An environmentally regulated pilus-like appendage involved in Campylobacter pathogenesis

Care, management, and use of ferrets in biomedical research

The ferret (Mustela putorius furo) is a small domesticated species of the family Mustelidae within the order Carnivora. The present article reviews and discusses the current state of knowledge about housing, care, breeding, and biomedical uses of ferrets. The management and breeding procedures of ferrets resemble those used for other carnivores. Understanding its behavior helps in the use of environmental enrichment and social housing, which promote behaviors typical of the species. Ferrets have been used in research since the beginning of the twentieth century. It is a suitable non-rodent model in biomedical research because of its hardy nature, social behavior, diet and other habits, small size, and thus the requirement of a relatively low amount of test compounds and early sexual maturity compared with dogs and non-human primates. Ferrets and humans have numerous similar anatomical, metabolic, and physiological characteristics, including the endocrine, respiratory, auditory, gastrointestinal, and immunological systems. It is one of the emerging animal models used in studies such as influenza and other infectious respiratory diseases, cystic fibrosis, lung cancer, cardiac research, gastrointestinal disorders, neuroscience, and toxicological studies. Ferrets are vulnerable to many human pathogenic organisms, like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), because air transmission of this virus between them has been observed in the laboratory. Ferrets draw the attention of the medical community compared to rodents because they occupy a distinct niche in biomedical studies, although they possess a small representation in laboratory research.

Evaluation of Bile Salts on the Survival and Modulation of Virulence of Aliarcobacter butzleri

Aliarcobacter butzleri is a Gram-negative bacterium associated with infections of the gastrointestinal tract and widely distributed in various environments. For successful infection, A. butzleri should be able to tolerate various stresses during gastrointestinal passage, such as bile. Bile represents an antimicrobial host barrier that acts against external noxious agents and consists of a variety of bile salts. The intestinal bile salts act as detergents involved in the antimicrobial host defense; although, on the bacterial side, they could also serve as a signal to activate virulence mechanisms. The aim of this work was to understand the effects of bile salts on the survival and virulence of A. butzleri. In our study, A. butzleri was able to survive in the presence of human physiological concentrations of bile salts. Regarding the virulence features, an increase in cellular hydrophobicity, a decrease in motility and expression of flaA gene, as well as an increase in biofilm formation with a concomitant change in the type of biofilm structure were observed in the presence of sub-inhibitory concentration of bile salts. Concerning adhesion and invasion ability, no significant difference was observed. Overall, the results demonstrated that A. butzleri is able to survive in physiological concentrations of bile salts and that exposure to bile salts could change its virulence mechanisms.

Comparative genomics and genome biology of Campylobacter showae

Campylobacter showae a bacterium historically linked to gingivitis and periodontitis, has recently been associated with inflammatory bowel disease and colorectal cancer. Our aim was to generate genome sequences for new clinical C. showae strains and identify functional properties explaining their pathogenic potential. Eight C. showae genomes were assessed, four strains isolated from inflamed gut tissues from paediatric Crohn’s disease patients, three strains from colonic adenomas, and one from a gastroenteritis patient stool. Genome assemblies were analyzed alongside the only 3 deposited C. showae genomes. The pangenome from these 11 strains consisted of 4686 unique protein families, and the core genome size was estimated at 1050 ± 15 genes with each new genome contributing an additional 206 ± 16 genes. Functional assays indicated that colonic strains segregated into 2 groups: adherent/invasive vs. non-adherent/non-invasive strains. The former possessed Type IV secretion machinery and S-layer proteins, while the latter contained Cas genes and other CRISPR associated proteins. Comparison of gene profiles with strains in Human Microbiome Project metagenomes showed that gut-derived isolates share genes specific to tongue dorsum and supragingival plaque counterparts. Our findings indicate that C. showae strains are phenotypically and genetically diverse and suggest that secretion systems may play an important role in virulence potential.

