Major structural differences and novel potential virulence mechanisms from the genomes of multiple campylobacter species

Rapid identification and quantification of Campylobacter coli and Campylobacter jejuni by real-time PCR in pure cultures and in complex samples

Background

Campylobacter spp., especially Campylobacter jejuni (C. jejuni) and Campylobacter coli (C. coli), are recognized as the leading human foodborne pathogens in developed countries. Livestock animals carrying Campylobacter pose an important risk for human contamination. Pigs are known to be frequently colonized with Campylobacter, especially C. coli, and to excrete high numbers of this pathogen in their faeces. Molecular tools, notably real-time PCR, provide an effective, rapid, and sensitive alternative to culture-based methods for the detection of C. coli and C. jejuni in various substrates. In order to serve as a diagnostic tool supporting Campylobacter epidemiology, we developed a quantitative real-time PCR method for species-specific detection and quantification of C. coli and C. jejuni directly in faecal, feed, and environmental samples.

Results

With a sensitivity of 10 genome copies and a linear range of seven to eight orders of magnitude, the C. coli and C. jejuni real-time PCR assays allowed a precise quantification of purified DNA from C. coli and C. jejuni. The assays were highly specific and showed a 6-log-linear dynamic range of quantification with a quantitative detection limit of approximately 2.5 × 10² CFU/g of faeces, 1.3 × 10² CFU/g of feed, and 1.0 × 10³ CFU/m² for the environmental samples. Compared to the results obtained by culture, both C. coli and C. jejuni real-time PCR assays exhibited a specificity of 96.2% with a kappa of 0.94 and 0.89 respectively. For faecal samples of experimentally infected pigs, the coefficients of correlation between the C. coli or C. jejuni real-time PCR assay and culture enumeration were R² = 0.90 and R² = 0.93 respectively.

Conclusion

The C. coli and C. jejuni real-time quantitative PCR assays developed in this study provide a method capable of directly detecting and quantifying C. coli and C. jejuni in faeces, feed, and environmental samples. These assays represent a new diagnostic tool for studying the epidemiology of Campylobacter by, for instance, investigating the carriage and excretion of C. coli and C. jejuni by pigs from conventional herds.

Cytolethal distending toxin: a conserved bacterial genotoxin that blocks cell cycle progression, leading to apoptosis of a broad range of mammalian cell lineages

Cytolethal distending toxin (CDT) is a heterotrimeric AB-type genotoxin produced by several clinically important Gram-negative mucocutaneous bacterial pathogens. Irrespective of the bacterial species of origin, CDT causes characteristic and irreversible cell cycle arrest and apoptosis in a broad range of cultured mammalian cell lineages. The active subunit CdtB has structural homology with the phosphodiesterase family of enzymes including mammalian DNase I, and alone is necessary and sufficient to account for cellular toxicity. Indeed, mammalian cells treated with CDT initiate a DNA damage response similar to that elicited by ionizing radiation-induced DNA double strand breaks resulting in cell cycle arrest and apoptosis. The mechanism of CDT-induced apoptosis remains incompletely understood, but appears to involve both p53-dependent and -independent pathways. While epithelial, endothelial and fibroblast cell lines respond to CDT by undergoing arrest of cell cycle progression resulting in nuclear and cytoplasmic distension that precedes apoptotic cell death, cells of haematopoietic origin display rapid apoptosis following a brief period of cell cycle arrest. In this review, the ecology of pathogens producing CDT, the molecular biology of bacterial CDT and the molecular mechanisms of CDT-induced cytotoxicity are critically appraised. Understanding the contribution of a broadly conserved bacterial genotoxin that blocks progression of the mammalian cell cycle, ultimately causing cell death, should assist with elucidating disease mechanisms for these important pathogens.

Campylobacter bacteriophages and bacteriophage therapy

Members of the genus Campylobacter are frequently responsible for human enteric disease with occasionally very serious outcomes. Much of this disease burden is thought to arise from consumption of contaminated poultry products. More than 80% of poultry in the UK harbour Campylobacter as a part of their intestinal flora. To address this unacceptably high prevalence, various interventions have been suggested and evaluated. Among these is the novel approach of using Campylobacter-specific bacteriophages, which are natural predators of the pathogen. To optimize their use as therapeutic agents, it is important to have a comprehensive understanding of the bacteriophages that infect Campylobacter, and how they can affect their host bacteria. This review will focus on many aspects of Campylobacter-specific bacteriophages including: their first isolation in the 1960s, their use in bacteriophage typing schemes, their isolation from the different biological sources and genomic characterization. As well as their use as therapeutic agents to reduce Campylobacter in poultry their future potential, including their use in bio-sanitization of food, will be explored. The evolutionary consequences of naturally occurring bacteriophage infection that have come to light through investigations of bacteriophages in the poultry ecosystem will also be discussed.

Genomic variations define divergence of water/wildlife-associated Campylobacter jejuni niche specialists from common clonal complexes

Although the major food-borne pathogen Campylobacter jejuni has been isolated from diverse animal, human and environmental sources, our knowledge of genomic diversity in C. jejuni is based exclusively on human or human food-chain-associated isolates. Studies employing multilocus sequence typing have indicated that some clonal complexes are more commonly associated with particular sources. Using comparative genomic hybridization on a collection of 80 isolates representing diverse sources and clonal complexes, we identified a separate clade comprising a group of water/wildlife isolates of C. jejuni with multilocus sequence types uncharacteristic of human food-chain-associated isolates. By genome sequencing one representative of this diverse group (C. jejuni 1336), and a representative of the bank-vole niche specialist ST-3704 (C. jejuni 414), we identified deletions of genomic regions normally carried by human food-chain-associated C. jejuni. Several of the deleted regions included genes implicated in chicken colonization or in virulence. Novel genomic insertions contributing to the accessory genomes of strains 1336 and 414 were identified. Comparative analysis using PCR assays indicated that novel regions were common but not ubiquitous among the water/wildlife group of isolates, indicating further genomic diversity among this group, whereas all ST-3704 isolates carried the same novel accessory regions. While strain 1336 was able to colonize chicks, strain 414 was not, suggesting that regions specifically absent from the genome of strain 414 may play an important role in this common route of Campylobacter infection of humans. We suggest that the genomic divergence observed constitutes evidence of adaptation leading to niche specialization.

