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

Campylobacter jejuni from no antibiotics ever (NAE) broilers: prevalence, antibiotic resistance, and virulence genes analysis

Campylobacter jejuni (C. jejuni) is a leading foodborne illness causing bacteria, and poultry is a major reservoir of this pathogen. With the recent increase in broiler production under the "no antibiotics ever" (NAE) system, this study aimed to assess the prevalence, antibiotic resistance, and virulence characteristics of C. jejuni isolated from NAE raised broilers. A total of 270 cloacal swabs were collected from the live-hang areas of 3 commercial processing plants over 9 wk. Each processing plant was visited 3 times at a 1-wk interval, and 30 samples were collected per visit. Among the total 270 cloacal swab samples, C. jejuni was isolated from 44 (16.3%) samples . Of these isolates, 65.9% possessed toxin-producing genes cdtA, cdtB, and cdtC, and invasion gene ciaB. The prevalence of antibioitc resistance genes aph (3')-IIIa, erm(B) were 59.1%, and 50%, respectively. Nine (20.45%) C. jejuni isolates were identified as multidrug resistant (MDR), and 18 (40.9%) isolates showed resistance to at least 1 tested antibiotic. The highest resistance was observed against tetracycline (29.5%), followed by nalidixic acid (25%), whereas 22.7% of isolates were resistant to 2 clinically important antibiotics, azithromycin and ciprofloxacin. These results suggest that there ishigh prevalence level of multi-drug resistant C. jejuni with toxin producing virulence genes in the NAE-raised broilers sampled in this study, indicating the potential for serious human illnesses if transmitted through the food chain.

Transmission of dominant strains of Campylobacter jejuni and Campylobacter coli between farms and retail stores in Ecuador: Genetic diversity and antimicrobial resistance

Thermotolerant Campylobacter is an important zoonotic pathogen known for causing gastroenteritis in humans, with poultry as its primary reservoir. A total of 468 samples were collected, of which 335 were chicken carcass samples (representing the food component), and 133 were chicken caeca samples (representing the animal component). These samples underwent culture, with colonies examined under a microscope. Species identification was achieved through multiplex PCR. Additionally, antimicrobial susceptibility profiles were determined using the Kirby-Bauer method, testing for sensitivity to gentamicin, ciprofloxacin, tetracycline, and erythromycin. Additionally, 55 C. jejuni (62.5%) and 33 C. coli (37.5%) isolates were selected for whole genome sequencing (WGS). A High prevalence of Campylobacter was observed, with rates of 95.5% (n = 127, CI95%: 92.5% - 98.5%) in the animal component and 72.5% (n = 243, CI95%: 69.9% - 75.1%) in the food component. Specifically, C. jejuni was detected in 33.1% (n = 42) of poultry farms and 38.3% (n = 93) of chicken carcasses, while C. coli was found in 64.6% (n = 82) of poultry farms and 60.5% (n = 147) of chicken carcasses. Antimicrobials with the highest rates of resistance (67%-100%) were ciprofloxacin and tetracycline, in both animal and food component isolates. Erythromycin resistance was notable, ranging from 22% to 33%, with only two C. jejuni isolates from retail were resistant to gentamicin. Furthermore, multidrug resistance was identified in 23% (20 isolates) of the Campylobacter isolates. Genetic analysis revealed the presence of fourteen resistance genes in both C. jejuni and C. coli isolates, including tet(O), blaOXA-460, blaOXA-184, blaOXA-489, blaOXA-193, blaOXA-784, blaOXA-603, aph(3')-IIIa, aad9, aph(2'')-If, aadE-Cc, sat4, and ant(6)-Ia. Additionally, twenty-five plasmids were detected in the 88 Campylobacter isolates examined. Interestingly, most isolates also harbored genes encoding putative virulence factors associated with pathogenicity, invasion, adherence, and production of cytolethal distending toxin (cdt): cheV, cheA, cheW, cheY, flaA, flgR, flaC, flaD, flgB, flgC, ciaB, ciaC. The WGS analysis showed the presence of several cgSTs in both animal and food components, with nine of them widely disseminated between components. Moreover, C. coli and C. jejuni isolates from different sources presented less than 11 single nucleotide polymorphisms (SNPs), suggesting clonality (16 isolates). Further analysis using SNP tree demonstrated widespread distribution of certain C. jejuni and C. coli clones across multiple farms and retail stores. This study presents, for the first-time, insights into the clonality, plasmid diversity, virulence, and antimicrobial resistance (AMR) of thermotolerant Campylobacter strains originating from the Ecuadorian poultry industry. The identification of AMR genes associated with the main antibiotics used in the treatment of campylobacteriosis in humans, highlights the importance of the prudent use of antimicrobials in the poultry industry. Additionally, this research remarks the need for regional studies to understand the epidemiology of this pathogen.

Revisiting bacterial cytolethal distending toxin structure and function

Cytolethal distending toxins (CDTs) are intracellular-acting bacterial genotoxins generated by a diverse group of mucocutaneous human pathogens. CDTs must successfully bind to the plasma membrane of host cells in order to exert their modulatory effects. Maximal toxin activity requires all three toxin subunits, CdtA, CdtB, and CdtC, which, based primarily on high-resolution structural data, are believed to preassemble into a tripartite complex necessary for toxin activity. However, biologically active toxin has not been experimentally demonstrated to require assembly of the three subunits into a heterotrimer. Here, we experimentally compared concentration-dependent subunit interactions and toxin cellular activity of the Campylobacter jejuni CDT (Cj-CDT). Co-immunoprecipitation and dialysis retention experiments provided evidence for the presence of heterotrimeric toxin complexes, but only at concentrations of Cj-CdtA, Cj-CdtB, and Cj-CdtC several logs higher than required for Cj-CDT-mediated arrest of the host cell cycle at the G2/M interface, which is triggered by the endonuclease activity associated with the catalytic Cj-CdtB subunit. Microscale thermophoresis confirmed that Cj-CDT subunit interactions occur with low affinity. Collectively, our data suggest that at the lowest concentrations of toxin sufficient for arrest of cell cycle progression, mixtures of Cj-CdtA, Cj-CdtB, and Cj-CdtC consist primarily of non-interacting, subunit monomers. The lack of congruence between toxin tripartite structure and cellular activity suggests that the widely accepted model that CDTs principally intoxicate host cells as preassembled heterotrimeric structures should be revisited.

