Effect of Cytolethal Distending Toxin of Campylobacter jejuni on Adhesion and Internalization in Cultured Cells and in Colonization of the Chicken Gut

The Enterotoxin Production and Antimicrobial Resistance of Campylobacter Strains Originating from Slaughter Animals

The pathogenicity of animal-origin Campylobacter strains, including antimicrobial resistance and enterotoxigenicity, was determined in this study. Overall, 149 Campylobacter isolates originating from cattle, swine and poultry were tested. The antimicrobial resistance profiles were examined by the diffusion disk method. The dominant resistance pattern was CIP_TET. The resistance rates for ciprofloxacin among swine, cattle and poultry isolates were 84%, 51% and 66%, respectively; for tetracycline, they were 82%, 57.1% and 76%, respectively. None of the obtained isolates was resistant to all four antimicrobials tested. The ability to produce enterotoxins was assessed by the use of a suckling mouse bioassay, with intestinal fluid accumulation as a positive result, and by CHO assay, with the elongation of cells as a positive result. The ability to produce enterotoxins was significantly higher among cattle isolates (61.2% and 71.4% positive isolates, respectively, in the bioassay and the CHO assay) than among swine (16% and 32% positive isolates, respectively) or poultry isolates (14% and 22% positive isolates, respectively). A strong positive correlation between in vitro and in vivo enterotoxicity tests was demonstrated.

Campylobacter jejuni Virulence Factors Identified by Modulating Their Synthesis on Ribosomes With Altered rRNA Methylation

Campylobacter jejuni is a major cause of food poisoning worldwide, and remains the main infective agent in gastroenteritis and related intestinal disorders in Europe and the USA. As with all bacterial infections, the stages of adhesion to host tissue, survival in the host and eliciting disease all require the synthesis of proteinaceous virulence factors on the ribosomes of the pathogen. Here, we describe how C. jejuni virulence is attenuated by altering the methylation of its ribosomes to disrupt the composition of its proteome, and how this in turn provides a means of identifying factors that are essential for infection and pathogenesis. Specifically, inactivation of the C. jejuni Cj0588/TlyA methyltransferase prevents methylation of nucleotide C1920 in the 23S rRNA of its ribosomes and reduces the pathogen’s ability to form biofilms, to attach, invade and survive in host cells, and to provoke the innate immune response. Mass spectrometric analyses of C. jejuni TlyA-minus strains revealed an array of subtle changes in the proteome composition. These included reduced amounts of the cytolethal distending toxin (CdtC) and the MlaEFD proteins connected with outer membrane vesicle (OMV) production. Inactivation of the cdtC and mlaEFD genes confirmed the importance of their encoded proteins in establishing infection. Collectively, the data identify a subset of genes required for the onset of human campylobacteriosis, and serve as a proof of principle for use of this approach in detecting proteins involved in bacterial pathogenesis.

Exploiting pglB Oligosaccharyltransferase-Positive and -Negative Campylobacter jejuni and a Multiprotease Digestion Strategy to Identify Novel Sites Modified by N-Linked Protein Glycosylation

Campylobacter jejuni is a bacterial pathogen encoding a unique N-linked glycosylation (pgl) system that mediates attachment of a heptasaccharide to N-sequon-containing membrane proteins by the PglB oligosaccharyltransferase (OST). Many targets of PglB are known, yet only a fraction of sequons are experimentally confirmed, and site occupancy remains elusive. We exploited pglB-positive (wild-type; WT) and -negative (ΔpglB) proteomes to identify potential glycosites. The nonglycosylated forms of known glycopeptides were typically increased in protein normalized abundance in ΔpglB relative to WT and restored by pglB reintroduction (ΔpglB::pglB). Sequon-containing peptide abundances were thus consistent with significant site occupancy in the presence of the OST. Peptides with novel sequons were either unaltered (likely not glycosylated) or showed abundance consistent with known glycopeptides. Topology analysis revealed that unaltered sequons often displayed cytoplasmic localization, despite originating from membrane proteins. Novel glycosites were confirmed using parallel multiprotease digestion, LC-MS/MS, and FAIMS-MS to define the glycoproteomes of WT and ΔpglB::pglB C. jejuni. We identified 142 glycosites, of which 32 were novel, and 83% of sites predicted by proteomics were validated. There are now 166 experimentally verified C. jejuni glycosites and evidence for occupancy or nonoccupancy of 31 additional sites. This study serves as a model for the use of OST-negative cells and proteomics for highlighting novel glycosites and determining occupancy in a range of organisms.