Discrimination of major capsular types of Campylobacter jejuni by multiplex PCR

The polysaccharide capsule (CPS) of Campylobacter jejuni is the major serodeterminant of the Penner serotyping scheme. There are 47 Penner serotypes of C. jejuni, 22 of which fall into complexes of related serotypes. A multiplex PCR method for determination of capsule types of Campylobacter jejuni which is simpler and more affordable than classical Penner typing was developed. Primers specific for each capsule type were designed on the basis of a database of gene sequences from the variable capsule loci of 8 strains of major serotypes sequenced in this study and 10 published sequences of other serotypes. DNA sequence analysis revealed a mosaic nature of the capsule loci, suggesting reassortment of genes by horizontal transfer, and demonstrated a high degree of conservation of genes within Penner complexes. The multiplex PCR can distinguish 17 individual serotypes in two PCRs with sensitivities and specificities ranging from 90 to 100% using 244 strains of known Penner type.

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

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

Identification of essential genes in C. jejuni genome highlights hyper-variable plasticity regions

A microarray transposon-based tracking approach was used to identify Campylobacter jejuni genes which are required for cell growth at 37°C, under a microaerophilic atmosphere and on a rich Mueller-Hinton medium. A transposon-based mutant library, comprised of 7,201 individual mutants was constructed, representing 4.48× coverage of the genome. An analysis of genes lacking a transposon insertion revealed 195 essential gene candidates. The function of these genes represent many of the expected core functions of the cell, such as energy metabolism, macromolecule and cofactor biosynthesis, cell structural proteins as well as basic cell processes. Forty-nine hypothetical proteins were also identified, further underlining the importance of currently unknown proteins and pathways within C. jejuni. Unlike other bacteria, the essential genes were not uniformly distributed along the chromosome with three main regions lacking essential genes. These particular regions corresponded to known hyper-variable plasticity regions of C. jejuni genome indicating, as expected, that these regions are dispensable in any given C. jejuni strain. Overall, this work identified dispensable and essential genes in C. jejuni that will ultimately lead to a better understanding of Campylobacter physiology.

Profound differences in the transcriptome of Campylobacter jejuni grown in two different, widely used, microaerobic atmospheres

It was noted that quantitative and qualitative differences occurred between the growth of Campylobacter in microaerobic atmospheres provided by a gas replacement jar and that in a modular atmosphere controlled system cabinet, despite the fact that oxygen levels were comparable. Hydrogen was, however, only present in the replacement mixture (3%). Investigations were therefore carried out to examine any accompanying physiological or transcriptional differences. Growth curves and motility studies using Campylobacter jejuni HPC5 showed that cultures growing in the cabinet were impaired, but only in the early stages of growth compared to growth in the jar. However, transcriptome studies highlighted profound changes in the transcript profiles of exponential cultures grown in the cabinet compared to the jar, including genes indicative of oxidative stress. Genes involved in detoxification, synthesis and modification of macromolecules, probable prophage genes and genes associated with inhibition of natural transformation showed relative increases in expression in the cabinet. Conversely, genes that function in energy metabolism, chaperones, heat shock and motility were increased in the jar, which was indicative of balanced growth. This work highlights the need to carefully annotate the different methods of atmosphere generation in the description of experiments in microarray databases; the assessment of these experimental details is crucial to overcome difficulties in comparing transcriptomic studies of campylobacter cultures between different laboratories.

A phylogenetic comparison of urease-positive thermophilic Campylobacter (UPTC) and urease-negative (UN) C. lari

In the present study, the reliability of full-length gene sequence information for several genes including 16S rRNA was examined, for the discrimination of the two representative Campylobacter lari taxa, namely urease-negative (UN) C. lari and urease-positive thermophilic Campylobacter (UPTC). As previously described, 16S rRNA gene sequence are not reliable for the molecular discrimination of UN C. lari from UPTC organisms employing both the unweighted pair group method using arithmetic means analysis (UPGMA) and neighbor joining (NJ) methods. In addition, three composite full-length gene sequences (ciaB, flaC and vacJ) out of seven gene loci examined were reliable for discrimination employing dendrograms constructed by the UPGMA method. In addition, all the dendrograms of the NJ phylogenetic trees constructed based on the nine gene information were not reliable for the discrimination. Three composite full-length gene sequences (ciaB, flaC and vacJ) were reliable for the molecular discrimination between UN C. lari and UPTC organisms employing the UPGMA method, as well as among four thermophilic Campylobacter species.

Epidemiological association of different Campylobacter jejuni groups with metabolism-associated genetic markers

In this study, multilocus sequence typing (MLST) was combined with the genetic detection of six genetic markers, ansB, dmsA, ggt, cj1585c, cjj81176-1367/71 (cj1365c), and the two-gene marker tlp7 (cj0951c plus cj0952c), to assess if their presence correlated with different C. jejuni clonal groups. Using a collection of 266 C. jejuni isolates from (in decreasing order of sample size) humans, chickens, cattle, and turkeys, it was further investigated whether the resulting genotypes correlated with the isolation source. We found combinations of the six marker genes to be mutually exclusive, and their patterns of presence or absence correlated to some degree with animal source. Together with MLST results, the obtained genotypes could be segregated into six groups. An association was identified for ansB, dmsA, and ggt with the MLST-clonal complexes (MLST-CC) 22, 42, 45, and 283, which formed the most prominent group, in which chickens were the most prevalent animal source. Two other groups, characterized by the presence of cj1585c, cjj81176-1367/71, and the two-gene marker tlp7, associated with either MLST-CC 21 or 61, were overrepresented in isolates of bovine origin. Mutually exclusive marker gene combinations were observed for ansB, dmsA, and ggt, typically found in CC 45 and the related CC 22, 42, and 283, whereas the other three marker genes were found mostly in CC 21, 48, and 206. The presence of the two-gene marker tlp7, which is typical for MLST 21 and 53 as well as for MLST-CC 61, strongly correlates with a bovine host; this is interpreted as an example of host adaptation. In cases of C. jejuni outbreaks, these genetic markers could be helpful for more effective source tracking.