Whole-genome-based characterization of Campylobacter jejuni from human patients with gastroenteritis collected over an 18 year period reveals increasing prevalence of antimicrobial resistance

Campylobacteriosis is the most common cause of acute gastrointestinal bacterial infection in Europe, with most infections linked to the consumption of contaminated food. While previous studies found an increasing rate of antimicrobial resistance (AMR) in Campylobacter spp. over the past decades, the investigation of additional clinical isolates is likely to provide novel insights into the population structure and mechanisms of virulence and drug resistance of this important human pathogen. Therefore, we combined whole-genome sequencing and antimicrobial-susceptibility testing of 340 randomly selected Campylobacter jejuni isolates from humans with gastroenteritis, collected in Switzerland over an 18 year period. In our collection, the most common multilocus sequence types (STs) were ST-257 (n=44), ST-21 (n=36) and ST-50 (n=35); the most common clonal complexes (CCs) were CC-21 (n=102), CC-257 (n=49) and CC-48 (n=33). High heterogeneity was observed among STs, with the most abundant STs recurring over the entire study period, while others were observed only sporadically. Source attribution based on ST assigned more than half of the strains to the 'generalist' category (n=188), 25  % as 'poultry specialist' (n=83), and only a few to 'ruminant specialist' (n=11) or 'wild bird' origin (n=9). The isolates displayed an increased frequency of AMR from 2003 to 2020, with the highest rates of resistance observed for ciprofloxacin and nalidixic acid (49.8 %), followed by tetracycline (36.9 %). Quinolone-resistant isolates carried chromosomal gyrA mutations T86I (99.4 %) and T86A (0.6 %), whereas tetracycline-resistant isolates carried tet(O) (79.8 %) or mosaic tetO/32/O (20.2 %) genes. A novel chromosomal cassette carrying several resistance genes, including aph(3')-III, satA and aad(6), and flanked by insertion sequence elements was detected in one isolate. Collectively, our data revealed an increasing prevalence of resistance to quinolones and tetracycline in C. jejuni isolates from Swiss patients over time, linked to clonal expansion of gyrA mutants and acquisition of the tet(O) gene. Investigation of source attribution suggests that infections are most likely related to isolates from poultry or generalist backgrounds. These findings are relevant to guide future infection prevention and control strategies.

Delivery, structure, and function of bacterial genotoxins

Bacterial genotoxins are peptide or protein virulence factors produced by several pathogens, which make single-strand breaks (SSBs) and/or double-strand DNA breaks (DSBs) in the target host cells. If host DNA inflictions are not resolved on time, host cell apoptosis, cell senescence, and/or even bacterial pathogen-related cancer may occur. Two multi-protein AB toxins, cytolethal distending toxin (CDT) produced by over 30 bacterial pathogens and typhoid toxin from Salmonella Typhi, as well as small polyketide-peptides named colibactin that causes the DNA interstrand cross-linking and subsequent DSBs is the most well-characterized bacterial genotoxins. Using these three examples, this review discusses the mechanisms by which these toxins deliver themselves into the nucleus of the target host cells and exert their genotoxic functions at the structural and functional levels.

Present and pioneer methods of early detection of food borne pathogens

Food-borne pathogens are a severe threat to human illness and death world-wide. Researchers have reported more than 250 food-borne diseases. Most of these are infections caused by a wide variety of bacteria, viruses, and parasites. It has a significant economic impact also. Detection of pathogenic microbes is thus essential for food safety. Such identification techniques could meet the following parameters viz., the accuracy of detection techniques that are quick, efficient, economical, highly sensitive, specific, and non-labor intensive. The various available methods for detecting food pathogens are classified into different groups, each having its advantages and disadvantages. The conventional methods are usually the first choice of detection even though they are laborious. Modern techniques such as biosensors, immunological assays, and macromolecule-based (nucleic acid) methods are being developed and refined to overcome traditional methods' limitations. Early detection of pathogens and secure food safety at each stage of food processing to storage, utilizing improved methodologies are mandatory. This review summarizes the deadly food pathogens leading to significant outbreaks and discusses the importance of early detection methods and advanced detection methods in comparison.

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.

Antimicrobial Resistance Profiles, Virulence Genes, and Genetic Diversity of Thermophilic Campylobacter Species Isolated From a Layer Poultry Farm in Korea

Thermophilic Campylobacter species are among the major etiologies of bacterial enteritis globally. This study aimed at assessing the antimicrobial resistance (AMR) profiles, virulence genes, and genetic diversity of thermophilic Campylobacter species isolated from a layer poultry farm in South Korea. One hundred fifty-three chicken feces were collected from two layer poultry farms in Gangneung, South Korea. The Campylobacter species were isolated by cultural techniques, while PCR and sequencing were used for species confirmation. Antimicrobial susceptibility testing for six antimicrobials [ciprofloxacin (CIP), nalidixic acid (NAL), sitafloxacin (SIT), erythromycin (ERY), tetracycline (TET), and gentamicin (GEN)] was carried out by broth microdilution. Three AMR and nine virulence genes were screened by PCR. Genotyping was performed by flaA-restriction fragment length polymorphism (RFLP) and multilocus sequence typing (MLST). Of the 153 samples, Campylobacter spp. were detected in 55 (35.9%), with Campylobacter jejuni and Campylobacter coli being 49 (89.1%) and six (10.9%), respectively. High-level resistance was observed for CIP (100%), NAL (100%), and TET (C. jejuni, 93.9%; C. coli: 83.3%). No resistance was observed for SIT. The missense mutation (C257T) in gyrA gene was confirmed by sequencing, while the tet(O) gene was similar to known sequences in GenBank. The rate of multidrug-resistant (MDR) strains was 8.2%, and they all belonged to C. jejuni. All Campylobacter isolates possessed five virulence genes (cdtB, cstII, flaA, cadF, and dnaJ), but none possessed ggt, while the rates for other genes (csrA, ciaB, and pldA) ranged between 33.3 and 95.9%. The flaA-RFLP yielded 26 flaA types (C. jejuni: 21 and C. coli: five), while the MLST showed 10 sequence types (STs) for C. jejuni and three STs for C. coli, with CC-607 (STs 3611) and CC-460 (ST-460) being predominant. Among the 10 STs of C. jejuni, three were newly assigned. The findings of this study highlight the increased resistance to quinolones and TET, the virulence potential, and the diverse genotypes among Campylobacter strains isolated from the layer poultry farm.

A genomic concept in cellular interaction of clinical Campylobacter spp. with human epithelial colorectal adenocarcinoma cells

This study aimed to realize the genomic concept of cellular interaction of clinical Campylobacter spp. with human epithelial colorectal adenocarcinoma cells. It was indicated that the mean adherence and invasion rate of C.jejuni isolates was significantly higher than C.coli and the highest adhesion rate among the C.jejuni and C.coli belonged to strains harboring 4 (flaA, cadF, peb1A, and flpA) and 3 (flaA, cadF, and peb1A) adherence genes, respectively, which indicates that the adhesion potential of C.coli and C.jejuni strains is associated with the coordinate function and cumulative effect of selected virulence-associated genes. The highest invasion rate in C.jejuni (10.3%) and C.coli (8.4%) isolates belonged to strains which concomitantly contained 3 (ciaB, iamA, and tlp1) and 2 (ciaB and iamA) invasion-associated genes which emphasizes on the cooperative roles of these genes in C.jejuni and C.coli invasion to Caco-2 cells. The toxicity of C.jejuni for Caco-2 cells was proved higher than that of C.coli. There was a positive correlation between adherence, invasion and toxicity of both C.jejuni and C.coli isolates. Moreover, the expression levels of CDT-producing genes in C.jejuni strains was significantly higher than that of C.coli. The average cytotoxicity of the strains with all three CDT-encoding genes (cdtA, cdtB and cdtC) was statistically higher than those lacking one or more CDT subunits. A crucial contribution of CdtB to the cytotoxicity of Campylobacter strains was detected. Following the treatment of epithelial cells with C.jejuni or C.coli, IL-8 and TNF-α were significantly increased compared to untreated Caco-2 cells, and the highest IL-8 expression was observed in both C.jejuni and C.coli expressing all CDTs (cdtA, cdtB, and cdtC). We, for the first time, indicated the major contribution of TLR2 and TLR4 in campylobacter initiation of pathogenesis, while increased invasiveness and cytotoxicity was significantly associated with the increased expression of TLR4 in C.jejuni isolates.

