Significance of flagella in colonization resistance of rabbits immunized with Campylobacter spp

The prospect of orally administered monoclonal secretory IgA (SIgA) antibodies to prevent enteric bacterial infections

Eliminating diarrheal diseases as a leading cause of childhood morbidity and mortality in low- and middle-income countries (LMICs) will require multiple intervention strategies. In this review, we spotlight a series of preclinical studies investigating the potential of orally administered monoclonal secretory IgA (SIgA) antibodies (MAbs) to reduce disease associated with three enteric bacterial pathogens: Campylobacter jejuni, enterotoxigenic Escherichia coli (ETEC), and invasive Salmonella enterica serovar Typhimurium. IgA MAbs targeting bacterial surface antigens (flagella, adhesins, and lipopolysaccharide) were generated from mice, humanized mice, and human tonsillar B cells. Recombinant SIgA1 and/or SIgA2 derivates of those MAbs were purified from supernatants following transient transfection of 293 cells with plasmids encoding antibody heavy and light chains, J-chain, and secretory component (SC). When administered to mice by gavage immediately prior to (or admixed with) the bacterial challenge, SIgA MAbs reduced infection C. jejuni, ETEC, and S. Typhimurium infections. Fv-matched IgG1 MAbs by comparison were largely ineffective against C. jejuni and S. Typhimurium under the same conditions, although they were partially effective against ETEC. While these findings highlight future applications of orally administered SIgA, the studies also underscored the fundamental challenges associated with using MAbs as prophylactic tools against enteric bacterial diseases.

Fecal metatranscriptomics of macaques with idiopathic chronic diarrhea reveals altered mucin degradation and fucose utilization

BACKGROUND

Idiopathic chronic diarrhea (ICD) is a common cause of morbidity and mortality among juvenile rhesus macaques. Characterized by chronic inflammation of the colon and repeated bouts of diarrhea, ICD is largely unresponsive to medical interventions, including corticosteroid, antiparasitic, and antibiotic treatments. Although ICD is accompanied by large disruptions in the composition of the commensal gut microbiome, no single pathogen has been concretely identified as responsible for the onset and continuation of the disease.

RESULTS

Fecal samples were collected from 12 ICD-diagnosed macaques and 12 age- and sex-matched controls. RNA was extracted for metatranscriptomic analysis of organisms and functional annotations associated with the gut microbiome. Bacterial, fungal, archaeal, protozoan, and macaque (host) transcripts were simultaneously assessed. ICD-afflicted animals were characterized by increased expression of host-derived genes involved in inflammation and increased transcripts from bacterial pathogens such as Campylobacter and Helicobacter and the protozoan Trichomonas. Transcripts associated with known mucin-degrading organisms and mucin-degrading enzymes were elevated in the fecal microbiomes of ICD-afflicted animals. Assessment of colon sections using immunohistochemistry and of the host transcriptome suggests differential fucosylation of mucins between control and ICD-afflicted animals. Interrogation of the metatranscriptome for fucose utilization genes reveals possible mechanisms by which opportunists persist in ICD. Bacteroides sp. potentially cross-fed fucose to Haemophilus whereas Campylobacter expressed a mucosa-associated transcriptome with increased expression of adherence genes.

CONCLUSIONS

The simultaneous profiling of bacterial, fungal, archaeal, protozoan, and macaque transcripts from stool samples reveals that ICD of rhesus macaques is associated with increased gene expression by pathogens, increased mucin degradation, and altered fucose utilization. The data suggest that the ICD-afflicted host produces fucosylated mucins that are leveraged by potentially pathogenic microbes as a carbon source or as adhesion sites.

Engineering the Campylobacter jejuni N-glycan to create an effective chicken vaccine

Campylobacter jejuni is a predominant cause of human gastroenteritis worldwide. Source-attribution studies indicate that chickens are the main reservoir for infection, thus elimination of C. jejuni from poultry would significantly reduce the burden of human disease. We constructed glycoconjugate vaccines combining the conserved C. jejuni N-glycan with a protein carrier, GlycoTag, or fused to the Escherichia coli lipopolysaccharide-core. Vaccination of chickens with the protein-based or E. coli-displayed glycoconjugate showed up to 10-log reduction in C. jejuni colonization and induced N-glycan-specific IgY responses. Moreover, the live E. coli vaccine was cleared prior to C. jejuni challenge and no selection for resistant campylobacter variants was observed. Analyses of the chicken gut communities revealed that the live vaccine did not alter the composition or complexity of the microbiome, thus representing an effective and low-cost strategy to reduce C. jejuni in chickens and its subsequent entry into the food chain.

Reducing Campylobacter jejuni colonization of poultry via vaccination

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

Is the Campylobacter jejuni secretory protein Cj0069 a suitable antigen for serodiagnostics?

Campylobacter spp. is the most common bacterial pathogen of gastroenteritis worldwide. Poultry is the main reservoir and consequently the main origin of infections for humans. As a consequence of a primary Campylobacter infection which typically manifests as diarrhea, there is an increased risk to suffer from post-infectious complications such as reactive arthritis, neuropathia, myositis or a Guillain-Barré Syndrome. Usually the verification of acute campylobacteriosis is made by stool culture. In contrast, post-infectious complications can be diagnosed by serological assays. Since most of them are based on whole cell lysates, an insufficient specificity results from cross-reactions between related species. Therefore, the use of recombinant antigens becomes more and more favorable. Campylobacter is able to secrete a number of proteins, which are amongst others necessary for cell invasion and therefore play a crucial role for virulence. One of these, Cj0069, has a similar specificity and sensitivity in the detection of anti-Campylobacter jejuni IgG compared to the well-established antigens OMP18 and P39. This makes it a suitable antigen for diagnosing C. jejuni post-infectious complications.

Characterisation of a multi-ligand binding chemoreceptor CcmL (Tlp3) of Campylobacter jejuni

Campylobacter jejuni is the leading cause of human gastroenteritis worldwide with over 500 million cases annually. Chemotaxis and motility have been identified as important virulence factors associated with C. jejuni colonisation. Group A transducer-like proteins (Tlps) are responsible for sensing the external environment for bacterial movement to or away from a chemical gradient or stimulus. In this study, we have demonstrated Cj1564 (Tlp3) to be a multi-ligand binding chemoreceptor and report direct evidence supporting the involvement of Cj1564 (Tlp3) in the chemotaxis signalling pathway via small molecule arrays, surface plasmon and nuclear magnetic resonance (SPR and NMR) as well as chemotaxis assays of wild type and isogenic mutant strains. A modified nutrient depleted chemotaxis assay was further used to determine positive or negative chemotaxis with specific ligands. Here we demonstrate the ability of Cj1564 to interact with the chemoattractants isoleucine, purine, malic acid and fumaric acid and chemorepellents lysine, glucosamine, succinic acid, arginine and thiamine. An isogenic mutant of cj1564 was shown to have altered phenotypic characteristics of C. jejuni, including loss of curvature in bacterial cell shape, reduced chemotactic motility and an increase in both autoagglutination and biofilm formation. We demonstrate Cj1564 to have a role in invasion as in in vitro assays the tlp3 isogenic mutant has a reduced ability to adhere and invade a cultured epithelial cell line; interestingly however, colonisation ability of avian caeca appears to be unaltered. Additionally, protein-protein interaction studies revealed signal transduction initiation through the scaffolding proteins CheV and CheW in the chemotaxis sensory pathway. This is the first report characterising Cj1564 as a multi-ligand receptor for C. jejuni, we therefore, propose to name this receptor CcmL, Campylobacterchemoreceptor for multiple ligands. In conclusion, this study identifies a novel multifunctional role for the C. jejuni CcmL chemoreceptor and illustrates its involvement in the chemotaxis pathway and subsequent survival of this organism in the host.