Identification of pathogenic genes in Campylobacter jejuni isolated from broiler carcasses and broiler slaughterhouses

Campylobacter jejuni is one of the most common causes of foodborne diseases worldwide. There are few reports on Campylobacter strains isolated from Latin-American countries. Here, 140 C. jejuni strains isolated from cloacal and transport boxes swabs, water from chiller tanks, and broiler carcasses of five poultry companies in Southern Brazil were identified using phenotypic and genotypic methods. Polymerase chain reaction (PCR) was used to analyze eight C. jejuni virulence markers: flaA, cadF, and invasion-associated (iam) genes, cdtABC operon (associated with the cytolethal distending toxin), and plasmidial virB11 and wlaN genes were present in 78.5%, 77.8%, 0%, 74.2%, 22.1%, and 10.7% of samples, respectively. There were 25 different virulence profiles: 1 (cdtA, cdtB, cdtC, flaA, and cadF), 2 (cdtA, cdtB, cdtC, flaA, cadF, and virB11), and 3 (cdtA, cdtB, cdtC, flaA, cadF, and wlaN) were the most common (> 60% of strains). We provide insight into factors related to the occurrence of this pathogen and their epidemiology.

Competitive reduction of poultry-borne enteric bacterial pathogens in chicken gut with bioactive Lactobacillus casei

In this study, the effect of sustainable probiotics on Campylobacter jejuni colonization and gut microbiome composition was evaluated using chicken as a model organism. Chickens were given Lactobacillus casei over-expressing myosin-cross-reactive antigen (LC+mcra). LC+mcra can generate bioactive compounds in larger quantity including conjugated linoleic acid. A total of 120 chickens were used in duplicate trials to investigate the effectiveness of LC+mcra in decreasing C. jejuni colonization by means of kanamycin resistant strain compared to the control group. We observed that LC+mcra can efficiently colonize various parts of the chicken gut and competitively reduce colonization of natural and challenged C. jejuni and natural Salmonella enterica. LC+mcra was found to reduce C. jejuni colonization in cecum, ileum and jejunum, by more than one log CFU/g when compared to the no-probiotic control group. Furthermore, 16S rRNA compositional analysis revealed lower abundance of Proteobacteria, higher abundance of Firmicutes, along with enriched bacterial genus diversity in gut of LC+mcra fed chicken. Decreased contamination of drinking water by C. jejuni and S. enterica was also observed, suggesting a potential function of reducing horizontal transfer of enteric bacteria in poultry. Outcomes of this study reveal high potential of LC+mcra as sustainable approach to decrease colonization of C. jejuni and S. enterica in poultry gut along with other beneficial attributes.

Comparative transcriptional analysis for Toll-like receptors, inflammatory cytokines, and apoptotic genes in response to different cytolethal-encoding and noncoding isolates of Salmonella enterica and Campylobacter jejuni from food and human stool

Diversity of Campylobacter and Salmonella strains in interaction with epithelial cells may explain distinct modes of the pathogenesis, varying from mild watery to severe inflammatory diarrhea. We analyzed impact of this diversity, in relation to carriage and expression of cytholethal distending toxin B (cdtB), on alteration of IL-8, TNF-α, TLR2, TLR4, TLR5, CASP3 mRNA and cytokine levels in HT-29 cell line. A diversity was observed for induction of genes among different strains. Great diversity in IL-8 induction was detected between cdtB⁺ and cdtB^- strains. Early analysis showed down-regulation of TNF-α, mostly among cdtB⁺ strains. Any increase or decrease in expression of TLR2 in the cdtB^-C. jejuni strains was orderly correlated with increase or decrease of TLR4 and TNF-α. Up-regulation of CASP3 was followed by upregulation of TLR2, -4 and/or TNF-α, regardless to the cdtB status. In conclusion, induction of inflammatory response could mediate by distinct C. jejuni and S. enterica strains by several ways.