In Sickness and in Health: The Relationships Between Bacteria and Bile in the Human Gut

Colonization of a human host with a commensal microbiota has a complex interaction in which bacterial communities provide numerous health benefits to the host. An equilibrium between host and microbiota is kept in check with the help of biliary secretions by the host. Bile, composed primarily of bile salts, promotes digestion. It also provides a barrier between host and bacteria. After bile salts are synthesized in the liver, they are stored in the gallbladder to be released after food intake. The set of host-secreted bile salts is modified by the resident bacteria. Because bile salts are toxic to bacteria, an equilibrium of modified bile salts is reached that allows commensal bacteria to survive, yet rebuffs invading pathogens. In addition to direct toxic effects on cells, bile salts maintain homeostasis as signaling molecules, tuning the immune system. To cause disease, gram-negative pathogenic bacteria have shared strategies to survive this harsh environment. Through exclusion of bile, efflux of bile, and repair of bile-induced damage, these pathogens can successfully disrupt and outcompete the microbiota to activate virulence factors.

Bile salts induce long polar fimbriae expression favouring Crohn's disease-associated adherent-invasive Escherichia coli interaction with Peyer's patches

Ileal lesions of patients with Crohn's disease are colonized by adherent-invasive Escherichia coli (AIEC). The earliest lesions of recurrent Crohn's disease are erosions of Peyer's patches (PP). We recently reported the presence of a functional lpf operon in AIEC, encoding long polar fimbriae (LPF), that allows AIEC bacteria to interact with PP and to translocate across M cells. The aim of this study was to analyse the effect of gastrointestinal conditions on LPF expression in AIEC strains. The LF82 bacterial growth in an acid pH medium or at high osmolarity medium had no effect on lpf transcription level, in contrast to bacterial growth in the presence of bile salts, which promoted activation of lpf transcription. When cultured in the presence of bile salt, LF82 wild-type bacteria, but not the isogenic mutant deleted for lpfA, exhibited a higher level of interaction with PP and a higher level of translocation through M cell monolayers. The FhlA transcriptional factor was found to be a key bacterial regulator at the origin of LPF expression in the presence of bile salts.

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.

Campylobacter jejuni colonization of mice with limited enteric flora

We have developed experimental murine Campylobacter infection models which demonstrate efficient establishment and reproducible, high-level colonization. Following oral inoculation, wild-type C3H mice with normal enteric flora were colonized inconsistently and inefficiently by C. jejuni strain 81-176. However, C3H mice with a limited gut flora (LF) were efficiently colonized at high levels (10(8) CFU/g of stool or large intestine tissue) followed by clearance after several weeks. Large intestine tissue showed minimal to mild inflammation at days 7 and 28 postinoculation. In striking contrast, C3H SCID mice with the same limited flora remained persistently colonized at a consistently high level until they were euthanized 8 months postinoculation. Lower gastrointestinal tract tissue from LF-SCID mice showed marked to severe inflammation in the colon and cecum at days 7 and 28 and intense inflammation of the stomach at day 28. These findings indicate that although the innate response alone cannot block colonization persistence, it is sufficient to orchestrate marked gut inflammation. Moreover, the adaptive immune response is critical to mediate C. jejuni clearance from the colonized gut. To validate our LF murine model, we verified that motility and chemotaxis are critical for colonization. Insertion-deletion mutations were generated in motB and fliI, which encode products essential for motility and flagellar assembly, and in the presumptive chemotaxis gene cheA (histidine kinase). All mutants failed to establish colonization in LF mice. Our limited flora murine colonization models serve as tractable, reproducible tools to define host responses to C. jejuni infection and to identify and characterize virulence determinants required for colonization.

Novel surface polypeptides of Campylobacter jejuni as traveller's diarrhoea vaccine candidates discovered by proteomics

Campylobacter jejuni is one of the most common causes of traveller's diarrhoea and food poisoning, therefore development of a vaccine is important. Using biochemical fractionation and mass spectrometry analysis, we identified more than 110 surface polypeptides. Eight C. jejuni identified surface proteins were expressed in Escherichia coli and purified. Mice were immunized with different doses of these purified proteins and challenged orally with C. jejuni strains ML1 and ML53. The degree of protection of mice was tested by intestinal colonization. At least two groups of mice vaccinated with purified proteins clear the infection faster than control mice. Here, we present the use of a proteomics based approach for the identification of novel protein based C. jejuni vaccines for the first time.