Bacterial chemotaxis is an important part in initiation of colonisation and subsequent pathogenicity. In this study, we report direct evidence supporting the involvement of C. jejuni transducer-like protein Cj1564 (Tlp3) in the chemotaxis signalling pathway via small molecule arrays, surface plasmon and nuclear magnetic resonance (SPR and NMR) as well as chemotaxis assays of wild type and isogenic mutants. We further demonstrate its ability to interact with chemoattractants isoleucine, purine, malic acid and fumaric acid and chemorepellents lysine, glucosamine, succinic acid, arginine and thiamine. This is the first report identifying Cj1564 as a multi-ligand receptor for Campylobacter jejuni and its signal transduction initiation through the CheV and CheW proteins. Finally, our characterisation of C. jejuni Cj1564 provides additional basis for elucidating the roles of other group A chemoreceptors and their importance in the chemotaxis signalling pathway.

Pentavalent single-domain antibodies reduce Campylobacter jejuni motility and colonization in chickens

Campylobacter jejuni is the leading cause of bacterial foodborne illness in the world, with symptoms ranging from acute diarrhea to severe neurological disorders. Contaminated poultry meat is a major source of C. jejuni infection, and therefore, strategies to reduce this organism in poultry, are expected to reduce the incidence of Campylobacter-associated diseases. We have investigated whether oral administration of C. jejuni-specific single-domain antibodies would reduce bacterial colonization levels in chickens. Llama single-domain antibodies specific for C. jejuni were isolated from a phage display library generated from the heavy chain IgG variable domain repertoire of a llama immunized with C. jejuni flagella. Two flagella-specific single-domain antibodies were pentamerized to yield high avidity antibodies capable of multivalent binding to the target antigen. When administered orally to C. jejuni-infected two-day old chicks, the pentabodies significantly reduced C. jejuni colonization in the ceca. In vitro, the motility of the bacteria was also reduced in the presence of the flagella-specific pentabodies, suggesting the mechanism of action is through either direct interference with flagellar motility or antibody-mediated aggregation. Fluorescent microscopy and Western blot analyses revealed specific binding of the anti-flagella pentabodies to the C. jejuni flagellin.

Virulence characteristics of five new Campylobacter jejuni chicken isolates

Campylobacter enteritis has emerged as one of the most common forms of human diarrheal illness. In this study we have investigated the virulence potential of five new C. jejuni chicken isolates (RO14, RO19, RO24, RO29 and RO37) originated from private households in the rural regions of Banat and Transylvania in Romania. Following isolation and in vitro virulence assay, on HCT-8 cells, our results show that all the C. jejuni chicken isolates overcome the virulence abilities of the highly virulent strain C. jejuni 81-176. Motility, an important virulence factor was significantly improved in all the new chicken isolates. The ability to survive to the antimicrobial activity of the human serum, to resist to the violent attack of bile acids and to survive in the presence of synthetic antibiotics was increased in all the chicken isolates. However, these were statistically significant only for isolates RO29 and RO37. In conclusion our study shows, based on invasiveness and motility, and also on the data provided by the serum and bile resistance experiments that all the new chicken isolates are able to infect human cells, in vitro, and could potentially represent a health hazard for humans.

Comparative analysis of Campylobacter populations within individual market-age broilers using Fla gene typing method

Campylobacter species is the most common human pathogen causing gastrointestinal infections in humans, and poultry is considered a major source of this pathogen. In this project, we aim to study the genetic diversity of Campylobacter populations within individual chickens using cecal samples to understand the nature of intestinal colonization in chickens by Campylobacter species. Genotyping was conducted based on the DNA sequence of short variable regions (SVR) in the flaA gene. Cecal samples were collected from 9 market-age broiler chickens and used for isolation of Campylobacter genomic DNA. The SVR fragments of 400 bp were amplified using SVR-specific primers, cloned, and sequenced. Sequencing results obtained from 86 clones (~10 clones/bird) showed that on an average 23.25% of clones had mutations within individuals. The mutations did not show any consistent pattern, suggesting a random nature of the mutations. When translated SVR sequences were analyzed, on average 20.57% of strains carried altered amino acid sequences in SVR within individuals. Four translated sequences had nonsense mutations to produce truncated proteins. These results suggest that there are multiple genotypes colonizing in a cecum and the occurrence of truncated FlaA protein may represent a novel mechanism for evasion of adaptive immune responses.

Oral immunization with cholera toxin provides protection against Campylobacter jejuni in an adult mouse intestinal colonization model

Immunity to Campylobacter jejuni, a major diarrheal pathogen, is largely Penner serotype specific. For broad protection, a vaccine should be based on a common antigen(s) present in all strains. In our previous study (M. J. Albert, S. Haridas, D. Steer, G. S. Dhaunsi, A. I. Smith, and B. Adler, Infect. Immun. 75:3070–3073, 2007), we demonstrated that antibody to cholera toxin (CT) cross-reacted with the major outer membrane proteins (MOMPs) of all Campylobacter jejuni strains tested. In the current study, we investigated whether immunization with CT protects against intestinal colonization by C. jejuni in an adult mouse model and whether the nontoxic subunit of CT (CT-B) is the portion mediating cross-reaction. Mice were orally immunized with CT and later challenged with C. jejuni strains (48, 75, and 111) of different serotypes. Control animals were immunized with phosphate-buffered saline. Fecal shedding of challenge organisms was studied daily for 9 days. Serum and fecal antibody responses were studied by enzyme-linked immunosorbent assay (ELISA) and immunoblotting. The cross-reactivity of rabbit CT-B antibody to MOMP was studied by immunoblotting. The reactivity of 21 overlapping 30-mer oligopeptides (based on MOMP’s sequence) against rabbit CT antibody was tested by ELISA. Test animals produced antibodies to CT and MMP in serum and feces and showed resistance to colonization, the vaccine efficacies being 49% (for strain 48), 37% (for strain 75), and 34% (for strain 111) (P, ≤0.05 to ≤0.001). One peptide corresponding to a variable region of MOMP showed significant reactivity. CT-B antibody cross-reacted with MOMP. Since CT-B is a component of oral cholera vaccines, it might be possible to control C. jejuni diarrhea with these vaccines.

