basis for altered cell motility. Finally, we observed that infection of epithelial cells with the C. jejuni wild-type strain in the presence of a protein synthesis inhibitor, a C. jejuni CadF and FlpA fibronectin-binding protein mutant, or a C. jejuni flagellar export mutant blunts paxillin phosphorylation and partially reestablishes individual host cell motility and collective cell migration. These findings provide a potential mechanism for the restricted intestinal repair observed in C. jejuni-infected animals and raise the possibility that bacteria targeting extracellular matrix components can alter cell behavior after binding and internalization by manipulating focal adhesions.

The Campylobacter jejuni CiaD effector co-opts the host cell protein IQGAP1 to promote cell entry

Campylobacter jejuni is a foodborne pathogen that binds to and invades the epithelial cells lining the human intestinal tract. Maximal invasion of host cells by C. jejuni requires cell binding as well as delivery of the Cia proteins (Campylobacter invasion antigens) to the host cell cytosol via the flagellum. Here, we show that CiaD binds to the host cell protein IQGAP1 (a Ras GTPase-activating-like protein), thus displacing RacGAP1 from the IQGAP1 complex. This, in turn, leads to the unconstrained activity of the small GTPase Rac1, which is known to have roles in actin reorganization and internalization of C. jejuni. Our results represent the identification of a host cell protein targeted by a flagellar secreted effector protein and demonstrate that C. jejuni-stimulated Rac signaling is dependent on IQGAP1.

Revisiting Campylobacter jejuni Virulence and Fitness Factors: Role in Sensing, Adapting, and Competing

Campylobacter jejuni is the leading cause of bacterial foodborne gastroenteritis world wide and represents a major public health concern. Over the past two decades, significant progress in functional genomics, proteomics, enzymatic-based virulence profiling (EBVP), and the cellular biology of C. jejuni have improved our basic understanding of this important pathogen. We review key advances in our understanding of the multitude of emerging virulence factors that influence the outcome of C. jejuni–mediated infections. We highlight, the spatial and temporal dynamics of factors that promote C. jejuni to sense, adapt and survive in multiple hosts. Finally, we propose cohesive research directions to obtain a comprehensive understanding of C. jejuni virulence mechanisms.

Immunopathological properties of the Campylobacter jejuni flagellins and the adhesin CadF as assessed in a clinical murine infection model

Background

Campylobacter jejuni infections constitute serious threats to human health with increasing prevalences worldwide. Our knowledge regarding the molecular mechanisms underlying host–pathogen interactions is still limited. Our group has established a clinical C. jejuni infection model based on abiotic IL-10^−/− mice mimicking key features of human campylobacteriosis. In order to further validate this model for unraveling pathogen-host interactions mounting in acute disease, we here surveyed the immunopathological features of the important C. jejuni virulence factors FlaA and FlaB and the major adhesin CadF (Campylobacter adhesin to fibronectin), which play a role in bacterial motility, protein secretion and adhesion, respectively.

Methods and results

Therefore, abiotic IL-10^−/− mice were perorally infected with C. jejuni strain 81-176 (WT) or with its isogenic flaA/B (ΔflaA/B) or cadF (ΔcadF) deletion mutants. Cultural analyses revealed that WT and ΔcadF but not ΔflaA/B bacteria stably colonized the stomach, duodenum and ileum, whereas all three strains were present in the colon at comparably high loads on day 6 post-infection. Remarkably, despite high colonic colonization densities, murine infection with the ΔflaA/B strain did not result in overt campylobacteriosis, whereas mice infected with ΔcadF or WT were suffering from acute enterocolitis at day 6 post-infection. These symptoms coincided with pronounced pro-inflammatory immune responses, not only in the intestinal tract, but also in other organs such as the liver and kidneys and were accompanied with systemic inflammatory responses as indicated by increased serum MCP-1 concentrations following C. jejuni ΔcadF or WT, but not ΔflaA/B strain infection.

Conclusion

For the first time, our observations revealed that the C. jejuni flagellins A/B, but not adhesion mediated by CadF, are essential for inducing murine campylobacteriosis. Furthermore, the secondary abiotic IL-10^−/− infection model has been proven suitable not only for detailed investigations of immunological aspects of campylobacteriosis, but also for differential analyses of the roles of distinct C. jejuni virulence factors in induction and progression of disease.

