Homonucleotide stretches in chromosomal DNA of Campylobacter jejuni display high frequency polymorphism as detected by direct PCR analysis

How does feedback from phage infections influence the evolution of phase variation in Campylobacter?

Campylobacter jejuni (C. jejuni) causes gastroenteritis following the consumption of contaminated poultry meat, resulting in a large health and economic burden worldwide. Phage therapy is a promising technique for eradicating C. jejuni from poultry flocks and chicken carcasses. However, C. jejuni can resist infections by some phages through stochastic, phase-variable ON/OFF switching of the phage receptors mediated by simple sequence repeats (SSR). While selection strength and exposure time influence the evolution of SSR-mediated phase variation (PV), phages offer a more complex evolutionary environment as phage replication depends on having a permissive host organism. Here, we build and explore several continuous culture bacteria-phage computational models, each analysing different phase-variable scenarios calibrated to the experimental SSR rates of C. jejuni loci and replication parameters for the F336 phage. We simulate the evolution of PV rates via the adaptive dynamics framework for varying levels of selective pressures that act on the phage-resistant state. Our results indicate that growth reducing counter-selection on a single PV locus results in the stable maintenance of the phage, while compensatory selection between bacterial states affects the evolutionary stable mutation rates (i.e. very high and very low mutation rates are evolutionarily disadvantageous), whereas, in the absence of either selective pressure the evolution of PV rates results in mutation rates below the basal values. Contrastingly, a biologically-relevant model with two phase-variable loci resulted in phage extinction and locking of the bacteria into a phage-resistant state suggesting that another counter-selective pressure is required, instance, the use of a distinct phage whose receptor is an F336-phage-resistant state. We conclude that a delicate balance between counter-selection and phage-attack can result in both the evolution of phase-variable phage receptors and persistence of PV-receptor-specific phage.

Globally rising rates of antibiotic resistance have renewed interest in phage therapy. Bacteriophages (phages) act on bacteria to select for resistance mechanisms such as loss of phage receptors by phase variation (PV). Phase-variable genes mediate rapid adaption by stochastic switching of gene expression. Campylobacter jejuni is a common commensal of birds but also causes serious gastrointestinal infections in humans. Optimisation of phage therapy against C. jejuni requires an in-depth understanding of how PV has evolved and mediates phage resistance. Here, we use a detailed continuous culture model for nutrient-limited bacteria-phage interactions, with PV rates calibrated to match the experimental observations for C.jejuni and phage F336. Evolution within a model accounting for two phase-variable loci closely matches the experimental results when growth reducing counter-selection is imposed on all phage-resistant states, but, not when restricted to the particular states associated with resistance to immune effectors. Our results emphasize that delicate balancing of selective pressures, imposed by single and multiple distinct phages, are necessary for effective use of phage therapy against C. jejuni.

Comparison of relative expressions of genes involved in iron acquisition and regulation in fluoroquinolone-resistant and wild-type Campylobacter jejuni

Campylobacteriosis caused by C. jejuni is a serious yet common foodborne disease in the U.S. The prevalence of fluoroquinolone-resistant C. jejuni from poultry has continued to increase despite the withdrawal of fluoroquinolone use in the U.S. poultry industry in 2005. To date, no clear selective pressures that explain this effect have been documented. In this study, we investigated limited bioavailability of iron in poultry and enhanced iron uptake and regulation as potential indirect selective pressures conferring fitness advantages in fluoroquinolone-resistant C. jejuni compared to its susceptible wild-type counterpart. Five fluoroquinolone-susceptible C. jejuni isolates were selected from litter collected from commercial broiler farms. Using antibiotic selection, five fluoroquinolone-resistant strains were created. Relative expressions of six genes involved in iron acquisition and regulation were compared between the resistant and susceptible strains using RT-qPCR under normal and iron-limiting conditions. High variability in the relative gene expressions was observed among the strains, with only one resistant strain showing the consistent upregulation of the measured genes compared to the matching susceptible wild-type. Our results suggest that the hypothesis tested in the study may not be an adequate explanation of the molecular mechanism behind the enhanced fitness of fluoroquinolone-resistant C. jejuni compared to susceptible C. jejuni. This study highlights the need for a better understanding of the complex ecology and dynamics of fluoroquinolone resistance in C. jejuni in poultry environment and warrants an examination of fluoroquinolone-resistant C. jejuni strains recovered from the natural broiler chicken environment.

Pathogenic potential and genotypic diversity of Campylobacter jejuni: a neglected food-borne pathogen in Brazil

Purpose and methodology.Campylobacter jejuni is a major zoonotic pathogen that causes food-borne gastroenteritis worldwide. However, there are only a few studies available that have molecularly characterized C. jejuni strains isolated in Brazil. The aim of this study was to genotype 111 C. jejuni strains isolated from sick humans (43), monkey faeces (19), chicken faeces (14), chicken meat (33) and sewage (2) between 1996 and 2016 in Brazil using flaA-SVR (short variable region) sequencing and PFGE. Furthermore, the presence of 16 virulence genes was analysed by PCR.