Campylobacter jejuni is a major cause of diarrhea worldwide. Patients who recover from C. jejuni diarrhea develop immunity to the infecting serotype and remain susceptible to infection with other serotypes. A vaccine based on a common protective antigen(s) present in all C. jejuni serotypes is expected to provide broad protection. In our previous study, we showed that antibody to cholera toxin (CT) reacted with the major outer membrane proteins (MOMPs) from different strains of C. jejuni. We assumed that the B subunit of the toxin (CT-B), which is nontoxic and a component of licensed oral cholera vaccines, might be the component that cross-reacts with MOMP. In the current study, we showed that orally immunizing mice with CT protected them against colonization upon challenge with different serotypes of C. jejuni. We also showed that CT-B is the component mediating cross-reaction. Therefore, it might be possible to use cholera vaccines to prevent C. jejuni diarrhea. This could result in significant savings in vaccine development and treatment of the disease.

Chemotaxis in Campylobacter jejuni

Chemotaxis is the common way of flagellated bacteria to direct their locomotion to sites of most favourable living conditions, that are sites with the highest concentrations of energy sources and the lowest amounts of bacteriotoxic substances. The general prerequisites for chemotaxis are chemoreceptors, a chemosensory signal-transduction system and the flagellar apparatus. Epsilonproteobacteria like Campylobacter sp. show specific variations of the common chemotaxis components. CheV, a CheW-like linking-protein with an additional response regulator (RR) domain, was identified as commonly used coupling scaffold protein of Campylobacter jejuni. It attaches the histidine autokinase (CheAY), which also has an additional RR-domain, to the chemoreceptors signalling domains. These additional RR-domains seem to play an important role in the regulation of the CheAY-phosphorylation state and thereby in sensory adaptation. The Campylobacter-chemoreceptors are arranged into the three groups A, B, and C. Group A contains membrane-anchored receptors sensing periplasmic signals, group B consists only of one receptor with two cytoplasmic ligand-proteins representing a bipartite energy taxis system that senses pyruvate and fumarate, and group C receptors are cytoplasmic signalling domains with mostly unknown cytoplasmic ligand-binding proteins as sensory constituents. Recent findings demonstrating different alleles of the TLP7 chemoreceptor, specific for formic acid, led to an amendment of this grouping.

Phenotypic and genotypic methods for typing Campylobacter jejuni and Campylobacter coli in poultry

Human campylobacteriosis, an infection caused by the bacterium Campylobacter, is a major issue in the United States food system, especially for poultry products. According to the Center for Disease Control, campylobacterosis is estimated to affect over 2.4 million people annually. Campylobacter jejuni and Campylobacter coli are 2 species responsible for the majority of campylobacterosis infections. Phenotypic and genotypic typing methods are often used to discriminate between bacteria at the species and subspecies level and are often used to identify pathogenic organisms, such as C. jejuni and C. coli. This review describes the design as well as advantages and disadvantages for 3 current phenotypic techniques (biotyping, serotyping, and multilocus enzyme electrophoresis) and 6 genotypic techniques (multilocus sequence typing, PCR, pulse-field gel electrophoresis, ribotyping, flagellin typing, and amplified fragment length polymorphisms) for typing pathogenic Campylobacter spp.

Sulphite : cytochrome c oxidoreductase deficiency in Campylobacter jejuni reduces motility, host cell adherence and invasion

Campylobacter jejuni lacks the enzyme phosphofructokinase and, consequently, is incapable of metabolizing glucose. Instead, the pathogen uses a number of other chemicals to serve as electron donors. Like chemolithotrophic bacteria, C. jejuni is able to respire sulphite in the presence of a sulphite : cytochrome c oxidoreductase (SOR) that is encoded by the genes cj0004c and cj0005c; the former encodes a monohaem cytochrome c oxidoreductase and the latter a molybdopterin oxidoreductase. After screening of a transposon-based mutant library, we identified a mutant with an insertion in gene cj0005c that was strongly reduced in its capacity to infect Caco2 cells. Further characterization of a corresponding non-random knockout mutant together with a complemented mutant and the parental strain showed the cj0005c-deficient mutant to exhibit clearly reduced motility and diminished adherence to host cells. Furthermore, the transcription of genes responsible for the synthesis of, in particular, legionaminic acid was downregulated and the mutant had a reduced capacity to autoagglutinate. In contrast, neither the proliferation of the mutant, nor its intracellular ATP content, was altered compared to the parental strain.

Recombinant PorA, the major outer membrane protein of Campylobacter jejuni, provides heterologous protection in an adult mouse intestinal colonization model

Immunity against Campylobacter jejuni, a major food-borne pathogen causing diarrhea, is largely serotype specific. The major outer membrane protein (MOMP) of C. jejuni, PorA, is a common antigen with the potential to provide broad protection. Adult BALB/c mice were orally immunized with a recombinant glutathione S-transferase (GST) fused to PorA prepared from Campylobacter jejuni C31 (O:6,7) (GST-PorA) combined with a modified heat-labile enterotoxin of Escherichia coli as an adjuvant and later orally challenged with C31 strain or three heterologous strains: 48 (O:19), 75 (O:3), and 111 (O:1,44). Protection from colonization with the challenge organism was studied by fecal screening daily for 9 days. Serum and intestinal lavage fluid antibodies against the vaccine and Sarkosyl-purified MOMP from C31 were measured by using an enzyme-linked immunosorbent assay. The vaccine produced robust antibody responses against both antigens in serum and secretion. Since strain C31 was a poor colonizer, homologous protection could not be studied. The protective efficacies of heterologous strains were 43% (for strain 48, P < 0.001), 29% (for strain 75, P < 0.005), and 42% (for strain 111, P < 0.001) for the 9-day period compared to control mice given phosphate-buffered saline. Thus, PorA provided appreciable protection against colonization with heterologous serotypes.

Modification of the Campylobacter jejuni flagellin glycan by the product of the Cj1295 homopolymeric-tract-containing gene

The Campylobacter jejuni flagellin protein is O-glycosylated with structural analogues of the nine-carbon sugar pseudaminic acid. The most common modifications in the C. jejuni 81-176 strain are the 5,7-di-N-acetylated derivative (Pse5Ac7Ac) and an acetamidino-substituted version (Pse5Am7Ac). Other structures detected include O-acetylated and N-acetylglutamine-substituted derivatives (Pse5Am7Ac8OAc and Pse5Am7Ac8GlnNAc, respectively). Recently, a derivative of pseudaminic acid modified with a di-O-methylglyceroyl group was detected in C. jejuni NCTC 11168 strain. The gene products required for Pse5Ac7Ac biosynthesis have been characterized, but those genes involved in generating other structures have not. We have demonstrated that the mobility of the NCTC 11168 flagellin protein in SDS-PAGE gels can vary spontaneously and we investigated the role of single nucleotide repeats or homopolymeric-tract-containing genes from the flagellin glycosylation locus in this process. One such gene, Cj1295, was shown to be responsible for structural changes in the flagellin glycoprotein. Mass spectrometry demonstrated that the Cj1295 gene is required for glycosylation with the di-O-methylglyceroyl-modified version of pseudaminic acid.