Electronic supplementary material

The online version of this article (10.1186/s13099-019-0306-9) contains supplementary material, which is available to authorized users.

Host cellular unfolded protein response signaling regulates Campylobacter jejuni invasion

Campylobacter jejuni is a major cause of bacterial foodborne illness in humans worldwide. Bacterial entry into a host eukaryotic cell involves the initial steps of adherence and invasion, which generally activate several cell-signaling pathways that induce the activation of innate defense systems, which leads to the release of proinflammatory cytokines and induction of apoptosis. Recent studies have reported that the unfolded protein response (UPR), a system to clear unfolded proteins from the endoplasmic reticulum (ER), also participates in the activation of cellular defense mechanisms in response to bacterial infection. However, no study has yet investigated the role of UPR in C. jejuni infection. Hence, the aim of this study was to deduce the role of UPR signaling via induction of ER stress in the process of C. jejuni infection. The results suggest that C. jejuni infection suppresses global protein translation. Also, 12 h of C. jejuni infection induced activation of the eIF2α pathway and expression of the transcription factor CHOP. Interestingly, bacterial invasion was facilitated by knockdown of UPR-associated signaling factors and treatment with the ER stress inducers, thapsigargin and tunicamycin, decreased the invasive ability of C. jejuni. An investigation into the mechanism of UPR-mediated inhibition of C. jejuni invasion showed that UPR signaling did not affect bacterial adhesion to or survival in the host cells. Further, Salmonella Enteritidis or FITC-dextran intake were not regulated by UPR signaling. These results indicated that the effect of UPR on intracellular intake was specifically found in C. jejuni infection. These findings are the first to describe the role of UPR in C. jejuni infection and revealed the participation of a new signaling pathway in C. jejuni invasion. UPR signaling is involved in defense against the early step of C. jejuni invasion and thus presents a potential therapeutic target for the treatment of C. jejuni infection.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

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.

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.

Caecal transcriptome analysis of colonized and non-colonized chickens within two genetic lines that differ in caecal colonization by Campylobacter jejuni

Campylobacter jejuni is one of the most common causes of human bacterial enteritis worldwide. The molecular mechanisms of the host responses of chickens to C. jejuni colonization are not well understood. We have previously found differences in C. jejuni colonization at 7-days post-inoculation (pi) between two genetic broiler lines. However, within each line, not all birds were colonized by C. jejuni (27.5% colonized in line A, and 70% in line B). Therefore, the objective of the present experiments was to further define the differences in host gene expression between colonized and non-colonized chickens within each genetic line. RNA isolated from ceca of colonized and non-colonized birds within each line was applied to a chicken 44K Agilent microarray for the pair comparison. There were differences in the mechanisms of host resistant to C. jejuni colonization between line A and line B. Ten times more differentially expressed genes were observed between colonized and non-colonized chickens within line B than those within line A. Our study supports the fact that the MAPK pathway is important in host response to C. jejuni colonization in line B, but not in line A. The data indicate that inhibition of small GTPase-mediated signal transduction could enhance the resistance of chickens to C. jejuni colonization and that the tumour necrosis factor receptor superfamily genes play important roles in determining C. jejuni non-colonization in broilers.

Galactose specific adhesin of enteroaggregative E. coli induces IL-8 secretion via activation of MAPK and STAT-3 in INT-407 cells

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) is one of the most common bacterial pathogens associated with the etiology of persistent diarrhea. A characteristic feature of EAEC-pathogenesis is the induction of profound inflammatory response in the intestinal epithelium. The present study was designed to investigate the underlying mechanism of inflammatory responses induced by a novel galactose specific adhesin of T7 strain of EAEC (EAEC-T7) in human intestinal epithelial cell line (INT-407).

METHODS

INT-407 cells were stimulated with the adhesin in the absence and presence of anti-adhesin (IgG(AD))/d-galactose/H7/staurosporin (inhibitor of PKC)/PD098059 (inhibitor of MEK)/SB203580 (inhibitor of p38-MAPkinase)/AG490 (inhibitor of JAK (-2,-3)/STAT-3 pathway). The expression of activated Raf-1, MEK-1, ERK1/2, JNK, p38-MAPK and STAT-3 was analyzed by Western immunoblot. Release of interleukin-8 (IL-8) was measured by ELISA.