RESULTS

Using PFGE and flaA-SVR sequencing, the 111 C. jejuni strains studied were grouped into three and two clusters, respectively, and some strains of different origin presented a similarity of ≥80 %. In total, 35 flaA-SVR alleles were detected. Alleles gt45, gt49 and gt57 were the most prevalent, in contrast with those frequently described in the PubMLST database. All 111 C. jejuni strains contained the genes flaA, flhA, cadF, docA, cdtA, cdtB, cdtC, iamA, ciaB, sodB, dnaJ, pldA, racR and csrA. The wlaN gene was detected in 11 strains (9.9 %), and the virB11 in just one strain (0.9 %).

CONCLUSIONS

In conclusion, the pathogenic potential of the C. jejuni strains studied was highlighted by the high frequency of the majority of the virulence genes searched. The flaA-SVR sequencing and PFGE results showed that some of the strains studied presented a high genotypic similarity, suggesting potential for transmission between animal sources and humans in this country. Altogether, the results characterize further C. jejuni isolates from Brazil, an important producer and exporter of chicken meat.

Antimicrobial Resistance and Virulence-Associated Genes of Campylobacter spp. Isolated from Raw Milk, Fish, Poultry, and Red Meat

This study was designed and conducted to evaluate the frequency, antimicrobial resistance, and presence of six virulence-associated genes among thermophilic Campylobacters isolated from raw milk, poultry (chicken, turkey, and duck), fish, cattle, and sheep meat. Out of 590 samples, which were recovered from different origins, 141 (23.9%) samples were positive for Campylobacters. Campylobacter spp. was isolated in 40.8% (106/260), 14% (28/200), and 8.7% (7/80) of poultry meat, red meat, and milk samples, respectively. Antimicrobial susceptibility test indicated a high frequency of resistance to ciprofloxacin, tetracycline, and nalidixic acid among the isolates. Furthermore, prevalence of waaC, ciaB, and pldA genes were 91.7%, 86.7%, and 80.8%, respectively; and, none of the isolates harbored both wlaN and cgtB genes, simultaneously. Moreover, there was a weak correlation between antibiotics resistance and presence of the pathogen genes. However, the existence of Campylobacter spp. isolates in food animal products, with high resistance to antibiotics and several virulence gene possessions, is alarming and increases the attention to the widespread use of antibiotics.

Identification and initial characterisation of a protein involved in Campylobacter jejuni cell shape

Campylobacter jejuni is the leading cause of bacterial food borne illness. While helical cell shape is considered important for C. jejuni pathogenesis, this bacterium is capable of adopting other morphologies. To better understand how helical-shaped C. jejuni maintain their shape and thus any associated colonisation, pathogenicity or other advantage, it is first important to identify the genes and proteins involved. So far, two peptidoglycan modifying enzymes Pgp1 and Pgp2 have been shown to be required for C. jejuni helical cell shape. We performed a visual screen of ∼2000 transposon mutants of C. jejuni for cell shape mutants. Whole genome sequence data of the mutants with altered cell shape, directed mutants, wild type stocks and isolated helical and rod-shaped ‘wild type’ C. jejuni, identified a number of different mutations in pgp1 and pgp2, which result in a change in helical to rod bacterial cell shape. We also identified an isolate with a loss of curvature. In this study, we have identified the genomic change in this isolate, and found that targeted deletion of the gene with the change resulted in bacteria with loss of curvature. Helical cell shape was restored by supplying the gene in trans. We examined the effect of loss of the gene on bacterial motility, adhesion and invasion of tissue culture cells and chicken colonisation, as well as the effect on the muropeptide profile of the peptidoglycan sacculus. Our work identifies another factor involved in helical cell shape.

•

A C. jejuni isolate with a loss of curvature was identified.

•

A targeted gene deletion of CJJ81176_1105 in 81–176 and CJM1_1064 in M1 were created.

•

Defined gene deletion mutants of CJJ81176_1105 and CJM1_1064 alter C. jejuni motility and interaction with Caco-2 cells.

•

Defined gene deletion mutant of CJM1_1064 does not alter C. jejuni colonisation of chickens.