Novel approaches for Campylobacter control in poultry

The Gram-negative bacterium Campylobacter is the most common bacterial cause of human gastroenteritis in the United States and many industrialized countries. Poultry, particularly chickens, is considered a major source of human campylobacteriosis. Thus, on-farm control of Campylobacter in poultry would reduce the risk of human exposure to this pathogen and have a significant impact on food safety and public health. To date, three general strategies have been proposed to control Campylobacter in poultry at the farm level: (1) reduction of environmental exposure (biosecurity measures), (2) an increase in poultry's host resistance to reduce Campylobacter carriage in the gut (e.g., competitive exclusion, vaccination, and host genetics selection), and (3) the use of antimicrobial alternatives to reduce and even eliminate Campylobacter from colonized chickens (e.g., bacteriophage therapy and bacteriocin treatment). Except for biosecurity measures, the other intervention approaches are currently not commercially available and are still under development. This review is focused on two promising strategies--vaccination and bacteriocin treatment. In particular, we extensively review recent research aimed at discovering and characterizing potent anti-Campylobacter bacteriocins to reduce Campylobacter load at the primary production level in poultry.

Role of the Helicobacter hepaticus flagellar sigma factor FliA in gene regulation and murine colonization

The enterohepatic Helicobacter species Helicobacter hepaticus colonizes the murine intestinal and hepatobiliary tract and is associated with chronic intestinal inflammation, gall stone formation, hepatitis, and hepatocellular carcinoma. Thus far, the role of H. hepaticus motility and flagella in intestinal colonization is unknown. In other, closely related bacteria, late flagellar genes are mainly regulated by the sigma factor FliA (sigma(28)). We investigated the function of the H. hepaticus FliA in gene regulation, flagellar biosynthesis, motility, and murine colonization. Competitive microarray analysis of the wild type versus an isogenic fliA mutant revealed that 11 genes were significantly more highly expressed in wild-type bacteria and 2 genes were significantly more highly expressed in the fliA mutant. Most of these were flagellar genes, but four novel FliA-regulated genes of unknown function were identified. H. hepaticus possesses two identical copies of the gene encoding the FliA-dependent major flagellin subunit FlaA (open reading frames HH1364 and HH1653). We characterized the phenotypes of mutants in which fliA or one or both copies of the flaA gene were knocked out. flaA_1 flaA_2 double mutants and fliA mutants did not synthesize detectable amounts of FlaA and possessed severely truncated flagella. Also, both mutants were nonmotile and unable to colonize mice. Mutants with either flaA gene knocked out produced flagella morphologically similar to those of wild-type bacteria and expressed FlaA and FlaB. flaA_1 mutants which had flagella but displayed reduced motility did not colonize mice, indicating that motility is required for intestinal colonization by H. hepaticus and that the presence of flagella alone is not sufficient.

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.

Deletion of peb4 gene impairs cell adhesion and biofilm formation in Campylobacter jejuni

Campylobacter jejuni is a microaerophilic bacterium that causes diarrhea in humans. The first step in establishing an infection is adherence to a host cell, which involves two major cell-binding proteins, Peb1A (CBF1) and Peb4 (CBF2). Because the functional role of Peb4 on the cell adhesion remains unclear compared with that of Peb1A, a C. jejuni peb4 deletion mutant was constructed and cell adherence and ability to colonize mouse intestine were studied. The result showed that adherence of the peb4 mutant strain to INT407 cells was 1-2% that of the wild-type strain. Mouse challenge experiments showed a reduced level and duration of intestinal colonization by the mutant compared with the wild-type strain. In addition, fewer peb4 mutant cells than wild-type cells responded to stress by forming a biofilm. Proteomic analysis revealed that the expression levels of proteins involved in various adhesion, transport, and motility functions, which are required for biofilm formation by the pathogen, were lower in the peb4 mutant than in the wild-type strain. A Peb4 homolog has prolyl cis/trans-isomerase activity, suggesting that the loss of this activity in the mutant strain may be responsible for the repression of these proteins.

Serological assessment of synthetic peptides of Campylobacter jejuni NCTC11168 FlaA protein using antibodies against multiple serotypes

The flagellum of Campylobacter jejuni is not only responsible for initiating colonization of the gastrointestinal tract of host animals but is also a major antigen that induces protective immune responses. However, protection is limited to the homologous strain and the ability to protect against multiple serotypes has yet to be determined. In this study, we have shown that FlaA is an immunodominant protein on NCTC11168 CJ1 flagella and we mapped the immunoreactive epitopes on the protein by probing a series of overlapping synthetic peptides spanning the entire sequence with sera against multiple C. jejuni serotypes. Amino acid residues 176-205 (P8), 376-405 (P16) and 501-530 (P21) were immunodominant and cross-reactive. The mucosal IgA in the intestinal secretions of CJ1-infected birds reacted significantly with peptides P16 and P21 indicating that the specificity of the mucosal response is different from the systemic response. Antisera raised against formalin-killed CJ1 cells and purified flagellin showed positive reactivity with a subset of peptides identified by antisera against live C. jejuni. This study provides insight into the specificity of the host immune responses to the FlaA protein of C. jejuni and suggests that these sequences merit further testing for their immunogenicity and potential as subunit vaccine candidates for multiple serotypes.

TLR5 and Ipaf: dual sensors of bacterial flagellin in the innate immune system

The innate immune system precisely modulates the intensity of immune activation in response to infection. Flagellin is a microbe-associated molecular pattern that is present on both pathogenic and nonpathogenic bacteria. Macrophages and dendritic cells are able to determine the virulence of flagellated bacteria by sensing whether flagellin remains outside the mammalian cell, or if it gains access to the cytosol. Extracellular flagellin is detected by TLR5, which induces expression of proinflammatory cytokines, while flagellin within the cytosol of macrophages is detected through the Nod-like receptor (NLR) Ipaf, which activates caspase-1. In macrophages infected with Salmonella typhimurium or Legionella pneumophila, Ipaf becomes activated in response to flagellin that appears to be delivered to the cytosol via specific virulence factor transport systems (the SPI1 type III secretion system (T3SS) and the Dot/Icm type IV secretion system (T4SS), respectively). Thus, TLR5 responds more generally to flagellated bacteria, while Ipaf responds to bacteria that express both flagellin and virulence factors.

Host protein binding and adhesive properties of H6 and H7 flagella of attaching and effacing Escherichia coli

It had been suggested that the flagella of enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) might contribute to host colonization. In this study, we set out to investigate the adhesive properties of H7 and H6 flagella. We studied the abilities of EHEC EDL933 (O157:H7) and EPEC E2348/69 (O127:H6) flagella to bind to bovine mucus, host proteins such as mucins, and extracellular matrix proteins. Through several approaches, we found that H6 and H7 flagella and their flagellin monomers bind to mucins I and II and to freshly isolated bovine mucus. A genetic approach showed that EHEC and EPEC fliC deletion mutants were significantly less adherent to bovine intestinal tissue than the parental wild-type strains. In addition, we found that EPEC bacteria and H6 flagella, but not EHEC, bound largely, in a dose-dependent manner, to collagen and to a lesser extent to laminin and fibronectin. We also report that EHEC O157:H7 strains agglutinate rabbit red blood cells via their flagella, a heretofore unknown phenotype in this pathogroup. Collectively, our data demonstrate that the H6 and H7 flagella possess adhesive properties, particularly the ability to bind mucins, that may contribute to colonization of mucosal surfaces.