Role of Toll-like receptors in health and diseases of gastrointestinal tract

The human gastrointestinal (GI) tract is colonized by non-pathogenic commensal microflora and frequently exposed to many pathogenic organisms. For the maintenance of GI homeostasis, the host must discriminate between pathogenic and non-pathogenic organisms and initiate effective and appropriate immune and inflammatory responses. Mammalian toll-like receptors (TLRs) are members of the pattern-recognition receptor (PRR) family that plays a central role in the initiation of innate cellular immune responses and the subsequent adaptive immune responses to microbial pathogens. Recent studies have shown that gastrointestinal epithelial cells express almost all TLR subtypes characterized to date and that the expression and activation of TLRs in the GI tract are tightly and coordinately regulated. This review summarizes the current understanding of the crucial dual roles of TLRs in the development of host innate and adaptive immune responses to GI infections and the maintenance of the immune tolerance to commensal bacteria through down-regulation of surface expression of TLRs in intestinal epithelial cells.

The role of Klebsiella pneumoniae urease in intestinal colonization and resistance to gastrointestinal stress

The first step in nosocomial infections due to Klebsiella pneumoniae is colonization of the patient's gastrointestinal (GI) tract. In a previous work, signature-tagged mutagenesis was used in a murine model to identify 13 genes required for efficient colonization, two of which were involved in urea metabolism. The role of urease was further investigated by the construction and analysis of an isogenic urease-deficient mutant. The behavior of both the wild-type strain and the urease-deficient mutant was tested under hostile conditions, reproducing stresses encountered in the GI environment. The wild-type strain had an acid tolerance response (ATR) to inorganic acid, was resistant to organic acids (38.5% survival) and was able to survive concentrations of bile encountered in vivo. The absence of urease did not affect the resistance of K. pneumoniae to acid and bile stresses, but the enhanced adhesion response to Int-407 cells after exposure to bile observed with the wild-type strain was no longer detected with the urease mutant. When tested in the murine intestinal colonization model, both strains were mainly recovered in the large intestine parts, and the mutant was impaired in its colonization capacities, but only when tested in competition with the wild-type strain. These findings emphasize the prominent role played by metabolic function in the colonization process of such a complex ecosystem as the host GI tract.

Campylobacter vaccine development:a key to controlling enteric diseases

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

Identification of Campylobacter jejuni genes involved in commensal colonization of the chick gastrointestinal tract

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in humans in developed countries throughout the world. This bacterium frequently promotes a commensal lifestyle in the gastrointestinal tracts of many animals including birds and consumption or handling of poultry meats is a prevalent source of C. jejuni for infection in humans. To understand how the bacterium promotes commensalism, we used signature-tagged transposon mutagenesis and identified 29 mutants representing 22 different genes of C. jejuni strain 81-176 involved in colonization of the chick gastrointestinal tract. Among the determinants identified were two adjacent genes, one encoding a methyl-accepting chemotaxis protein (MCP), presumably required for proper chemotaxis to a specific environmental component, and another gene encoding a putative cytochrome c peroxidase that may function to reduce periplasmic hydrogen peroxide stress during in vivo growth. Deletion of either gene resulted in attenuation for growth throughout the gastrointestinal tract. Further examination of 10 other putative MCPs or MCP-domain containing proteins of C. jejuni revealed one other required for wild-type levels of caecal colonization. This study represents one of the first genetic screens focusing on the bacterial requirements necessary for promoting commensalism in a vertebrate host.

Campylobacter infection: small bowel and colon

The important contribution of Campylobacter infections to human enteric disease is well established. Recent completion of the genomic sequence of a Campylobacter jejuni strain has heralded a renaissance in the field of Campylobacter pathogenesis research. With the application of novel, powerful technologies, our understanding of how these organisms mediate disease is set to evolve rapidly from its current, relatively neglected status.

A phase-variable capsule is involved in virulence of Campylobacter jejuni 81-176

Campylobacter jejuni strain 81-176 (HS36, 23) synthesizes two distinct glycan structures, as visualized by immunoblotting of proteinase K-digested whole-cell preparations. A site-specific insertional mutant in the kpsM gene results in loss of expression of a high-molecular-weight (HMW) glycan (apparent Mr 26 kDa to > 85 kDa) and increased resolution of a second ladder-like glycan (apparent Mr 26-50 kDa). The kpsM mutant of 81-176 is no longer typeable in either HS23 or HS36 antisera, indicating that the HMW glycan structure is the serodeterminant of HS23 and HS36. Both the kpsM-dependent HMW glycan and the kpsM-independent ladder-like structure appear to be capsular in nature, as both are attached to phospholipid rather than lipid A. Additionally, the 81-176 kpsM gene can complement a deletion in Escherichia coli kpsM, allowing the expression of an alpha2,8 polysialic acid capsule in E. coli. Loss of the HMW glycan in 81-176 kpsM also increases the surface hydrophobicity and serum sensitivity of the bacterium. The kpsM mutant is also significantly reduced in invasion of INT407 cells and reduced in virulence in a ferret diarrhoeal disease model. The expression of the kpsM-dependent capsule undergoes phase variation at a high frequency.