Phenotypic and genotypic evidence for L-fucose utilization by Campylobacter jejuni

Campylobacter jejuni remains among the leading causes of bacterial food-borne illness. The current understanding of Campylobacter physiology suggests that it is asaccharolytic and is unable to catabolize exogenous carbohydrates. Contrary to this paradigm, we provide evidence for l-fucose utilization by C. jejuni. The fucose phenotype, shown in chemically defined medium, is strain specific and linked to an 11-open reading frame (ORF) plasticity region of the bacterial chromosome. By constructing a mutation in fucP (encoding a putative fucose permease), one of the genes in the plasticity region, we found that this locus is required for fucose utilization. Consistent with their function in fucose utilization, transcription of the genes in the locus is highly inducible by fucose. PCR screening revealed a broad distribution of this genetic locus in strains derived from various host species, and the presence of this locus was consistently associated with fucose utilization. Birds inoculated with the fucP mutant strain alone were colonized at a level comparable to that by the wild-type strain; however, in cocolonization experiments, the mutant was significantly outcompeted by the wild-type strain when birds were inoculated with a low dose (10⁵ CFU per bird). This advantage was not observed when birds were inoculated at a higher inoculum dose (10⁸ CFU per bird). These results demonstrated a previously undescribed substrate that supports growth of C. jejuni and identified the genetic locus associated with the utilization of this substrate. These findings substantially enhance our understanding of the metabolic repertoire of C. jejuni and the role of metabolic diversity in Campylobacter pathobiology.

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 affects sole carbon utilization patterns of Campylobacter coli 49941

Campylobacter spp. are small, asaccharolytic bacteria exhibiting unique nutritional and environmental requirements. Campylobacter spp. exist as commensal organisms in some animal species, yet are estimated to be the most common causative agents of foodborne illness in humans. C. jejuni is most often associated with poultry, while C. coli are more frequently associated with swine. Temperature has been suggested to trigger potential colonization or virulence factors in C. jejuni, and recent studies have demonstrated temperature-dependent genes are important to colonization. It is possible that temperature-dependent colonization factors are in part responsible for the species-specific colonization characteristics of C. coli also. We determined utilization of 190 different sole carbon substrates by C. coli ATCC 49941 at 37 and 42°C using phenotype microarray (PM) technology. Temperature did affect amino acid utilization. L-asparagine and L-serine allowed significantly (P = 0.004) more respiration by C. coli ATCC 49941 at the lower temperature of 37°C as compared to 42°C. Conversely, L-glutamine was utilized to a significantly greater extent (P = 0.015) at the higher temperature of 42°C. Other organic substrates exhibited temperature-dependent utilization including succinate, D,L-malate, and propionate which all supported active respiration by C. coli to a significantly greater extent at 42°C. Further investigation is needed to determine the basis for the temperature-dependent utilization of substrates by Campylobacter spp. and their possible role in species-specific colonization.

Ribosomal operon intergenic sequence region (ISR) heterogeneity in Campylobacter coli and Campylobacter jejuni

AIMS

The intergenic sequence regions (ISR) between the 16S and 23S genes of Campylobacter jejuni and Campylobacter coli are markedly different for each species. However, in the genomic sequence for Camp. coli RM2228, two rRNA operons have an ISR that is characteristic of Camp. coli, and the third operon is characteristic of Camp. jejuni. The aim of this study was to determine the prevalence of ISR heterogeneity in these organisms.

METHODS AND RESULTS

PCR primers were designed to yield a 327-base pair (bp) product for Camp. coli and 166-bp product for Camp. jejuni. A strain like Camp. coli RM2228 should yield products of both sizes. DNA from a panel of Camp. coli (n=133) and Camp. jejuni (n=134) isolates were tested. All of the isolates yielded products of the predicted size for the species. To verify the data for Camp. coli RM2228, each ribosomal operon from the isolate was individually amplified by PCR and tested with the ISR primer pair. Products of both sizes were produced as predicted.

CONCLUSIONS

The cross-species heterogeneity of the ISR seen in Camp. coli RM2228 is uncommon.

SIGNIFICANCE AND IMPACT OF THE STUDY

The heterogeneity must have been caused by horizontal gene transfer at a frequency lower than predicted from housekeeping gene data. Thus, it can be expected that species identification based on the ISR can be confused in rare isolates.

Differences in methylation at GATC sites in genomic DNA of Campylobacter coli from turkeys and swine

A significant fraction (46/108, 43%) of swine isolates of Campylobacter coli but none of 81 isolates of C. coli from turkeys had genomic DNA that was resistant to digestion by MboI, suggesting methylation of adenines at GATC sites. No consistent association was noted between antimicrobial resistance and MboI resistance. Seven swine-associated multilocus sequence typing-based sequence types (STs) were detected among multiple isolates with MboI-resistant DNA. The data suggest host-associated DNA modification system(s) specific for adenine at GATC sites in C. coli from swine.

Genomic characterization of Campylobacter jejuni strain M1

Campylobacter jejuni strain M1 (laboratory designation 99/308) is a rarely documented case of direct transmission of C. jejuni from chicken to a person, resulting in enteritis. We have sequenced the genome of C. jejuni strain M1, and compared this to 12 other C. jejuni sequenced genomes currently publicly available. Compared to these, M1 is closest to strain 81116. Based on the 13 genome sequences, we have identified the C. jejuni pan-genome, as well as the core genome, the auxiliary genes, and genes unique between strains M1 and 81116. The pan-genome contains 2,427 gene families, whilst the core genome comprised 1,295 gene families, or about two-thirds of the gene content of the average of the sequenced C. jejuni genomes. Various comparison and visualization tools were applied to the 13 C. jejuni genome sequences, including a species pan- and core genome plot, a BLAST Matrix and a BLAST Atlas. Trees based on 16S rRNA sequences and on the total gene families in each genome are presented. The findings are discussed in the background of the proven virulence potential of M1.

