FlaC, a protein of Campylobacter jejuni TGH9011 (ATCC43431) secreted through the flagellar apparatus, binds epithelial cells and influences cell invasion

Distribution of flagella secreted protein and integral membrane protein among Campylobacter jejuni isolated from Thailand

Background

Campylobacter jejuni, a gram-negative bacterium, is a frequent cause of gastrointestinal food-borne illness in humans throughout the world. There are several reports that the virulence of C. jejuni might be modulated by non-flagellar proteins that are secreted through the filament. Recently, FspA (Flagella secreted proteins) have been described. Two alleles of fspA (fspA1 and fspA2) based on sequence analysis were previously reported and only the fspA2 allele was found in Thai isolates. The aim of this study is to analyze the deduced amino acid sequences fspA and the adjacent putative integral membrane protein from 103 Thai C. jejuni isolates.

Results

A total of 103 representative C. jejuni isolates were amplified by PCR for the fspA gene and the adjacent integral membrane protein gene. Two PCR product sizes were amplified using the same primers, an approximately 1600-bp PCR product from 19 strains that contained fspA and integral membrane protein genes and an approximately 800-bp PCR product from 84 strains that contained only the fspA gene. DNA sequencing was performed on the amplified products. The deduced amino acid sequences of both genes were analyzed separately using CLC Free Workbench 4 software. The analysis revealed three groups of FspA. Only FspA group 1 sequences (19/103) (corresponding to fspA1) consisting of 5 subgroups were associated with the adjacent gene encoding the integral membrane protein. FspA group 2 was the largest group (67/103) consisting of 9 subgroups. FspA group 2p (17/103) consisting of 7 subgroups was found to contain stop codons at a position before the terminal 142 position.

Conclusions

This study reveals greater heterogeneity of FspA (group 1, 2 and 2p) among Thai C. jejuni isolates than previously reported. Furthermore, the subgroups of FspA groups 1 were associated with groups of integral membrane protein. The significance of these different FspA variants to virulence requires further study.

Impact of erythromycin resistance on the virulence properties and fitness of Campylobacter jejuni

Epidemiological studies of macrolide resistance in Campylobacter jejuni demonstrated that infections with macrolide-resistant C. jejuni could be associated with an increased risk of adverse events, development of invasive illness or death compared to macrolide-susceptible isolates. In this study, an in vitro induction experiment was conducted using susceptible C. jejuni strain and erythromycin as a selecting agent to obtain Ery-resistant mutant with 23S rRNA gene mutation (A2074C). Changes in the virulence characteristics and fitness between the susceptible parent strain and Ery-resistant mutant were examined. Ery-resistant mutant demonstrated slightly more resistance to bile in the bile tolerance assay compared to the susceptible strain but with no statistical significant difference. However Ery-resistant mutant apparently demonstrated reduced adhesion and invasion characteristics to intestinal epithelial cells, murine macrophage and short time intracellular survivability within macrophage compared to the susceptible strain. Co-inoculation of the two strains in the mice resulted in low colonization level of the resistant strain compared to the susceptible strain. Competition experiments resulted in mutant that grew significantly slower than the susceptible parent strain and the mutation imposed a fitness cost in Ery-resistant mutant. Taken together these findings demonstrated the increment of the virulence characteristics of Ery-susceptible strain rather than Ery-resistant strain. The adverse events previously observed in the epidemiological studies for macrolide-resistant strains infection, we suggested this maybe attributed to the resistivity of the resistant strains to the treatment and consequently prolonged the symptoms and compromised the disease in patients.

Change is good: variations in common biological mechanisms in the epsilonproteobacterial genera Campylobacter and Helicobacter

Microbial evolution and subsequent species diversification enable bacterial organisms to perform common biological processes by a variety of means. The epsilonproteobacteria are a diverse class of prokaryotes that thrive in diverse habitats. Many of these environmental niches are labeled as extreme, whereas other niches include various sites within human, animal, and insect hosts. Some epsilonproteobacteria, such as Campylobacter jejuni and Helicobacter pylori, are common pathogens of humans that inhabit specific regions of the gastrointestinal tract. As such, the biological processes of pathogenic Campylobacter and Helicobacter spp. are often modeled after those of common enteric pathogens such as Salmonella spp. and Escherichia coli. While many exquisite biological mechanisms involving biochemical processes, genetic regulatory pathways, and pathogenesis of disease have been elucidated from studies of Salmonella spp. and E. coli, these paradigms often do not apply to the same processes in the epsilonproteobacteria. Instead, these bacteria often display extensive variation in common biological mechanisms relative to those of other prototypical bacteria. In this review, five biological processes of commonly studied model bacterial species are compared to those of the epsilonproteobacteria C. jejuni and H. pylori. Distinct differences in the processes of flagellar biosynthesis, DNA uptake and recombination, iron homeostasis, interaction with epithelial cells, and protein glycosylation are highlighted. Collectively, these studies support a broader view of the vast repertoire of biological mechanisms employed by bacteria and suggest that future studies of the epsilonproteobacteria will continue to provide novel and interesting information regarding prokaryotic cellular biology.

The extracellular proteome of Rhizobium etli CE3 in exponential and stationary growth phase

Background

The extracellular proteome or secretome of symbiotic bacteria like Rhizobium etli is presumed to be a key element of their infection strategy and survival. Rhizobia infect the roots of leguminous plants and establish a mutually beneficial symbiosis. To find out the possible role of secreted proteins we analyzed the extracellular proteome of R. etli CE3 in the exponential and stationary growth phases in minimal medium, supplemented with succinate-ammonium.