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.

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

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

Phase-variable surface structures are required for infection of Campylobacter jejuni by bacteriophages

This study characterizes the interaction between Campylobacter jejuni and the 16 phages used in the United Kingdom typing scheme by screening spontaneous mutants of the phage-type strains and transposon mutants of the sequenced strain NCTC 11168. We show that the 16 typing phages fall into four groups based on their patterns of activity against spontaneous mutants. Screens of transposon and defined mutants indicate that the phage-bacterium interaction for one of these groups appears to involve the capsular polysaccharide (CPS), while two of the other three groups consist of flagellatropic phages. The expression of CPS and flagella is potentially phase variable in C. jejuni, and the implications of these findings for typing and intervention strategies are discussed.

Prevention of disease in ferrets fed an inactivated whole cell Campylobacter jejuni vaccine

Ferrets were used to demonstrate the potential of a killed whole cell vaccine prepared from Campylobacter jejuni to protect against disease. C. jejuni strain 81-176 was grown in BHI broth, formalin-fixed, and resuspended in PBS to a concentration of 10(10) cells per ml. This vaccine (CWC) or live organisms were delivered orally with a nasogastric tube into anesthetized animals treated to reduce gastric acidity and intestinal motility. When 5x10(10) CFU of the vaccine strain (Lior serotype 5) or one of two other serotypes, CGL-7 (Lior 4) or BT44 (Lior 9), was used to challenge the ferrets, all of the animals developed a mucoid diarrhea. If the animals had been challenged with 5x10(9) CFU of the homologous strain 1 month before challenge with 10(10) CFU, 80-100% protection against disease was seen. This protection was also obtained after an initial exposure to the 81-176 strain followed by challenge with either of the heterologous strains. CWC was used to see if protection demonstrated with the live organisms could be produced with the non-living preparation. When 10(9) cells of CWC was given as two doses 7 days apart with or without 25mug of a coadministered mucosal adjuvant, LT(R192G), only 40-60% of the animals were protected. If the regimen was changed to four doses given 48h apart, 80% of the animals were free of diarrhea after subsequent challenge. Increasing the number of cells in the four dose regimen to 10(10) cells did not improve protection. Animals given four doses of 10(10) cells combined with LT(R192G) were subsequently challenged with 10(10) cells of the homologous strain or the heterologous strain CGL-7. The CWC protected against both strains. Serum IgG antibody titers determined by ELISA showed little increase following the CWC four dose vaccination regimen, compared to animals given one dose of the live organism. On subsequent challenge, however, both CWC vaccinated and live-challenged ferrets showed comparable antibody titer increases above those obtained following the initial challenge or vaccination. Western blots were used to show that the immunodominant antigen in vaccinated animals was a 45kDa protein, while in ferrets challenged with live organisms the immunodominant antigen was a 62kDa protein. These data show that the CWC can be used to protect against disease caused by Campylobacter. They also show that protection and serum IgG responses do not depend upon the use of the mucosal adjuvant and that cross protection among some of the major serotypes of Campylobacter responsible for human disease is possible.

Evasion of Toll-like receptor 5 by flagellated bacteria

Toll-like receptor 5 (TLR5) recognizes an evolutionarily conserved site on bacterial flagellin that is required for flagellar filament assembly and motility. The alpha and epsilon Proteobacteria, including the important human pathogens Campylobacter jejuni, Helicobacter pylori, and Bartonella bacilliformis, require flagellar motility to efficiently infect mammalian hosts. In this study, we demonstrate that these bacteria make flagellin molecules that are not recognized by TLR5. We map the site responsible for TLR5 evasion to amino acids 89-96 of the N-terminal D1 domain, which is centrally positioned within the previously defined TLR5 recognition site. Salmonella flagellin is strongly recognized by TLR5, but mutating residues 89-96 to the corresponding H. pylori flaA sequence abolishes TLR5 recognition and also destroys bacterial motility. To preserve bacterial motility, alpha and epsilon Proteobacteria possess compensatory amino acid changes in other regions of the flagellin molecule, and we engineer a mutant form of Salmonella flagellin that evades TLR5 but retains motility. These results suggest that TLR5 evasion is critical for the survival of this subset of bacteria at mucosal sites in animals and raise the intriguing possibility that flagellin receptors provided the selective force to drive the evolution of these unique subclasses of bacterial flagellins.

Considerations for development of whole cell bacterial vaccines to prevent diarrheal diseases in children in developing countries

Enteric pathogens constitute a major pediatric threat in the developing world through their impact on morbidity and mortality, physical and cognitive development and cause and effect relationship with malnutrition. Although many bacterial pathogens can cause diarrheal diseases, a group of less than 10 including Shigella spp., enterotoxigenic Escherichia coli (ETEC), Vibrio cholerae, and possibly, Campylobacter jejuni account for a significant percentage of these diseases in developing countries. Rotavirus is also a major cause of diarrheal diseases. Vaccines against these agents offer a potentially effective control measure against these diseases, but safe, practical, and effective vaccines for many of these agents have yet to be realized. Many vaccine development approaches are under investigation, but the one that is currently most advanced and that has been most widely applied to enteric pathogens is the use of orally administered live or killed whole pathogen preparations. If inactivated, these vaccines will probably be administered as multiple doses with approximately 10(10) to 10(11) total particles per dose, but they are relatively safe for oral administration. Further, they may not require a buffer for delivery and can be stored in liquid formulations. Fewer doses may be required for some live attenuated pathogen vaccines, but a buffer will most likely be required for oral delivery and the product must be stored in a dried formulation. Also, safety becomes more of a concern with live pathogens depending on the degree of attenuation, host immunocompetence, and the total number and kinds of attenuated pathogens which may be present in a combined agent vaccine. Both live and killed whole pathogen vaccines can be immunogenic and have the possibility to serve as vectors for other antigens. Although many organisms and serotypes are clinically important, by exploiting antigenic cross reactivity and using some pathogen components as vectors for cloned antigens of other pathogens, it could be possible to induce immunity against major enteric pathogens/serotypes with <10 whole pathogen components in a multi-agent vaccine. Safe and effective mucosal adjuvants may in the future be useful in whole pathogen vaccines, but they do not seem to be essential for immunization. Further, dietary supplements such as zinc, mixed routes of delivery and new regimens are under study which may in the future enhance further the effectiveness of the whole pathogen vaccines which now seem realizable in the near term. For this to happen, however, a coordinated and committed effort is necessary now to address the immunologic, regulatory, manufacturing, testing and implementation issues which will be involved in the realization of this important product to benefit children's health worldwide.