Genomic variations leading to alterations in cell morphology of Campylobacter spp

Campylobacter jejuni, the most common cause of bacterial diarrhoeal disease, is normally helical. However, it can also adopt straight rod, elongated helical and coccoid forms. Studying how helical morphology is generated, and how it switches between its different forms, is an important objective for understanding this pathogen. Here, we aimed to determine the genetic factors involved in generating the helical shape of Campylobacter. A C. jejuni transposon (Tn) mutant library was screened for non-helical mutants with inconsistent results. Whole genome sequence variation and morphological trends within this Tn library, and in various C. jejuni wild type strains, were compared and correlated to detect genomic elements associated with helical and rod morphologies. All rod-shaped C. jejuni Tn mutants and all rod-shaped laboratory, clinical and environmental C. jejuni and Campylobacter coli contained genetic changes within the pgp1 or pgp2 genes, which encode peptidoglycan modifying enzymes. We therefore confirm the importance of Pgp1 and Pgp2 in the maintenance of helical shape and extended this to a wide range of C. jejuni and C. coli isolates. Genome sequence analysis revealed variation in the sequence and length of homopolymeric tracts found within these genes, providing a potential mechanism of phase variation of cell shape.

Antibiotic susceptibility profiling and virulence potential of Campylobacter jejuni isolates from different sources in Pakistan

OBJECTIVE

To determine antibiotic resistance patterns and virulence potential of Campylobacter jejuni (C. jejuni) isolates from clinical human diarrheal infections, cattle and healthy broilers.

METHODS

Antibiotic sensitivity patterns of C. jejuni isolates were determined by Kirby Bauer Disc Diffusion assay. These isolates were then subjected to virulence profiling for the detection of mapA (membrane-associated protein), cadF (fibronectin binding protein), wlaN (beta-l,3-galactosyltransferase) and neuAB (sialic acid biosynthesis gene). Further C. jejuni isolates were grouped by random amplification of polymorphic DNA (RAPD) profiling.

RESULTS

A total of 436 samples from poultry (n=88), cattle (n=216) and humans (n=132) from different locations were collected. Results revealed percentage of C. jejuni isolates were 35.2% (31/88), 25.0% (54/216) and 11.3% (15/132) among poultry, cattle and clinical human samples respectively. Antibiotic susceptibility results showed that similar resistance patterns to cephalothin was ie. 87.0%, 87.1% and 89%among humans, poultry and cattle respectively, followed by sulfamethoxazole+trimethoprim 40.0%, 38.7% and 31.0% in humans, poultry and cattle and Ampicillin 40%, 32% and 20% in humans, poultry and cattle respectively. Beta-lactamase activity was detected in 40.00% humans, 20.37% cattle and 32.25% in poultry C. jejuni isolates. CadF and mapA were present in all poultry, cattle and human C. jejuni isolates, wlaN was not detected in any isolate and neuAB was found in 9/31 (36%) poultry isolates. RAPD profiling results suggested high diversity of C. jejuni isolates.

CONCLUSIONS

Detection of multidrug resistant C. jejuni strains from poultry and cattle is alarming as they can be potential hazard to humans. Moreover, predominant association of virulence factors, cadF and mapA (100% each) in C. jejuni isolates from all sources and neuAB (36%) with poultry isolates suggest the potential source of transmission of diverse types of C. jejuni to humans.

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.

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.

Prediction of ligand binding site by insilico approach in cold resistant protein isolated from cold resistant mutant of Pseudomonas fluorescens

Cold shock proteins perform vital functions, such as mRNA masking, coupling of transcription to translation and developmental timing and regulation, which aids in survival of microbes in cold stress. Pseudomonas fluorescens is an ecologically important bacterium which helps in plant growth promotion. Since the cold tolerant mutant of the bacterium is able to grow at the temperature ranges from 30 to 4°C, it is of interest to study the process of its survival in the extreme temperatures. Therefore, this study is focused on the three dimensional structure and molecular modeling of cold resistant protein (CRP) from P. fluorescens to predict its molecular mechanism. Investigating the structure of CRP confirmed the presence of a conserved domain characteristic of the cold shock domain (CSD) family and a single nucleotide binding domain. When 3D structure of CRP was compared with the existing cold shock proteins, major deviations were found in the loop regions connecting the β2-β3, β3-β4 and β4-β5 sheets. Docking studies showed that CRP forms a significant clamp like structure at the substrate binding cleft which stabilizes the ligand. Therefore, it can be concluded that CRP has a strong affinity for the poly thymidine (poly T) stretch and can be considered a candidate for transcription regulation.

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.