RESULTS

The adhesin was found to induce activation of Raf-1, MEK-1, ERK1/2, p38-MAPK and STAT-3, which was reduced in the presence of IgG(AD)/d-galactose. The activation of Raf-1 was found to be attenuated in the presence of H7/staurosporin. The expression of phosphorylated STAT-3 was downregulated in the presence of AG490 and PD098059. Further, the adhesin induced IL-8 secretion was reduced in the presence of the inhibitors of MEK (PD098059), p38-MAPK (SB203580) and JAK (-2,-3)/STAT-3 pathway (AG490).

CONCLUSIONS

We propose that STAT-3 activation is quintessential for the galactose specific adhesin induced IL-8 secretion by INT-407 cells and must occur in concert with the activation of ERK1/2.

GENERAL SIGNIFICANCE

Our contribution regarding the galactose specific adhesin mediated signaling leads to an improved understanding of the EAEC-pathogenesis and may provide novel therapeutic approaches to combat EAEC infection.

Molecular mechanisms of campylobacter infection

Campylobacter jejuni is the principal bacterial foodborne pathogen. A major challenge still is to identify the virulence strategies exploited by C. jejuni. Recent genomics, proteomics, and metabolomics approaches indicate that C. jejuni displays extensive inter- and intrastrain variation. The diverse behavior enables bacterial adaptation to different environmental conditions and directs interactions with the gut mucosa. Here, we report recent progress in understanding the molecular mechanisms and functional consequences of the phenotype diversity. The results suggest that C. jejuni actively penetrates the intestinal mucus layer, secretes proteins mainly via its flagellar apparatus, is engulfed by intestinal cells, and can disrupt the integrity of the epithelial lining. C. jejuni stimulates the proinflammatory pathway and the production of a large repertoire of cytokines, chemokines, and innate effector molecules. Novel experimental infection models suggest that the activation of the innate immune response is important for the development of intestinal pathology.

Atypical roles for Campylobacter jejuni amino acid ATP binding cassette transporter components PaqP and PaqQ in bacterial stress tolerance and pathogen-host cell dynamics

Campylobacter jejuni is a human pathogen causing severe diarrheal disease; however, our understanding of the survival of C. jejuni during disease and transmission remains limited. Amino acid ATP binding cassette (AA-ABC) transporters in C. jejuni have been proposed as important pathogenesis factors. We have investigated a novel AA-ABC transporter system, encoded by cj0467 to cj0469, by generating targeted deletions of cj0467 (the membrane transport component) and cj0469 (the ATPase component) in C. jejuni 81-176. The analyses described here have led us to designate these genes paqP and paqQ, respectively (pathogenesis-associated glutamine [q] ABC transporter permease [P] and ATPase [Q]). We found that loss of either component resulted in amino acid uptake defects, most notably diminished glutamine uptake. Altered resistance to a series of environmental and in vivo stresses was also observed: both mutants were hyperresistant to aerobic and organic peroxide stress, and while the DeltapaqP mutant was also hyperresistant to heat and osmotic shock, the DeltapaqQ mutant was more susceptible than the wild type to the latter two stresses. The DeltapaqP and DeltapaqQ mutants also displayed a surprising but statistically significant increase in recovery from macrophages and epithelial cells in short-term intracellular survival assays. Annexin V, 4',6-diamidino-2-phenylindole (DAPI), and Western blot analyses revealed that macrophages infected with the DeltapaqP or DeltapaqQ mutant exhibited transient but significant decreases in cell death and extracellular signal-regulated kinase-mitogen-activated protein kinase activation compared to levels in wild-type-infected cells. The DeltapaqP mutant was not defective in either short-term or longer-term mouse colonization, consistent with its increased stress survival and diminished host cell damage phenotypes. Collectively, these results demonstrate a unique correlation of an AA-ABC transporter with bacterial stress tolerances and host cell responses to pathogen infection.

Pathogenesis of Campylobacter

PURPOSE OF REVIEW

Molecular pathogenesis of Campylobacter jejuni has lagged behind that of other enteric pathogens. This review summarizes advances in the biology and pathogenesis of C. jejuni.

