Phase variation of a beta-1,3 galactosyltransferase involved in generation of the ganglioside GM1-like lipo-oligosaccharide of Campylobacter jejuni

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.

Distribution of virulence-associated genes in a selection of Campylobacter isolates

This study tested 24 Campylobacter isolates for the presence of 35 virulence genes using the polymerase chain reaction. The target genes included those involved in motility (flaA, flaB, flhA, flhB, flgB, flgE2, fliM, fliY), chemotaxis (cheA, cheB, cheR, cheW, cheY, cheZ), cell adhesion (cadF, dnaJ, jlpA, pldA, racR, virB11), invasion (iamA, ciaB, ceuE), cytotoxin production (cdtA, cdtB, cdtC, wlaN), capsule (kpsM), multidrug and bile resistance (cmeA, cmeB, cmeC), stress response/survival (katA, sodB), and the iron uptake system (cfrA, fur). The motility genes (with the exception of flaB), the CmeABC efflux system, cdtABC genes, and the sodB gene were commonly distributed among Campylobacter strains while the virB11 and wlaN genes were rarely detected. Interestingly, the findings suggest that flaB is not essential for full motility and C. coli lacking the flhA gene may be highly invasive. This study provides additional information on the distribution of Campylobacter virulence factors and the effect of their presence/absence on adhesion and invasion. It will inform future studies designed to elucidate the exact mechanisms of pathogenesis in Campylobacter.

Campylobacter virulence and survival factors

Despite over 30 years of research, campylobacteriosis is the most prevalent foodborne bacterial infection in many countries including in the European Union and the United States of America. However, relatively little is known about the virulence factors in Campylobacter or how an apparently fragile organism can survive in the food chain, often with enhanced pathogenicity. This review collates information on the virulence and survival determinants including motility, chemotaxis, adhesion, invasion, multidrug resistance, bile resistance and stress response factors. It discusses their function in transition through the food processing environment and human infection. In doing so it provides a fundamental understanding of Campylobacter, critical for improved diagnosis, surveillance and control.

Genomic and global approaches to unravelling how hypermutable sequences influence bacterial pathogenesis

Rapid adaptation to fluctuations in the host milieu contributes to the host persistence and virulence of bacterial pathogens. Adaptation is frequently mediated by hypermutable sequences in bacterial pathogens. Early bacterial genomic studies identified the multiplicity and virulence-associated functions of these hypermutable sequences. Thus, simple sequence repeat tracts (SSRs) and site-specific recombination were found to control capsular type, lipopolysaccharide structure, pilin diversity and the expression of outer membrane proteins. We review how the population diversity inherent in the SSR-mediated mechanism of localised hypermutation is being unlocked by the investigation of whole genome sequences of disease isolates, analysis of clinical samples and use of model systems. A contrast is presented between the problematical nature of analysing simple sequence repeats in next generation sequencing data and in simpler, pragmatic PCR-based approaches. Specific examples are presented of the potential relevance of this localized hypermutation to meningococcal pathogenesis. This leads us to speculate on the future prospects for unravelling how hypermutable mechanisms may contribute to the transmission, spread and persistence of bacterial pathogens.

Comparative variation within the genome of Campylobacter jejuni NCTC 11168 in human and murine hosts

Campylobacteriosis incited by C. jejuni is a significant enteric disease of human beings. A person working with two reference strains of C. jejuni National Collection of Type Cultures (NCTC) 11168 developed symptoms of severe enteritis including bloody diarrhea. The worker was determined to be infected by C. jejuni. In excess of 50 isolates were recovered from the worker's stool. All of the recovered isolates and the two reference strains were indistinguishable from each other based on comparative genomic fingerprint subtyping. Whole genome sequence analysis indicated that the worker was infected with a C. jejuni NCTC 11168 obtained from the American Type Culture Collection; this strain (NCTC 11168-GSv) is the genome sequence reference. After passage through the human host, major genetic changes including indel mutations within twelve contingency loci conferring phase variations were detected in the genome of C. jejuni. Specific and robust single nucleotide polymorphism (SNP) changes in the human host were also observed in two loci (Cj0144c, Cj1564). In mice inoculated with an isolate of C. jejuni NCTC 11168-GSv from the infected person, the isolate underwent further genetic variation. At nine loci, mutations specific to inoculated mice including five SNP changes were observed. The two predominant SNPs observed in the human host reverted in mice. Genetic variations occurring in the genome of C. jejuni in mice corresponded to increased densities of C. jejuni cells associated with cecal mucosa. In conclusion, C. jejuni NCTC 11168-GSv was found to be highly virulent in a human being inciting severe enteritis. Host-specific mutations in the person with enteritis occurred/were selected for in the genome of C. jejuni, and many were not maintained in mice. Information obtained in the current study provides new information on host-specific genetic adaptation by C. jejuni.

Single cell stochastic regulation of pilus phase variation by an attenuation-like mechanism

The molecular triggers leading to virulence of a number of human-adapted commensal bacteria such as Streptococcus gallolyticus are largely unknown. This opportunistic pathogen is responsible for endocarditis in the elderly and associated with colorectal cancer. Colonization of damaged host tissues with exposed collagen, such as cardiac valves and pre-cancerous polyps, is mediated by appendages referred to as Pil1 pili. Populations of S. gallolyticus are heterogeneous with the majority of cells weakly piliated while a smaller fraction is hyper piliated. We provide genetic evidences that heterogeneous pil1 expression depends on a phase variation mechanism involving addition/deletion of GCAGA repeats that modifies the length of an upstream leader peptide. Synthesis of longer leader peptides potentiates the transcription of the pil1 genes through ribosome-induced destabilization of a premature stem-loop transcription terminator. This study describes, at the molecular level, a new regulatory mechanism combining phase variation in a leader peptide-encoding gene and transcription attenuation. This simple and robust mechanism controls a stochastic heterogeneous pilus expression, which is important for evading the host immune system while ensuring optimal tissue colonization.