Results

The extracellular proteins were obtained by phenol extraction and identified by LC-ESI MS/MS. We identified 192 and 191 proteins for the exponential and stationary phases respectively. Using the software Signal P, we predicted signal peptides for 12.95% and 35.60% of the proteins identified in the exponential and stationary phases, respectively, which could therefore be secreted by the Sec pathway. For the exponential growth phase, we found in abundance proteins like the ribosomal proteins, toxins and proteins belonging to the group "defence mechanisms". For the stationary growth phase, we found that the most abundant proteins were those with unknown function, and in many of these we identified characteristic domains of proteases and peptidases.

Conclusions

Our study provided the first dataset of the secretome of R. etli and its modifications, which may lead to novel insights into the adaptive response of different stages of growth. In addition, we found a high number of proteins with unknown function; these proteins could be analyzed in future research to elucidate their role in the extracellular proteome of R. etli.

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.

Temperature-dependent FlgM/FliA complex formation regulates Campylobacter jejuni flagella length

Regulation of the biosynthesis of the flagellar filament in bacteria containing multiple flagellin genes is not well understood. The major food-borne pathogen Campylobacter jejuni possesses on both poles a flagellum that consists of two different flagellin subunits, FlaA and FlaB. Here we identify the protein Cj1464 as a regulator of C. jejuni flagellin biosynthesis. The protein shares characteristics of the FlgM family of anti-sigma factor proteins: it represses transcription of sigma(28)-dependent genes, forms a complex with sigma factor FliA, and is secreted through the flagellar filament. However, unlike other FlgM proteins, the interaction of C. jejuni FlgM with FliA is regulated by temperature and the protein does not inhibit FliA activity during the formation of the hook-basal body complex (HBB). Instead, C. jejuni FlgM limits the length of the flagellar filament by suppressing the synthesis of both the sigma(28)- and the sigma(54)-dependent flagellins. The main function of the C. jejuni FlgM therefore is not to silence sigma(28)-dependent genes until the HBB is completed, but to prevent unlimited elongation of the flagellum, which otherwise leads to reduced bacterial motility.

The secretome of Campylobacter concisus

A higher prevalence of Campylobacter concisus and higher levels of IgG antibodies specific to C. concisus in Crohn's disease patients than in controls were recently detected. In this study, 1D and 2D gel electrophoresis coupled with LTQ FT-MS and QStar tandem MS, respectively, were performed to characterize the secretome of a C. concisus strain isolated from a Crohn's disease patient. Two hundred and one secreted proteins were identified, of which 86 were bioinformatically predicted to be secreted. Searches were performed on the genome of C. concisus strain 13826, and 25 genes that have been associated with virulence or colonization in other organisms were identified. The zonula occludens toxin was found only in C. concisus among the Campylobacterales, although expanded searches revealed that this protein was present in two epsilon-proteobacterial species from extreme marine environments. Alignments and structural threading indicated that this toxin shared features with that of other virulent pathogens, including Neisseria meningitidis and Vibrio cholerae. Further comparative analyses identified several associations between the secretome of C. consisus and putative virulence factors of this bacterium. This study has identified several factors putatively associated with disease outcome, suggesting that C. concisus is a pathogen of the gastrointestinal tract.

Biofilm formation by Campylobacter jejuni is increased under aerobic conditions

The microaerophilic human pathogen Campylobacter jejuni is the leading cause of food-borne bacterial gastroenteritis in the developed world. During transmission through the food chain and the environment, the organism must survive stressful environmental conditions, particularly high oxygen levels. Biofilm formation has been suggested to play a role in the environmental survival of this organism. In this work we show that C. jejuni NCTC 11168 biofilms developed more rapidly under environmental and food-chain-relevant aerobic conditions (20% O(2)) than under microaerobic conditions (5% O(2), 10% CO(2)), although final levels of biofilms were comparable after 3 days. Staining of biofilms with Congo red gave results similar to those obtained with the commonly used crystal violet staining. The level of biofilm formation by nonmotile aflagellate strains was lower than that observed for the motile flagellated strain but nonetheless increased under aerobic conditions, suggesting the presence of flagellum-dependent and flagellum-independent mechanisms of biofilm formation in C. jejuni. Moreover, preformed biofilms shed high numbers of viable C. jejuni cells into the culture supernatant independently of the oxygen concentration, suggesting a continuous passive release of cells into the medium rather than a condition-specific active mechanism of dispersal. We conclude that under aerobic or stressful conditions, C. jejuni adapts to a biofilm lifestyle, allowing survival under detrimental conditions, and that such a biofilm can function as a reservoir of viable planktonic cells. The increased level of biofilm formation under aerobic conditions is likely to be an adaptation contributing to the zoonotic lifestyle of C. jejuni.

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.

Sense and sensibility: flagellum-mediated gene regulation

The flagellum, a rotary engine required for motility in many bacteria, plays key roles in gene expression. It has been known for some time that flagellar substructures serve as checkpoints that coordinate flagellar gene expression with assembly. Less well understood, however, are other more global effects on gene expression. For instance, the flagellum acts as a 'wetness' sensor in Salmonella typhimurium, and as a mechanosensor in other bacteria. Additionally, it has been implicated in a variety of bacterial processes, including biofilm formation, pathogenesis and symbiosis. Although for many of these processes it might be simply that motility is required, in other cases it seems that the flagellum plays an underappreciated role in regulating gene expression.