Identification and characterization of a new ferric enterobactin receptor, CfrB, in Campylobacter

The ferric enterobactin (FeEnt) receptor CfrA is present in the majority of Campylobacter jejuni isolates and is responsible for high-affinity iron acquisition. Our recent work and that of others strongly suggested the existence of another FeEnt uptake system in Campylobacter. Here we have identified and characterized a new FeEnt receptor (designated CfrB) using both in vitro and in vivo systems. CfrB, a homolog of C. jejuni NCTC 11168 Cj0444, shares approximately 34% of amino acid identity with CfrA. Alignment of complete CfrB sequences showed that the CfrB is highly conserved in Campylobacter. Immunoblotting analysis using CfrB-specific antiserum demonstrated that CfrB was dramatically induced under iron-restricted conditions and was produced in the majority of Campylobacter coli (41 out of 45) and in some C. jejuni (8 out of 32) primary strains from various sources and from geographically diverse areas. All of the CfrB-producing C. coli strains also produced CfrA, which was rarely observed in the tested C. jejuni strains. Isogenic cfrB, cfrA, and cfrA cfrB double mutants were constructed in 43 diverse Campylobacter strains. Growth promotion assays using these mutants demonstrated that CfrB has a major role in FeEnt iron acquisition in C. coli. Chicken colonization experiments indicated that inactivation of the cfrB gene alone greatly reduced and even abolished Campylobacter colonization of the intestines. A growth assay using CfrB-specific antiserum strongly suggested that specific CfrB antibodies could block the function of CfrB and diminish FeEnt-mediated growth promotion under iron-restricted conditions. Together, this work reveals the complexity of FeEnt systems in the two closely related Campylobacter species and demonstrates the important role of the new FeEnt receptor CfrB in Campylobacter iron acquisition and in vivo colonization.

Campylobacter concisus and other Campylobacter species in children with newly diagnosed Crohn's disease

BACKGROUND

Campylobacter concisus and other members of the Campylobacter genus have recently been suggested as possible etiological agents of Crohn's disease (CD). To further investigate this issue we determined the prevalence of these organisms in pediatric patients newly diagnosed with CD.

METHODS

DNA was extracted from fecal specimens collected from 54 children with CD, 27 noninflammatory bowel disease (non-IBD), and 33 healthy controls and subjected to polymerase chain reaction (PCR) sequencing.

RESULTS

Detection of C. concisus DNA using a newly developed PCR assay targeting the 16S rRNA gene of C. concisus showed that 65% (35/54) of fecal samples from CD children were positive, a prevalence significantly higher than that in the healthy (33%, 11/33, P = 0.008) and non-IBD controls (37%, 10/27, P = 0.03). The prevalence of all Campylobacter DNA using genus-specific primers in children with CD was 72% (39/54), which was significantly higher than the 30% (10/33, P = 0.0002) and 30% (8/27, P = 0.0003) observed in healthy and non-IBD controls, respectively.

CONCLUSIONS

Given the strengthening evidence for a significantly higher prevalence of C. concisus and other non-jejuni Campylobacter species in pediatric CD, investigation into the role of these non-jejuni Campylobacter species in the initiation of human IBD is clearly a priority.

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.

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

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

Contribution of the multidrug efflux transporter CmeABC to antibiotic resistance in different Campylobacter species

CmeABC, a multidrug efflux system in Campylobacter jejuni, plays an important role in the resistance to different antimicrobials and toxic compounds. Although this efflux system has been well characterized in C. jejuni and to a less extent in C. coli, it is unknown if CmeABC homologs are functional in other Campylobacter spp. In this study, the cmeABC homologs were identified and functionally characterized in five Campylobacter species including C. jejuni, C. coli, C. lari, C. upsaliensis, and C. fetus. Our results indicated that cmeABC is present in all five Campylobacter spp. and the genomic organization of this efflux operon is similar among the Campylobacter spp. Insertional mutagenesis of cmeB increased the susceptibilities of all the five Campylobacter spp. to structurally diverse antimicrobials. Together, these results indicated that the CmeABC efflux system is conserved at both the genomic and functional levels in all five Campylobacter spp. examined in this study, further highlighting the significant role of CmeABC in Campylobacter pathobiology.

Comparative genomics and proteomics of Helicobacter mustelae, an ulcerogenic and carcinogenic gastric pathogen

Background

Helicobacter mustelae causes gastritis, ulcers and gastric cancer in ferrets and other mustelids. H. mustelae remains the only helicobacter other than H. pylori that causes gastric ulceration and cancer in its natural host. To improve understanding of H. mustelae pathogenesis, and the ulcerogenic and carcinogenic potential of helicobacters in general, we sequenced the H. mustelae genome, and identified 425 expressed proteins in the envelope and cytosolic proteome.

Results

The H. mustelae genome lacks orthologs of major H. pylori virulence factors including CagA, VacA, BabA, SabA and OipA. However, it encodes ten autotransporter surface proteins, seven of which were detected in the expressed proteome, and which, except for the Hsr protein, are of unknown function. There are 26 putative outer membrane proteins in H. mustelae, some of which are most similar to the Hof proteins of H. pylori. Although homologs of putative virulence determinants of H. pylori (NapA, plasminogen adhesin, collagenase) and Campylobacter jejuni (CiaB, Peb4a) are present in the H. mustelae genome, it also includes a distinct complement of virulence-related genes including a haemagglutinin/haemolysin protein, and a glycosyl transferase for producing blood group A/B on its lipopolysaccharide. The most highly expressed 264 proteins in the cytosolic proteome included many corresponding proteins from H. pylori, but the rank profile in H. mustelae was distinctive. Of 27 genes shown to be essential for H. pylori colonization of the gerbil, all but three had orthologs in H. mustelae, identifying a shared set of core proteins for gastric persistence.

Conclusions

The determination of the genome sequence and expressed proteome of the ulcerogenic species H mustelae provides a comparative model for H. pylori to investigate bacterial gastric carcinogenesis in mammals, and to suggest ways whereby cag minus H. pylori strains might cause ulceration and cancer.

The genome sequence was deposited in EMBL/GenBank/DDBJ under accession number FN555004.

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.

Never take candy from a stranger: the role of the bacterial glycome in host–pathogen interactions

With the comprehensive study and complete sequencing of the Haemophilus influenzae genome in 1995 came the term ‘genomics’ and the beginning of the ‘omics’ era. Since this time, several analogous fields, such as transcriptomics and proteomics, have emerged. While growth and advancement in these fields have increased understanding of microbial virulence, the study of bacterial glycomes is still in its infancy and little is known concerning their role in host–pathogen interactions. Bacterial glycomics is challenging owing to the diversity of glyco-conjugate molecules, vast array of unusual sugars and limited number of analytical approaches available. However, recent advances in glycomics technologies offer the potential for exploration and characterization of both the structures and functions of components of bacterial glycomes in a systematic manner. Such characterization is a prerequisite for discerning the role of bacterial glycans in the interaction between host defences and bacterial virulence factors.