Streptococcus gallolyticus (formely known as S. bovis biotype I) is an emerging cause of septicemia and endocarditis in the elderly. Intriguingly, epidemiological studies revealed a strong association, up to 65%, between endocarditis due to S. gallolyticus and colorectal malignancies. Whether S. gallolyticus infection is a cause or a consequence of colon cancer remains to be investigated. We previously showed that colonization of damaged cardiac valves with exposed collagen is mediated by the Pil1 pilus in S. gallolyticus. In the present work, we report that Pil1 is heterogeneously expressed at the single cell level, giving rise to two distinct bacterial subpopulations, a majority of weakly piliated cells and a minority of hyper-piliated cells. We have characterized, at the molecular level, a novel regulatory mechanism responsible for Pil1 heterogeneous expression combining phase variation in the leader peptide and transcriptional attenuation. Pili are highly immunogenic proteins proposed as vaccine candidate in pathogenic streptococci whose expression involves a fitness cost due to the selective pressure of host immune responses. Hence, this robust and simple system mitigates susceptibility to immune defenses while ensuring optimal colonization of host tissues.

Distribution of nine virulence-associated genes in Campylobacter jejuni and C. coli isolated from broiler feces in Shiraz, Southern Iran

To investigate the prevalence of nine virulence and toxin genes of Campylobacter, a total of 90 Campylobacter strains including 48 C. jejuni and 42 C. coli were recovered from chicken feces by cultivation methods. The isolates were identified on the basis of polymerase chain reaction (PCR) detection of 16SrRNA and multiplex PCR for determining two species. For confirmed strains, PCR was carried out for the presence of virulence genes using specific primers. Data were analyzed by SPSS software, version 12.0.1. The cadF gene and three genes associated with cytolethal distending toxin were present in 100% of isolates. Plasmid virB11 gene was not found in any of the Campylobacter isolates, and the prevalence of pldA, wlaN, iamA, and cgtB genes were 92.22%, 82.22%, 81.11%, and 22.22%, respectively. The findings revealed that the distribution of the majority of these genes were not dissimilar among Campylobacter species. The results emphasized that many of the pathogenic C. jejuni and C. coli may have these genes, and the Campylobacter strains with poultry origin have pathogenic potential properties for humans.

Genetic heterogeneity of Campylobacter jejuni NCTC 11168 upon human infection

Campylobacter jejuni NCTC 11168 variants before and after accidental human infection were sequenced with Illumina technology and mapped against the isogenic reference genome applying the Breseq pipeline. Only the frequencies of length variations of homopolymeric tracts in the contingency genes Cj0045c, Cj0456c, Cj1139c, Cj1145c, and Cj1306c and a deletion in Cj0184c were significantly different after human passage (p<0.01). Our results highlight differences in the selection of C. jejuni variants after human infection compared with those observed in animal models, emphasizing the genetic diversity of C. jejuni NCTC 11168 and the possible role of the host in the selection of bacterial determinants that might be involved in the adaptation and disease development.

The mutation rate of mycobacterial repetitive unit loci in strains of M. tuberculosis from cynomolgus macaque infection

Background

Mycobacterial interspersed repetitive units (MIRUs) are minisatellites within the Mycobacterium tuberculosis (Mtb) genome. Copy number variation (CNV) in MIRU loci is used for epidemiological typing, making the rate of variation important for tracking the transmission of Mtb strains. In this study, we developed and assessed a whole-genome sequencing (WGS) approach to detect MIRU CNV in Mtb. We applied this methodology to a panel of Mtb strains isolated from the macaque model of tuberculosis (TB), the animal model that best mimics human disease. From these data, we have estimated the rate of MIRU variation in the host environment, providing a benchmark rate for future epidemiologic work.

Results

We assessed variation at the 24 MIRU loci used for typing in a set of Mtb strains isolated from infected cynomolgus macaques. We previously performed WGS of these strains and here have applied both read depth (RD) and paired-end mapping (PEM) metrics to identify putative copy number variants. To assess the relative power of these approaches, all MIRU loci were resequenced using Sanger sequencing. We detected two insertion/deletion events both of which could be identified as candidates by PEM criteria. With these data, we estimate a MIRU mutation rate of 2.70 × 10^-03 (95% CI: 3.30 × 10^-04- 9.80 × 10^-03) per locus, per year.

Conclusion

Our results represent the first experimental estimate of the MIRU mutation rate in Mtb. This rate is comparable to the highest previous estimates gathered from epidemiologic data and meta-analyses. Our findings allow for a more rigorous interpretation of data gathered from MIRU typing.

The polysaccharide capsule of Campylobacter jejuni modulates the host immune response

Campylobacter jejuni is a major cause of bacterial diarrheal disease worldwide. The organism is characterized by a diversity of polysaccharide structures, including a polysaccharide capsule. Most C. jejuni capsules are known to be decorated nonstoichiometrically with methyl phosphoramidate (MeOPN). The capsule of C. jejuni 81-176 has been shown to be required for serum resistance, but here we show that an encapsulated mutant lacking the MeOPN modification, an mpnC mutant, was equally as sensitive to serum killing as the nonencapsulated mutant. A nonencapsulated mutant, a kpsM mutant, exhibited significantly reduced colonization compared to that of wild-type 81-176 in a mouse intestinal colonization model, and the mpnC mutant showed an intermediate level of colonization. Both mutants were associated with higher levels of interleukin 17 (IL-17) expression from lamina propria CD4(+) cells than from cells from animals infected with 81-176. In addition, reduced levels of Toll-like receptor 4 (TLR4) and TLR2 activation were observed following in vitro stimulation of human reporter cell lines with the kpsM and mpnC mutants compared to those with wild-type 81-176. The data suggest that the capsule polysaccharide of C. jejuni and the MeOPN modification modulate the host immune response.