Deletion of one nucleotide within the homonucleotide tract present in the hsdS gene alters the DNA sequence specificity of type I restriction-modification system NgoAV

As a result of a frameshift mutation, the hsdS locus of the NgoAV type IC restriction and modification (RM) system comprises two genes, hsdS(NgoAV1) and hsdS(NgoAV2). The specificity subunit, HsdS(NgoAV), the product of the hsdS(NgoAV1) gene, is a naturally truncated form of an archetypal specificity subunit (208 N-terminal amino acids instead of 410). The presence of a homonucleotide tract of seven guanines (poly[G]) at the 3' end of the hsdS(NgoAV1) gene makes the NgoAV system a strong candidate for phase variation, i.e., stochastic addition or reduction in the guanine number. We have constructed mutants with 6 guanines instead of 7 and demonstrated that the deletion of a single nucleotide within the 3' end of the hsdS(NgoAV1) gene restored the fusion between the hsdS(NgoAV1) and hsdS(NgoAV2) genes. We have demonstrated that such a contraction of the homonucleotide tract may occur in vivo: in a Neisseria gonorrhoeae population, a minor subpopulation of cells appeared to have only 6 guanines at the 3' end of the hsdS(NgoAV1) gene. Escherichia coli cells carrying the fused gene and expressing the NgoAVΔ RM system were able to restrict λ phage at a level comparable to that for the wild-type NgoAV system. NgoAV recognizes the quasipalindromic interrupted sequence 5'-GCA(N(8))TGC-3' and methylates both strands. NgoAVΔ recognizes DNA sequences 5'-GCA(N(7))GTCA-3' and 5'-GCA(N(7))CTCA-3', although the latter sequence is methylated only on the complementary strand within the 5'-CTCA-3' region of the second recognition target sequence.

Following an imaginary Campylobacter population from farm to fork and beyond: a bacterial perspective

It has been known for decades that poultry meat is the most common single source for campylobacteriosis, yet the problem has not been solved. This review identifies some of the reasons why our attempts to reduce the incidence of this pathogen have largely failed. Based on the literature, the events a virtual population of Campylobacter may encounter, from growing in the gut of a broiler to eventually infecting humans and causing disease, are reviewed. Most steps in the farm-to-fork process are well studied, though there are gaps in our knowledge about survival and spread of Campylobacter populations before they enter the farm. Key events in the farm-to-fork chain that are suitable targets for prevention and control, to reduce food-borne campylobacteriosis, are indicated. Novel insights into the pathogenic mechanism responsible for disease in humans are summarized, which hypothesize that an overactive immune response is the reason for the typical inflammatory diarrhoea. A role of genetic microheterogeneity within a clonal population in this chain of events is being proposed here. The human host is not necessary for the survival of the bacterial species, nor have these bacteria specifically evolved to cause disease in that host. More likely, the species evolved for a commensal life in birds, and human disease can be considered as collateral damage owing to an unfortunate host-microbe interaction. The indirect environmental burden that results from poultry production should not be ignored as it may pose a diffuse, but possibly significant risk factor for disease.

Standing genetic variation in contingency loci drives the rapid adaptation of Campylobacter jejuni to a novel host

The genome of the food-borne pathogen Campylobacter jejuni contains multiple highly mutable sites, or contingency loci. It has been suggested that standing variation at these loci is a mechanism for rapid adaptation to a novel environment, but this phenomenon has not been shown experimentally. In previous work we showed that the virulence of C. jejuni NCTC11168 increased after serial passage through a C57BL/6 IL-10^-/- mouse model of campylobacteriosis. Here we sought to determine the genetic basis of this adaptation during passage. Re-sequencing of the 1.64Mb genome to 200-500X coverage allowed us to define variation in 23 contingency loci to an unprecedented depth both before and after in vivo adaptation. Mutations in the mouse-adapted C. jejuni were largely restricted to the homopolymeric tracts of thirteen contingency loci. These changes cause significant alterations in open reading frames of genes in surface structure biosynthesis loci and in genes with only putative functions. Several loci with open reading frame changes also had altered transcript abundance. The increase in specific phases of contingency loci during in vivo passage of C. jejuni, coupled with the observed virulence increase and the lack of other types of genetic changes, is the first experimental evidence that these variable regions play a significant role in C. jejuni adaptation and virulence in a novel host.

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.

Simple sequence repeats and genome plasticity in Streptococcus agalactiae

Simple sequence repeats (SSRs) and their role in phase variation have been extensively studied in Gram-negative organisms, where they have been associated with antigenic variation and other adaptation strategies. In this study, we apply comparative genomics in order to find evidence of slipped-strand mispairing in the human Gram-positive pathogen Streptococcus agalactiae. In two consecutive screenings, 2,233 (650 + 1,583) SSRs were identified in our reference genome 2603V/R, and these loci were examined in seven other S. agalactiae genomes. A total of 56 SSR loci were found to exhibit variation, where gain or loss of repeat units was observed in at least one other genome, resulting in aberrant genotypes. Homopolymeric adenine tracts predominated among the repeats that varied. Positional analysis revealed that long polyadenine tracts were overrepresented in the 5' ends of open reading frames (ORFs) and underrepresented in the 3' ends. Repeat clustering in ORFs was also examined, and the highest degree of clustering was observed for a capsule biosynthesis gene and a pilus sortase. A statistical analysis of observed over expected ratios suggested a selective pressure against long homopolymeric tracts. Altered phenotypes were verified for three genes encoding surface-attached proteins, in which frameshifts or fusions led to truncation of proteins and/or affected surface localization through loss or gain of the cell wall sorting signal. The data suggest that SSRs contributes to genome plasticity in S. agalactiae but that the bet-hedging strategy is different from Gram-negative organisms.