Functional analysis of the RdxA and RdxB nitroreductases of Campylobacter jejuni reveals that mutations in rdxA confer metronidazole resistance

Campylobacter jejuni is a leading cause of gastroenteritis in humans and a commensal bacterium of the intestinal tracts of many wild and agriculturally significant animals. We identified and characterized a locus, which we annotated as rdxAB, encoding two nitroreductases. RdxA was found to be responsible for sensitivity to metronidazole (Mtz), a common therapeutic agent for another epsilonproteobacterium, Helicobacter pylori. Multiple, independently derived mutations in rdxA but not rdxB resulted in resistance to Mtz (Mtz(r)), suggesting that, unlike the case in H. pylori, Mtz(r) might not be a polygenic trait. Similarly, Mtz(r) C. jejuni was isolated after both in vitro and in vivo growth in the absence of selection that contained frameshift, point, insertion, or deletion mutations within rdxA, possibly revealing genetic variability of this trait in C. jejuni due to spontaneous DNA replication errors occurring during normal growth of the bacterium. Similar to previous findings with H. pylori RdxA, biochemical analysis of C. jejuni RdxA showed strong oxidase activity, with reduction of Mtz occurring only under anaerobic conditions. RdxB showed similar characteristics but at levels lower than those for RdxA. Genetic analysis confirmed that rdxA and rdxB are cotranscribed and induced during in vivo growth in the chick intestinal tract, but an absence of these genes did not strongly impair C. jejuni for commensal colonization. Further studies indicate that rdxA is a convenient locus for complementation of mutants in cis. Our work contributes to the growing knowledge of determinants contributing to susceptibility to Mtz (Mtz(s)) and supports previous observations of the fundamental differences in the activities of nitroreductases from epsilonproteobacteria.

23S rRNA mutation A2074C conferring high-level macrolide resistance and fitness cost in Campylobacter jejuni

To examine the development of macrolide resistance in Campylobacter jejuni and assess the fitness of the macrolide-resistant mutants, two macrolide-susceptible C. jejuni strains, American Type Culture Collection (ATCC) 33291 and H1, from different geographic areas were exposed to tylosin in vitro. Multiple mutant strains were obtained from the selection. Most of the high-level macrolide-resistant strains derived from the selection exhibited the A2074C transversion in all three copies of 23S rRNA and displayed strong stability in the absence of antibiotic selection pressure. The competition experiments demonstrated that the strains containing the A2074C transversion imposed a fitness cost in competition mixtures. In addition, the fitness cost of the mutation was not ameliorated after approximately 500 generations of evolution under laboratory conditions. These findings indicate that the A2074C transversion in C. jejuni is not only correlated with stable and high-level macrolide resistance but also associated with a fitness cost.

23S rRNA gene mutations contributing to macrolide resistance in Campylobacter jejuni and Campylobacter coli

The genetic basis of macrolide resistance in Campylobacter coli (n = 17) and C. jejuni (n = 35) isolates previously subjected to in vivo selective pressure was investigated to determine if the number of copies of 23S rRNA genes with macrolide-associated mutations affects the minimum inhibitory concentration (MIC) of macrolides. Sequence data for domain V of the 23S rRNA gene revealed that two macrolide-resistant C. coli isolates had adenine-->guanine transitions at position 2059 (A2059G, Escherichia coli numbering). One of the two isolates had the A2059G transition in only two of the three gene copies. Among the macrolide-resistant C. jejuni isolates (n = 9), two different point mutations within domain V were observed. Three macrolide-resistant C. jejuni isolates had A2059G transitions. One of these three C. jejuni isolates had the A2059G transition in only two of the three gene copies. Six macrolide-resistant C. jejuni isolates had an adenine-->cytosine transversion at position 2058 (A2058C, E. coli numbering) in all three copies of the 23S rRNA gene. Campylobacter jejuni isolates with the A2058C transversion had higher erythromycin MICs (>256 microg/mL) compared to C. jejuni isolates with A2059G transitions (64-128 microg/mL). In addition, the C. jejuni and C. coli isolates with only two copies of the 23S rRNA gene having A2059G substitutions had lower macrolide MICs compared to isolates with all three copies of the gene mutated. No isolates were observed having only one copy of the 23S rRNA gene with a mutation. Sequence analysis of ribosomal proteins L4 (rplD) and L22 (rplV) indicated that ribosomal protein modifications did not contribute to macrolide resistance among the collection of Campylobacter examined.

Comparative ICE genomics: insights into the evolution of the SXT/R391 family of ICEs

Integrating and conjugative elements (ICEs) are one of the three principal types of self-transmissible mobile genetic elements in bacteria. ICEs, like plasmids, transfer via conjugation; but unlike plasmids and similar to many phages, these elements integrate into and replicate along with the host chromosome. Members of the SXT/R391 family of ICEs have been isolated from several species of gram-negative bacteria, including Vibrio cholerae, the cause of cholera, where they have been important vectors for disseminating genes conferring resistance to antibiotics. Here we developed a plasmid-based system to capture and isolate SXT/R391 ICEs for sequencing. Comparative analyses of the genomes of 13 SXT/R391 ICEs derived from diverse hosts and locations revealed that they contain 52 perfectly syntenic and nearly identical core genes that serve as a scaffold capable of mobilizing an array of variable DNA. Furthermore, selection pressure to maintain ICE mobility appears to have restricted insertions of variable DNA into intergenic sites that do not interrupt core functions. The variable genes confer diverse element-specific phenotypes, such as resistance to antibiotics. Functional analysis of a set of deletion mutants revealed that less than half of the conserved core genes are required for ICE mobility; the functions of most of the dispensable core genes are unknown. Several lines of evidence suggest that there has been extensive recombination between SXT/R391 ICEs, resulting in re-assortment of their respective variable gene content. Furthermore, our analyses suggest that there may be a network of phylogenetic relationships among sequences found in all types of mobile genetic elements.