A "successful allele" at Campylobacter jejuni contingency locus Cj0170 regulates motility; "successful alleles" at locus Cj0045 are strongly associated with mouse colonization

Campylobacter jejuni is an important foodborne pathogen of humans and its primary reservoir is the gastrointestinal (GI) tract of chickens. Our previous studies demonstrated that phase variation to specific "successful alleles" at C. jejuni contingency loci Cj0045 (successful alleles carry 9G or 10G homopolymeric tracts) and Cj0170 (successful allele carries a 10G homopolymeric tract) in C. jejuni populations is strongly associated with colonization and enteritis in C57BL/6 IL-10 deficient mice. In the current study, we strengthened the association between locus Cj0170, Cj0045, and mouse colonization. We generated 8 independent strains derived from C. jejuni 11168 strain KanR4 that carried a Cj0170 gene disruption and these were all non motile. Two randomly chosen strains with the Cj0170 gene disruption (DM0170-2 and DM0170-6) were gavaged into mice. DM0170-2 and DM0170-6 failed to colonize mice while the control strain that carried a "successful"Cj0170 10G allele was motile and did colonize mice. In parallel studies, when we inoculated C. jejuni strain 33292 into mice, the "unsuccessful"Cj0045 11G allele experienced phase variation to "successful" 9G and 10G alleles in 2 independent experiments prior to d4 post inoculation in mice while the "successful" 9G allele in the control strain remained stable through d21 post inoculation or shifted to other successful alleles. These data confirm that locus Cj0170 regulates motility in C. jejuni strain KanR4 and is a virulence factor in the mouse model. The data also support a possible role of locus Cj0045 as a virulence factor in strain 33292 in infection of mice.

Phase variable O antigen biosynthetic genes control expression of the major protective antigen and bacteriophage receptor in Vibrio cholerae O1

The Vibrio cholerae lipopolysaccharide O1 antigen is a major target of bacteriophages and the human immune system and is of critical importance for vaccine design. We used an O1-specific lytic bacteriophage as a tool to probe the capacity of V. cholerae to alter its O1 antigen and identified a novel mechanism by which this organism can modulate O antigen expression and exhibit intra-strain heterogeneity. We identified two phase variable genes required for O1 antigen biosynthesis, manA and wbeL. manA resides outside of the previously recognized O1 antigen biosynthetic locus, and encodes for a phosphomannose isomerase critical for the initial step in O1 antigen biosynthesis. We determined that manA and wbeL phase variants are attenuated for virulence, providing functional evidence to further support the critical role of the O1 antigen for infectivity. We provide the first report of phase variation modulating O1 antigen expression in V. cholerae, and show that the maintenance of these phase variable loci is an important means by which this facultative pathogen can generate the diverse subpopulations of cells needed for infecting the host intestinal tract and for escaping predation by an O1-specific phage.

Structural heterogeneity of terminal glycans in Campylobacter jejuni lipooligosaccharides

Lipooligosaccharides of the gastrointestinal pathogen Campylobacter jejuni are regarded as a major virulence factor and are implicated in the production of cross-reactive antibodies against host gangliosides, which leads to the development of autoimmune neuropathies such as Guillain-Barré and Fisher Syndromes. C. jejuni strains are known to produce diverse LOS structures encoded by more than 19 types of LOS biosynthesis clusters. This study demonstrates that the final C. jejuni LOS structure cannot always be predicted from the genetic composition of the LOS biosynthesis cluster, as determined by novel lectin array analysis of the terminal LOS glycans. The differences were shown to be partially facilitated by the differential on/off status of three genes wlaN, cst and cj1144-45. The on/off status of these genes was also analysed in C. jejuni strains grown in vitro and in vivo, isolated directly from the host animal without passaging, using immunoseparation. Importantly, C. jejuni strains 331, 421 and 520 encoding cluster type C were shown to produce different LOS, mimicking asialo GM₁, asialo GM₂ and a heterogeneous mix of gangliosides and other glycoconjugates respectively. In addition, individual C. jejuni colonies were shown to consistently produce heterogeneous LOS structures, irrespective of the cluster type and the status of phase variable genes. Furthermore we describe C. jejuni strains (351 and 375) with LOS clusters that do not match any of the previously described LOS clusters, yet are able to produce LOS with asialo GM₂-like mimicries. The LOS biosynthesis clusters of these strains are likely to contain genes that code for LOS biosynthesis machinery previously not identified, yet capable of synthesising LOS mimicking gangliosides.

Phase variable genes of Campylobacter jejuni exhibit high mutation rates and specific mutational patterns but mutability is not the major determinant of population structure during host colonization

Phase variation of surface structures occurs in diverse bacterial species due to stochastic, high frequency, reversible mutations. Multiple genes of Campylobacter jejuni are subject to phase variable gene expression due to mutations in polyC/G tracts. A modal length of nine repeats was detected for polyC/G tracts within C. jejuni genomes. Switching rates for these tracts were measured using chromosomally-located reporter constructs and high rates were observed for cj1139 (G8) and cj0031 (G9). Alteration of the cj1139 tract from G8 to G11 increased mutability 10-fold and changed the mutational pattern from predominantly insertions to mainly deletions. Using a multiplex PCR, major changes were detected in ‘on/off’ status for some phase variable genes during passage of C. jejuni in chickens. Utilization of observed switching rates in a stochastic, theoretical model of phase variation demonstrated links between mutability and genetic diversity but could not replicate observed population diversity. We propose that modal repeat numbers have evolved in C. jejuni genomes due to molecular drivers associated with the mutational patterns of these polyC/G repeats, rather than by selection for particular switching rates, and that factors other than mutational drift are responsible for generating genetic diversity during host colonization by this bacterial pathogen.

Passage of Campylobacter jejuni through the chicken reservoir or mice promotes phase variation in contingency genes Cj0045 and Cj0170 that strongly associates with colonization and disease in a mouse model

Human illness due to Camplyobacter jejuni infection is closely associated with consumption of poultry products. We previously demonstrated a 50 % shift in allele frequency (phase variation) in contingency gene Cj1139 (wlaN) during passage of C. jejuni NCTC11168 populations through Ross 308 broiler chickens. We hypothesized that phase variation in contingency genes during chicken passage could promote subsequent colonization and disease in humans. To test this hypothesis, we passaged C. jejuni strains NCTC11168, 33292, 81-176, KanR4 and CamR2 through broiler chickens and analysed the ability of passaged and non-passaged populations to colonize C57BL6 IL-10-deficient mice, our model for human colonization and disease. We utilized fragment analysis and nucleotide sequence analysis to measure phase variation in contingency genes. Passage through the chicken reservoir promoted phase variation in five specific contingency genes, and these 'successful' populations colonized mice. When phase variation did not occur in these same five contingency genes during chicken passage, these 'unsuccessful' populations failed to colonize mice. Phase variation during chicken passage generated small insertions or deletions (indels) in the homopolymeric tract (HT) in contingency genes. Single-colony isolates of C. jejuni strain KanR4 carrying an allele of contingency gene Cj0170 with a10G HT colonized mice at high frequency and caused disease symptoms, whereas single-colony isolates carrying the 9G allele failed to colonize mice. Supporting results were observed for the successful 9G allele of Cj0045 in strain 33292. These data suggest that phase variation in Cj0170 and Cj0045 is strongly associated with mouse colonization and disease, and that the chicken reservoir can play an active role in natural selection, phase variation and disease.