Campylobacter jejuni--microtubule-dependent invasion

Campylobacter jejuni is the leading bacterial cause of food-borne illness worldwide and a major cause of Guillain-Barré paralysis. Recent molecular and cellular studies of one well-characterized C. jejuni strain have begun to unravel the details of an unusual microtubule-dependent (actin-filament-independent) gut-invasion mechanism, through which at least some C. jejuni initiate disease. Although responsible for causing a human dysenteric syndrome remarkably similar to that triggered by Shigella spp., current evidence suggests that C. jejuni use some markedly different molecular mechanisms of pathogenesis compared with shigellae.

Natural transformation in mesophilic and thermophilic bacteria: identification and characterization of novel, closely related competence genes in Acinetobacter sp. strain BD413 and Thermus thermophilus HB27

The mesophile Acinetobacter sp. strain BD413 and the extreme thermophile Thermus thermophilus HB27 display high frequencies of natural transformation. In this study we identified and characterized a novel competence gene in Acinetobacter sp. strain BD413, comA, whose product displays significant similarities to the competence proteins ComA and ComEC in Neisseria and Bacillus species. Transcription of comA correlated with growth phase-dependent transcriptional regulation of the recently identified pilin-like factors of the transformation machinery. This finding strongly suggests that comA is part of a competence regulon. Examination of the genome sequence of T. thermophilus HB27 led to detection of a comA/comEC-like open reading frame (ORF) which is flanked by an ORF whose product shows significant similarities to the Bacillus subtilis competence protein ComEA. To examine whether these two ORFs, designated comEC and comEA, are implicated in natural transformation of T. thermophilus HB27, both were disrupted by using a thermostable kanamycin resistance marker. Natural transformation in comEC mutants was reduced 1,000-fold, whereas in comEA mutants the natural transformation phenotype was completely eliminated. These results strongly suggest that both genes, comEC and comEA, are required for natural transformation in T. thermophilus HB27. Several transmembrane alpha-helices are predicted based on the amino acid sequences of ComA in Acinetobacter sp. strain BD413 and ComEC in T. thermophilus HB27, which suggests that ComA and ComEC are located in the inner membrane and function in DNA transport through the cytoplasmic membrane.

Molecular cloning, sequence and characterization of cjsT, a putative protease from Rickettsia rickettsii

The cloning and sequencing of a gene from Rickettsia rickettsii which confers haemolytic activity on Escherichia coli strain TB1 is described. The open reading frame of the haemolysis-promoting gene, cjsT, is 1041 bp and encodes a putative protein with a molecular mass of 33 825 Da. CjsT has high sequence similarity to several bacterial proteases, particularly type IV signal peptidases. Cell lysates from an E. coli clone containing cjsT in pUC19 (pJON1) exhibited greater protease activity in functional assays than found in E. coli containing pUC19 alone. Disruption of the cjsT gene by insertional inactivation with a kanamycin cassette reduced both the protease and haemolytic activities conferred by cjsT. The protease inhibitors antipain and diisopropylfluorophosphate (DFP) both reduced the proteolytic activity of pJON1. The mechanism by which the R. rickettsii cjsT promotes haemolysis in E. coli remains unclear.

JlpA, a novel surface-exposed lipoprotein specific to Campylobacter jejuni, mediates adherence to host epithelial cells