Campylobacter jejuni: a brief overview on pathogenicity-associated factors and disease-mediating mechanisms

Campylobacter jejuni has long been recognized as a cause of bacterial food-borne illness, and surprisingly, it remains the most prevalent bacterial food-borne pathogen in the industrial world to date. Natural reservoirs for this Gram-negative, spiral-shaped bacterium are wild birds, whose intestines offer a suitable biological niche for the survival and dissemination of C. jejuni Chickens become colonized shortly after birth and are the most important source for human infection. In the last decade, effective intervention strategies to limit infections caused by this elusive pathogen were hindered mainly because of a paucity in understanding the virulence mechanisms of C. jejuni and in part, unavailability of an adequate animal model for the disease. However, recent developments in deciphering molecular mechanisms of virulence of C. jejuni made it clear that C. jejuni is a unique pathogen, being able to execute N-linked glycosylation of more than 30 proteins related to colonization, adherence, and invasion. Moreover, the flagellum is not only depicted to facilitate motility but as well secretion of Campylobacter invasive antigens (Cia). The only toxin of C. jejuni, the so-called cytolethal distending toxin (CdtA,B,C), seems to be important for cell cycle control and induction of host cell apoptosis and has been recognized as a major pathogenicity-associated factor. In contrast to other diarrhoea-causing bacteria, no other classical virulence factors have yet been identified in C. jejuni. Instead, host factors seem to play a major role for pathogenesis of campylobacteriosis of man. Indeed, several lines of evidence suggest exploitation of different adaptation strategies by this pathogen depending on its requirement, whether to establish itself in the natural avian reservoir or during the course of human infection.

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.

Type III secretion: a secretory pathway serving both motility and virulence (Review)

'Type III secretion' (T3S) refers to a secretion pathway that is common to the flagellae of eubacteria and the injectisomes of some gram-negative bacteria. Flagellae are rotary nanomachines allowing motility but they contain a built-in secretion apparatus that exports their own distal components to the distal end of the growing structure where they polymerize. In some cases they have been shown to export non-flagellar proteins. Injectisomes are transkingdom communication apparatuses allowing bacteria docked at the surface of a eukaryotic cell membrane to inject effector proteins across the two bacterial membranes and the eukaryotic cell membrane. Both nanomachines share a similar basal body embedded in the two bacterial membranes, topped either by a hook and a filament or by a stiff short needle. Both appear to be assembled in the same fashion. They recognize their substrate by a loose N-terminal peptide signal and the help of individual chaperones of a new type.

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.

Update on Campylobacter jejuni vaccine development for preventing human campylobacteriosis

Campylobacteriosis constitutes a serious medical and socioeconomic problem worldwide. Rapidly increasing antibiotic resistance of bacterial strains compels us to develop alternative therapeutic strategies and to search for efficient immunoprophylactic methods. The vast majority of Campylobacter infections in developed countries occur as sporadic cases, mainly caused by eating undercooked Campylobacter-contaminated poultry. The most efficient strategy of decreasing the number of human Campylobacter infections is by implementing protective vaccinations for humans and/or chickens. Despite more than 10 years of research, an effective anti-Campylobacter vaccine has not been developed. This review highlights our increasing knowledge of Campylobacter interaction with host cells and focuses on recently published data describing the efficacy of anti-Campylobacter vaccine prototypes.

Advances in Campylobacter biology and implications for biotechnological applications

Campylobacter jejuni is a major foodborne pathogen of animal origin and a leading cause of bacterial gastroenteritis in humans. During the past decade, especially since the publication of the first C. jejuni genome sequence, major advances have been made in understanding the pathobiology and physiology of this organism. It is apparent that C. jejuni utilizes sophisticated mechanisms for effective colonization of the intestinal tracts in various animal species. Although Campylobacter is fragile in the environment and requires fastidious growth conditions, it exhibits great flexibility in the adaptation to various habitats including the gastrointestinal tract. This high adaptability is attributable to its genetically, metabolically and phenotypically diverse population structure and its ability to change in response to various challenges. Unlike other enteric pathogens, such as Escherichia coli and Salmonella, Campylobacter is unable to utilize exogenous glucose and mainly depends on the catabolism of amino acids as a carbon source. Campylobacter proves highly mutable in response to antibiotic treatments and possesses eukaryote‐like dual protein glycosylation systems, which modify flagella and other surface proteins with specific sugar structures. In this review we will summarize the distinct biological traits of Campylobacter and discuss the potential biotechnological approaches that can be developed to control this enteric pathogen.

Campylobacter jejuni mediated disruption of polarized epithelial monolayers is cell-type specific, time dependent, and correlates with bacterial invasion

The precise mechanism by which the most common cause of bacterial enterocolitis in humans, Campylobacter jejuni, perturbs the intestinal mucosa remains elusive. To define effects of C. jejuni infection on mucosal permeability, Madin-Darby canine kidney (MDCK)-I and T84 cell monolayers were infected with C. jejuni for up to 48 h. All three tested C. jejuni strains caused a 73-78% reduction in transepithelial electrical resistance (TER) in intestinal (T84) cell monolayers, whereas only one strain slightly reduced TER of MDCK-I cells by 25% after 48 h infection. Infection with C. jejuni strains also caused a 2.3-4.5-fold increase in dextran permeability, but only in T84 cells. C. jejuni infection of monolayers also caused morphologic changes in desmosomes, observed by transmission electron microscopy. The cell-type specificity, demonstrated by increased T84 monolayer permeability, correlated with higher bacterial invasion into these cells, relative to MDCK-I cells. In T84 cells, invasion and bacterial translocation preceded barrier disruption and inhibition of C. jejuni invasion using a pharmacological inhibitor of phosphoinositide 3-kinase, reduced the drop in TER. These findings suggest that C. jejuni disruption of monolayers is mediated by invasion, provide new insights into C. jejuni-host epithelial barrier interactions, and offer potential mechanisms of intestinal injury and chronic immune stimulation.