Campylobacter polysaccharide capsules: virulence and vaccines

Campylobacter jejuni remains a major cause of bacterial diarrhea worldwide and is associated with numerous sequelae, including Guillain Barré Syndrome, inflammatory bowel disease, reactive arthritis, and irritable bowel syndrome. C. jejuni is unusual for an intestinal pathogen in its ability to coat its surface with a polysaccharide capsule (CPS). These capsular polysaccharides vary in sugar composition and linkage, especially those involving heptoses of unusual configuration and O-methyl phosphoramidate linkages. This structural diversity is consistent with CPS being the major serodeterminant of the Penner scheme, of which there are 47 C. jejuni serotypes. Both CPS expression and expression of modifications are subject to phase variation by slip strand mismatch repair. Although capsules are virulence factors for other pathogens, the role of CPS in C. jejuni disease has not been well defined beyond descriptive studies demonstrating a role in serum resistance and for diarrhea in a ferret model of disease. However, perhaps the most compelling evidence for a role in pathogenesis are data that CPS conjugate vaccines protect against diarrheal disease in non-human primates. A CPS conjugate vaccine approach against this pathogen is intriguing, but several questions need to be addressed, including the valency of CPS types required for an effective vaccine. There have been numerous studies of prevalence of CPS serotypes in the developed world, but few studies from developing countries where the disease incidence is higher. The complexity and cost of Penner serotyping has limited its usefulness, and a recently developed multiplex PCR method for determination of capsule type offers the potential of a more rapid and affordable method. Comparative studies have shown a strong correlation of the two methods and studies are beginning to ascertain CPS-type distribution worldwide, as well as examination of correlation of severity of illness with specific CPS types.

Glycoconjugates play a key role in Campylobacter jejuni Infection: interactions between host and pathogen

Glycan based interactions between host and pathogen are critical in many bacterial and viral diseases. Glycan interactions range from initial receptor based adherence to protecting the infective agent from the host’s immune response through molecular mimicry. Campylobacter jejuni is an ideal model for studying the role of glycans in host–pathogen interactions, as well as the role of bacterial surface glycoconjugates in infection. Using glycan array analysis, C. jejuni has been shown to interact with a wide range of host glycoconjugates. Mannose and sialic acid residues appear to play a role in initial interactions between host and pathogen following environmental exposure, whereas fucose and galactose based interactions are likely to be required for prolonged colonization. Other studies have highlighted potential decoy receptor type interactions between host’s intestinal mucins and C. jejuni, demonstrating the importance of host glycoproteins as defense against C. jejuni infection as well as the role for glycoconjugates found in human breast milk in protection of breast feeding infants from infection with C. jejuni. C. jejuni can produce N- and O-linked glycoproteins, capsular polysaccharide (CPS) and/or lipooligosaccharide (LOS) which results in C. jejuni presenting its own diverse sugar coated displays on the cell surface. Bacterial glycans play an important and versatile role in infection and disease. Of these, the best understood is the molecular mimicry of human gangliosides presented by C. jejuni’s LOS and its link to the onset of autoimmune neuropathies such as the Guillain Barrè syndrome (GBS). However, the role of glycoconjugates presented by C. jejuni extends beyond expression of sialylated ganglioside structures involved in initiation of GBS. Expression of surface glycans by C. jejuni may also relate to the ability of this organism to interact with the glycoproteins for initial host–pathogen interactions and continued infectivity.

Closely related Campylobacter jejuni strains from different sources reveal a generalist rather than a specialist lifestyle

Background

Campylobacter jejuni and Campylobacter coli are human intestinal pathogens of global importance. Zoonotic transmission from livestock animals or animal-derived food is the likely cause for most of these infections. However, little is known about their general and host-specific mechanisms of colonization, or virulence and pathogenicity factors. In certain hosts, Campylobacter species colonize persistently and do not cause disease, while they cause acute intestinal disease in humans.

Results

Here, we investigate putative host-specificity using phenotypic characterization and genome-wide analysis of genetically closely related C. jejuni strains from different sources. A collection of 473 fresh Campylobacter isolates from Germany was assembled between 2006 and 2010 and characterized using MLST. A subset of closely related C. jejuni strains of the highly prevalent sequence type ST-21 was selected from different hosts and isolation sources. PCR typing of strain-variable genes provided evidence that some genes differed between these strains. Furthermore, phenotypic variation of these strains was tested using the following criteria: metabolic variation, protein expression patterns, and eukaryotic cell interaction. The results demonstrated remarkable phenotypic diversity within the ST-21 group, which however did not correlate with isolation source. Whole genome sequencing was performed for five ST-21 strains from chicken, human, bovine, and food sources, in order to gain insight into ST-21 genome diversity. The comparisons showed extensive genomic diversity, primarily due to recombination and gain of phage-related genes. By contrast, no genomic features associated with isolation source or host were identified.

Conclusions

The genome information and phenotypic data obtained in vitro and in a chicken infection model provided little evidence of fixed adaptation to a specific host. Instead, the dominant C. jejuni ST-21 appeared to be characterized by phenotypic flexibility and high genetic microdiversity, revealing properties of a generalist. High genetic flexibility might allow generalist variants of C. jejuni to reversibly express diverse fitness factors in changing environments.