Gut Microbiota and Colon Cancer: A Role for Bacterial Protein Toxins?

Accumulating evidence indicates that the human intestinal microbiota can contribute to the etiology of colorectal cancer. Triggering factors, including inflammation and bacterial infections, may favor the shift of the gut microbiota from a mutualistic to a pro-carcinogenic configuration. In this context, certain bacterial pathogens can exert a pro-tumoral activity by producing enzymatically-active protein toxins that either directly induce host cell DNA damage or interfere with essential host cell signaling pathways involved in cell proliferation, apoptosis, and inflammation. This review is focused on those toxins that, by mimicking carcinogens and cancer promoters, could represent a paradigm for bacterially induced carcinogenesis.

Functional Study of Haemophilus ducreyi Cytolethal Distending Toxin Subunit B

The Cytolethal Distending Toxin (CDT) is produced by many Gram-negative pathogenic bacteria responsible for major foodborne diseases worldwide. CDT induces DNA damage and cell cycle arrest in host-cells, eventually leading to senescence or apoptosis. According to structural and sequence comparison, the catalytic subunit CdtB is suggested to possess both nuclease and phosphatase activities, carried by a single catalytic site. However, the impact of each activity on cell-host toxicity is yet to be characterized. Here, we analyze the consequences of cell exposure to different CDT mutated on key CdtB residues, focusing on cell viability, cell cycle defects, and DNA damage induction. A first class of mutant, devoid of any activity, targets putative catalytic (H160A), metal binding (D273R), and DNA binding residues (R117A-R144A-N201A). The second class of mutants (A163R, F156-T158, and the newly identified G114T), which gathers mutations on residues potentially involved in lipid substrate binding, has only partially lost its toxic effects. However, their defects are alleviated when CdtB is artificially introduced inside cells, except for the F156-T158 double mutant that is defective in nuclear addressing. Therefore, our data reveal that CDT toxicity is mainly correlated to CdtB nuclease activity, whereas phosphatase activity may probably be involved in CdtB intracellular trafficking.

Pathogenicity of Campylobacter strains of poultry and human origin from Poland

The aim of this study was to determine the pathogenic markers associated with Campylobacter infection in humans. A total of 104 Campylobacter isolates obtained from poultry and humans were examined for the presence of nine virulence genes and their ability to adhere to, invade and produce cytotoxin were defined using HeLa cells. The diversity of the Campylobacter spp. isolates was studied based on sequencing of the SVR-region of flaA gene. Altogether 45 flaA-SVR alleles were identified among 104 Campylobacter isolates of poultry and human origin. All Campylobacter isolates possessed flaA, cadF and racR genes involved in adherence. Accordingly, all poultry and human isolates exhibited adherence towards HeLa cells at mean levels of 0.95% and 0.82% of starting viable inoculum, respectively. The genes involved in invasion (iam and pldA) and cytotoxin production (cdtA, cdtB and cdtC) were also widely distributed among the human and poultry Campylobacter isolates. Significantly higher invasiveness was observed for poultry isolates (mean level of 0.002% of starting bacterial inoculum) compared to human isolates (0.0005%). Interestingly the iam gene, associated with invasion, was more common in human (100%) than poultry (84%) isolates, and the poultry isolates lacking the iam gene showed a marked reduction in their ability to invade HeLa cells. Moreover, virB11 was present in 22% of the poultry and 70.4% of the human isolates. Strains lacking virB11 showed a slight reduction in invasion, however in the absence of iam even the poultry isolates containing virB11 were unable to invade HeLa cells. The mean cytotoxicity of Campylobacter isolates from poultry and human was 26.7% and 38.7%, respectively. Strains missing both the cdtB and cdtC genes were non-cytotoxic compared to strains containing all three cdtABC genes, which were the most cytotoxic among the C. jejuni and C. coli isolates from both sources. No cytotoxic effect was observed in only 4% of poultry and 5.6% of human isolates.

Oral and intestinal bacterial exotoxins: Potential linked to carcinogenesis

Growing evidence suggests that imbalances in resident microbes (dysbiosis) can promote chronic inflammation, immune-subversion, and production of carcinogenic metabolites, thus leading to neoplasia. Yet, evidence to support a direct link of individual bacteria species to human sporadic cancer is still limited. This chapter focuses on several emerging bacterial toxins that have recently been characterized for their potential oncogenic properties toward human orodigestive cancer and the presence of which in human tissue samples has been documented. These include cytolethal distending toxins produced by various members of gamma and epsilon Proteobacteria, Dentilisin from mammalian oral Treponema, Pasteurella multocida toxin, two Fusobacterial toxins, FadA and Fap2, Bacteroides fragilis toxin, colibactin, cytotoxic necrotizing factors and α-hemolysin from Escherichia coli, and Salmonella enterica AvrA. It was clear that these bacterial toxins have biological activities to induce several hallmarks of cancer. Some toxins directly interact with DNA or chromosomes leading to their breakdowns, causing mutations and genome instability, and others modulate cell proliferation, replication and death and facilitate immune evasion and tumor invasion, prying specific oncogene and tumor suppressor pathways, such as p53 and β-catenin/Wnt. In addition, most bacterial toxins control tumor-promoting inflammation in complex and diverse mechanisms. Despite growing laboratory evidence to support oncogenic potential of selected bacterial toxins, we need more direct evidence from human studies and mechanistic data from physiologically relevant experimental animal models, which can reflect chronic infection in vivo, as well as take bacterial-bacterial interactions among microbiome into consideration.

Virulence Traits of Inpatient Campylobacter jejuni Isolates, and a Transcriptomic Approach to Identify Potential Genes Maintaining Intracellular Survival

There are still major gaps in our understanding of the bacterial factors that influence the outcomes of human Campylobacter jejuni infection. The aim of this study was to compare the virulence-associated features of 192 human C. jejuni strains isolated from hospitalized patients with diarrhoea (150/192, 78.1%), bloody diarrhoea (23/192, 11.9%), gastroenteritis (3/192, 1.6%), ulcerative colitis (3/192, 1.5%), and stomach ache (2/192, 1.0%). Traits were analysed with genotypic and phenotypic methods, including PCR and extracellular matrix protein (ECMP) binding, adhesion, and invasion capacities. Results were studied alongside patient symptoms, but no distinct links with them could be determined. Since the capacity of C. jejuni to invade host epithelial cells is one of its most enigmatic attributes, a high throughput transcriptomic analysis was performed in the third hour of internalization with a C. jejuni strain originally isolated from bloody diarrhoea. Characteristic groups of genes were significantly upregulated, outlining a survival strategy of internalized C. jejuni comprising genes related (1) to oxidative stress; (2) to a protective sheath formed by the capsule, LOS, N-, and O- glycosylation systems; (3) to dynamic metabolic activity supported by different translocases and the membrane-integrated component of the flagellar apparatus; and (4) to hitherto unknown genes.