A 1116 bp open reading frame (ORF), designated jlpA, encoding a novel species-specific lipoprotein of Campylobacter jejuni TGH9011, was identified from recombinant plasmid pHIP-O. The jlpA gene encodes a polypeptide (JlpA) of 372 amino acid residues with a molecular mass of 42.3 kDa. JlpA contains a typical signal peptide and lipoprotein processing site at the N-terminus. The presence of a lipid moiety on the JlpA molecule was confirmed by the incorporation of [3H]-palmitic acid. Immunoblotting analysis of cell surface extracts prepared using glycine-acid buffer (pH 2.2) and proteinase K digestion of whole cells indicated that JlpA is a surface-exposed lipoprotein in C. jejuni. JlpA is loosely associated with the cell surface, as it is easily extracted from the C. jejuni outer membrane by detergents, such as sarcosyl and Triton X-100. JlpA is released to the culture medium, and its concentration increases in a time-dependent fashion. The adherence of both insertion and deletion mutants of jlpA to HEp-2 epithelial cells was reduced compared with that of parental C. jejuni TGH9011. Adherence of C. jejuni to HEp-2 cells was inhibited in a dose-dependent manner when the bacterium was preincubated with anti-GST-JlpA antibodies or when HEp-2 cells were preincubated with JlpA protein. A ligand-binding immunoblotting assay showed that JlpA binds to HEp-2 cells, which suggests that JlpA is C. jejuni adhesin.

Bile-induced 'pili' in Campylobacter jejuni are bacteria-independent artifacts of the culture medium

In 1996, it was reported that the enteric pathogen Campylobacter jejuni produces pilus-like appendages in response to bile salts such as deoxycholate (DOC), and that the formation of these appendages requires the putative peptidase PspA. Pili were known to be important virulence determinants in other pathogenic bacteria but had never before been observed for C. jejuni. We report here that these appendages are not pili, but are instead a bacteria-independent morphological artifact of the growth medium. Furthermore, the pspA gene is not required for their formation. Broth cultures containing a threshold concentration of DOC inoculated with no bacteria produced identical abundant, fibrous, pilus-like structures as those cultures that had been inoculated with C. jejuni. These fibres were also found in growth media from DOC-containing pspA:CmR mutant cultures. These results are consistent with the absence of candidate pilin monomers in protein gel analyses as well as the dearth of pilin-like genes and pilus formation gene clusters in the C. jejuni genome.

Detection and initial characterization of novel capsular polysaccharide among diverse Campylobacter jejuni strains using alcian blue dye

We have recently demonstrated that most strains of Campylobacter jejuni produce capsular polysaccharide (CPS), which can be detected by immunoblotting with homologous Penner antisera on polyvinylidene difluoride membranes (A. V. Karlyshev, D. Linton, N. A. Gregson, A. J. Lastovica, and B. W. Wren, Mol. Microbiol. 35:529-541, 2000). In this report, we describe a universal and rapid staining procedure using Alcian blue for C. jejuni CPS, which does not rely on the availability of antisera and identifies CPS in untypeable strains. Furthermore, Alcian blue staining identified CPS in its lipid-free form directly on Tricine gels, and we demonstrate that CPS is thermostable and is accumulated in the culture supernatant in a lipid-free form. The identification of a newly described CPS and its lipid-free form in C. jejuni should prove invaluable in studying the pathogenesis and epidemiology of this important pathogen.

Campylobacter jejuni cytolethal distending toxin mediates release of interleukin-8 from intestinal epithelial cells

Live cells of Campylobacter jejuni and Campylobacter coli can induce release of interleukin-8 (IL-8) from INT407 cells. Additionally, membrane fractions of C. jejuni 81-176, but not membrane fractions of C. coli strains, can also induce release of IL-8. Membrane preparations from 81-176 mutants defective in any of the three membrane-associated protein subunits of cytolethal distending toxin (CDT) were unable to induce IL-8. The presence of the three cdt genes on a shuttle plasmid in trans restored both CDT activity and the ability to release IL-8 to membrane fractions. However, CDT mutations did not affect the ability of 81-176 to induce IL-8 during adherence to or invasion of INT407 cells. When C. jejuni cdt genes were transferred on a shuttle plasmid into a C. coli strain lacking CDT, membrane preparations became positive in both CDT and IL-8 assays. Growth of C. jejuni in physiological levels of sodium deoxycholate released all three CDT proteins, as well as CDT activity and IL-8 activity, from membranes into supernatants. Antibodies against recombinant forms of each of the three CDT subunit proteins neutralized both CDT activity and the activity responsible for IL-8 release. The data suggest that C. jejuni can induce IL-8 release from INT407 cells by two independent mechanisms, one of which requires adherence and/or invasion and the second of which requires CDT.