Campylobacter jejuni, Campylobacter coli, and cytolethal distending toxin (CDT) genes in common teals (Anas crecca)

To evaluate the presence of Campylobacter spp. and related cdt genes, cloacal swabs were collected from 70 common teals (Anas crecca) and analyzed by culture methods and polymerase chain reaction. In addition, C. jejuni were examined also for the presence of wlaN gene. This is believed to be the first report of Campylobacter spp. in common teal and our results confirm the very common occurrence of C. jejuni (n=40) and C. coli (n=13) in waterfowls. Furthermore, the cdt genes were frequently present in both C. jejuni and C. coli isolated. Moreover, seven C. jejuni isolates carried also the wlaN gene which is presumably involved in the expression of ganglioside mimics in Guillain-Barré syndrome.

Campylobacter jejuni isolates in Finnish patients differ according to the origin of infection

BACKGROUND

Campylobacter jejuni is a significant cause of bacterial enteritis worldwide. Very little is known about the pathogenicity mechanisms and virulence factors of this important enteropathogen. C. jejuni isolates from 166 Finnish patients, collected from July to December in 2006, were studied for the presence of putative virulence factors and susceptibility to antimicrobials. Isolates were tested for production of γ-glutamyltransferase (GGT) as well as the presence of genes ceuE, cgtB, ciaB, cj0486, pldA, virB11, wlaN, and the gene cluster cdtABC. Bacterial characteristics were compared to information on foreign travel history as well as information on the course and the symptoms of disease obtained from questionnaires returned by patients.

RESULTS

Except for one domestic isolate, antimicrobial resistance was only detected in isolates of foreign origin. Univariate analyses showed association between bloody stools and both GGT production (p = 0.025) and the presence of cgtB (p = 0.034). Multivariate analysis verified that GGT production was more prevalent in domestic isolates (p < 0.0001), while the genes cj0486 (p < 0.0001) and ceuE (p < 0.0001) were associated with C. jejuni isolates of foreign origin.

CONCLUSIONS

The results indicate that imported and domestic C. jejuni isolates differ significantly in several aspects from each other.

Temperature-dependent phenotypic variation of Campylobacter jejuni lipooligosaccharides

BACKGROUND

Campylobacter jejuni is a major bacterial cause of food-borne enteritis, and its lipooligosaccharide (LOS) plays an initiating role in the development of the autoimmune neuropathy, Guillain-Barré syndrome, by induction of anti-neural cross-reactive antibodies through ganglioside molecular mimicry.

RESULTS

Herein we describe the existence and heterogeneity of multiple LOS forms in C. jejuni strains of human and chicken origin grown at 37 °C and 42 °C, respectively, as determined on sodium dodecyl sulphate-polyacrylamide electrophoresis gels with carbohydrate-specific silver staining and blotting with anti-ganglioside ligands, and confirmed by nuclear magnetic resonance (NMR) spectroscopy. The C. jejuni NCTC 11168 original isolate (11168-O) was compared to its genome-sequenced variant (11168-GS), and both were found to have a lower-M(r) LOS form, which was different in size and structure to the previously characterized higher-M(r) form bearing GM₁ mimicry. The lower-M(r) form production was found to be dependent on the growth temperature as the production of this form increased from ~5%, observed at 37 °C to ~35% at 42 °C. The structure of the lower-M(r) form contained a β-D-Gal-(1→3)-β-D-GalNAc disaccharide moiety which is consistent with the termini of the GM₁, asialo-GM₁, GD₁, GT₁ and GQ₁ gangliosides, however, it did not display GM₁ mimicry as assessed in blotting studies but was shown in NMR to resemble asialo-GM₁. The production of multiple LOS forms and lack of GM1 mimicry was not a result of phase variation in the genes tested of NCTC 11168 and was also observed in most of the human and chicken isolates of C. jejuni tested.

CONCLUSION

The presence of differing amounts of LOS forms at 37 and 42 °C, and the variety of forms observed in different strains, indicate that LOS form variation may play a role in an adaptive mechanism or a stress response of the bacterium during the colonization of different hosts.

Genetic diversity in Campylobacter jejuni is associated with differential colonization of broiler chickens and C57BL/6J IL10-deficient mice

Previous studies have demonstrated that Campylobacter jejuni, the leading causative agent of bacterial food-borne disease in the USA, exhibits high-frequency genetic variation that is associated with changes in cell-surface antigens and ability to colonize chickens. To expand our understanding of the role of genetic diversity in the disease process, we analysed the ability of three C. jejuni human disease isolates (strains 11168, 33292 and 81-176) and genetically marked derivatives to colonize Ross 308 broilers and C57BL/6J IL10-deficient mice. C. jejuni colonized broilers at much higher efficiency (all three strains, 23 of 24 broilers) than mice (11168 only, 8 of 24 mice). C. jejuni 11168 genetically marked strains colonized mice at very low efficiency (2 of 42 mice); however, C. jejuni reisolated from mice colonized both mice and broilers at high efficiency, suggesting that this pathogen can adapt genetically in the mouse. We compared the genome composition in the three wild-type C. jejuni strains and derivatives by microarray DNA/DNA hybridization analysis; the data demonstrated a high degree of genetic diversity in three gene clusters associated with synthesis and modification of the cell-surface structures capsule, flagella and lipo-oligosaccharide. Finally, we analysed the frequency of mutation in homopolymeric tracts associated with the contingency genes wlaN (GC tract) and flgR (AT tracts) in culture and after passage through broilers and mice. C. jejuni adapted genetically in culture at high frequency and the degree of genetic diversity was increased by passage through broilers but was nearly eliminated in the gastrointestinal tract of mice. The data suggest that the broiler gastrointestinal tract provides an environment which promotes outgrowth and genetic variation in C. jejuni; the enhancement of genetic diversity at this location may contribute to its importance as a human disease reservoir.

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.

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.