Use of genome-wide expression profiling and mutagenesis to study the intestinal lifestyle of Campylobacter jejuni

Campylobacter jejuni is the most common bacterial cause of diarrhea worldwide. To colonize the gut and cause infection, C. jejuni must successfully compete with endogenous microbes for nutrients, resist host defenses, persist in the intestine, and ultimately infect the host. These challenges require the expression of a battery of colonization and virulence determinants. In this study, the intestinal lifestyle of C. jejuni was studied using whole-genome microarray, mutagenesis, and a rabbit ileal loop model. Genes associated with a wide range of metabolic, morphological, and pathological processes were expressed in vivo. The in vivo transcriptome of C. jejuni reflected its oxygen-limited, nutrient-poor, and hyperosmotic environment. Strikingly, the expression of several C. jejuni genes was found to be highly variable between individual rabbits. In particular, differential gene expression suggested that C. jejuni extensively remodels its envelope in vivo by differentially expressing its membrane proteins and by modifying its peptidoglycan and glycosylation composition. Furthermore, mutational analysis of seven genes, hspR, hrcA, spoT, Cj0571, Cj0178, Cj0341, and fliD, revealed an important role for the stringent and heat shock response in gut colonization. Overall, this study provides new insights on the mechanisms of gut colonization, as well as possible strategies employed by Campylobacter to resist or evade the host immune responses.

Campylobacter vaccine development:a key to controlling enteric diseases

Worldwide, Campylobacter jejuni is a major cause of diarrhoea and dysentery, with approximately 400 million cases occurring annually. Control of the disease through public health and antibiotic measures is insufficient, and vaccination offers the most promising solution. Infection produces immunity from disease, suggesting that vaccination may produce similar protection. Epidemiological data suggest that there are conserved antigens among serotypes; immunity against which protects against disease. Therefore a monovalent serotype vaccine seems practical. Several antigens on Campylobacter have been found to be immunogenic and, in some cases, associated with virulence. However, none of these proteins have been produced recombinantly in the proper conformation, nor have they been protective in preclinical models. For this reason, live attenuated or inactivated Campylobacter whole cell (CWC) vaccines may be the best approach. Development of an attenuated strain of Campylobacter has been complicated by the fact that the organism is highly transformable. Rec A mutants of Campylobacter have recently been constructed in an attempt to avoid this trait. Such mutants have been made defective in various virulence properties and are being evaluated for safety in preclinical models. Antex Biologics has made an inactivated CWC vaccine using the Company's patented NST (nutriment signal transduction) technology, whereby the cells are grown using physiologically logical conditions to maximise the expression of antigens associated with in vivo virulence. This vaccine has been shown to be safe, immunogenic, and protective in preclinical models of infection. Inclusion of a mucosal adjuvant in the vaccine increases the immunological response to the antigen. Recent Phase I and Phase II clinical trials, using the CWC vaccine formulated with an adjuvant and orally administered, show that the vaccine is safe and immunogenic in human volunteers. The approach used to develop this inactivated whole cell Campylobacter vaccine is also applicable for the rapid development of new vaccines against a variety of mucosal pathogens.

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

Type III secretion systems identified in bacterial pathogens of animals and plants transpose effectors and toxins directly into the cytosol of host cells or into the extracellular milieu. Proteins of the type III secretion apparatus are conserved among diverse and distantly related bacteria. Many type III apparatus proteins have homologues in the flagellar export apparatus, supporting the notion that type III secretion systems evolved from the flagellar export apparatus. No type III secretion apparatus genes have been found in the complete genomic sequence of Campylobacter jejuni NCTC11168. In this study, we report the characterization of a protein designated FlaC of C. jejuni TGH9011. FlaC is homologous to the N- and C-terminus of the C. jejuni flagellin proteins, FlaA and FlaB, but lacks the central portion of these proteins. flaC null mutants form a morphologically normal flagellum and are highly motile. In wild-type C. jejuni cultures, FlaC is found predominantly in the extracellular milieu as a secreted protein. Null mutants of the flagellar basal rod gene (flgF) and hook gene (flgE) do not secrete FlaC, suggesting that a functional flagellar export apparatus is required for FlaC secretion. During C. jejuni infection in vitro, secreted FlaC and purified recombinant FlaC bind to HEp-2 cells. Invasion of HEp-2 cells by flaC null mutants was reduced to a level of 14% compared with wild type, suggesting that FlaC plays an important role in cell invasion.

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

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

Critical role of multidrug efflux pump CmeABC in bile resistance and in vivo colonization of Campylobacter jejuni

CmeABC functions as a multidrug efflux pump contributing to the resistance of Campylobacter to a broad range of antimicrobials. In this study, we examined the role of CmeABC in bile resistance and its contribution to the adaptation of Campylobacter jejuni in the intestinal tract of the chicken, a natural host and a major reservoir for Campylobacter. Inactivation of cmeABC drastically decreased the resistance of Campylobacter to various bile salts. Addition of choleate (2 mM) in culture medium impaired the in vitro growth of the cmeABC mutants but had no effect on the growth of the wild-type strain. Bile concentration varied in the duodenum, jejunum, and cecum of chicken intestine, and the inhibitory effect of the intestinal extracts on the in vitro growth of Campylobacter was well correlated with the total bile concentration in the individual sections of chicken intestine. When inoculated into chickens, the wild-type strain colonized the birds as early as day 2 postinoculation with a density as high as 10(7) CFU/g of feces. In contrast, the cmeABC mutants failed to colonize any of the inoculated chickens throughout the study. The minimum infective dose for the cmeABC mutant was at least 2.6 x 10(4)-fold higher than that of the wild-type strain. Complementation of the cmeABC mutants with a wild-type cmeABC allele in trans fully restored the in vitro growth in bile-containing media and the in vivo colonization to the levels of the wild-type strain. Immunoblotting analysis indicated that CmeABC is expressed and immunogenic in chickens experimentally infected with C. jejuni. Together, these findings provide compelling evidence that CmeABC, by mediating resistance to bile salts in the intestinal tract, is required for successful colonization of C. jejuni in chickens. Inhibition of CmeABC function may not only control antibiotic resistance but also prevent the in vivo colonization of pathogenic Campylobacter.

Gene expression profile of Campylobacter jejuni in response to growth temperature variation

The foodborne pathogen Campylobacter jejuni is the primary causative agent of gastroenteritis in humans. In the present study a whole genome microarray of C. jejuni was constructed and validated. These DNA microarrays were used to measure changes in transcription levels over time, as C. jejuni cells responded to a temperature increase from 37 to 42 degrees C. Approximately 20% of the C. jejuni genes were significantly up- or downregulated over a 50-min period after the temperature increase. The global change in C. jejuni transcriptome was found to be essentially transient, with only a small subset of genes still differentially expressed after 50 min. A substantial number of genes with a downregulated coexpression pattern were found to encode for ribosomal proteins. This suggests a short growth arrest upon temperature stress, allowing the bacteria to reshuffle their energy toward survival and adaptation to the new growth temperature. Genes encoding chaperones, chaperonins, and heat shock proteins displayed the most dramatic and rapid upregulation immediately after the temperature change. Interestingly, genes encoding proteins involved in membrane structure modification were differentially expressed, either up- or downregulated, suggesting a different protein membrane makeup at the two different growth temperatures. Overall, these data provide new insights into the primary response of C. jejuni to surmount a sudden temperature upshift, allowing the bacterium to survive and adapt its transcriptome to a new steady state.