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.

Competing isogenic Campylobacter strains exhibit variable population structures in vivo

Consumption of poultry contaminated with Campylobacter jejuni is a risk factor for human gastrointestinal disease. The rational development of control strategies for Campylobacter within chickens requires an understanding of the colonization process at the molecular and population levels, both within and between hosts. Experiments employing competing strains of Campylobacter have been used to investigate colonization. Implicit in these studies is the assumption that the behavior of competing strains is reproducible between experiments. Variability in the recovery of mutants from the chicken gastrointestinal tract during signature-tagged mutagenesis studies demonstrated that this is not always the case. To further investigate this phenomenon in the absence of confounding factors due to phenotypic differences between mutants, we constructed individually identifiable wild-type isogenic tagged strains (WITS) that have indistinguishable phenotypes in pure culture. By using mixtures of WITS, it is possible to monitor the relative amounts of subpopulations of essentially wild-type bacteria. Using a 2-week-old chicken model of colonization, we observed unpredictable variations in population structure both within and between experiments, even in the simplest case of two competing strains. This variation occurred both when birds were simultaneously infected with two WITS and when birds inoculated with different WITS were cohoused. We present evidence for founder effects during initial colonization with subsequent bird-to-bird transmission. We suggest that these and phenotypic variation contribute to the observed variability. These factors render simple models of colonization which do not take them into account inappropriate for Campylobacter and impact the planning and interpretation of competition experiments using this organism.

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.

Genetic instability is associated with changes in the colonization potential of Campylobacter jejuni in the avian intestine

AIMS

A panel of pulsed field gel electrophoresis (PFGE) type variants of Campylobacter jejuni, previously identified as of clonal origin, were investigated to determine whether genomic instability could be observed during competitive growth.

METHODS AND RESULTS

Upon recovery from frozen storage, some variants had undergone alterations in PFGE profiles, but subsequent culture produced constant genotypes. Individual variants did not display differences in colonization potential when tested in orally challenged 1-day-old chickens. However, competitive colonization using mixtures of two or three PFGE types generally resulted, by 4 weeks postchallenge, in one predominant PFGE type in all birds. For some variant mixtures, a minor population of novel PFGE types was detected in individual birds. The creation of new variants appeared to be dependent on the extent of competition and of the individual host. Genomic rearrangements most likely explain this increase in genetic diversity, apparently without the involvement of natural transformation or plasmid acquisition. In vitro cultivation of mixed inoculations were again selected for particular variants; but genetic diversity was not generated, suggesting that the selection pressures in vitro differed from those active in vivo.

CONCLUSION

These observations support the hypothesis that by generating genetic diversity, C. jejuni can improve its phenotypic fitness to survive and colonize subsequent hosts.

SIGNIFICANCE AND IMPACT OF THE STUDY

The consequences of such observations for the development of campylobacter control strategies for poultry may be substantial.

Simple sequence repeats in prokaryotic genomes

Simple sequence repeats (SSRs) in DNA sequences are composed of tandem iterations of short oligonucleotides and may have functional and/or structural properties that distinguish them from general DNA sequences. They are variable in length because of slip-strand mutations and may also affect local structure of the DNA molecule or the encoded proteins. Long SSRs (LSSRs) are common in eukaryotes but rare in most prokaryotes. In pathogens, SSRs can enhance antigenic variance of the pathogen population in a strategy that counteracts the host immune response. We analyze representations of SSRs in >300 prokaryotic genomes and report significant differences among different prokaryotes as well as among different types of SSRs. LSSRs composed of short oligonucleotides (1-4 bp length, designated LSSR(1-4)) are often found in host-adapted pathogens with reduced genomes that are not known to readily survive in a natural environment outside the host. In contrast, LSSRs composed of longer oligonucleotides (5-11 bp length, designated LSSR(5-11)) are found mostly in nonpathogens and opportunistic pathogens with large genomes. Comparisons among SSRs of different lengths suggest that LSSR(1-4) are likely maintained by selection. This is consistent with the established role of some LSSR(1-4) in enhancing antigenic variance. By contrast, abundance of LSSR(5-11) in some genomes may reflect the SSRs' general tendency to expand rather than their specific role in the organisms' physiology. Differences among genomes in terms of SSR representations and their possible interpretations are discussed.

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.