Differential carbon source utilization by Campylobacter jejuni 11168 in response to growth temperature variation

Campylobacter spp. readily colonize the intestinal tracts of both human and avian species. While most often commensal organisms in birds, campylobacters remain the leading cause of bacterial gastroenteritis in humans. The association of campylobacters with poultry is well established as a primary route for human exposure. The difference in normal core body temperature between chickens (42 degrees C) and humans (37 degrees C) has been suggested to trigger potential colonization or virulence factors and investigators have demonstrated differential gene expression at the two temperatures. Campylobacter spp. exhibit unique nutritional requirements and have been thought to only utilize amino acids and Kreb cycle intermediates as carbon sources for growth. We evaluated the ability of the genome-sequenced strain of Campylobacter jejuni 11168 (GS) to oxidize 190 different substrates as sole carbon sources at 37 degrees C and 42 degrees C using phenotype microarray (PM) technology. Results indicate that the expected amino acids, l-serine, l-aspartic acid, l-asparagine, and l-glutamic acid were utilized in addition to a number of organic acids. In general, oxidation of the substrates was greater at 42 degrees C than at 37 degrees C with a few exceptions. By employing the PM method, we observed a number of potential false-positive reactions for substrates including the triose, dihydroxyacetone; and the pentose sugars, d-xylose, d-ribose, l-lyxose, and d- and l-arabinose. The presence of genes possibly responsible for utilization of pentose sugars is supported by the genomic sequence data, but actual utilization as sole carbon sources for active respiration has not been observed. A better understanding of the metabolic pathways and nutritional requirements of campylobacters could lead to improvements in culture media for detection and isolation of the pathogen and to future intervention methods to reduce human exposure.

Transposon mutagenesis in a hyper-invasive clinical isolate of Campylobacter jejuni reveals a number of genes with potential roles in invasion

Transposon mutagenesis has been applied to a hyper-invasive clinical isolate of Campylobacter jejuni, 01/51. A random transposon mutant library was screened in an in vitro assay of invasion and 26 mutants with a significant reduction in invasion were identified. Given that the invasion potential of C. jejuni is relatively poor compared to other enteric pathogens, the use of a hyper-invasive strain was advantageous as it greatly facilitated the identification of mutants with reduced invasion. The location of the transposon insertion in 23 of these mutants has been determined; all but three of the insertions are in genes also present in the genome-sequenced strain NCTC 11168. Eight of the mutants contain transposon insertions in one region of the genome (approximately 14 kb), which when compared with the genome of NCTC 11168 overlaps with one of the previously reported plasticity regions and is likely to be involved in genomic variation between strains. Further characterization of one of the mutants within this region has identified a gene that might be involved in adhesion to host cells.

Comparison of PCR binary typing (P-BIT), a new approach to epidemiological subtyping of Campylobacter jejuni, with serotyping, pulsed-field gel electrophoresis, and multilocus sequence typing methods

To overcome some of the deficiencies with current molecular typing schema for Campylobacter spp., we developed a prototype PCR binary typing (P-BIT) approach. We investigated the distribution of 68 gene targets in 58 Campylobacter jejuni strains, one Campylobacter lari strain, and two Campylobacter coli strains for this purpose. Gene targets were selected on the basis of distribution in multiple genomes or plasmids, and known or putative status as an epidemicity factor. Strains were examined with Penner serotyping, pulsed-field gel electrophoresis (PFGE; using SmaI and KpnI enzymes), and multilocus sequence typing (MLST) approaches for comparison. P-BIT provided 100% typeability for strains and gave a diversity index of 98.5%, compared with 97.0% for SmaI PFGE, 99.4% for KpnI PFGE, 96.1% for MLST, and 92.8% for serotyping. Numerical analysis of the P-BIT data clearly distinguished strains of the three Campylobacter species examined and correlated somewhat with MLST clonal complex assignations and with previous classifications of "high" and "low" risk. We identified 18 gene targets that conferred the same level of discrimination as the 68 initially examined. We conclude that P-BIT is a useful approach for subtyping, offering advantages of speed, cost, and potential for strain risk ranking unavailable from current molecular typing schema for Campylobacter spp.

Nucleases encoded by the integrated elements CJIE2 and CJIE4 inhibit natural transformation of Campylobacter jejuni

The species Campylobacter jejuni is naturally competent for DNA uptake; nevertheless, nonnaturally transformable strains do exist. For a subset of strains we previously showed that a periplasmic DNase, encoded by dns, inhibits natural transformation in C. jejuni. In the present study, genetic factors coding for DNase activity in the absence of dns were identified. DNA arrays indicated that nonnaturally transformable dns-negative strains contain putative DNA/RNA nonspecific endonucleases encoded by CJE0566 and CJE1441 of strain RM1221. These genes are located on C. jejuni integrated elements 2 and 4. Expression of CJE0566 and CJE1441 from strain RM1221 and a homologous gene from strain 07479 in DNase-negative Escherichia coli and C. jejuni strains indicated that these genes code for DNases. Genetic transfer of the genes to a naturally transformable C. jejuni strain resulted in a decreased efficiency of natural transformation. Modeling suggests that the C. jejuni DNases belong to the Serratia nuclease family. Overall, the data indicate that the acquisition of prophage-encoded DNA/RNA nonspecific endonucleases inhibits the natural transformability of C. jejuni through hydrolysis of DNA.

Identification and characterization of intervening sequences within 23S rRNA genes from more than 200 Campylobacter isolates from seven species including atypical campylobacters

Background

Identification and characterization of intervening sequences (IVSs) within 23S rRNA genes from Campylobacter organisms including atypical campylobacters were carried out using two PCR primer pairs, designed to generate helix 25 and 45 regions.