DNA sequence and mutational analyses of the pVir plasmid of Campylobacter jejuni 81-176

The circular pVir plasmid of Campylobacter jejuni strain 81-176 was determined to be 37,468 nucleotides in length with a G+C content of 26%. A total of 83% of the plasmid represented coding information, and all but 2 of the 54 predicted open reading frames were encoded on the same DNA strand. There were seven genes on the plasmid in a continguous region of 8.9 kb that encoded orthologs of type IV secretion proteins found in Helicobacter pylori, including four that have been described previously (D. J. Bacon, R. A. Alm, D. H. Burr, L. Hu, D. J. Kopecko, C. P. Ewing, T. J. Trust, and P. Guerry, Infect. Immun. 68:4384-4390, 2000). There were seven other pVir-encoded proteins that showed significant similarities to proteins encoded by the plasticity zones of either H. pylori J99 or 26695. Mutational analyses of 19 plasmid genes identified 5 additional genes that affect in vitro invasion of intestinal epithelial cells. These included one additional gene encoding a component of a type IV secretion system, an ortholog of Cj0041 from the chromosome of C. jejuni NCTC 11168, two Campylobacter plasmid-specific genes, and an ortholog of HP0996 from the plasticity zone of H. pylori 26695.

Helicobacter pylori uses motility for initial colonization and to attain robust infection

Helicobacter pylori has been shown to require flagella for infection of the stomach. To analyze whether flagella themselves or motility is needed by these pathogens, we constructed flagellated nonmotile mutants. This was accomplished by using both an insertion mutant and an in-frame deletion of the motB gene. In vitro, these mutants retain flagella (Fla(+)) but are nonmotile (Mot(-)). By using FVB/N mice, we found that these mutants had reduced ability to infect mice in comparison to that of their isogenic wild-type counterparts. When these mutants were coinfected with wild type, we were unable to detect any motB mutant. Finally, by analyzing the 50% infectious dose, we found that motility is needed for initial colonization of the stomach mucosa. These results support a model in which motility is used for the initial colonization of the stomach and also to attain full infection levels.

Localized reversible frameshift mutation in the flhA gene confers phase variability to flagellin gene expression in Campylobacter coli

Phase variation of flagellin gene expression in Campylobacter coli UA585 was correlated with high-frequency, reversible insertion and deletion frameshift mutations in a short homopolymeric tract of thymine residues located in the N-terminal coding region of the flhA gene. Mutation-based phase variation in flhA may generate functional diversity in the host and environment.

Evaluation of a truncated recombinant flagellin subunit vaccine against Campylobacter jejuni

A recombinant protein comprising the maltose-binding protein (MBP) of Escherichia coli fused to amino acids 5 to 337 of the FlaA flagellin of Campylobacter coli VC167 was evaluated for immunogenicity and protective efficacy against challenge by a heterologous strain of campylobacter, Campylobacter jejuni 81-176, in two murine models. The sequence of the flaA gene of strain 81-176 revealed a predicted protein which was 98.1% similar to that of VC167 FlaA over the region expressed in the fusion protein. Mice were immunized intranasally with two doses of 3 to 50 microgram of MBP-FlaA, given 8 days apart, with or without 5 microgram of the mutant E. coli heat-labile enterotoxin (LT(R192G)) as a mucosal adjuvant. The full range of MBP-FlaA doses were effective in eliciting antigen-specific serum immunoglobulin G (IgG) responses, and these responses were enhanced by adjuvant use, except in the highest dosing group. Stimulation of FlaA-specific intestinal secretory IgA (sIgA) responses required immunization with higher doses of MBP-FlaA (>/=25 microgram) or coadministration of lower doses with the adjuvant. When vaccinated mice were challenged intranasally 26 days after immunization, the best protection was seen in animals given 50 microgram of MBP-FlaA plus LT(R192G). The protective efficacies of this dose against disease symptoms and intestinal colonization were 81.1 and 84%, respectively. When mice which had been immunized with 50 microgram of MBP-FlaA plus LT(R192G) intranasally were challenged orally with 8 x 10(10), 8 x 10(9), or 8 x 10(8) cells of strain 81-176, the protective efficacies against intestinal colonization at 7 days postinfection were 71.4, 71.4, and 100%, respectively.

Pathophysiology of Campylobacter jejuni infections of humans

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

Campylobacter jejuni-stimulated secretion of interleukin-8 by INT407 cells

Incubation of INT407 cells with various clinical isolates of Campylobacter jejuni resulted in secretion of interleukin-8 (IL-8) at levels ranging from 96 to 554 pg/ml at 24 h. The strains which produced the highest levels of IL-8 secretion were 81-176 and BT44. Induction of IL-8 secretion required live cells of 81-176 and was dependent on de novo protein synthesis. Site-specific mutants of 81-176, which were previously shown to be defective in adherence and invasion, resulted in reduced levels of secretion of IL-8, and cheY mutants of strains 81-176 and 749, which are hyperadherent and hyperinvasive, resulted in higher levels of IL-8 secretion. Another mutant of 81-176, which adheres at about 43% of the wild-type levels but is noninvasive, also showed marked reduction in IL-8 levels, suggesting that invasion is necessary for high levels of IL-8 secretion. When gentamicin was added to INT407 cells at 2 h after infection with 81-176, IL-8 secretion 22 h later was equivalent to that of controls without gentamicin, suggesting that the events which trigger induction and release of IL-8 occur early in the interactions of bacteria and eukaryotic cells.

Expression of the flgFG operon of Campylobacter jejuni in Escherichia coli yields an extra fusion protein

Two Campylobacter jejuni genes with homology to the Escherichia coli flgF and flgG genes encoding two of the basal body rod proteins were isolated, and the nucleotide sequence was determined and analyzed. These two C. jejuni genes were shown, by Northern hybridization analysis, to function as a single operon (flgFG). Two transcriptional start sites were detected upstream of flgF, corresponding to the two RNA transcripts detected in the Northern blot. Western blot immunoassays using anti-FlgF and anti-FlgG antibodies demonstrated the synthesis of FlgF and FlgG proteins in C. jejuni and in Escherichia coli containing the C. jejuni flgF and flgG genes. Maxicell analysis and Western immunoblots using anti-FlgF antibodies to probe flgFG-encoded proteins in E. coli revealed the presence of a protein with a molecular mass of approximately the combined mass of the FlgF and FlgG proteins. Anti-FlgF antibodies detected in C. jejuni cell extracts the native FlgF protein and also a higher-molecular-weight protein that is likely encoded by the flgF and part of the flgG sequences.