Campylobacter in an Urban Estuary: Public Health Insights from Occurrence, HeLa Cytotoxicity, and Caco-2 Attachment Cum Invasion

Aquatic recreation in urban estuaries worldwide is often restricted by fecal pollution. Variability in the occurrence of fecal pathogens and their differential virulence potentials within these estuaries may result in variable public health risks. To address this hypothesis, Campylobacter were isolated from the Yarra River estuary, Australia and then characterized via HeLa cell cytotoxicity and attachment to and the invasion of Caco-2 monolayers. Overall, 54% (n=216) of estuarine samples (water and sediment combined) yielded biochemically confirmed culturable Campylobacter; higher detection was recorded in water (92%, n=90) than in the bank and bed sediments combined (27%, n=126). The seasonality of occurrence was not significant. HeLa cell cytotoxicity revealed that estuarine Campylobacter had low cytotoxin titers; the 95% confidence interval (CI) ranged between 61 and 85, which was markedly lower than the mean value (~386) for the C. jejuni 11168 reference pathogenic strain. The Caco-2 attachment of estuarine Campylobacter isolates (n=189) revealed that the 95%CI for the attachment efficiency of the test strains ranged between 0.09 and 0.1%, with only 3.7% having a higher efficiency than the 5^th percentile value for C. jejuni 11168. None of the estuarine strains exhibited Caco-2 invasion capabilities. In contrast to the common assumption during quantitative microbial/risk assessments (QMRAs) that all environmental strains are pathogenic, the present results revealed that Campylobacter within the Yarra River estuary had very low virulence potential. Since this is the first study to use human epithelial cell lines to characterize estuary-borne pathogens, these results generate valuable insights for a better understanding of the public health risks in urban estuaries that will underpin more robust QMRAs.

Human campylobacteriosis: A public health concern of global importance

Campylobacter species are among the leading cause of bacterial foodborne and waterborne infections. In addition, Campylobacter is one of the major causative agent of bacterial gastrointestinal infections and the rise in the incidence of Campylobacter infections have been reported worldwide. Also, the emergence of some Campylobacter species as one of the main causative agent of diarrhea and the propensity of these bacteria species to resist the actions of antimicrobial agents; position them as a serious threat to the public health. This paper reviews Campylobacter pathogenicity, infections, isolation and diagnosis, their reservoirs, transmission pathways, epidemiology of Campylobacter outbreaks, prevention and treatment option, antibiotics resistance and control of antibiotics use.

Cytolethal Distending Toxin Subunit B: A Review of Structure-Function Relationship

The Cytolethal Distending Toxin (CDT) is a bacterial virulence factor produced by several Gram-negative pathogenic bacteria. These bacteria, found in distinct niches, cause diverse infectious diseases and produce CDTs differing in sequence and structure. CDTs have been involved in the pathogenicity of the associated bacteria by promoting persistent infection. At the host-cell level, CDTs cause cell distension, cell cycle block and DNA damage, eventually leading to cell death. All these effects are attributable to the catalytic CdtB subunit, but its exact mode of action is only beginning to be unraveled. Sequence and 3D structure analyses revealed similarities with better characterized proteins, such as nucleases or phosphatases, and it has been hypothesized that CdtB exerts a biochemical activity close to those enzymes. Here, we review the relationships that have been established between CdtB structure and function, particularly by mutation experiments on predicted key residues in different experimental systems. We discuss the relevance of these approaches and underline the importance of further study in the molecular mechanisms of CDT toxicity, particularly in the context of different pathological conditions.

Evaluations of Alkyl hydroperoxide reductase B cell antigen epitope as a potential epitope vaccine against Campylobacter jejuni

OBJECTIVE

The present study aimed to screen and find alkyl hydroperoxide reductase (AhpC) B cell dominant epitope of Campylobacter jejuni (C. jejuni).

MATERIALS AND METHODS

Bio-informatic algorithms were used to predict B cell epitopes of AhpC. The AhpC protein and chemically synthesized antigenic epitopes of C. jejuni were considered as antigens, and the AhpC antibody was used as the primary antibody, ELISA and dot blot were used to analyze and screen the dominant epitope. The specific IgG of mice serum and IL-4 in splenocyte culture supernatant were detected by ELISA. The protective efficacy was evaluated by animal disease index and tissue histopathological staining of the jejunum.

RESULTS

Seven epitopes of AhpC were predicted, one epitope (AhpC4-16) was found to recognize the antibodies of AhpC and had strong antigenicity by ELISA and dot blot analysis. In epitope AhpC4-16 immunized mice, specific IgG of serum and IL-4 in splenocyte culture supernatant were significantly higher. The illness index decreased significantly, the protective rate was 66.67%. Histopathology displayed that the jejunum morphology was better than the control group.

CONCLUSIONS

These findings suggested that epitope AhpC4-16 showed effective protective role against C. jejuni and is a candidate epitope of vaccine against this pathogen.

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.

Evolution of Campylobacter jejuni of poultry origin in Brazil

Campylobacter jejuni is the most common pathogen associated with foodborne diseases. Persistent presence of this pathogen contaminating the environment in slaughterhouses and chicken products have been reported worldwide. Although many efforts have been employed for reducing C. jejuni contamination, few studies have been conducted to understand the dynamics of C. jejuni in slaughterhouses over time. In this study, we evaluated the virulence, antibiotic resistance and genetic diversity profiles of 99 C. jejuni isolated from chilled chicken carcasses collected in Brazilian slaughterhouses during two distinct periods (2011-2012 and 2015-2016). The virulence profile was evaluated for the presence of flaA, ciaB, cadF, pldA and cdtABC genes. Antibiotic resistance was evaluated for amoxicillin-clavulanic acid, gentamicin, erythromycin and tetracycline. Genetic diversity was assessed using RAPD-PCR. The prevalence of C. jejuni was significantly reduced in 2015-2016 as well the number of antibiotic (and multidrug) resistant isolates, except for tetracycline. However, isolates from 2015 to 2016 showed higher prevalence of multiple virulence genes and genetic diversity profile compared to isolates from 2011 to 2012. During the studied period, stricter regulations to control pathogens in poultry farms and slaughterhouses were implemented in Brazil, which may have contributed to the profile variation observed due to changes of selective pressures on bacterial populations.

Ocorrência de Campylobacter e Enterobacteriaceae em aves silvestres e frangos de corte

RESUMO As aves silvestres podem ser reservatório de bactérias patogênicas e atuar como veiculadoras desses microrganismos para o ambiente, os animais domésticos e o homem. Portanto, o objetivo deste trabalho foi verificar a ocorrência de Campylobacter spp., Yersinia enterocolitica e Salmonella enterica em aves silvestres capturadas nas áreas próximas de aviários e em frangos de corte alojados nesses estabelecimentos, além de verificar a presença dos genes cdtA, cdtB e cdtC nos isolados de Campylobacter e identificar os sorotipos de Salmonella encontrados. Amostras de fezes de 189 aves silvestres capturadas com redes de neblina nas áreas próximas de 10 aviários e de 200 frangos de corte foram processadas para pesquisa de Campylobacter spp., S. enterica e Y. enterocolitica. Duas espécies de aves silvestres, Sicalis flaveola (canário-da-terra) e Zonotrichia capensis (tico-tico), foram positivas para Salmonella e Campylobacter, respectivamente. Foram isolados Campylobacter spp., S. enterica e Y. enterocolitica de frangos. Todos os isolados de Campylobacter analisados apresentaram os genes cdt. Em dois aviários, Campylobacter foi isolado tanto de frangos como de aves silvestres, entretanto a contaminação mútua entre essas aves não foi comprovada. Este foi o primeiro relato de isolamento de Campylobacter de Z. capensis e de Salmonella do sorotipo Derby de S. flaveola.