Results

Only C. sputorum biovar sputorum LMG7975 and fecalis LMG8531, LMG8534 and LMG6728 of a total of 204 Campylobacter isolates (n = 56 C. jejuni; n = 11 C. coli; n = 33 C. fetus; n = 43 C. upsaliensis; n = 30 C. hyointestinalis; n = 4 C. sputorum biovar sputorum; n = 5 C. sputorum biovar fecalis; n = 5 C. sputorum biovar paraureolyticus; n = 10 C. concisus; n = 7 C. curvus) were shown to carry IVSs in helix 25 region. C. sputorum biovar fecalis LMG8531 and LMG8534, interestingly, carried two different kinds of the 23S rRNA genes with and without the IVS, respectively. Consequently, in a total of 265 isolates of 269, including 65 C. lari isolates examined previously, the absence of IVSs was identified in the helix 25 region. In the helix 45 region, all the C. hyointestinalis, C. sputorum and C. concisus isolates were shown not to carry any IVSs. However, the 30 of 56 C. jejuni isolates (54%), 5 of 11 C. coli (45%), 25 of 33 C. fetus (76%), 30 of 43 C. upsaliensis (70%) and 6 of 7 C. curvus (90%) were shown to carry IVSs. In C. jejuni and C. upsaliensis isolates, two different kinds of the 23S rRNA genes were also identified to occur with and without IVSs in the helix 45 region, respectively.

Conclusions

Secondary structure models were also constructed with all the IVSs identified in the present study. In the purified RNA fractions from the isolates which carried the 16S or 23S rRNA genes with the IVSs, no 16S or 23S rRNA was evident, respectively.

A genomic island defines subspecies-specific virulence features of the host-adapted pathogen Campylobacter fetus subsp. venerealis

The pathogen Campylobacter fetus comprises two subspecies, C. fetus subsp. fetus and C. fetus subsp. venerealis. Although these taxa are highly related on the genome level, they are adapted to distinct hosts and tissues. C. fetus subsp. fetus infects a diversity of hosts, including humans, and colonizes the gastrointestinal tract. In contrast, C. fetus subsp. venerealis is largely restricted to the bovine genital tract, causing epidemic abortion in these animals. In light of their close genetic relatedness, the specific niche preferences make the C. fetus subspecies an ideal model system to investigate the molecular basis of host adaptation. In this study, a subtractive-hybridization approach was applied to the genomes of the subspecies to identify different genes potentially underlying this specificity. The comparison revealed a genomic island uniquely present in C. fetus subsp. venerealis that harbors several genes indicative of horizontal transfer and that encodes the core components necessary for bacterial type IV secretion. Macromolecular transporters of this type deliver effector molecules to host cells, thereby contributing to virulence in various pathogens. Mutational inactivation of the putative secretion system confirmed its involvement in the pathogenicity of C. fetus subsp. venerealis.

Binary genomotyping using lipooligosaccharide biosynthesis genes distinguishes between Campylobacter jejuni isolates within poultry-associated multilocus sequence types

Campylobacter jejuni is a leading cause of human bacterial gastroenteritis throughout the industrialized world. We investigated whether or not differences in gene complement at the lipooligosaccharide (LOS) biosynthesis locus can identify epidemiologically useful binary genomotypes in 87 C. jejuni isolates from poultry-associated multilocus sequence types (STs) collected during the course of a sentinel surveillance study. Using a PCR-based approach, we correlated assignment of both isolate LOS locus class and binary genomotype with ST. We found that isolates within STs 45, 190, 354 and 474 displayed mosaicism in gene complement at the intra-ST level. For example, based upon their binary genomotypes, we assigned individual ST-45 isolates from human clinical cases as probably originating from either a poultry or wild-bird source. However, intra-ST mosaicism in gene complement was observed alongside broader patterns of congruence in LOS locus class and gene complement that distinguished between isolates from different STs.

Analysis of the pan genome of Campylobacter jejuni isolates recovered from poultry by pulsed-field gel electrophoresis, multilocus sequence typing (MLST), and repetitive sequence polymerase chain reaction (rep-PCR) reveals different discriminatory capabilities

Campylobacter jejuni is one of the leading bacterial causes of food-borne illness in the USA. Molecular typing methods are often used in food safety for identifying sources of infection and pathways of transmission. Moreover, the identification of genetically related isolates (i.e., clades) may facilitate the development of intervention strategies for control and prevention of food-borne diseases. We analyzed the pan genome (i.e., core and variable genes) of 63 C. jejuni isolates recovered from chickens raised in conventional, organic, and free-range poultry flocks to gain insight into the genetic diversity of C. jejuni isolates recovered from different environments. We assessed the discriminatory power of three genotyping methods [i.e., pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and repetitive extragenic palindromic polymerase chain reaction (rep-PCR)]. The rep-PCR fingerprint was generated by determining the presence of repetitive sequences that are interspersed throughout the genome via repetitive extragenic palindromic PCR, enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR), and BOX element PCR (BOX-PCR) and combining the data to form a composite fingerprint. The genetic fingerprints were subjected to computer-assisted pattern analysis. Comparison of the three genotypic methods revealed that repREB-PCR showed greater discriminatory power than PFGE and MLST. ERIC-PCR and BOX-PCR yielded the highest number of PCR products and greatest reproducibility. Regardless of the genotyping method, C. jejuni isolates recovered from chickens reared in conventional, organic, and free-range environments all exhibit a high level of genotypic diversity.

Importance of polyphosphate kinase 1 for Campylobacter jejuni viable-but-nonculturable cell formation, natural transformation, and antimicrobial resistance

Campylobacter jejuni, a gram-negative, microaerophilic bacterium, is a predominant cause of bacterial gastroenteritis in humans. Although considered fragile and fastidious and lacking many classical stress response mechanisms, C. jejuni exhibits a remarkable capacity for survival and adaptation, successfully infecting humans and persisting in the environment. Consequently, understanding the physiological and genetic properties that allow C. jejuni to survive and adapt to various stress conditions is crucial for therapeutic interventions. Of importance is polyphosphate (poly-P) kinase 1 (PPK1), which is a key enzyme mediating the synthesis of poly-P, an essential molecule for survival, mediating stress responses, host colonization, and virulence in many bacteria. Therefore, we investigated the role of PPK1 in C. jejuni pathogenesis, stress survival, and adaptation. Our findings demonstrate that a C. jejuni Deltappk1 mutant was deficient in poly-P accumulation, which was associated with a decreased ability to form viable-but-nonculturable cells under acid stress. The Deltappk1 mutant also showed a decreased frequency of natural transformation and an increased susceptibility to various antimicrobials. Furthermore, the Deltappk1 mutant was characterized by a dose-dependent deficiency in chicken colonization. Complementation of the Deltappk1 mutant with the wild-type copy of ppk1 restored the deficient phenotypes to levels similar to those of the wild type. Our results suggest that poly-P plays an important role in stress survival and adaptation and might contribute to genome plasticity and the spread and development of antimicrobial resistance in C. jejuni. These findings highlight the potential of PPK1 as a novel target for therapeutic interventions.