Conserved residues in the HAMP domain define a new family of proposed bipartite energy taxis receptors

HAMP domains, found in many bacterial signal transduction proteins, generally transmit an intramolecular signal between an extracellular sensory domain and an intracellular signaling domain. Studies of HAMP domains in proteins where both the input and output signals occur intracellularly are limited to those of the Aer energy taxis receptor of Escherichia coli, which has both a HAMP domain and a sensory PAS domain. Campylobacter jejuni has an energy taxis system consisting of the domains of Aer divided between two proteins, CetA (HAMP domain containing) and CetB (PAS domain containing). In this study, we found that the CetA HAMP domain differs significantly from that of Aer in the predicted secondary structure. Using similarity searches, we identified 55 pairs of HAMP/PAS proteins encoded by adjacent genes in a diverse group of microorganisms. We propose that these HAMP/PAS pairs form a new family of bipartite energy taxis receptors. Within these proteins, we identified nine residues in the HAMP domain and proximal signaling domain that are highly conserved, at least three of which are required for CetA function. Additionally, we demonstrated that CetA contributes to the invasion of human epithelial cells by C. jejuni, while CetB does not. This finding supports the hypothesis that members of HAMP/PAS pairs possess the capacity to act independently of each other in cellular traits other than energy taxis.

Structure of a sigma28-regulated nonflagellar virulence protein from Campylobacter jejuni

Campylobacter jejuni, a Gram-negative motile bacterium, is a leading cause of human gastrointestinal infections. Although the mechanism of C.jejuni-mediated enteritis appears to be multifactorial, flagella play complex roles in the virulence of this human pathogen. Cj0977 is a recently identified virulence factor in C. jejuni and is expressed by a sigma(28) promoter that controls late genes in the flagellar regulon. A Cj0977 mutant strain is fully motile but significantly reduced in the invasion of intestinal epithelial cells in vitro. Here, we report the crystal structure of the major structural domain of Cj0977, which reveals a homodimeric "hot-dog" fold architecture. Of note, the characteristic hot-dog fold has been found in various coenzyme A (CoA) compound binding proteins with numerous oligomeric states. Structural comparison with other known hot-dog fold proteins locates a putative binding site for an acyl-CoA compound in the Cj0977 protein. Structure-based site-directed mutagenesis followed by invasion assays indicates that key residues in the putative binding site are indeed essential for the Cj0977 virulence function, suggesting a possible function of Cj0977 as an acyl-CoA binding regulatory protein.

Immunogenicity and protective efficacy of recombinant Campylobacter jejuni flagellum-secreted proteins in mice

Immunogenicity and protective efficacy of three Campylobacter jejuni flagellum-secreted proteins, FlaC, FspA1, and FspA2, were compared by use of a mouse model. Mice were immunized intranasally with each protein with or without LTR192G as the adjuvant and challenged intranasally with C. jejuni 81-176 or CG8486. All three proteins were immunogenic, although FspA1 induced the highest levels of serum immunoglobulin G (IgG) and fecal IgA. Although immunogenic, FlaC provided only 18% protection against disease from C. jejuni 81-176. Immunization with FspA1 resulted in 57.8% protection without adjuvant or 63.8% protection with adjuvant against homologous challenge with 81-176. Alternatively, immunization with FspA2 provided 38.4% (without adjuvant) or 47.2% (with adjuvant) protection against disease from homologous challenge with CG8486. In contrast to FspA2, FspA1 provided some heterologous protection against C. jejuni CG8486 when delivered with (31.2%) or without (44.8%) LTR192G. These results suggest that FspA1 may be a good subunit vaccine candidate against C. jejuni disease.

A proteome-wide protein interaction map for Campylobacter jejuni

'Systematic identification of protein interactions for the bacterium Campylobacter jejuni using high-throughput yeast two-hybrid screens detected interactions for 80% of the organism's proteins.

Background

Data from large-scale protein interaction screens for humans and model eukaryotes have been invaluable for developing systems-level models of biological processes. Despite this value, only a limited amount of interaction data is available for prokaryotes. Here we report the systematic identification of protein interactions for the bacterium Campylobacter jejuni, a food-borne pathogen and a major cause of gastroenteritis worldwide.

Results

Using high-throughput yeast two-hybrid screens we detected and reproduced 11,687 interactions. The resulting interaction map includes 80% of the predicted C. jejuni NCTC11168 proteins and places a large number of poorly characterized proteins into networks that provide initial clues about their functions. We used the map to identify a number of conserved subnetworks by comparison to protein networks from Escherichia coli and Saccharomyces cerevisiae. We also demonstrate the value of the interactome data for mapping biological pathways by identifying the C. jejuni chemotaxis pathway. Finally, the interaction map also includes a large subnetwork of putative essential genes that may be used to identify potential new antimicrobial drug targets for C. jejuni and related organisms.

Conclusion

The C. jejuni protein interaction map is one of the most comprehensive yet determined for a free-living organism and nearly doubles the binary interactions available for the prokaryotic kingdom. This high level of coverage facilitates pathway mapping and function prediction for a large number of C. jejuni proteins as well as orthologous proteins from other organisms. The broad coverage also facilitates cross-species comparisons for the identification of evolutionarily conserved subnetworks of protein interactions.

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.