Presence of genes associated with adhesion, invasion, and toxin production in Campylobacter jejuni isolates and effect of temperature on their expression

The aims of this study were to evaluate the presence of genes associated with adhesion (cadF), invasion (ciaB), and cytotoxin production (cdtA, cdtB, and cdtC) among Campylobacter jejuni isolates from a poultry slaughterhouse and to investigate the effect of different temperatures on the expression of these virulence-associated genes. A total of 88 C. jejuni isolates from cecum, liver, chicken carcasses, chilled water, and scalding water were submitted to PCR assay for detection of virulence genes. Representative isolates were selected for gene expression evaluation at 37 and 42 °C, according to their virulence gene profile and genotypic typing. All C. jejuni isolates carried the five virulence-associated genes, which play an important role in the infectious process. Differential gene expression by RT-qPCR was observed among C. jejuni isolates at 37 and 42 °C. The expression levels at 37 °C showed upregulation of the ciaB, cdtA, cdtB, and cdtC genes in five isolates, with the exception of ciaB for isolate 4. At 42 °C, upregulation was observed for ciaB and cdtC, cdtA and cdtB, and cadF in four, three, and two isolates, respectively. The C. jejuni isolates expressed the virulence genes evaluated, and the expression is gene- and isolate-dependent and varied according the temperature.

Campylobacter jejuni Colonization in the Crow Gut Involves Many Deletions within the Cytolethal Distending Toxin Gene Cluster

Campylobacter spp. are major causes of gastroenteritis worldwide. The virulence potential of Campylobacter shed in crow feces obtained from a roost area in Bothell, Washington, was studied and compared with that from isolates from other parts of Washington and from a different crow species 7,000 miles away in Kolkata, India. Campylobacter organisms were isolated from 61% and 69% of the fecal samples obtained from Washington and Kolkata, respectively, and were confirmed to be C. jejuni The cytolethal distending toxin (CDT) gene cluster from these isolates revealed a truncated sequence of approximately 1,350 bp. Sequencing of the gene cluster revealed two types of mutations: a 668-bp deletion across cdtA and cdtB and a 51-bp deletion within cdtB Some strains had additional 20-bp deletions in cdtB In either case, a functional toxin is not expected; a functional toxin is produced by the expression of three tandem genes, cdtA, cdtB, and cdtC Reverse transcriptase PCR with total RNA extracted from the isolates showed no expression of cdtB A toxin assay performed with these isolates on HeLa cells failed to show cytotoxic effects on the cells. However, the isolates were able to colonize the chicken ceca for a period of at least 4 weeks, similar to that of a clinical isolate. Other virulence gene markers, flagellin A and CadF, were present in 100% of the isolates. Our study suggests that crows carry the bacterium C. jejuni but with a dysfunctional toxin protein that is expected to drastically reduce its potential to cause diarrhea.IMPORTANCE Campylobacters are a major cause of gastroenteritis in humans. Since outbreaks have most often been correlated with poultry or unpasteurized dairy products, contact with farm animals, or contaminated water, historically, the majority of the studies have been with campylobacter isolates from poultry, domestic animals, and human patients. However, the bacterium has a broad host range that includes birds. These reservoirs need to be investigated, because the identification of the source and a determination of the transmission routes for a pathogen are important for the development of evidence-based disease control programs. In this study, two species of the human-commensal crow, from two different geographical regions separated by 7,000 miles of land and water, have been examined for their ability to cause disease by shedding campylobacters. Our results show that the crow may not play a significant role in campylobacteriosis, because the campylobacter organisms they shed produce a nonfunctional toxin.

Heterogeneous Family of Cyclomodulins: Smart Weapons That Allow Bacteria to Hijack the Eukaryotic Cell Cycle and Promote Infections

Some bacterial pathogens modulate signaling pathways of eukaryotic cells in order to subvert the host response for their own benefit, leading to successful colonization and invasion. Pathogenic bacteria produce multiple compounds that generate favorable conditions to their survival and growth during infection in eukaryotic hosts. Many bacterial toxins can alter the cell cycle progression of host cells, impairing essential cellular functions and impeding host cell division. This review summarizes current knowledge regarding cyclomodulins, a heterogeneous family of bacterial effectors that induce eukaryotic cell cycle alterations. We discuss the mechanisms of actions of cyclomodulins according to their biochemical properties, providing examples of various cyclomodulins such as cycle inhibiting factor, γ-glutamyltranspeptidase, cytolethal distending toxins, shiga toxin, subtilase toxin, anthrax toxin, cholera toxin, adenylate cyclase toxins, vacuolating cytotoxin, cytotoxic necrotizing factor, Panton-Valentine leukocidin, phenol soluble modulins, and mycolactone. Special attention is paid to the benefit provided by cyclomodulins to bacteria during colonization of the host.

Campylobacter upsaliensis isolated from dogs produces high titer of cytolethal distending toxin

Cytolethal distending toxin (CDT) consisting of CdtA, CdtB and CdtC has been reported to be a possible virulence factor of campylobacters including Campylobacter upsaliensis. In our previous study, the cdtB gene-based PCR-restriction fragment length polymorphism (RFLP) assay for detection and differentiation of 7 Campylobacter species yielded 3 different RFLP patterns (Cu-I to Cu-III). In this study, entire cdt (Cucdt) genes of each pattern were sequenced to see whether there are any differences in cdt genes, its amino acid sequences and biological activity of CuCDT. We found that all 3 representative strains harbor the entire Cucdt genes and homology between prototype and newly determined Cucdt genes was 94 to 98% with cdtA, 93 to 94% with cdtB and 92 to 93% with cdtC, while that between amino acids of CuCDT was 95 to 99% with CdtA, 97 to 98% with CdtB and 92 to 93% with CdtC. Furthermore, CDT activity produced by C. upsaliensis strains was examined by cytotoxicity assay with HeLa cells. Interestingly, C. upsaliensis produced 64 to 2,340 times higher CDT titer in comparison to other campylobacters did. In addition, Cu-III showed 64 times higher CDT titer than Cu-II, although CDT production level was almost the same by western blotting. These data suggest that CDT produced by C. upsaliensis might contribute more to human diseases in comparison to that produced by other campylobacters and Cu-III CDT seems to be more toxic to HeLa cells in comparison to Cu-I and Cu-II CDTs.

A PCR-RFLP assay to detect and type cytolethal distending toxin (cdt) genes in Campylobacter hyointestinalis

Campylobacter hyointestinalis is considered as an emerging zoonotic pathogen. We have recently identified two types of cytolethal distending toxin (cdt) gene in C. hyointestinalis and designated them as Chcdt-I and Chcdt-II. In this study, we developed a PCR-restriction fragment length polymorphism (RFLP) assay that can differentiate Chcdt-I from Chcdt-II. When the PCR-RFLP assay was applied to 17 other Campylobacter strains and 25 non-Campylobacter strains, PCR products were not obtained irrespective of their cdt gene-possession, indicating that the specificity of the PCR-RFLP assay was 100%. In contrast, when the PCR-RFLP assay was applied to 35 C. hyointestinalis strains including 23 analyzed in the previous study and 12 newly isolated from pigs and bovines, all of them showed the presence of cdt genes. Furthermore, a restriction digest by EcoT14-I revealed that 29 strains contained both Chcdt-I and Chcdt-II and 6 strains contained only Chcdt-II, showing 100% sensitivity. Unexpectedly, however, PCR products obtained from 7 C. hyointestinalis strains were not completely digested by EcoT14-I. Nucleotide sequence analysis revealed that the undigested PCR product was homologous to cdtB but not to Chcdt-IB or Chcdt-IIB, indicating the presence of another cdt gene-variant. Then, we further digested the PCR products with DdeI in addition to EcoT14-I, showing that all three cdt genes, including a possible new Chcdt variant, could be clearly differentiated. Thus, the PCR-RFLP assay developed in this study is a valuable tool for evaluating the Chcdt gene-profile of bacteria.