Heterogeneity of cytolethal distending toxin sequence types of Campylobacter jejuni and correlation to invasion/cytotoxicity potential: The first molecular survey from Iran

The aim of this study was to evaluate the cytotoxicity and attachment/invasion potential of thermophilic Campylobacter isolates regarding their cdt_ABC sequence types and virulence-associated gene content. A total of 33 Campylobacter spp. were identified from 750 stool samples isolated from patients characterized with diarrhea. The prevalence rates of flaA, ciaB, and pldA genes among the isolates were 97, 100, and 15%, respectively. The iam gene was found in 100% of the C. coli isolates while it was not detected in C. jejuni isolates. Four PCR primer pairs jointly amplifying the entire cdt_ABC genes array and sequence analysis revealed variations dispersed along the sequence array. The isolates attachment to HeLa cells ranged from 89 ± 2-100%, and the range of invasions was also from 0 to 11 ± 0.04%. The cytotoxicity value was between 2 and 32 in cdt⁺ isolates with no significant correlation to any of the cdt_ABC sequence types. Moreover, the cdt_ABC encoding strains had increased invasion to HeLa cells, and all of the related patients presented much higher white and red blood cell shedding in stool specimens (P-value≤ 0.001). No significant difference was observed between cdt⁺ and cdt^- isolates in their attachment rate to HeLa cells. About 48% of all the Iranian Campylobacter population lacked a complete set of cdt_ABC genes array, suggesting low invasion and cytotoxicity potential of the isolates which are heterogeneous in their cdt genes and virulence.

Prediction of CTL epitope, in silico modeling and functional analysis of cytolethal distending toxin (CDT) protein of Campylobacter jejuni

Background

Campylobacter jejuni is a potent bacterial pathogen culpable for diarrheal disease called campylobacteriosis. It is realized as a major health issue attributable to unavailability of appropriate vaccines and clinical treatment options. As other pathogens, C. jejuni entails host cellular components of an infected individual to disseminate this disease. These host–pathogen interfaces during C. jejuni infection are complex, vibrant and involved in the nicking of host cell environment, enzymes and pathways. Existing therapies are trusted only on a much smaller number of drugs, most of them are insufficient because of their severe host toxicity or drug-resistance phenomena. To find out remedial alternatives, the identification of new biotargets is highly anticipated. Understanding the molecules involved in pathogenesis has the potential to yield new and exciting strategies for therapeutic intervention. In this direction, advances in bioinformatics have opened up new possibilities for the rapid measurement of global changes during infection and this could be exploited to understand the molecular interactions involved in campylobacteriosis.

Methods

In this study, homology modeling, epitope prediction and identification of ligand binding sites has been explored. Further attempt to generate strapping 3D model of cytolethal distending toxin protein from C. jejuni have been described for the first time.

Results

CDT protein isolated from C. jejuni was analyzed using various bioinformatics and immuno-informatics tools including sequence and structure tools. A total of fifty five antigenic determinants were predicted and prediction results of CTL epitopes revealed that five MHC ligand are found in CDT. The three potential pocket binding site are found in the sequence that can be useful for drug designing.

Conclusions

This model, we hope, will be of help in designing and predicting novel CDT inhibitors and vaccine candidates.