Deletion of a previously uncharacterized flagellar-hook-length control gene fliK modulates the sigma54-dependent regulon in Campylobacter jejuni

A previously unannotated, putative fliK gene was identified in the Campylobacter jejuni genome based on sequence analysis; deletion mutants in this gene had a 'polyhook' phenotype characteristic of fliK mutants in other genera. The mutants greatly overexpressed the sigma(54)-dependent flagellar hook protein FlgE, to form unusual filamentous structures resembling straight flagella in addition to polyhooks. The genome sequence reveals only one gene predicted to encode an orthologue of the NtrC-family activator required for sigma(54)-dependent transcription. Hence, all sigma(54)-dependent genes in the genome would be overexpressed in the fliK mutant together with flgE. Microarray analysis of genome-wide transcription in the mutant showed increased transcription of a subset of genes, often downstream of sigma(54)-dependent promoters identified by a quality-predictive algorithm applied to the whole genome. Assessment of genome-wide transcription in deletion mutants in rpoN, encoding sigma(54), and in the sigma(54)-activator gene flgR, showed reciprocally reduced transcription of genes that were overexpressed in the fliK mutant. The fliA (sigma(28))-dependent regulon was also analysed. Together the data clearly define the roles of the alternative sigma factors RpoN and FliA in flagellar biogenesis in C. jejuni, and identify additional putative members of their respective regulons.

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 flagella: not just for motility

Campylobacter jejuni and Campylobacter coli are among the major causes of diarrheal disease worldwide. The motility imparted by the polar flagella of these pathogens is required for colonization of the mucus lining of the gastrointestinal tract. However, recent studies have revealed a more complex role for flagella in Campylobacter pathogenesis that includes the ability to secrete non-flagellar proteins that modulate virulence and the co-regulation of secreted and non-secreted virulence factors with the flagella regulon. Campylobacter flagellins are heavily glycosylated and changes in glycan composition affect autoagglutination and microcolony formation on intestinal epithelial cells; these traits are associated with disease in an animal model. Here, these recent advances in our understanding of the multifaceted role of flagella in Campylobacter virulence are summarized.

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.

Comprehensive analysis of transport proteins encoded within the genome of Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus is a bacterial parasite with an unusual lifestyle. It grows and reproduces in the periplasm of a host prey bacterium. The complete genome sequence of B. bacteriovorus has recently been reported. We have reanalyzed the transport proteins encoded within the B. bacteriovorus genome according to the current content of the Transporter Classification Database. A comprehensive analysis is given on the types and numbers of transport systems that B. bacteriovorus has. In this regard, the potential protein secretory capabilities of at least four types of inner-membrane secretion systems and five types of outer-membrane secretion systems are described. Surprisingly, B. bacteriovorus has a disproportionate percentage of cytoplasmic membrane channels and outer-membrane porins. It has far more TonB/ExbBD-type systems and MotAB-type systems for energizing outer-membrane transport and motility than does Escherichia coli. Analysis of probable substrate specificities of its transporters provides clues to its metabolic preferences. Interesting examples of gene fusions and of potentially overlapping genes are also noted. Our analyses provide a comprehensive, detailed appreciation of the transport capabilities of B. bacteriovorus. They should serve as a guide for functional experimental analyses.

Friend and foe: the two faces of Xenorhabdus nematophila

Comparisons of mutualistic and pathogenic relationships are necessary to decipher the common language of microorganism-host interactions, as well as the subtle differences in dialect that distinguish types of symbiosis. One avenue towards making such comparisons is to study a single organism that speaks both dialects, such as the gamma-proteobacterium Xenorhabdus nematophila. X. nematophila inhabits and influences the lives of two host animals, helping one to reproduce optimally while killing the other.

Vaccination of chickens against Campylobacter

The gram-negative bacterium Campylobacter is the leading cause of bacterial entero-colitis in humans and is associated with the occurrence of life-threatening auto-immune based neurological disorders. Chickens, which are often heavily colonized with Campylobacter without signs of pathology, are considered the most important source for human infection. Although vaccination is a well established and effective method to combat various microbes in poultry, a commercial vaccine against Campylobacter has not yet been developed. For the development of such a vaccine, three main challenges can be identified: (1) the identification of novel cross-protection-inducing antigens, (2) the induction of a rapid, potent immune response, and (3) the development of novel adjuvants to further stimulate immunity against Campylobacter. The rapidly emerging knowledge of the biology of Campylobacter in combination with the recent advances in the fields of molecular vaccinology and immunology provide the required setting for the development of an effective vaccine against Campylobacter in poultry.

Heterogeneity of a Campylobacter jejuni protein that is secreted through the flagellar filament

Cj0859c, or FspA, is a small, acidic protein of Campylobacter jejuni that is expressed by a sigma(28) promoter. Analysis of the fspA gene in 41 isolates of C. jejuni revealed two overall variants of the predicted protein, FspA1 and FspA2. Secretion of FspA occurs in broth-grown bacteria and requires a minimum flagellar structure. The addition of recombinant FspA2, but not FspA1, to INT407 cells in vitro resulted in a rapid induction of apoptosis. These data define a novel C. jejuni virulence factor, and the observed heterogeneity among fspA alleles suggests alternate virulence potential among different strains.

Targeted metabolomics analysis of Campylobacter coli VC167 reveals legionaminic acid derivatives as novel flagellar glycans

Glycosylation of Campylobacter flagellin is required for the biogenesis of a functional flagella filament. Recently, we used a targeted metabolomics approach using mass spectrometry and NMR to identify changes in the metabolic profile of wild type and mutants in the flagellar glycosylation locus, characterize novel metabolites, and assign function to genes to define the pseudaminic acid biosynthetic pathway in Campylobacter jejuni 81-176 (McNally, D. J., Hui, J. P., Aubry, A. J., Mui, K. K., Guerry, P., Brisson, J. R., Logan, S. M., and Soo, E. C. (2006) J. Biol. Chem. 281, 18489-18498). In this study, we use a similar approach to further define the glycome and metabolomic complement of nucleotide-activated sugars in Campylobacter coli VC167. Herein we demonstrate that, in addition to CMP-pseudaminic acid, C. coli VC167 also produces two structurally distinct nucleotide-activated nonulosonate sugars that were observed as negative ions at m/z 637 and m/z 651 (CMP-315 and CMP-329). Hydrophilic interaction liquid chromatography-mass spectrometry yielded suitable amounts of the pure sugar nucleotides for NMR spectroscopy using a cold probe. Structural analysis in conjunction with molecular modeling identified the sugar moieties as acetamidino and N-methylacetimidoyl derivatives of legionaminic acid (Leg5Am7Ac and Leg5AmNMe7Ac). Targeted metabolomic analyses of isogenic mutants established a role for the ptmA-F genes and defined two new ptm genes in this locus as legionaminic acid biosynthetic enzymes. This is the first report of legionaminic acid in Campylobacter sp. and the first report of legionaminic acid derivatives as modifications on a protein.