Bioengineered bugs expressing oligosaccharide receptor mimics: toxin-binding probiotics for treatment and prevention of enteric infections

Many microbial pathogens recognize oligosaccharides displayed on the surface of host cells as receptors for toxins and adhesins. These ligand-receptor interactions are critical for disease pathogenesis, making them promising targets for novel anti-infectives. One strategy with particular utility against enteric infections involves expression of molecular mimics of host oligosaccharides on the surface of harmless bacteria capable of surviving in the gut. This can be achieved in Gram-negative bacteria by manipulating the outer core region of the lipopolysaccharide (LPS) through expression of cloned heterologous glycosyltransferases. The resultant chimeric LPS molecules are incorporated into the outer membrane by the normal assembly route and presented as a closely packed 2-D array of receptor mimics. Several such "designer probiotics" have been constructed, and these bind bacterial toxins in the gut lumen with very high avidity, blocking their uptake by host cells and thereby preventing disease.

N-linked glycosylation in bacteria: an unexpected application

Traditionally, glycoproteins have been considered the exclusive property of eukaryotes and archaea, but it is now evident that glycoproteins are found in all domains of life. In recent years N-linked glycosylation among some epsilon-proteobacteria has emerged as a new and exciting research area and represents a useful model to understand this complex process in simple, genetically tractable bacteria. Above all, the transfer of N-linked glycosylation systems to the work-horse bacterium, Escherichia coli, has enabled, for the first time, the production of recombinant glycoproteins. This has potentially provided the option for tailor-made glycoproteins and has opened up the field of glycoengineering, particularly with respect to the development of glycoconjugate vaccines.

Recombinant interleukin-4 enhances Campylobacter jejuni invasion of intestinal pig epithelial cells (IPEC-1)

Campylobacter jejuni, a leading cause of bacterial gastroenteritis, has a diverse spectrum of disease expression. Polymicrobial infections may contribute to this, such as Trichuris, which elicits type 2 cytokines (including IL-4) and downregulates type 1 immunity. In previous studies, gnotobiotic piglets infected with C. jejuni and Trichuris suis had bloody diarrhea and marked gastrointestinal pathology, including bacterial invasion into epithelial cells and macrophages. Neonatal swine given these dual infections had elevated IL-4 and IL-10 responses in feces. In the studies reported here, we hypothesized that IL-4 or IL-10 enhances invasion of intestinal pig epithelial cells (IPEC-1) by C. jejuni. 10-14-day-old IPEC-1 cells were pretreated with recombinant IL-4 (rIL-4) or rIL-10 for 5h and then challenged with C. jejuni. Cells pretreated with rIL-4 were viable and showed approximately 6-fold increases in C. jejuni (but not Escherichia coli DH5alpha) internalization compared to cells with no pretreatment. Enhanced C. jejuni invasion was rIL-4 dose-dependent and reversed by addition of anti-IL-4 antibody. Preincubation with rIL-10 did not significantly alter C. jejuni internalization. Transepithelial electrical resistance (TEER) was significantly reduced following rIL-4 treatment, but not rIL-10 treatment. After rIL-4 pretreatment and C. jejuni challenge, light microscopy showed vacuolated cells with damaged paracellular junctions. Transmission electron microscopy (TEM) showed multiple internalized bacteria. Most were in the cytoplasm, but some were within or adjacent to vacuoles. We conclude that rIL-4 damages paracellular junctions and alters the physiology of these epithelial cells allowing increased invasion of C. jejuni.

Multiple factors interact to produce responses resembling spectrum of human disease in Campylobacter jejuni infected C57BL/6 IL-10-/- mice

BACKGROUND

Campylobacter jejuni infection produces a spectrum of clinical presentations in humans--including asymptomatic carriage, watery diarrhea, and bloody diarrhea--and has been epidemiologically associated with subsequent autoimmune neuropathies. This microorganism is genetically variable and possesses genetic mechanisms that may contribute to variability in nature. However, relationships between genetic variation in the pathogen and variation in disease manifestation in the host are not understood. We took a comparative experimental approach to explore differences among different C. jejuni strains and studied the effect of diet on disease manifestation in an interleukin-10 deficient mouse model.

RESULTS

In the comparative study, C57BL/6 interleukin-10-/- mice were infected with seven genetically distinct C. jejuni strains. Four strains colonized the mice and caused disease; one colonized with no disease; two did not colonize. A DNA:DNA microarray comparison of the strain that colonized mice without disease to C. jejuni 11168 that caused disease revealed that putative virulence determinants, including loci encoding surface structures known to be involved in C. jejuni pathogenesis, differed from or were absent in the strain that did not cause disease. In the experimental study, the five colonizing strains were passaged four times in mice. For three strains, serial passage produced increased incidence and degree of pathology and decreased time to develop pathology; disease shifted from watery to bloody diarrhea. Mice kept on an ~6% fat diet or switched from an approximately 12% fat diet to an approximately 6% fat diet just before infection with a non-adapted strain also exhibited increased incidence and severity of disease and decreased time to develop disease, although the effects of diet were only statistically significant in one experiment.

CONCLUSION

C. jejuni strain genetic background and adaptation of the strain to the host by serial passage contribute to differences in disease manifestations of C. jejuni infection in C57BL/6 IL-10-/- mice; differences in environmental factors such as diet may also affect disease manifestation. These results in mice reflect the spectrum of clinical presentations of C. jejuni gastroenteritis in humans and contribute to usefulness of the model in studying human disease.

Campylobacter jejuni cocultured with epithelial cells reduces surface capsular polysaccharide expression

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

Antiganglioside antibodies and their pathophysiological effects on Guillain-Barré syndrome and related disorders--a review

Guillain-Barré syndrome (GBS) is an acute immune-mediated polyradiculoneuropathy which can cause acute quadriplegia. Infection with micro-organisms, including Campylobacter jejuni (C. jejuni), Haemophilus influenzae, and Cytomegalovirus (CMV), is recognized as a main triggering event for the disease. Lipooligosaccharide (LOS) genes are responsible for the formation of human ganglioside-like LOS structures in infectious micro-organisms that can induce GBS. Molecular mimicry of LOSs on the surface of infectious agents and of ganglioside antigens on neural cells is thought to induce cross-reactive humoral and cellular immune responses. Patients with GBS develop antibodies against those gangliosides, resulting in autoimmune targeting of peripheral nerve sites, leading to neural damage. Heterogeneity of ganglioside expression in the peripheral nervous system (PNS) may underlie the differential clinical manifestation of the GBS variants. Recent studies demonstrate that some GBS sera react with ganglioside complexes consisting of two different gangliosides, such as GD1a and GD1b, or GM1 and GD1a, but not with each constituent ganglioside alone. The discovery of antiganglioside complex antibodies not only improves the detection rate of autoantibodies in GBS, but also provides a new concept in the antibody-antigen interaction through clustered carbohydrate epitopes. Although ganglioside mimicry is one of the possible etiological causes of GBS, unidentified factors may also contribute to the pathogenesis of GBS. While GBS is not considered a genetic disease, host factors, particularly human lymphocyte antigen type, appear to have a role in the pathogenesis of GBS following C. jejuni infection.