The Cytolethal Distending Toxin Contributes to Microbial Virulence and Disease Pathogenesis by Acting As a Tri-Perditious Toxin

This review summarizes the current status and recent advances in our understanding of the role that the cytolethal distending toxin (Cdt) plays as a virulence factor in promoting disease by toxin-producing pathogens. A major focus of this review is on the relationship between structure and function of the individual subunits that comprise the AB₂ Cdt holotoxin. In particular, we concentrate on the molecular mechanisms that characterize this toxin and which account for the ability of Cdt to intoxicate multiple cell types by utilizing a ubiquitous binding partner on the cell membrane. Furthermore, we propose a paradigm shift for the molecular mode of action by which the active Cdt subunit, CdtB, is able to block a key signaling cascade and thereby lead to outcomes based upon programming and the role of the phosphatidylinositol 3-kinase (PI-3K) in a variety of cells. Based upon the collective Cdt literature, we now propose that Cdt is a unique and potent virulence factor capable of acting as a tri-perditious toxin that impairs host defenses by: (1) disrupting epithelial barriers; (2) suppressing acquired immunity; (3) promoting pro-inflammatory responses. Thus, Cdt plays a key role in facilitating the early stages of infection and the later stages of disease progression by contributing to persistence and impairing host elimination.

Impact of CDT Toxin on Human Diseases

Cytolethal distending toxin (CDT) is found in Gram-negative bacteria, especially in certain Proteobacteria such as the Pasteurellaceae family, including Haemophilus ducreyi and Aggregatibacter (Actinobacillus) actinomycetemcomitans, in the Enterobacteriaceae family and the Campylobacterales order, including the Campylobacter and Helicobacter species. In vitro and in vivo studies have clearly shown that this toxin has a strong effect on cellular physiology (inflammation, immune response modulation, tissue damage). Some works even suggest a potential involvement of CDT in cancers. In this review, we will discuss these different aspects.

Prevalence of Virulence/Stress Genes in Campylobacter jejuni from Chicken Meat Sold in Qatari Retail Outlets

Chicken meat from the shelves of supermarkets in Qatar was tested for the presence of Campylobacter spp. and the presence of five virulence genes (htrB, cdtB, clpP, cadF and ciaB) was assessed in isolates. Forty eight percent of the chickens provided for supermarkets by Saudi (53%) and Qatari (45.9%) producers were found to be contaminated and the most important factor affecting the overall prevalence of contaminated chickens was the store from which chicken samples originated. Variation in prevalence of Campylobacter in chicken meat from different stores was evident even when the same producer supplied the three stores in our survey. Differences in the prevalence and in the combinations of virulence genes in isolates that can and cannot grow in a classic maintenance medium (Karmali) were identified, providing a starting point for linking presence/absence of particular virulence genes with actual in vivo virulence and pathogenicity. Because of the relatively low infective doses of Campylobacter that are required to initiate infection in humans, it will be important to explore further the relationships we identified between certain Campylobacter virulence genes and their capacity for survival in poultry meat, and hence their contribution to the incidence of campylobacteriosis.

Genotyping and antibiotic resistance of thermophilic Campylobacter isolated from chicken and pig meat in Vietnam

BACKGROUND

Campylobacter species are recognized as the most common cause of foodborne bacterial gastroenteritis in humans. In this study nine Campylobacter strains isolated from chicken meat and pork in Hanoi, Vietnam, were characterized using molecular methods and tested for antibiotic resistance.

RESULTS

The nine isolates (eight C. jejuni and one C. coli) were identified by multiplex PCR, and tested for the presence or absence of 29 gene loci associated with virulence, lipooligosaccharide (LOS) biosynthesis and further functions. flaA typing, multilocus sequence typing and microarray assay investigation showed a high degree of genetic diversity among these isolates. In all isolates motility genes (flaA, flaB, flhA, fliM), colonization associated genes (cadF, docB), toxin production genes (cdtA, cdtB, secD, secF), and the LOS biosynthesis gene pglB were detected. Eight gene loci (fliY, virB11, Cje1278, Cj1434c, Cj1138, Cj1438c, Cj1440c, Cj1136) could not be detected by PCR. A differing presence of the gene loci ciaB (22.2 %), Cje1280 (77.8 %), docC (66.7 %), and cgtB (55.6 %) was found. iamA, cdtC, and the type 6 secretion system were present in all C. jejuni isolates but not in C. coli. flaA typing resulted in five different genotypes within C. jejuni, MLST classified the isolates into seven sequence types (ST-5155, ST-6736, ST-2837, ST-4395, ST-5799, ST-4099 and ST-860). The microarray assay analysis showed a high genetic diversity within Vietnamese Campylobacter isolates which resulted in eight different types for C. jejuni. Antibiotic susceptibility profiles showed that all isolates were sensitive to gentamicin and most isolates (88.8 %) were sensitive to chloramphenicol, erythromycin and streptomycin. Resistance rates to nalidixic acid, tetracycline and ciprofloxacin were 88.9, 77.8 and 66.7 %, respectively.

CONCLUSIONS

To the best of our knowledge, this study is the first report that shows high genetic diversity and remarkable antibiotic resistance of Campylobacter strains isolated from meat in Vietnam which can be considered of high public health significance. These preliminary data show that large scale screenings are justified to assess the relevance of Campylobacter infections on human health in Vietnam.

Determination of the cytotoxic activity of Campylobacter strains isolated from bovine and swine carcasses in north-eastern Poland

The study was carried out to determine the cytotoxin production by Campylobacter spp. isolated from slaughtered cattle and swine in north-eastern Poland. In total three commercial slaughterhouses were sampled during one year. Carcass swabs were taken to detect the level of Campylobacter spp. contamination. Campylobacter spp. was found in 50 (34%) out of 147 swine carcasses examined. PCR analysis revealed 4 (8%) isolates to be C. jejuni, and 46 (92%) to be C. coli. From a total of 373 bovine carcasses, Campylobacter spp. were isolated from 49 (13.1%) samples. The results regarding the occurrence of cdt genes associated with cytotoxicity indicated that 100% of C. jejuni and 67.4% C. coli obtained from pigs had all three cdtA, cdtB and cdtC genes. In case of C. jejuni strains isolated from cattle all cdt genes were confirmed in 93.9% isolates. The isolates possessesing all cdt genes had higher cytotoxic activity against cell lines used. The isolates both from cattle and swine were characterized by the highest cytotoxicity against HeLa cells. The values obtained reached 80.8% for C. jejuni isolates from cattle and 76.2% for C. jejuni and 69.0% for C. coli isolates from swine. High prevalence of cytotoxicity in Campylobacter spp. indicates a significant epidemiological role of this pathogen in human infections.