Role of motAB in adherence and internalization in polarized Caco-2 cells and in cecal colonization of Campylobacter jejuni

Campylobacter jejuni, a gram-negative motile bacterium commonly found in the chicken gastrointestinal tract, is one of the leading causes of bacterial gastroenteritis in humans worldwide. An intact and functional flagellum is important for C. jejuni virulence and colonization. To understand the role of C. jejuni motility in adherence and internalization in polarized Caco-2 cells and in cecal colonization of chickens we constructed a C. jejuni NCTC11168 V1 deltamotAB mutant. The motAB genes code for the flagellar motor, which enables the rotation of the flagellum. The nonmotile deltamotAB mutant expressed a full-length flagellum, which allowed us to differentiate between the roles of full-length flagella and motility in the ability of C. jejuni to colonize. To study the adherence and invasion abilities of the C. jejuni deltamotAB mutant we chose to use polarized Caco-2 cells, which are thought to be more representative of in vivo intestinal cell architecture and function. Although the C. jejuni deltamotAB mutant adhered significantly better than the wild type to the Caco-2 cells, we observed a significant reduction in the ability to invade the cells. In this study we obtained evidence that the flagellar rotation triggers C. jejuni invasion into polarized Caco-2 cells and we believe that C. jejuni is propelled into the cell with a drill-like rotation. The deltamotAB mutant was also tested for its colonization potential in a 1-day-old chicken model. The nonmotile C. jejuni deltamotAB mutant was not able to colonize any birds at days 3 and 7, suggesting that motility is essential for C. jejuni colonization.

Enhancement of chicken macrophage cytokine response to Salmonella Typhimurium when combined with bacteriophage P22

Salmonella infections are reported as the second most common pathogen caused foodborne disease in the United States, and several Salmonella serovars can colonize in the intestinal tracts of poultry. Reducing Salmonella in poultry is crucial to decrease the incidence of salmonellosis in humans. In this study, we evaluated the immune response of chicken macrophage cells (HD-11) and effects of bacteriophage P22 against the extra- and intracellular S. Typhimurium LT2. Four treatments, (1) HD-11 cells as control, (2) HD-11 cells with LT2, (3) HD-11 cells with LT2 and P22, and (4) HD-11 cells with P22, were administered, and IL-8 responses of HD-11 cells were measured using an ELISA. Also, four cytokine (IL-4, IL-8, IL-10, and IFN-γ) gene expression levels in the presence of LT2 and/or P22 were quantified by qRT-PCR. We found that P22 lysed the extra- and intracellular LT2, which adhered and were taken up by the HD-11 cells. The ELISA indicated that HD-11 cells produced significantly higher IL-8 cytokine levels in the supernatant during the intracellular lyses of LT2 by P22 (P < 0.05). The IL-8 expression levels measured by qRT-PCR also exhibited similar results with the IL-8 production based on ELISA measurements.

Cytolethal distending toxin (CDT) of the Haemophilus parasuis SC096 strain contributes to serum resistance and adherence to and invasion of PK-15 and PUVEC cells

Cytolethal distending toxin (CDT) is proposed to be an important virulence determinant of many pathogens. Although two cdt gene cluster loci have been identified in Haemophilus parasuis strain SH0165, the characteristics of CDTs associated with pathogenesis remain unclear. In this study, three CDT-deficient mutants, cdt-1, cdt-2 and the double-knockout cdt-1cdt-2 (Δcdt-1, Δcdt-2 and Δcdt-1Δcdt-2, respectively), were obtained in the H. parasuis serovar 4 clinical strain SC096 using a natural transformation method. Compared to the wild-type SC096 strain, the Δcdt-1, Δcdt-2 and Δcdt-1Δcdt-2 mutants showed subtle growth defects and clearly exhibited an increased sensitivity to the bactericidal action of porcine and rabbit sera. Additionally, these mutants had a significantly reduced ability to adhere to and invade porcine umbilicus vein endothelial cells (PUVEC) and porcine kidney epithelial cells (PK-15). These findings suggest that both CDTs in the H. parasuis SC096 strain are involved in serum resistance and adherence and invasion of host cells.