Campylobacter in poultry: filling an ecological niche

Epidemiological studies indicate that Campylobacter species may be responsible for the majority of cases of sporadic gastroenteritis in humans. These studies also suggest that poultry may be one of the most common sources of the bacteria for humans. Campylobacter and related genera in the family Campylobacteraceae are oral and intestinal commensals of vertebrates and some nonvertebrates, a characteristic that complicates rational approaches to controlling Campylobacter contamination of poultry. This review will discuss the phylogeny, genomics, and physiology of campylobacters with the intention of revealing how these organisms have evolved to fill their intestinal ecological niche in poultry and how their physiology must be understood in order to enact effective control strategies.

Analysis of distribution indicates diverse functions of simple sequence repeats in Mycoplasma genomes

Simple sequence repeats (SSRs) composed of extensive tandem iterations of a single nucleotide or a short oligonucleotide are rare in most bacterial genomes, but they are common among Mycoplasma. Some of these repeats act as contingency loci in association with families of surface antigens. By contraction or expansion during replication, these SSRs increase genetic variance of the population and facilitate avoidance of the immune response of the host. Occurrence and distribution of SSRs are analyzed in complete genomes of 11 Mycoplasma and 3 related Mollicutes in order to gain insights into functional and evolutionary diversity of the SSRs in Mycoplasma. The results revealed an unexpected variety of SSRs with respect to their distribution and composition and suggest that it is unlikely that all SSRs function as contingency loci or recombination hot spots. Various types of SSRs are most abundant in Mycoplasma hyopneumoniae, whereas Mycoplasma penetrans, Mycoplasma mobile, and Mycoplasma synoviae do not contain unusually long SSRs. Mycoplasma hyopneumoniae and Mycoplasma pulmonis feature abundant short adenine and thymine runs periodically spaced at 11 and 12 bp, respectively, which likely affect the supercoiling propensities of the DNA molecule. Physiological roles of long adenine and thymine runs in M. hyopneumoniae appear independent of location upstream or downstream of genes, unlike contingency loci that are typically located in protein-coding regions or upstream regulatory regions. Comparisons among 3 M. hyopneumoniae strains suggest that the adenine and thymine runs are rarely involved in genome rearrangements. The results indicate that the SSRs in the Mycoplasma genomes play diverse roles, including modulating gene expression as contingency loci, facilitating genome rearrangements via recombination, affecting protein structure and possibly protein-protein interactions, and contributing to the organization of the DNA molecule in the cell.

PCR detection of virulence-associated genes in Campylobacter jejuni strains with differential ability to invade Caco-2 cells and to colonize the chick gut

In this study, the presence of 20 putative virulence genes was examined in 11 Campylobacter jejuni isolates with different colonization and invasion abilities as determined in a chick colonization model and on Caco-2 cells, respectively. The majority of the genes were detected in all strains. Among them, there were genes of the flagellar secretion apparatus like flhA, flhB, flgB, flgE2, the flagellin genes flaA and flaB, invasion-associated genes like ciaB and iamA, the cytotoxin genes cdtA-C, the adhesion related gene cadF, and some genes involved in the colonization process (docA, docB). The plasmid gene virB11 could not be detected in any strain. Specific differences between the isolates were observed only in genes cgtB and wlaN involved in lipo-oligosaccharide (LOS) biosynthesis. The gene cgtB was only detectable in three of five strains with strong colonization and invasion abilities. Probably, wlaN can overcome the lack of cgtB in the two cgtB- isolates.

Diversity within the Campylobacter jejuni type I restriction-modification loci

The type I restriction-modification (hsd) systems of 73 Campylobacter jejuni strains were characterized according to their DNA and amino acid sequences, and/or gene organization. A number of new genes were identified which are not present in the sequenced strain NCTC 11168. The closely related organism Helicobacter pylori has three type I systems; however, no evidence was found that C. jejuni strains contain multiple type I systems, although hsd loci are present in at least two different chromosomal locations. Also, unlike H. pylori, intervening ORFs are present, in some strains, between hsdR and hsdS and between hsdS and hsdM. No definitive function can be ascribed to these ORFs, designated here as rloA-H (R-linked ORF) and mloA-B (M-linked ORF). Based on parsimony analysis of amino acid sequences to assess character relatedness, the C. jejuni type I R-M systems are assigned to one of three families: 'IAB', 'IC' or 'IF'. This study confirms that HsdM proteins within a family are highly conserved but share little homology with HsdM proteins from other families. The 'IC' hsd loci are >99 % identical at the nucleotide level, as are the 'IF' hsd loci. Additionally, whereas the nucleotide sequences of the 'IAB' hsdR and hsdM genes show a high degree of similarity, the nucleotide sequences of the 'IAB' hsdS and rlo genes vary considerably. This diversity suggests that recombination between 'IAB' hsd loci would lead not only to new hsdS alleles but also to the exchange of rlo genes; five C. jejuni hsd loci are presumably the result of such recombination. The importance of these findings with regard to the evolution of C. jejuni type I R-M systems is discussed.