Campylobacter jejuniresponse to ox-bile stress

Campylobacter jejuni is a pathogen that colonizes the intestinal tract of humans and some animals. The in vitro responses of the bacterium to ox-bile were studied using proteomics to understand the molecular mechanisms employed by C. jejuni to survive bile stress. Its in vitro tolerance to bile was determined by growing the bacterium for 18 h in liquid cultures containing different bile concentrations. Significant growth inhibition was observed in the presence of 2.5% bile, and a decrease of 1.12 log units was measured at a bile concentration of 5%. Protein expression profiles of bacteria grown with and without bile were compared using two-dimensional polyacrylamide gel electrophoresis. Proteins with differential intensities greater than two-fold were identified using tandem mass spectrometry. Nuclear magnetic resonance spectroscopy and spectrophotometry were employed to measure enzyme activities in cell extracts from bacteria grown with and without bile. Together with proteins known to be involved in C. jejuni bile tolerance, the presence of bile modulated the expression of proteins such as elongation factors, ferritin, chaperones, ATP synthase and others, previously unknown to be implicated in the response of the bacterium to bile.

FtcR is a new master regulator of the flagellar system of Brucella melitensis 16M with homologs in Rhizobiaceae

The flagellar regulon of Brucella melitensis 16M contains 31 genes clustered in three loci on the small chromosome. These genes encode a polar sheathed flagellum that is transiently expressed during vegetative growth and required for persistent infection in a mouse model. By following the expression of three flagellar genes (fliF, flgE, and fliC, corresponding to the MS ring, hook, and filament monomer, respectively), we identified a new regulator gene, ftcR (flagellar two-component regulator). Inactivation of ftcR led to a decrease in flagellar gene expression and to impaired Brucella virulence. FtcR has a two-component response regulator domain as well a DNA binding domain and is encoded in the first flagellar locus of B. melitensis. Both the ftcR sequence and its genomic context are conserved in other related alpha-proteobacteria. During vegetative growth in rich medium, ftcR expression showed a peak during the early exponential phase that paralleled fliF gene expression. VjbR, a quorum-sensing regulator of the LuxR family, was previously found to control fliF and flgE gene expression. Here, we provide some new elements suggesting that the effect of VjbR on these flagellar genes is mediated by FtcR. We found that ftcR expression is partially under the control of VjbR and that the expression in trans of ftcR in a vjbR mutant restored the production of the hook protein (FlgE). Finally, FtcR binds directly to the upstream region of the fliF gene. Therefore, our data support the role of FtcR as a flagellar master regulator in B. melitensis and perhaps in other related alpha-proteobacteria.

Proteomic analysis of Campylobacter jejuni 11168 biofilms reveals a role for the motility complex in biofilm formation

Campylobacter jejuni remains the leading cause of bacterial gastroenteritis in developed countries, and yet little is known concerning the mechanisms by which this fastidious organism survives within its environment. We have demonstrated that C. jejuni 11168 can form biofilms on a variety of surfaces. Proteomic analyses of planktonic and biofilm-grown cells demonstrated differences in protein expression profiles between the two growth modes. Proteins involved in the motility complex, including the flagellins (FlaA, FlaB), the filament cap (FliD), the basal body (FlgG, FlgG2), and the chemotactic protein (CheA), all exhibited higher levels of expression in biofilms than found in stationary-phase planktonic cells. Additional proteins with enhanced expression included those involved in the general (GroEL, GroES) and oxidative (Tpx, Ahp) stress responses, two known adhesins (Peb1, FlaC), and proteins involved in biosynthesis, energy generation, and catabolic functions. An aflagellate flhA mutant not only lost the ability to attach to a solid matrix and form a biofilm but could no longer form a pellicle at the air-liquid interface of a liquid culture. Insertional inactivation of genes that affect the flagellar filament (fliA, flaA, flaB, flaG) or the expression of the cell adhesin (flaC) also resulted in a delay in pellicle formation. These findings demonstrate that the flagellar motility complex plays a crucial role in the initial attachment of C. jejuni 11168 to solid surfaces during biofilm formation as well as in the cell-to-cell interactions required for pellicle formation. Continued expression of the motility complex in mature biofilms is unusual and suggests a role for the flagellar apparatus in the biofilm phenotype.