Salmonella enterica serovar typhimurium invasion is repressed in the presence of bile

As enteric pathogens, the salmonellae have developed systems by which they can sense and adapt appropriately to deleterious intestinal components that include bile. Previously, growth in the presence of bile was shown to repress the transcription of prgH, a locus encoding components of the Salmonella pathogenicity island I (SPI-1) type III secretion system (TTSS) necessary for eukaryotic cell invasion. This result suggested an existing interaction between salmonellae, bile, and eukaryotic cell invasion. Transcription assays demonstrated that invasion gene regulators (e.g., sirC and invF) are repressed by bile. However, bile does not interact with any of the invasion regulators directly but exerts its effect at or upstream of the two-component system at the apex of the invasion cascade, SirA-BarA. As suggested by the repression of invasion gene transcription in the presence of bile, Western blot analysis demonstrated that proteins secreted by the SPI-1 TTSS were markedly reduced in the presence of bile. Furthermore, Salmonella enterica serovar Typhimurium grown in the presence of bile was able to invade epithelial cells at only 4% of the level of serovar Typhimurium grown without bile. From these data, we propose a model whereby serovar Typhimurium uses bile as an environmental signal to repress its invasive capacity in the lumen of the intestine, but upon mucous layer penetration and association with intestinal epithelial cells, where the apparent bile concentration would be reduced, the system would become derepressed and invasion would be initiated.

Involvement of a plasmid in virulence of Campylobacter jejuni 81-176

Campylobacter jejuni strain 81-176 contains two, previously undescribed plasmids, each of which is approximately 35 kb in size. Although one of the plasmids, termed pTet, carries a tetO gene, conjugative transfer of tetracycline resistance to another strain of C. jejuni could not be demonstrated. Partial sequence analysis of the second plasmid, pVir, revealed the presence of four open reading frames which encode proteins with significant sequence similarity to Helicobacter pylori proteins, including one encoded by the cag pathogenicity island. All four of these plasmid-encoded proteins show some level of homology to components of type IV secretion systems. Mutation of one of these plasmid genes, comB3, reduced both adherence to and invasion of INT407 cells to approximately one-third that seen with wild-type strain 81-176. Mutation of comB3 also reduced the natural transformation frequency. A mutation in a second plasmid gene, a virB11 homolog, resulted in a 6-fold reduction in adherence and an 11-fold reduction in invasion compared to the wild type. The isogenic virB11 mutant of strain 81-176 also demonstrated significantly reduced virulence in the ferret diarrheal disease model. The virB11 homolog was detected on plasmids in 6 out of 58 fresh clinical isolates of C. jejuni, suggesting that plasmids are involved in the virulence of a subset of C. jejuni pathogens.

Mechanisms of bacterial resistance and response to bile

Enteric bacteria are resistant to the bactericidal effects of intestinal bile, but these resistance mechanisms are not completely understood. It is becoming increasingly apparent that enteric bacteria have evolved to utilize bile as a signal for the temporal production of virulence factors and other adaptive mechanisms. A greater understanding of the resistance and response of bacteria to bile may assist the development of novel therapeutic, prevention, and diagnostic strategies to treat enteric and extraintestinal infections.

The genome sequence of the food-borne pathogen Campylobacter jejuni reveals hypervariable sequences

Campylobacter jejuni, from the delta-epsilon group of proteobacteria, is a microaerophilic, Gram-negative, flagellate, spiral bacterium-properties it shares with the related gastric pathogen Helicobacter pylori. It is the leading cause of bacterial food-borne diarrhoeal disease throughout the world. In addition, infection with C. jejuni is the most frequent antecedent to a form of neuromuscular paralysis known as Guillain-Barré syndrome. Here we report the genome sequence of C. jejuni NCTC11168. C. jejuni has a circular chromosome of 1,641,481 base pairs (30.6% G+C) which is predicted to encode 1,654 proteins and 54 stable RNA species. The genome is unusual in that there are virtually no insertion sequences or phage-associated sequences and very few repeat sequences. One of the most striking findings in the genome was the presence of hypervariable sequences. These short homopolymeric runs of nucleotides were commonly found in genes encoding the biosynthesis or modification of surface structures, or in closely linked genes of unknown function. The apparently high rate of variation of these homopolymeric tracts may be important in the survival strategy of C. jejuni.