RECENT FINDINGS

Multiple genome sequences have defined conserved and hypervariable loci in the C. jejuni genome. Interaction of C. jejuni with eukaryotic cells results in numerous signal transduction changes and release of proinflammatory cytokines. In-vivo models based on immune knockout mice have also revealed new information on pathogenesis.

SUMMARY

New information and new methods are available that should provide important tools to further understand pathogenesis of this elusive pathogen.

Campylobacter jejuni-mediated disease pathogenesis: an update

Infection by Campylobacter jejuni is considered to be the most prevalent cause of bacterial-mediated diarrhoeal disease worldwide. Both in the developing and the developed world, young children remain most susceptible. Although disease is generally mild and self-limiting, severe post-infectious complications such as Gullain-Barré syndrome may occur. Despite the significant health burden caused by the organism, our current understanding of disease pathogenesis remains in its infancy. Elucidation of the genome sequences of many different C. jejuni strains in recent years has started to accelerate research in Campylobacter genetics, pathogenesis and host immunity in response to infection. Campylobacter jejuni is the first prokaryote shown to code for both O- and N-linked glycosylation systems, a feature that is likely to not only modulate bacterial virulence and survival, but also influence host-pathogen interactions and disease outcome. Here recent developments in C. jejuni research, with a particular focus on disease pathogenesis including early host immune responses, are highlighted.

Campylobacter jejuni: molecular biology and pathogenesis

Campylobacter jejuni is a foodborne bacterial pathogen that is common in the developed world. However, we know less about its biology and pathogenicity than we do about other less prevalent pathogens. Interest in C. jejuni has increased in recent years as a result of the growing appreciation of its importance as a pathogen and the availability of new model systems and genetic and genomic technologies. C. jejuni establishes persistent, benign infections in chickens and is rapidly cleared by many strains of laboratory mouse, but causes significant inflammation and enteritis in humans. Comparing the different host responses to C. jejuni colonization should increase our understanding of this organism.

The second century of Campylobacter research: recent advances, new opportunities and old problems

PURPOSE OF REVIEW

Despite the prevalence of Campylobacter jejuni and the importance of the disease, investigations into pathogenesis have been restricted because of the absence of a convenient animal model of disease. In particular it is still unclear how C. jejuni infection causes diarrhoea.

RECENT FINDINGS

Recent developments in improved models of infection and studies on the innate immune responses have provided a deeper understanding of host-pathogen interactions. From the organism's perspective, further genomics-based information including two new genome sequences has provided much basic information, particularly relating to cell surface glycostructures.

SUMMARY

Research over the last few years is starting to address the gaps in our knowledge of how this important human pathogen interacts with host cells and causes diarrhoeal disease. Further research is required for a detailed understanding of these interactions and also to develop intervention strategies to reduce the burden of C. jejuni-associated disease.

Comparison of virulence-associated in vitro properties of typed strains of Campylobacter jejuni from different sources

Campylobacter jejuni is a major cause of human diarrhoeal disease, but specific virulence mechanisms have not been well defined. This blinded study was undertaken with 40 C. jejuni isolates from different sources to determine their haemolytic, cytotoxic and adhesion and invasion activities towards mammalian cells. The results were correlated with source of isolation and genetic makeup by amplified fragment length polymorphism (AFLP) typing. The isolates had variable degrees of haemolytic activity against rabbit erythrocytes and cytotoxicity towards CaCo-2, HeLa and Vero cells. The data indicated that the haemolytic and cytotoxic activities were due to separate factors. A range of cytotoxicity was exhibited, whereby some strains had no activity against the target cells and others had activity against all three cell lines. Certain strains had activity against CaCo-2 cells but little or no activity against the other cells, while others exhibited the opposite phenotype. The data suggested that the cytotoxicity assay with the different cell lines may have detected more than one cytotoxin. A wide variation between isolates was observed for both adherence and invasion with all three cell lines, yet, overall, the strains showed a significantly greater invasion capacity for CaCo-2. There was no clear relationship between source of isolation or disease manifestation and possession of statistically significantly higher levels of particular virulence-associated factors although, in some cases, a correlation between cytotoxicity and cell invasion was evident. Five AFLP clusters, each representing two to eleven isolates with similar profiles, were observed at the 90 % similarity level. Some AFLP groups contained isolates with a common serotype, but each group had C. jejuni isolates from more than one source with the exception of group IV, which contained only human isolates. Isolates with high cytotoxic activity against CaCo-2 cells were confined to groups I, III and IV and a group of unrelated strains (U). Group II isolates had uniformly low cytotoxicity. Isolates in groups I, V and U were more invasive for CaCo-2 cells than isolates in groups II, III and IV. The strain differences in cytotoxicity or invasion did not correlate with source of isolation.