Virulence genes and cytokine profile in systemic murine Campylobacter coli infection

Campylobacter coli are one of the most common bacteria in bacterial gastroenteritis and acute enterocolitis in humans. However, relatively little is known regarding the mechanisms of pathogenesis and host response to C. coli infections. To investigate the influence of genetic changes, we first used PCR to demonstrate the presence of the known virulence genes cadF, virB11, cdtB, cdtC and ceuE in the clinical isolate C. coli 26536, which was isolated from the liver of infected BALB/c mice. Sequence analyses of the cadF, virB11, cdtB and ceuE genes in C. coli 26536 confirmed the stability in these virulence genes during their transmission through the host. We further investigated C. coli infection for the bacterial clearance from the liver and spleen of infected mice, and for their immune response. C. coli persisted well in both organs, with better survival in the liver. We also determined the levels of several pro-inflammatory cytokines (i.e., interleukin [IL]-6, IL-12, interferon-γ, tumor necrosis factor-α) and the anti-inflammatory cytokine IL-10 in plasma and in liver homogenates from the infected mice, using enzyme-linked immunosorbent assays. The lowest levels among these cytokines were for tumor necrosis factor-α in the plasma and IL-6 in the liver on days 1, 3 and 8 post-infection. The most pronounced production was for IL-10, in both plasma (days 1 and 8 post-infection) and liver (day 8 post-infection), which suggests that it has a role in healing of the organ inflammation. Our findings showed dynamic relationships between pro- and anti-inflammatory cytokines and thus contribute toward clarification of the healing processes involved in the resolution of C. coli infections.

Genomic evidence for the emergence and evolution of pathogenicity and niche preferences in the genus Campylobacter

The genus Campylobacter includes some of the most relevant pathogens for human and animal health; the continuous effort in their characterization has also revealed new species putatively involved in different kind of infections. Nowadays, the available genomic data for the genus comprise a wide variety of species with different pathogenic potential and niche preferences. In this work, we contribute to enlarge this available information presenting the first genome for the species Campylobacter sputorum bv. sputorum and use this and the already sequenced organisms to analyze the emergence and evolution of pathogenicity and niche preferences among Campylobacter species. We found that campylobacters can be unequivocally distinguished in established and putative pathogens depending on their repertory of virulence genes, which have been horizontally acquired from other bacteria because the nonpathogenic Campylobacter ancestor emerged, and posteriorly interchanged between some members of the genus. Additionally, we demonstrated the role of both horizontal gene transfers and diversifying evolution in niche preferences, being able to distinguish genetic features associated to the tropism for oral, genital, and gastrointestinal tissues. In particular, we highlight the role of nonsynonymous evolution of disulphide bond proteins, the invasion antigen B (CiaB), and other secreted proteins in the determination of niche preferences. Our results arise from assessing the previously unmet goal of considering the whole available Campylobacter diversity for genome comparisons, unveiling notorious genetic features that could explain particular phenotypes and set the basis for future research in Campylobacter biology.

First Polish outbreak of Clostridium difficile ribotype 027 infections among dialysis patients

This report describes an outbreak of Clostridium difficile infection (CDI) in a nephrology ward in 2012, caused by the fluoroquinolone- and clindamycin-resistant polymerase chain reaction (PCR) ribotype 027 strains. An increase in the number of cases of diarrhoea was noted among patients hospitalised between 26 November 2012 and 17 December 2012 in a hospital in North Poland. Eight patients were on haemodialysis in the outpatient dialysis facility, while one patient was receiving peritoneal dialysis. The 027 strain could be detected in eight haemodialysis patients. One strain, isolated from the patient receiving peritoneal dialysis, belonged to PCR ribotype 001. In this study, we documented the first outbreak of CDI caused by a fluoroquinolone-resistant (FQR) C. difficile PCR ribotype 027 strain in Polish dialysis patients.

Detection and functionality of the CdtB, PltA, and PltB from Salmonella enterica serovar Javiana

Salmonella infection is one of the major foodborne illnesses in the United States. Several Gram-negative bacterial pathogens, including Salmonella Typhi, produce cytolethal distending toxin (CDT), which arrests growth, induces apoptosis of infected host cells and extends persistence of pathogenic bacteria in the host. The aim of this study was to characterize the functionality of CDT (cdtB, pltA and pltB) from nontyphoidal Salmonella isolates. Fifty Salmonella enterica serovar Javiana isolates from food, environmental, and clinical samples were screened for cdtB, pltA, and pltB genes by PCR, and all were positive for all three genes. Nucleotide sequence analysis of all amplified PCR products showed 100% identity to S. Typhi cdtB. To understand the roles of CdtB, PltA, and PltB in S. Javiana, cdtB, pltA, and pltB deletion mutants were constructed using a lambda Red-based recombination system. In vitro-cultured HeLa cell lines were infected with a wild-type strain and its isogenic ∆cdtB, ∆pltA, and ∆pltB to determine whether the strains of S. Javiana are responsible for invasion and cytolethal distending intoxication, including cell cycle arrest, cytoplasmic distension, and nuclear enlargement of host target cells. The results showed that HeLa cells infected with S. Javiana wild type were arrested in G2 /M and had distended cytoplasm and nuclei that were larger than those infected with S. Javiana ∆cdtB and ∆pltA strains. The S. Javiana ∆pltB strain retained the ability to induce cytoplasmic distension and cell cycle arrest, whereas the complemented ∆cdtB and ∆pltA S. Javiana strains showed activity like the wild-type strains. CdtB and pltA from S. Javiana had apparent effects on the distension of both cytoplasm and nucleus as well as cell cycle arrest of HeLa cell lines after 72 h of infection. Our data show a significant difference between the wild-type cdtB strain and its isogenic ∆cdtB for invasion of the cell lines. Therefore, CdtB produced from S. Javiana strains may play an important role in pathogenesis in host cells.

The cytolethal distending toxin effects on Mammalian cells: a DNA damage perspective

The cytolethal distending toxin (CDT) is produced by many pathogenic Gram-negative bacteria and is considered as a virulence factor. In human cells, CDT exposure leads to a unique cytotoxicity associated with a characteristic cell distension and induces a cell cycle arrest dependent on the DNA damage response (DDR) triggered by DNA double-strand breaks (DSBs). CDT has thus been classified as a cyclomodulin and a genotoxin. Whereas unrepaired damage can lead to cell death, effective, but improper repair may be detrimental. Indeed, improper repair of DNA damage may allow cells to resume the cell cycle and induce genetic instability, a hallmark in cancer. In vivo, CDT has been shown to induce the development of dysplastic nodules and to lead to genetic instability, defining CDT as a potential carcinogen. It is therefore important to characterize the outcome of the CDT-induced DNA damage and the consequences for intoxicated cells and organisms. Here, we review the latest results regarding the host cell response to CDT intoxication and focus on DNA damage characteristics, cell cycle modulation and cell outcomes.

Prevalence of virulence genes in strains of Campylobacter jejuni isolated from human, bovine and broiler

Campylobacter jejuni isolates of different origins (bovine, broiler meat, human) were screened by polymerase chain reaction for the presence of 4 genes cdtB, cst-II, ggt, and virB11, previously linked to virulence such as adherence, invasion, colonization, molecular mimicry, and cytotoxin production. In addition, the isolates were screened for the presence of the global gene regulator csrA linked to oxidative stress responses, biofilms formation, and cell adhesion. All the C. jejuni isolates were positive for cdtB gene. The csrA gene was detected in 100% and 92% of C. jejuni isolates from human and animal origin and the virB11 gene was detected in 7.3% and 3.6% isolates from chicken and human respectively. All isolates from bovine were negative for the virB11 gene. The isolates showed a wide variation for the presence of the remaining genes. Of the C. jejuni recovered from human 83.6%, and 32.7% were positive for cst-II, and ggt respectively. Out of the isolates from chicken 40% and 5.5% isolates revealed the presence of cst-II, and ggt, respectively. Finally of the C. jejuni isolates from bovine, 97.7% and 22.7% were positive for cst-II, and ggt respectively. We conclude that the genes of this study circulate among humans and animals. These results led us to hypothesize that the isolates associated with enteritis (cdtB positives) are not selected by environmental or host-specific factors. On the other hand, the high frequencies of csrA gene in C. jejuni show that this gene is important for the survival of C. jejuni in animals and humans.