Evaluation of a truncated recombinant flagellin subunit vaccine against Campylobacter jejuni

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

Pathophysiology of Campylobacter jejuni infections of humans

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

Campylobacter jejuni 81-176 associates with microtubules and dynein during invasion of human intestinal cells

Campylobacter jejuni uptake into cultured INT407 cells was analyzed kinetically over a wide range of starting multiplicities of infection (MOI; from 0.02 to 20,000 bacteria/epithelial cell). The efficiency of internalization was the highest at MOI of 0.02 and decreased steadily at higher MOIs, presumably due to reported C. jejuni autoagglutination at higher densities. Total internalized Campylobacter CFU increased gradually from an MOI of 0.02 to a peak at an MOI of 200 (reaching an average of two bacteria internalized per epithelial cell) and decreased at higher MOIs. The invasion process was apparently saturated within 2 h at an MOI of 200, indicating stringent host cell limitations on this entry process. Furthermore, whereas control Salmonella typhi invaded all monolayer cells within 1 h, only two-thirds of monolayer cells were infected after 2 h with C. jejuni at MOIs of 200 to 2,000. The percentage of Campylobacter-infected host cells gradually increased to 85% after 7 h of infection, suggesting that C. jejuni entry may be host cell cycle dependent. Direct evidence of the involvement of microtubules in C. jejuni internalization, suggested previously by biochemical inhibitor studies, was obtained by time course immunofluorescence microscopic analyses. Bacteria initially bound to the tips of host cell membrane extensions containing microtubules, then aligned in parallel with microtubules during entry, colocalized specifically with microtubules and dynein but not with microfilaments, and moved over 4 h, presumably via microtubules to the perinuclear region of host cells. Orthovanadate, which inhibits dynein activity, specifically reduced C. jejuni 81-176 entry, suggesting that this molecular motor is involved in entry and endosome trafficking during this novel bacterial internalization process. Collectively, these data suggest that C. jejuni enters host cells in a targeted and tightly controlled process leading to uptake into an endosomal vacuole which apparently moves intracellularly along microtubules via the molecular motor, dynein, to the perinuclear region.

Bacterial secreted proteins are required for the internaliztion of Campylobacter jejuni into cultured mammalian cells

Presented here is the first evidence that Campylobacter jejuni secrete proteins upon co-cultivation with host cells and in INT 407 cell-conditioned medium. A C. jejuni gene designated ciaB for Campylobacter invasion antigen B was identified, using a differential screening technique, which is required for this secretion process and the efficient entry of this bacterium into a host cell. The C. jejuni ciaB gene encodes a protein of 610 amino acids with a calculated molecular mass of 73 154 Da. The deduced amino acid sequence of the CiaB protein shares similarity with type III secreted proteins associated with the invasion of host cells from other more extensively characterized bacterial pathogens. In vitro binding and internalization assays revealed that the binding of C. jejuni ciaB null mutants was indistinguishable from that of the parental isolate, whereas a significant reduction was noted in internalization. Confocal microscopic examination of C. jejuni-infected cells revealed that CiaB was translocated into the cytoplasm of the host cells. Culturing C. jejuni with INT 407 cells or in INT 407-conditioned medium resulted in the secretion of at least eight proteins, ranging in size from 12.8 to 108 kDa, into the culture medium. C. jejuni ciaB null mutants were deficient in the secretion of all eight proteins, indicating that CiaB is required for the secretion process. The identification of the C. jejuni ciaB gene represents a significant advance in understanding the molecular mechanism of C. jejuni internalization and the pathogenesis of C. jejuni-mediated enteritis.

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

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

A putative adhesin gene cloned from Campylobacter jejuni

Thirteen Campylobacter jejuni strains of human origin showed differing behaviours when analysed for their ability to bind the Caco-2 cell line in vitro, suggesting variations in genetic complements and/or regulation. We designed an oligonucleotide probe corresponding to a highly conserved part of adhesins from various Gram-negative bacteria. Among our laboratory collection, Southern hybridization has demonstrated that only a discrete number of strains harbour this sequence. The corresponding gene has been cloned from our prototype strain and sequence analysis has confirmed homology with Gram-negative bacterial adhesins. The ORF corresponded to 869 amino acids; we named this protein P95. Protein sequence similarity assessment demonstrated that this gene product belongs to the family of proteins including the filamentous haemagglutinin of Bordetella pertussis and the high-molecular-weight surface-exposed adhesins of Haemophilus influenzae. Comparison of adhesion and hybridization results emphasized the involvement of this gene in an essential pathogenic process of Campylobacter.