The specificity of antibody in chickens immunised to reduce intestinal colonisation with Campylobacter jejuni

Poultry consumption has been identified as a major risk factor for human infection with Campylobacter jejuni in developed countries. C. jejuni is present in the gastrointestinal tract of broiler chickens at the time of slaughter, and faecal contamination of carcases during processing results in significant campylobacter loads on carcases. One approach to reducing the level of carcase contamination with C. jejuni is to control campylobacter infection in broiler chickens. To this end, the study described here investigated the specificity of antibody in serum and intestinal secretions of chickens that had been immunised with campylobacter antigens and then challenged with viable bacteria. The immunodominant antigens in the serum of birds that showed a 2-log reduction in caecal colonisation with C. jejuni included flagellin protein (61-63 Kd) and three additional antigens of 67, 73.5 and 77.5 Kd. Only flagellin and the 67 Kd antigen were recognised by IgG antibody in gastrointestinal secretions of the same birds. Antibody from chickens immunised with purified native flagellin protein recognised flagellin protein and the 67 Kd antigen in Western blots probed with serum, but only the flagellin proteins (61-63 Kd) in Westerns probed with gastrointestinal secretions. Analysis of the specificity of the response to flagellin protein using recombinant clones that expressed regions of the flagellin gene suggests that epitopes in each region of the flagellin protein were immunogenic. Of the immunodominant antigens, only flagellin appeared to be surface-exposed on viable C. jejuni, although conformational epitopes of flagellin appeared to be sensitive to the method of antigen purification. The results of this study suggest that flagellin and possibly the 67 Kd antigen may be valuable for immunological control of intestinal infection with C. jejuni in chickens, but that further work is required to purify these as vaccine candidates by using methods that preserve conformational epitopes.

The flgE gene of Campylobacter coli is under the control of the alternative sigma factor sigma54

The flgE gene encoding the flagellar hook protein of Campylobacter coli VC167-T1 was cloned by immunoscreening of a genomic library constructed in lambdaZAP Express. The flgE DNA sequence was 2,553 bp in length and encoded a protein with a deduced molecular mass of 90,639 Da. The sequence had significant homology to the 5' and 3' sequences of the flgE genes of Helicobacter pylori, Treponema phagedenis, and Salmonella typhimurium. Primer extension analysis indicated that the VC167 flgE gene is controlled by a sigma54 promoter. PCR analysis showed that the flgE gene size and the 5' and 3' DNA sequences were conserved among C. coli and C. jejuni strains. Southern hybridization analyses confirmed that there is considerable sequence identity among the hook genes of C. coli and C. jejuni but that there are also regions within the genes which differ. Mutants of C. coli defective in hook production were generated by allele replacement. These mutants were nonmotile and lacked flagellar filaments. Analyses of flgE mutants indicated that the carboxy terminus of FlgE is necessary for assembly of the hook structure but not for secretion of FlgE and that, unlike salmonellae, the lack of flgE expression does not result in repression of flagellin expression.

A genetic locus involved in iron utilization unique to some Campylobacter strains

Two genes involved in iron utilization in Campylobacter coli VC167 T1 have been characterized. The cfrA gene encodes a protein with a predicted Mr of 77,653 which, after processing of the leader sequence, has a predicted Mr of 75,635. This protein has significant sequence identity to siderophore receptors of several bacteria, and site-specific mutants defective in cfrA do not synthesize one of two major iron-repressible outer membrane proteins. An adjacent gene encodes a TonB-like protein; a mutant in this gene lost the ability to utilize hemin, ferrichrome, and enterochelin as iron sources. The cfrA and tonB genes of VC167 T1 hybridized to all strains of C. coli and most strains of C. jejuni examined but did not hybridize to several other strains of C. jejuni, suggesting that the thermophilic campylobacters can be separated into two categories based on the presence of these two iron utilization genes.

Immunisation of chickens to reduce intestinal colonisation with Campylobacter jejuni

1. Systemic and intestinal antibody titres were measured in chickens following subcutaneous, intraperitoneal (i.p.), oral (p.o.) and combined i.p./p.o. administration of antigen, in soluble, emulsified or microparticulate form. Antigens tested included keyhole limpet haemocyanin (KLH), killed Campylobacter jejuni whole cells and purified campylobacter flagellin protein. 2. The effect of immunisation with purified flagellin protein or with killed C. jejuni whole cells in reducing intestinal colonisation was assessed. The ability of newlyhatched chicks to respond to immunisation was limited, possibly because of the immaturity of the immune system rather than maternal suppression of an immune response. Only 5 to 13 birds that were first immunised when 1-d-old with KLH showed a systemic response, even after 4 immunisations, whereas 10 of 11 birds that were first immunised at 24 d-old responded systemically. 3. In an immunisation and challenge experiment, birds that were immunised twice intraperitoneally, at 16 and 29 d-old, with killed C. jejuni whole cells, had fewer C. jejuni, in the caecal contents than unimmunised control birds. This reduction in intestinal colonisation, to less than 2% of bacterial numbers in control birds, was associated with an increase in specific IgG in intestinal secretions. There was no significant increase in specific IgA or IgM in intestinal secretions following immunisation and challenge. 4. These results indicate that immunisation can reduce the level of intestinal infection with C. jejuni. The protection may be enhanced by developing improved methods of immunisation that stimulate production of increased titres of specific antibody in intestinal secretions, particularly specific IgA antibody.

Restriction fragment length polymorphism of flagellin genes of Campylobacter jejuni and/or C. coli isolates from Egypt

The conservation of flagellin genes from thermophilic Campylobacter spp. strains isolated in Egypt was evaluated by a restriction fragment length polymorphism (RFLP) assay. The flaA and flaB genes were amplified from 59 independent clinical isolates and digested with EcoRI and PstI, and the resulting patterns were compared with each other and with previously described RFLP groups. The results indicate that the isolates fell into 14 groups for flaA and 11 groups for flaB, 9 of which have been described, and that considerable genetic variability exists among isolates belonging to the same LIO serogroup. In most cases, the flaB gene displayed the same RFLP pattern as that of the flaA gene of the same strain, although some variability was observed. The data suggest that more variability of flagellin genes exists within the LIO serogroups common to Campylobacter field isolates from Egypt than has previously been reported for North American isolates.

An environmentally regulated pilus-like appendage involved in Campylobacter pathogenesis

Examination of strains of Campylobacter jejuni, Campylobacter coli, and Campylobacter fetus by electron microscopy revealed that they produced peritrichous pilus-like appendages when the bacteria were grown in the presence of bile salts. Various bile-salt supplements were used and it was found that deoxycholate and chenodeoxycholic acid caused a significant enhancement of pilus production and resulted in a highly aggregative phenotype. Morphologically, the pili were between 4 and 7 nm in width and were greater than 1 micron in length. A gene, termed pspA, which encodes a predicted protein resembling protease IV of Escherichia coli, was identified in C. jejuni strain 81-176. A site-specific insertional mutation within this gene resulted in the loss of pilus synthesis as determined by electron microscopy. Insertions upstream and downstream of the gene had no effect on pilus production. The non-piliated mutant of strain 81-176 showed no reduction in adherence to or invasion of INT 407 cells in vitro. However, this mutant, while still possessing the ability to colonize ferrets, caused significantly reduced disease symptoms in this animal model.