Flagellin-independent regulation of chemokine host defense in Campylobacter jejuni-infected intestinal epithelium

Campylobacter jejuni is a leading cause of bacterial food-borne diarrheal disease throughout the world and the most frequent antecedent of autoimmune neuropathy Guillain-Barré syndrome. While infection is associated with immune memory, little is known regarding the role of the epithelium in targeting dendritic cells (DC) for initiating the appropriate adaptive immune response to C. jejuni. The objective of this study was to define the role for the intestinal epithelium in the induction of the adaptive immune response in C. jejuni infection by assessing the production of DC and T-cell chemoattractants. Human T84 epithelial cells were used as model intestinal epithelia. Infection of T84 cells with C. jejuni dose- and time-dependently up-regulated DC and T-cell chemokine gene transcription and secretion. Induction required live bacteria and was in the physiologically relevant direction for attraction of mucosal immunocytes. C. jejuni-activated NF-kappaB signaling was shown to be essential for proinflammatory chemokine secretion. Notably, C. jejuni secretion occurred independently of flagellin identification by Toll-like receptor 5. Secretion of a DC chemoattractant by differing clinical C. jejuni isolates suggested adherence/invasion were key virulence determinants of epithelial chemokine secretion. The regulated epithelial expression of DC and T-cell chemoattractants suggests a mechanism for the directed trafficking of immune cells required for the initiation of adaptive immunity in campylobacteriosis. Chemokine secretion occurs despite Campylobacter evasion of the flagellin pattern recognition receptor, suggesting that alternate host defense strategies limit disease pathogenesis.

Cj1121c, a novel UDP-4-keto-6-deoxy-GlcNAc C-4 aminotransferase essential for protein glycosylation and virulence in Campylobacter jejuni

Campylobacter jejuni produces glycoproteins that are essential for virulence. These glycoproteins carry diacetamidobacillosamine (DAB), a sugar that is not found in humans. Hence, the enzymes responsible for DAB synthesis represent potential therapeutic targets. We describe the biochemical characterization of Cj1121c, a putative aminotransferase encoded by the general protein glycosylation locus, to assess its role in DAB biosynthesis. By using overexpressed and affinity-purified enzyme, we demonstrate that Cj1121c has pyridoxal phosphate- and glutamate-dependent UDP-4-keto-6-deoxy-GlcNAc C-4 transaminase activity and produces UDP-4-amino-4,6-dideoxy-GlcNAc. This is consistent with a role in DAB biosynthesis and distinguishes Cj1121c from Cj1294, a homologous UDP-2-acetamido-2,6-dideoxy-beta-l-arabino-4-hexulose C-4 aminotransferase that we characterized previously. We show that Cj1121c can also use this 4-keto-arabino sugar indirectly as a substrate, that Cj1121c and Cj1294 are active simultaneously in C. jejuni, and that the activity of Cj1121c is preponderant under standard growth conditions. Kinetic data indicate that Cj1121c has a slightly higher catalytic efficiency than Cj1294 with regard to the 4-keto-arabino substrate. By site-directed mutagenesis, we show that residues Glu-158 and Leu-131 are not essential for catalysis or for substrate specificity contrary to expectations. We further demonstrate that a cj1121c knock-out mutant is impaired for flagella-mediated motility, for invasion of intestinal epithelial cells, and for persistence in the chicken intestine, clearly demonstrating that Cj1121c is essential for host colonization and virulence. Finally, we show that cj1121c is necessary for protein glycosylation by lectin Western blotting. Collectively, these results validate Cj1121c as a promising drug target and provide the means to assay for inhibitors.

A sigma28-regulated nonflagella gene contributes to virulence of Campylobacter jejuni 81-176

A Campylobacter jejuni 81-176 mutant in Cj0977 was fully motile but reduced >3 logs compared to the parent in invasion of intestinal epithelial cells in vitro. The mutant was also attenuated in a ferret diarrheal disease model. Expression of Cj0977 protein was dependent on a minimal flagella structure.

Components of the Legionella pneumophila flagellar regulon contribute to multiple virulence traits, including lysosome avoidance and macrophage death

Legionella pneumophila is a motile intracellular pathogen of macrophages and amoebae. When nutrients become scarce, the bacterium induces expression of transmission traits, some of which are dependent on the flagellar sigma factor FliA (sigma(28)). To test how particular components of the L. pneumophila flagellar regulon contribute to virulence, we compared a fliA mutant with strains whose flagellar construction is disrupted at various stages. We find that L. pneumophila requires FliA to avoid lysosomal degradation in murine bone marrow-derived macrophages (BMM), to regulate production of a melanin-like pigment, and to regulate binding to the dye crystal violet, whereas motility, flagellar secretion, and external flagella or flagellin are dispensable for these activities. Thus, in addition to flagellar genes, the FliA sigma factor regulates an effector(s) or regulator(s) that contributes to other transmissive traits, notably inhibition of phagosome maturation. Whether or not the microbes produced flagellin, all nonmotile L. pneumophila mutants bound BMM less efficiently than the wild type, resulting in poor infectivity and a loss of contact-dependent death of BMM. Therefore, bacterial motility increases contact with host cells during infection, but flagellin is not an adhesin. When BMM contact by each nonmotile strain was promoted by centrifugation, all the mutants bound BMM similarly, but only those microbes that synthesized flagellin induced BMM death. Thus, the flagellar regulon equips the aquatic pathogen L. pneumophila to coordinate motility with multiple traits vital to virulence.

Deduction of upstream sequences of Xanthomonas campestris flagellar genes responding to transcription activation by FleQ

Xanthomonas campestris pv. campestris (Xcc), a close relative to Pseudomonas aeruginosa, is the pathogen causing black rot in cruciferous plants. In P. aeruginosa, FleQ serves as a cognate activator of sigma54 in transcription from several sigma54-dependent promoters of flagellar genes. These P. aeruginosa promoters have been analyzed for FleQ-binding sequences; however, no consensus was deduced. Xcc, although lacks fleSR, has a fleQ homologue residing among over 40 contiguously clustered flagellar genes. A fleQ mutant, Xc17fleQ, constructed by insertional mutation is deficient in FleQ protein, non-flagellated, and immobile. Transcriptional fusion assays on six putative sigma54-dependent promoters of the flagellar genes, fliE, fliQ, fliL, flgG, flgB, and flhF, indicated that each of them is also FleQ dependent. Each of these promoters has a sequence with weak consensus to 5'-gaaacCCgccgCcgctTt-3', immediately upstream of the predicted sigma54-binding site, with an imperfect inverted repeat containing a GC-rich center flanked by several A and T at 5'- and 3'-ends, respectively. Replacing this region in fliE promoter with a HindIII recognition sequence abolished the transcription, indicating that this region responds to transcription activation by FleQ.