A tolerogenic mucosal immune response leads to persistent Campylobacter jejuni colonization in the chicken gut

Campylobacter enteritis is the most reported zoonotic disease in many developed countries where it imposes a serious health burden. Campylobacter transmission to humans occurs primarily through the chicken vector. Chicks are regarded as a natural host for Campylobacter species and are colonized with C. jejuni in particular. But despite carrying a very high bacterial load in their gastrointestinal tract, these birds, in contrast to humans, do not develop pathological signs. It seems that in chickens C. jejuni principally harbors in the cecal mucosal crypts, where an inefficient inflammatory response fails to clear the bacterium from the gut. Recent intensive research resulted in an increased insight into the cross talk between C. jejuni and its avian host. This review discusses the chicken intestinal mucosal immune response upon C. jejuni entrance, leading to tolerance and persistent cecal colonization. It might in addition provide a solid base for further research regarding this topic aiming to fully understand the host-bacterium dynamics of C. jejuni in chicks and to develop effective control measures to clear this zoonotic pathogen from poultry lines.

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.

Update on Campylobacter jejuni vaccine development for preventing human campylobacteriosis

Campylobacteriosis constitutes a serious medical and socioeconomic problem worldwide. Rapidly increasing antibiotic resistance of bacterial strains compels us to develop alternative therapeutic strategies and to search for efficient immunoprophylactic methods. The vast majority of Campylobacter infections in developed countries occur as sporadic cases, mainly caused by eating undercooked Campylobacter-contaminated poultry. The most efficient strategy of decreasing the number of human Campylobacter infections is by implementing protective vaccinations for humans and/or chickens. Despite more than 10 years of research, an effective anti-Campylobacter vaccine has not been developed. This review highlights our increasing knowledge of Campylobacter interaction with host cells and focuses on recently published data describing the efficacy of anti-Campylobacter vaccine prototypes.

Differences in virulence attributes between cytolethal distending toxin positive and negative Campylobacter jejuni strains

Campylobacter jejuni is a common gastrointestinal bacterial pathogen. Although cytolethal distending toxin (CDT) is proposed to be an important virulence determinant of this pathogen, how CDT(+) and CDT(-) strains differ in their biological properties remains largely unknown. The virulence properties of CDT(+) and CDT(-) strains were studied on HeLa cells and in the suckling mouse model. Presence of the cdtB gene in Campylobacter species was determined by PCR. Five each of CDT(+) and CDT(-) C. jejuni strains were subjected to adherence, invasion and cytotoxicity assay on the HeLa cell line. Bacterial culture supernatants with and without CDT activity were inoculated intragastrically into 2-day-old suckling mice. The mice were sacrificed within 48 h. Histopathological examination of stomach, jejunum, ileum and colon was performed by haematoxylin/eosin staining. cdtB was detected in 88 % and 14 % of C. jejuni and Campylobacter coli strains, respectively. CDT(+) C. jejuni strains adhered to and invaded HeLa cells in significantly higher numbers than CDT(-) strains [CDT(+) vs CDT(-), adherence 2.7 x 10(4)+/-3.5 x 10(4) vs 2.7 x 10(2)+/-1.9 x 10(2); invasion 1.0 x 10(3)+/-1.3 x 10(3) vs 1.4 x 10(1)+/-3.1 x 10(1); P<0.01]. Culture supernatants of all CDT(+) strains demonstrated CDT activity on HeLa cells. Mice inoculated with supernatant containing CDT activity had moderate to severe pathology in different parts of their gastrointestinal tract, with the colon being the major target. Mice inoculated with supernatant lacking CDT activity showed no significant pathology in the gastrointestinal tract. The results demonstrate that CDT(+) C. jejuni strains adhere to and invade epithelial cells more efficiently than CDT(-) strains. CDT is responsible for intestinal pathology and the colon is the major target.

Campylobacter jejuni: molecular biology and pathogenesis

Campylobacter jejuni is a foodborne bacterial pathogen that is common in the developed world. However, we know less about its biology and pathogenicity than we do about other less prevalent pathogens. Interest in C. jejuni has increased in recent years as a result of the growing appreciation of its importance as a pathogen and the availability of new model systems and genetic and genomic technologies. C. jejuni establishes persistent, benign infections in chickens and is rapidly cleared by many strains of laboratory mouse, but causes significant inflammation and enteritis in humans. Comparing the different host responses to C. jejuni colonization should increase our understanding of this organism.