Determinants of phase variation rate and the fitness implications of differing rates for bacterial pathogens and commensals

Phase variation (PV) of surface molecules and other phenotypes is a major adaptive strategy of pathogenic and commensal bacteria. Phase variants are produced at high frequencies and in a reversible manner by hypermutation or hypervariable methylation in specific regions of the genome. The major mechanisms of PV involve site-specific recombination, homologous recombination, simple sequence DNA repeat tracts or epigenetic modification by the dam methylase. PV rates of some of these mechanisms are subject to the influence of genome maintenance pathways such as DNA replication, recombination and repair while others are independent of these pathways. For each of these mechanisms, the rate of generation of phase variants is controlled by intrinsic and dispensable factors. These factors can impart environmental regulation on switching rates while many factors are subject to heterogeneity both within isolates of a species and between species. A major gap in our understanding is whether these environmental and epidemiological variations in PV rate have a major impact on fitness. Experimental approaches to studying the biological relevance of differing PV rates are being developed, and a recent intriguing finding is of a co-ordination of switching rates in the phase variable P-pili of uropathogenic bacteria.

Restoration of flagellar biosynthesis by varied mutational events in Campylobacter jejuni

Both a complex regulatory cascade involving the FlgSR two-component system and phase variation control expression of sigma(54)-dependent flagellar genes in Campylobacter jejuni. In this study, mutational mechanisms influencing production of the FlgS histidine kinase were discovered. Random non-motile, non-flagellated flgS variants were impaired for growth in the chick intestinal tract. Spontaneous revertants restored for flagellar biosynthesis, gene expression, and motility identified by in vivo and in vitro studies had undergone diverse intragenic and extragenic mutational events relative to flgS. Restorative intragenic events included true phase variation, second-site intragenic reversion, and insertion and deletion of short DNA segments within flgS. In vivo-isolated motile revertants possessed an identical, single extragenic mutation to create a partially constitutively active FlgR protein in the absence of FlgS. Considering that FlgR production is also influenced by phase variation, these new findings suggest that the FlgSR two-component system is unique in that each protein is controlled by phase variation and phosphorylation. In addition, this study highlights the mutational activities of C. jejuni and suggests that the bacterium may possess a repertoire of mutational mechanisms to overcome genetic lesions that impair production of virulence and colonization determinants while lacking a normal mismatch repair system.

Campylobacter sugars sticking out

The amazing repertoire of glycoconjugates that are found in Campylobacter jejuni includes lipooligosaccharides mimicking human glycolipids, capsular polysaccharides with complex and unusual sugars, and proteins that are post-translationally modified with either O- or N-linked glycans. Thus, the glycome of this important food-borne pathogen is an excellent toolbox for glycobiologists to understand the fundamentals of these pathways and their role in host-microbe interactions, develop new techniques for glycobiology and exploit these pathways for novel diagnostics and therapeutics. The exciting surge in recent research activities will be summarized in this review.

Comparison of lipooligosaccharide biosynthesis genes of Campylobacter jejuni strains with varying abilities to colonize the chicken gut and to invade Caco-2 cells

Campylobacter jejuni strains develop a high variability of lipooligosaccharide (LOS) structures on the cell surface based on variations in the genetic content of the LOS biosynthesis locus. While the importance of these variations for ganglioside mimicry as a critical factor in the triggering of Guillain-Barré syndrome has already been shown, little work has been done on the investigation of LOS structures and their function in the pathogenesis of gastrointestinal disease. In this study, the presence of several LOS genes in 40 C. jejuni strains with different abilities to colonize the chicken gut and to invade Caco-2 cells was investigated by PCR. Two genes, cgtB and wlaN, encoding putative beta-1,3-galactosyltransferases were detected in most strongly invasive strains and rarely in non-invasive strains. A homopolymeric tract within the wlaN gene resulted in an intact gene product only in strongly invasive strains. The specific function of these genes during LOS biosynthesis is still unknown. cgtB and wlaN gene products are suggested to be involved in development of the colonization and invasion ability of C. jejuni. After a classification of the complete LOS loci, an association between a particular LOS class and colonization and invasion ability of the C. jejuni strain could not be detected. Lack of the pglB gene involved in protein glycosylation in one strain could be responsible for the weak colonization and invasion ability of this strain. There is some evidence that different genetic characteristics were responsible for strong or weak colonization and the invasion ability of C. jejuni strains.

Prevalence of virulence genes and cytolethal distending toxin production in Campylobacter jejuni isolates from diarrheal patients in Bangladesh

From 300 stool samples, 58 Campylobacter strains were isolated by standard microbiological and biochemical methods. Of these, 40 strains were identified as Campylobacter jejuni and 5 as Campylobacter coli. The presence of flaA (100%), cadF (100%), racR (100%), dnaJ (100%), pldA (100%), ciaB (95%), virB11 (0%), ceuE (82.5%), cdtA (97.5%), cdtB (97.5%), cdtC (97.5%), and wlaN (7.5%) genes was detected in C. jejuni by PCR. All C. jejuni strains but one produced cytolethal distending toxin in a HeLa cell assay.

Pathogenesis of Campylobacter

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Campylobacter jejuni: 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.