Risk assessment prediction from genome sequences: promises and dreams

The application of bacterial genomics opens new avenues of research on foodborne pathogens. Foodborne pathogens must be able to colonize their hosts and survive transmission from host to host. Different groups of genes are involved in the processes of survival, colonization, and virulence, and such genes are potential targets for risk assessment and intervention strategies. Filtering from genome sequences the genes relevant to these processes is a major challenge, and although many tools are already available for analyses, this type of data mining is just beginning. For the simplest application, gene comparison, it is important to know how gene function, for instance in virulence, is being defined and tested. In other genomic applications, reserachers look for specific properties or characteristics of (virulence) genes to identify novel gene candidates. Each approach has pitfalls, and gene candidates must be tested in the lab to confirm their function. Models for colonization and virulence are available for most although not all pathogens. Models for survival and stress responses are needed to increase the utilization of genomic approaches to risk assessment. Here, I discuss how genome sequences are likely to help in microbial risk assessment of foodborne pathogens and how dreams may become promises.

The diversity within an expanded and redefined repertoire of phase-variable genes in Helicobacter pylori

Phase variation is a common mechanism used by pathogenic bacteria to generate intra-strain diversity that is important in niche adaptation and is strongly associated with virulence determinants. Previous analyses of the complete sequences of the Helicobacter pylori strains 26695 and J99 have identified 36 putative phase-variable genes among the two genomes through their association with homopolymeric tracts and dinucleotide repeats. Here a comparative analysis of the two genomes is reported and an updated and expanded list of 46 candidate phase-variable genes in H. pylori is described. These have been systematically investigated by PCR and sequencing for the presence of the genes, and the presence and variability in length of the repeats in strains 26695 and J99 and in a collection of unrelated H. pylori strains representative of the main global subdivisions recently suggested. This provides supportive evidence for the phase variability of 30 of the 46 candidates. Other differences in this subset of genes were observed (i) in the repeats, which can be present or absent among the strains, or stabilized in different strains and (ii) in the gene-complements of the strains. Differences between genes were not consistently correlated with the geographic population distribution of the strains. This study extends and provides new evidence for variation of this type in H. pylori, and of the high degree of diversity of the repertoire of genes which display phase-variable switching within individual strains.

Phase and antigenic variation in bacteria

Phase and antigenic variation result in a heterogenic phenotype of a clonal bacterial population, in which individual cells either express the phase-variable protein(s) or not, or express one of multiple antigenic forms of the protein, respectively. This form of regulation has been identified mainly, but by no means exclusively, for a wide variety of surface structures in animal pathogens and is implicated as a virulence strategy. This review provides an overview of the many bacterial proteins and structures that are under the control of phase or antigenic variation. The context is mainly within the role of the proteins and variation for pathogenesis, which reflects the main body of literature. The occurrence of phase variation in expression of genes not readily recognizable as virulence factors is highlighted as well, to illustrate that our current knowledge is incomplete. From recent genome sequence analysis, it has become clear that phase variation may be more widespread than is currently recognized, and a brief discussion is included to show how genome sequence analysis can provide novel information, as well as its limitations. The current state of knowledge of the molecular mechanisms leading to phase variation and antigenic variation are reviewed, and the way in which these mechanisms form part of the general regulatory network of the cell is addressed. Arguments both for and against a role of phase and antigenic variation in immune evasion are presented and put into new perspective by distinguishing between a role in bacterial persistence in a host and a role in facilitating evasion of cross-immunity. Finally, examples are presented to illustrate that phase-variable gene expression should be taken into account in the development of diagnostic assays and in the interpretation of experimental results and epidemiological studies.

Catastrophe and what to do about it if you are a bacterium: the importance of frameshift mutants

Key problems that bacteria have historically faced are the challenges of the lack of essential nutrients and the presence of antibiotics produced naturally, but there are many other challenges. It appears that for many of these challenges the bacteria have mechanisms encoded in their genomes that are not usually functioning, but may be "turned on" when needed, even if the need only occurs once in hundreds of thousands of generations. Such mechanisms at other times somehow need to be "turned off" because they may cause a slight disadvantage, or even a grave disadvantage to the cell compared with wild-type cells during the time the population is not being challenged. On the other hand, a gene cannot simply be discarded because it might be needed again. How do microorganisms solve the problem of responding to challenges that only occur rarely? I suggest that in most cases, the mutation must occur by the existence of a readily reversible mutation. The mutation in likely the result of a frameshift mutation that caused the response and later another frameshift occurs to return the genome to its original state.