Pumping iron: mechanisms for iron uptake by Campylobacter

Campylobacter requires iron for successful colonization of the host. In the last 7 years, a wealth of data has been generated allowing detailed molecular characterization of Campylobacter iron-uptake systems. Several exogenous siderophores have been identified as sources of ferric iron for Campylobacter. Ferri-enterochelin uptake requires both the outer-membrane receptor protein CfrA and the inner-membrane ABC transporter system CeuBCDE. Ferrichrome has been shown to support growth of some Campylobacter jejuni strains and the presence of homologues of Escherichia coli fhuABD genes was proposed; the Cj1658–Cj1663 system appears to be involved in the uptake of ferri-rhodotorulic acid. In addition to siderophores, the importance of host iron sources was highlighted by recent studies demonstrating that C. jejuni can exploit haem compounds and the transferrins using ChuABCDZ and Cj0173c–Cj0178, respectively. An additional putative receptor, Cj0444, present in some, but not all, strains has not yet been characterized. Following diffusion through the outer membrane, inner-membrane transport of ferrous iron can occur via the FeoB protein. While it may be assumed that all systems are not essential, there is growing evidence supporting the need for multiple iron-uptake systems for successful host colonization by Campylobacter. In light of this, comparative molecular characterization of iron systems in all Campylobacter strains is necessary to gain further insight into the pathogenesis of members of this genus.

Characterization of a Campylobacter jejuni VirK protein homolog as a novel virulence determinant

Campylobacter jejuni is a leading cause of food-borne illness in the United States. Despite significant recent advances, its mechanisms of pathogenesis are poorly understood. A unique feature of this pathogen is that, with some exceptions, it lacks homologs of known virulence factors from other pathogens. Through a genetic screen, we have identified a C. jejuni homolog of the VirK family of virulence factors, which is essential for antimicrobial peptide resistance and mouse virulence.

Demonstration of the absence of intervening sequences within 23S rRNA genes from Campylobacter lari

Cloning, sequencing and characterization of nearly full-length 23S rRNA genes in 12 urease-positive thermophilic Campylobacter (UPTC) isolates were carried out using two novel PCR primer pairs. Nucleotide sequences of the 23S rRNA genes from the 12 isolates were first shown not to carry any intervening sequences (IVSs) in both the 25 and 45 helix regions. Then, two PCR primer sets were designed in silico for amplification of the helix 25 and 45 regions within 23S rRNA gene sequences from Campylobacter lari. No IVSs were identified within the 23S rRNA genes among a total of 53 isolates of C. lari, following PCR amplification, TA cloning and sequencing procedures. Intact 23S rRNA was identified in all 65 C. lari isolates, resulting in no production of the fragmented 23S rRNA. These data suggest that C. lari may not have any opportunity to interact with any other source of IVSs until now, or has been unable to integrate IVSs into their own genomes.

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

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

First multi-locus sequence typing scheme for Arcobacter spp

Background

Arcobacter spp. are a common contaminant of food and water, and some species, primarily A. butzleri and A. cryaerophilus, have been isolated increasingly from human diarrheal stool samples. Here, we describe the first Arcobacter multilocus sequence typing (MLST) method for A. butzleri, A. cryaerophilus, A. skirrowii, A. cibarius and A. thereius.

Results

A sample set of 374 arcobacters, including 275 A. butzleri, 72 A. cryaerophilus, 15 A. skirrowii and 8 A. cibarius isolates from a wide variety of geographic locations and sources, was typed in this study. Additionally, this sample set contained four strains representing a new Arcobacter species, A. thereius. The seven loci used in the four-species Arcobacter MLST method are the same as those employed previously in C. jejuni, C. coli, C. helveticus and C. fetus (i.e. aspA, atpA(uncA), glnA, gltA, glyA, pgm and tkt). A large number of alleles were identified at each locus with the majority of isolates containing a unique sequence type. All Arcobacter isolates typed in this study contain two glyA genes, one linked to lysS (glyA1) and the other linked to ada (glyA2). glyA1 was incorporated into the Arcobacter MLST method while glyA2 was not because it did not increase substantially the level of discrimination.

Conclusion

No association of MLST alleles or sequence types with host or geographical source was observed with this sample set. Nevertheless, the large number of identified alleles and sequence types indicate that this MLST method will prove useful in both Arcobacter strain discrimination and in epidemiological studies of sporadic Arcobacter-related gastroenteritis. A new Arcobacter MLST database was created http://pubmlst.org/arcobacter/; allele and ST data generated in this study were deposited in this database and are available online.

Structural analysis of the full-length gene encoding a fibronectin-binding-like protein (CadF) and its adjacent genetic loci within Campylobacter lari

Background

The combined sequences encoding a partial and putative rpsI open reading frame (ORF), non-coding (NC) region, a putative ORF for the Campylobacter adhesin to fibronectin-like protein (cadF), a putative Cla_0387 ORF, NC region and a partial and putative Cla_0388 ORF, were identified in 16 Campylobacter lari isolates, using two novel degenerate primer pairs. Probable consensus sequence at the -35 and -10 regions were identified in all C. lari isolates, as a promoter.

Results

Thus, cadF (-like) gene is highly conserved among C. lari organisms. Transcription of the cadF (-like) gene in C. lari cells in vivo was also confirmed and the transcription initiation site was determined. A peptidoglycan-associating alpha-helical motif in the C-terminal regions of some bacterial cell-surface proteins was completely conserved amongst the putative cadF (-like) ORFs from the C. lari isolates.

Conclusion

The putative cadF (-like) ORFs from all C. lari isolates were nine amino acid larger than those from C. jejuni, and showed amino acid residues 137 -140 of FALG (50% identity), instead of the FRLS residues of the maximal fibronectin-binding activity site demonstrated within C. jejuni CadF. A neighbor joining tree constructed based on cadF (-like) gene sequence information formed a major cluster consisting of C. lari isolates, separating from the other three thermophilic campylobacters.