Campylobacter jejuni

This review describes characteristics of the family Campylobacteraceae and traits of Campylobacter jejuni. The review then focuses on the worldwide problem of C. jejuni antimicrobial resistance and mechanisms of pathogenesis and virulence. Unravelling these areas will help with the development of new therapeutic agents and ultimately decrease illness caused by this important human pathogen.

Commensal gut bacteria: mechanisms of immune modulation

Mucosal immune responses to pathogenic gut bacteria and the mechanisms that govern disease progression and outcome have been researched intensely for decades. More recently, the influence of the resident non-pathogenic or 'commensal' microflora on mucosal immune function and gut health has emerged as an area of scientific and clinical importance. Major differences occur in the mucosal immune response to pathogens and commensals. In part, this functional dichotomy is explained by the presence of virulence factors in pathogenic species, which are generally absent in commensals. Additionally, immunological 'unresponsiveness' towards the resident commensal microflora is thought to permit their successful colonisation and co-existence within the host gut. However, evidence of an active dialogue between members of the commensal microflora and the host mucosal immune system is rapidly unfolding. This crosstalk is likely to affect immunological tolerance and homeostasis within the gut and to explain some of the differential host responses to commensal and pathogenic bacteria.

Diverse roles for HspR in Campylobacter jejuni revealed by the proteome, transcriptome and phenotypic characterization of an hspR mutant

Campylobacter jejuni is a leading cause of bacterial gastroenteritis in the developed world. The role of a homologue of the negative transcriptional regulatory protein HspR, which in other organisms participates in the control of the heat-shock response, was investigated. Following inactivation of hspR in C. jejuni, members of the HspR regulon were identified by DNA microarray transcript profiling. In agreement with the predicted role of HspR as a negative regulator of genes involved in the heat-shock response, it was observed that the transcript amounts of 13 genes were increased in the hspR mutant, including the chaperone genes dnaK, grpE and clpB, and a gene encoding the heat-shock regulator HrcA. Proteomic analysis also revealed increased synthesis of the heat-shock proteins DnaK, GrpE, GroEL and GroES in the absence of HspR. The altered expression of chaperones was accompanied by heat sensitivity, as the hspR mutant was unable to form colonies at 44 degrees C. Surprisingly, transcriptome analysis also revealed a group of 17 genes with lower transcript levels in the hspR mutant. Of these, eight were predicted to be involved in the formation of the flagella apparatus, and the decreased expression is likely to be responsible for the reduced motility and ability to autoagglutinate that was observed for hspR mutant cells. Electron micrographs showed that mutant cells were spiral-shaped and carried intact flagella, but were elongated compared to wild-type cells. The inactivation of hspR also reduced the ability of Campylobacter to adhere to and invade human epithelial INT-407 cells in vitro, possibly as a consequence of the reduced motility or lower expression of the flagellar export apparatus in hspR mutant cells. It was concluded that, in C. jejuni, HspR influences the expression of several genes that are likely to have an impact on the ability of the bacterium to successfully survive in food products and subsequently infect the consumer.

In vitro cell culture methods for investigating Campylobacter invasion mechanisms

Studying the mechanisms of Campylobacter pathogenesis is complicated by the lack of simple animal models that mimic the disease seen in humans. In vitro cell culture methods provide a useful alternative to investigate the interactions between Campylobacter and the host epithelium that occur during infection. In the genomics era there is an increasing use of in vitro cell culture techniques to interrogate the potential role of different genes in pathogenesis. The aim of this review was to discuss the suitability and limitations of the various experimental approaches that might be adopted. We review current knowledge concerning the influence of cell-specific as well as bacterial factors required for Campylobacter invasion such as flagella and secreted proteins. The involvement and effects of phase variation on the results of invasion studies in cell culture emphasise the need to verify observed strain variations. We present the use of a mathematical Invasion Success Model to analyse Campylobacter invasion and show that it can be used to derive three strain dependent characteristics Imax, k, and I0. Even by combining data from independent experiments the Invasion Success Model can be used to statistically compare Campylobacter strains for their invasion of epithelial cells. Recommendations are given for the adoption of standard assay parameters and analytical methods such as the Invasion Success Model in order to facilitate comparison of data generated in different laboratories.

The sheathed flagellum of Brucella melitensis is involved in persistence in a murine model of infection

Persistence infection is the keystone of the ruminant and human diseases called brucellosis and Malta fever, respectively, and is linked to the intracellular tropism of Brucella spp. While described as non-motile, Brucella spp. have all the genes except the chemotactic system, necessary to assemble a functional flagellum. We undertook to determine whether these genes are expressed and are playing a role in some step of the disease process. We demonstrated that in the early log phase of a growth curve in 2YT nutrient broth, Brucella melitensis expresses genes corresponding to the basal (MS ring) and the distal (hook and filament) parts of the flagellar apparatus. Under these conditions, a polar and sheathed flagellar structure is visible by transmission electron microscopy (TEM). We evaluated the effect of mutations in flagellar genes of B. melitensis encoding various parts of the structure, MS ring, P ring, motor protein, secretion apparatus, hook and filament. None of these mutants gave a discernible phenotype as compared with the wild-type strain in cellular models of infection. In contrast, all these mutants were unable to establish a chronic infection in mice infected via the intraperitoneal route, raising the question of the biological role(s) of this flagellar appendage.