Transcriptional phase variation at the flhB gene of Pseudomonas putida DOT-T1E is involved in response to environmental changes and suggests the participation of the flagellar export system in solvent tolerance

Frameshift mutations in a poly(G) track at the flhB gene of Pseudomonas putida DOT-T1E are responsible for the diminished swimming of this strain on semisolid medium, which contrasts with the high swimming ability of P. putida KT2440, which does not exhibit a poly(G) track at the flhB gene. We previously showed that a mutant lacking FlhB was more sensitive to solvents than the wild-type strain (Segura et al., J. Bacteriol., 183:4127-4133, 2001). In this study, we show that swimming ability correlates with solvent tolerance in P. putida DOT-T1E, so that growth conditions favoring a functional flhB gene (growth on semisolid medium) resulted in increased innate tolerance to a sudden toluene shock.

Multilocus sequence typing for comparison of veterinary and human isolates of Campylobacter jejuni

Multilocus sequence typing (MLST) has been applied to 266 Campylobacter jejuni isolates, mainly from veterinary sources, including cattle, sheep, poultry, pigs, pets, and the environment, as well as isolates from human cases of campylobacteriosis. The populations of veterinary and human isolates overlap, suggesting that most veterinary sources should be considered reservoirs of pathogenic campylobacters. There were some associations between source and sequence type complex, indicating that host or source adaptation may exist. The pig isolates formed a distinct group by MLST and may well represent a potential pig-adapted clone of C. jejuni. A subset (n = 82) of isolates was reanalyzed with a second MLST scheme which provided a unique set of isolates that had been analyzed at a total of 12 loci. The distribution of isolates among the complexes in each of the two schemes was similar but not identical. In addition to isolates from human outbreaks, one group of isolates that were not epidemiologically linked was also identical at all 12 loci. This group of isolates is believed to represent another stable strain of C. jejuni.

Variation of the natural transformation frequency of Campylobacter jejuni in liquid shake culture

Natural transformation, a mechanism that generates genetic diversity in Campylobacter jejuni, was studied in a novel liquid shake culturing system that allowed an approximately 10 000-fold increase in cell density. C. jejuni transformation frequency was analysed in this system under 10 %, 5·0 % and 0·7 % CO2 atmospheres. At 5·0 % and 10 % CO2 concentrations, when purified isogenic chromosomal DNA was used to assess competence, transformation frequency ranged from 10−3 to 10−4 at low cell concentrations and declined as cell density increased. Transformation frequency under a 0·7 % CO2 atmosphere was more stable, maintaining 10−3 levels at high cell densities, and was 10- to 100-fold higher than that under a 10 % CO2 atmosphere. Three of four C. jejuni strains tested under a 5·0 % CO2 atmosphere were naturally competent for isogenic DNA; competent strains demonstrated a lack of barriers to intraspecies genetic exchange by taking up and incorporating chromosomal DNA from multiple C. jejuni donors. C. jejuni showed a preference for its own DNA at the species level, and co-cultivation demonstrated that DNA transfer via natural transformation occurred between isogenic populations during short periods of exposure in liquid medium when cell density and presumably DNA concentrations were low. Transformation frequency during co-cultivation of isogenic populations was also influenced by CO2 concentration. Under a 0·7 % CO2 atmosphere, co-cultivation transformation frequency increased approximately 500-fold in a linear fashion with regard to cell density, and was 1000- to 10 000-fold higher during late-exponential-phase growth when compared to cultures grown under a 10 % CO2 atmosphere.

Recent developments in Campylobacter pathogenesis

PURPOSE OF REVIEW

The Campylobacter species jejuni and coli are leading causes of enteritis and enterocolitis worldwide. Arthritis, Reiter syndrome, and Guillain-Barré syndrome represent post-infectious sequelae. Although the acute and chronic clinical manifestations highlight Campylobacter species as excellent models for the identification of mechanisms involved in pathogenesis, detailed investigations at the molecular level are complicated by the fastidious growth requirements of the bacteria and by the tremendous variability displayed by Campylobacter isolates. Thus, research activities in this field constitute a substantial challenge for scientists of many different disciplines. The genome information has greatly stimulated investigations at the molecular level and the resulting modern research trends lead to a better understanding of Campylobacter-associated diseases providing the basis for new developments in prevention and therapy.

RECENT FINDINGS

This review summarizes results from the most recent investigations in the field of Campylobacter pathogenesis. Topics include genome analysis, surface structures and post-infectious complications, adaptation, host cell interaction and cell toxicity.

SUMMARY

During its coevolution with human and other vertebrate hosts, Campylobacter species have developed specific survival strategies, which are required for host adaptation and establishment in the intestinal environment. The bacterial factors involved in these processes are the subject of intensive research activities. With a focus on molecular aspects of the most important human pathogen, C. jejuni, this review intends to summarize the recent trends and developments in Campylobacter research by highlighting selected publications in the field of microbial pathogenesis.