Fimbrial expression in enteric bacteria: a critical step in intestinal pathogenesis

The ability of species of enteric bacteria to recognize and colonize unique niches along the intestine is mainly based on receptor distribution and interpretation of a combination of environmental signals leading to the expression of specific adherence factors. Such elaborate orchestration of events is critical during the initial steps of pathogenesis.

Mutation in the peb1A locus of Campylobacter jejuni reduces interactions with epithelial cells and intestinal colonization of mice

Campylobacter jejuni is one of the leading causes of bacterial diarrhea throughout the world. We previously found that PEB1 is a homolog of cluster 3 binding proteins of bacterial ABC transporters and that a C. jejuni adhesin, cell-binding factor 1 (CBF1), if not identical to, contains PEB1. A single protein migrating at approximately 27 to 28 kDa was recognized by anti-CBF1 and anti-PEB1. To determine the role that the operon encoding PEB1 plays in C. jejuni adherence, peb1A, the gene encoding PEB1, was disrupted in strain 81-176 by insertion of a kanamycin resistance gene through homologous recombination. Inactivation of this operon completely abolished expression of CBF1, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. In comparison to the wild-type strain, the mutant strain showed 50- to 100-fold less adherence to and 15-fold less invasion of epithelial cells in culture. Mouse challenge studies showed that the rate and duration of intestinal colonization by the mutant were significantly lower and shorter than with the wild-type strain. In summary, PEB1 is identical to a previously identified cell-binding factor, CBF1, in C. jejuni, and the peb1A locus plays an important role in epithelial cell interactions and in intestinal colonization in a mouse model.

TheCampylobacter fetusS layer is not essential for initial interaction with HEp-2 cells

In vitro adherence assays were used to determine whether the S layer mediated interactions between Campylobacter fetus subsp. venerealis strains and HEp-2 cells. At multiplicity of infection ratios ranging from 0.1:1 through 100:1, quantitation of bacterial adherence by light microscopy revealed that S layer deficient isogenic C. fetus 809K and C. fetus 810K were not less efficient in their attachment to HEp-2 cells; either S layer deficient C. fetus strains interacted with HEp-2 cells in greater numbers than the corresponding wild-type parent strains 809 and 810 or there was no significant difference in adherence levels between wild-type and mutant strains. Adherence of C. fetus strains to HEp-2 cells increased most during the first 2 h of a 22-h incubation period with only a slight increase in C. fetus cell numbers occuring subsequent to 2 h. At each assay point throughout this 22-h time period, equivalent numbers of wild-type and S layer deficient C. fetus strains were observed associated with HEp-2 cells. Prior to 2 h, adherence levels of all C. fetus strains exceeded those of Escherichia coli AB264 and Salmonella typhimurium SL1344. And, unlike S. typhimurium, C. fetus did not undergo significant replication following initial adherence to HEp-2 cells. Campylobacter fetus did not adhere to HEp-2 cells in a localized or aggregative pattern but were randomly distributed over individual HEp-2 cells and at no time during the assay with C. fetus were changes in HEp-2 cell morphology apparent. These data suggest that the S layer is not essential for mediating initial interactions between C. fetus and HEp-2 cells.Key words: Campylobacter fetus, S layer, HEp-2.

Toxin production by Campylobacter spp

Of all the virulence factors that were proposed for Campylobacter jejuni and related species to cause disease in humans, the discovery of toxin production was the most promising but led to a rather confusing and even disappointing stream of data. The discussion of whether proteinaceous exotoxins are relevant in disease remains open. One important reason for this lack of consensus is the anecdotal nature of the literature reports. To provide a basis for an unbiased opinion, this review compiles all described exotoxins, compares their reported properties, and provides a summary of animal model studies and clinical data. The toxins are divided into enterotoxins and cytotoxins and are sorted according to their biochemical properties. Since many Campylobacter toxins have been compared with toxins of other species, some key examples of the latter are also discussed. Future directions of toxin research that appear promising are defined.

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

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

Campylobacter-host cell interactions

The enteric pathogens Campylobacter jejuni and Campylobacter coli are a major cause of infectious diarrhoea. Their ability to adhere to human epithelial cells is ubiquitous and their propensity to invade cells is also well documented and requires motility and de novo protein synthesis, as well as several host factors. The molecular basis of the interaction between campylobacters and host cells is only beginning to be elucidate. The characteristics of this interaction promise to be interesting and may provide new insights into host-pathogen interactions in other enteric diseases.