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.

C57BL/6 and congenic interleukin-10-deficient mice can serve as models of Campylobacter jejuni colonization and enteritis

Campylobacter jejuni is a globally distributed cause of human food-borne enteritis and has been linked to chronic joint and neurological diseases. We hypothesized that C. jejuni 11168 colonizes the gastrointestinal tract of both C57BL/6 mice and congenic C57BL/6 interleukin-10-deficient (IL-10(-/-)) mice and that C57BL/6 IL-10(-/-) mice experience C. jejuni 11168-mediated clinical signs and pathology. Individually housed mice were challenged orally with C. jejuni 11168, and the course of infection was monitored by clinical examination, bacterial culture, C. jejuni-specific PCR, gross pathology, histopathology, immunohistochemistry, and anti-C. jejuni-specific serology. Ceca of C. jejuni 11168-infected mice were colonized at high rates: ceca of 50/50 wild-type mice and 168/170 IL-10(-/-) mice were colonized. In a range from 2 to 35 days after infection with C. jejuni 11168, C57BL/6 IL-10(-/-) mice developed severe typhlocolitis best evaluated at the ileocecocolic junction. Rates of colonization and enteritis did not differ between male and female mice. A dose-response experiment showed that as little as 10(6) CFU produced significant disease and pathological lesions similar to responses seen in humans. Immunohistochemical staining demonstrated C. jejuni antigens within gastrointestinal tissues of infected mice. Significant anti-C. jejuni plasma immunoglobulin levels developed by day 28 after infection in both wild-type and IL-10-deficient animals; antibodies were predominantly T-helper-cell 1 (Th1)-associated subtypes. These results indicate that the colonization of the mouse gastrointestinal tract by C. jejuni 11168 is necessary but not sufficient for the development of enteritis and that C57BL/6 IL-10(-/-) mice can serve as models for the study of C. jejuni enteritis in humans.

Disruption of tight junctions and induction of proinflammatory cytokine responses in colonic epithelial cells by Campylobacter jejuni

Campylobacter jejuni is a leading cause of human enterocolitis and is associated with postinfectious complications, including irritable bowel syndrome and Guillain-Barré syndrome. However, the pathogenesis of C. jejuni infection remains poorly understood. Paracellular pathways in intestinal epithelial cells are gated by intercellular junctions (tight junctions and adherens junctions), providing a functional barrier between luminal microbes and host immune cells in the lamina propria. Here we describe alterations in tight junctions in intestinal epithelial monolayers following C. jejuni infection. Apical infection of polarized T84 monolayers caused a time-dependent decrease in transepithelial electrical resistance (TER). Immunofluorescence microscopy revealed a redistribution of the tight junctional transmembrane protein occludin from an intercellular to an intracellular location. Subcellular fractionation using equilibrium sucrose density gradients demonstrated decreased hyperphosphorylated occludin in lipid rafts, Triton X-100-soluble fractions, and the Triton X-100-insoluble pellet following apical infection. Apical infection with C. jejuni also caused rapid activation of NF-kappaB and AP-1, phosphorylation of extracellular signal-regulated kinase, Jun N-terminal protein kinase, and p38 mitogen-activated protein kinases, and basolateral secretion of the CXC chemokine interleukin-8 (IL-8). Basolateral infection with C. jejuni caused a more rapid decrease in TER, comparable redistribution of tight-junction proteins, and secretion of more IL-8 than that seen with apical infection. These results suggest that compromised barrier function and increased chemokine expression contribute to the pathogenesis of C. jejuni-induced enterocolitis.