Variants of the β1,3-Galactosyltransferase CgtB from the Bacterium Campylobacter Jejuni have Distinct Acceptor Specificities

The gene clusters encoding the lipooligosaccharide biosynthesis glycosyltransferases from Campylobacter jejuni have previously been divided in eight classes based on their genetic organization. Here, three variants of the beta1,3-galactosyltransferase CgtB from two classes were purified as fusions with the maltose-binding protein (MalE) from Escherichia coli and their acceptor preference was determined. The acceptor preference of each CgtB variant was directly related to the presence or absence of sialic acid in the acceptor, which correlated with the core oligosaccharide structure in vivo. The three variants were evaluated for their ability to use a derivitized monosaccharide, a GM2 ganglioside mimic, a GA2 ganglioside mimic as well as a peptide containing alpha-linked GalNAc. This characterization shows the flexibility of these galactosyltransferases for diverse acceptors. The CgtB variants were engineered via carboxy-terminal deletions and inversion of the gene fusion order. The combination of a 20 to 30 aa deletion in CgtB followed by MalE at its carboxy terminus significantly improved the glycosyltransferase activity (up to a 51.8-fold increase of activity compared to the full length enzyme) in all cases regardless of the acceptor tested. The improved enzyme CgtB(OH4384)DeltaC-MalE was used to galactosylate a glyco-peptide acceptor based on the interferon alpha2b protein O-linked glycosylation site as confirmed by the CE-MS analysis of the reaction products. This improved enzyme was also used successfully to galactosylate the human therapeutic protein IFNalpha2b[GalNAcalpha]. This constitutes the first report of the in vitro synthesis of the O-linked T-antigen glycan on a human protein by a bacterial glycosyltransferase and illustrates the potential of bacterial glycosyltransferases as tools for in vitro glycosylation of human proteins of therapeutic value.

Genome dynamics of Campylobacter jejuni in response to bacteriophage predation

Campylobacter jejuni is a leading cause of food-borne illness. Although a natural reservoir of the pathogen is domestic poultry, the degree of genomic diversity exhibited by the species limits the application of epidemiological methods to trace specific infection sources. Bacteriophage predation is a common burden placed upon C. jejuni populations in the avian gut, and we show that amongst C. jejuni that survive bacteriophage predation in broiler chickens are bacteriophage-resistant types that display clear evidence of genomic rearrangements. These rearrangements were identified as intra-genomic inversions between Mu-like prophage DNA sequences to invert genomic segments up to 590 kb in size, the equivalent of one-third of the genome. The resulting strains exhibit three clear phenotypes: resistance to infection by virulent bacteriophage, inefficient colonisation of the broiler chicken intestine, and the production of infectious bacteriophage CampMu. These genotypes were recovered from chickens in the presence of virulent bacteriophage but not in vitro. Reintroduction of these strains into chickens in the absence of bacteriophage results in further genomic rearrangements at the same locations, leading to reversion to bacteriophage sensitivity and colonisation proficiency. These findings indicate a previously unsuspected method by which C. jejuni can generate genomic diversity associated with selective phenotypes. Genomic instability of C. jejuni in the avian gut has been adopted as a mechanism to temporarily survive bacteriophage predation and subsequent competition for resources, and would suggest that C. jejuni exists in vivo as families of related meta-genomes generated to survive local environmental pressures.

Free-range layer chickens as a source of Campylobacter bacteriophage

Bacteriophage specific for Campylobacter were isolated from chicken excreta collected from established free-range layer breed stock. Bacteriophage were either propagated on a Campylobacter jejuni host with broad susceptibility to bacteriophage (NCTC 12662) or on Campylobacter isolates from the same samples. Campylobacters were confirmed as being C. jejuni and or C. coli, using a combination of standard biochemical tests and PCR analysis with genus and species specific primers. The bacteriophage displayed differential patterns of susceptibility against reference NCTC strains and contemporary C. jejuni /C. coli isolates from chicken excreta. Electron microscopy demonstrated that the phage possessed icosahedral heads and rigid contractile tails. Pulsed-field gel electrophoresis revealed the bacteriophage genomes to be double stranded DNA in the range of 140 kb in size and the restriction enzyme patterns of the DNAs indicate they are genetically related members of the Myoviridae family. This study showed that Campylobacter bacteriophage could easily be isolated from free-range chickens and form part of their normal microbiological biota of environmentally exposed birds.

Bacterial contingency loci: the role of simple sequence DNA repeats in bacterial adaptation

Bacterial pathogens face stringent challenges to their survival because of the many unpredictable, often precipitate, and dynamic changes that occur in the host environment or in the process of transmission from one host to another. Bacterial adaptation to their hosts involves either a mechanism for sensing and responding to external changes or the selection of variants that arise through mutation. Here we review how bacterial pathogens exploit localized hypermutation, through polymerase slippage of simple sequence repeats (SSRs), to generate phenotypic variation and enhanced fitness. These SSRs are located within the reading frame or in the promoter of a subset of genes, often termed contingency loci, whose functions are usually involved in direct interactions with host structures.

CapA, an autotransporter protein of Campylobacter jejuni, mediates association with human epithelial cells and colonization of the chicken gut

Two putative autotransporter proteins, CapA and CapB, were identified in silico from the genome sequence of Campylobacter jejuni NCTC11168. The genes encoding each protein contain homopolymeric tracts, suggestive of phase variation mediated by a slipped-strand mispairing mechanism; in each case the gene sequence contained frameshifts at these positions. The C-terminal two-thirds of the two genes, as well as a portion of the predicted signal peptides, were identical; the remaining N-terminal portions were gene specific. Both genes were cloned and expressed; recombinant polypeptides were purified and used to raise rabbit polyclonal monospecific antisera. Using immunoblotting, expression of the ca.116-kDa CapA protein was demonstrated for in vitro-grown cells of strain NCTC11168, for 4 out of 11 recent human fecal isolates, and for 2 out of 8 sequence-typed strains examined. Expression of CapB was not detected for any of the strains tested. Surface localization of CapA was demonstrated by subcellular fractionation and immunogold electron microscopy. Export of CapA was inhibited by globomycin, reinforcing the bioinformatic prediction that the protein is a lipoprotein. A capA insertion mutant had a significantly reduced capacity for association with and invasion of Caco-2 cells and failed to colonize and persist in chickens, indicating that CapA plays a role in host association and colonization by Campylobacter. In view of this demonstrated role, we propose that CapA stands for Campylobacter adhesion protein A.