Ocorrência de Campylobacter em carne de frango, fezes de frango e humanas e pesquisa dos genes cdt

Foram coletadas 100 amostras de conteúdo fecal de aves de corte, 100 de produtos de frango (coxa, sobrecoxa, asa, dorso, carne moída e fígado) e 100 de fezes de humanos, e analisadas para pesquisa de Campylobacter. Realizou-se a determinação da espécie e da presença dos genes cdt, responsáveis pela codificação da toxina citoletal distensiva (CDT), através da técnica da PCR. A bactéria foi isolada de 61% das amostras de fezes de frango, 20% de produtos de frango e 3% de fezes de humanos. A maioria dos isolados foi determinada como C. jejuni . Destes, 93,5% apresentaram os genes para a toxina CDT. Apesar de a ocorrência de Campylobacter em fezes de humanos ter sido baixa, a prevalência em frangos de corte e produtos de frango foi elevada, fato que, aliado à presença dos genes cdt na maioria dos isolados, representa risco potencial para os consumidores. Esses resultados são indicativos da necessidade de medidas preventivas no sistema de produção e de boas práticas de fabricação na indústria, de forma a minimizar a contaminação dos produtos e diminuir o risco para os consumidores.

Proteomic identification of immunodominant membrane-related antigens in Campylobacter jejuni associated with sheep abortion

Campylobacter jejuni clone SA is the predominant agent inducing sheep abortion and a zoonotic agent causing gastroenteritis in humans in the United States. In an attempt to identify antigens of clone SA that may be useful for vaccine development, immunoproteomic analyses were conducted to characterize the membrane proteome of C. jejuni clone SA. 2-DE of C. jejuni membrane-related proteins was followed by immunoblotting analyses using convalescent sera that were derived from ewes naturally infected by C. jejuni clone SA. Totally 140 immunoreactive spots were identified, 50 of which were shared by all tested convalescent sheep sera. Conserved and immunodominant spots were identified by mass spectrometry. Among the 26 identified immunogenic proteins, there were 8 cytoplasmic proteins, 2 cytoplasmic membrane proteins, 11 periplasmic proteins, 3 outer membrane proteins, and 2 extracellular proteins. Notably, many of the immunodominant antigens were periplasmic proteins including HtrA, ZnuA, CjaA, LivK, CgpA, and others, some of which were previously shown to induce protective immunity. Interestingly, 11 immunoreactive proteins including 9 periplasmic proteins are known N-linked glycosylated proteins. These findings reveal immunogens that may potentially elicit protective immune responses and provide a foundation for developing vaccines against C. jejuni induced sheep abortion.

BIOLOGICAL SIGNIFICANCE

Campylobacter jejuni clone SA is the predominant agent inducing sheep abortion and incurs a significant economic loss to sheep producers. This emergent strain is also a zoonotic agent, causing gastroenteritis in humans. However, the immunogens of C. jejuni induced abortion are largely unknown. Considering the significance of C. jejuni clone SA in causing sheep abortion and foodborne illnesses, protective vaccines are needed to control its transmission and spread. Additionally, immunological markers are required for detection and identification of this highly pathogenic clone. To address these needs, we applied an immunoproteomic approach to identify the membrane-associated antigens of this highly virulent C. jejuni clone associated with sheep abortions in the U.S. The findings reveal immunogens that may potentially elicit protective immune responses and provide a foundation for developing vaccines against C. jejuni induced sheep abortion.

Identification and functional analysis of the cytolethal distending toxin gene from Avibacterium paragallinarum

Avibacterium paragallinarum is the causative agent of infectious coryza, an important respiratory disease of chickens. Cytolethal distending toxins (CDTs) are a family of protein cytotoxins that cause cell cycle arrest and apoptosis in eukaryotic cells. Whole-genome sequencing analysis showed that Av. paragallinarum contains cdtABC genes. Filter-sterilized lysates prepared from Av. paragallinarum or from recombinant Escherichia coli expressing cdtABC genes exhibited CDT activity on HeLa cells and chicken embryo fibroblast (DF-1) cells. In vitro DNase assays showed that purified recombinant CdtB has DNase activity. Polymerase chain reaction and sequencing analysis revealed that the cdtABC genes are present in all strains of Av. paragallinarum examined in this study. This is the first report of the identification and functional analysis of cdtABC genes from Av. paragallinarum. The gene products of cdtABC genes may be involved in the pathogenesis of the disease caused by Av. paragallinarum.

Investigation of virulence and cytolethal distending toxin genes in Campylobacter spp. isolated from sheep in Turkey

The presence of virulence and cytolethal distending toxin (Cdt) genes was investigated in isolates of Campylobacter jejuni, C. coli, C. lanienae, and C. lari that originated from intestinal contents and gallbladders of clinically healthy sheep. These genes have important roles in the pathogenicity of campylobacters. A total of 363 Campylobacter isolates (221 C. jejuni, 135 C. coli, five C. lanienae, and two C. lari) were used in this study. The frequency of racR, dnaJ, ciaB, pldA, flaA, and cadF virulence genes in all the isolates were determined to be 34.4%, 30%, 24.8%, 30.9%, 95%, and 81.3%, respectively, while the virB11 virulence gene could not be detected in any isolates. CdtA, cdtB, and cdtC genes were detected in 54.5%, 55.9%, and 52.3% of the isolates, respectively. None of the virulence and toxin genes examined here were detected in a total of 19 Campylobacter isolates consisting of 10 C. jejuni and nine C. coli. This is the first study investigating the presence of virulence and toxin genes in a large number of Campylobacter species isolated from clinically healthy sheep by scanning a large area. In addition, this is the first report investigating the presence of virulence and toxin genes in sheep-originated C. lanienae and C. lari isolates.

Role of Cytolethal Distending Toxin in Altered Stool Form and Bowel Phenotypes in a Rat Model of Post-infectious Irritable Bowel Syndrome

BACKGROUND/AIMS

Campylobacter jejuni infection is a leading cause of acute gastroenteritis, which is a trigger for post-infectious irritable bowel syndrome (PI-IBS). Cytolethal distending toxin (CDT) is expressed by enteric pathogens that cause PI-IBS. We used a rat model of PI-IBS to investigate the role of CDT in long-term altered stool form and bowel phenotypes.

METHODS

Adult Sprague-Dawley rats were gavaged with wildtype C. jejuni (C+), a C. jejunicdtB knockout (CDT-) or saline vehicle (controls). Four months after gavage, stool from 3 consecutive days was assessed for stool form and percent wet weight. Rectal tissue was analyzed for intraepithelial lymphocytes, and small intestinal tissue was stained with anti-c-kit for deep muscular plexus interstitial cells of Cajal (DMP-ICC).

RESULTS

All 3 groups showed similar colonization and clearance parameters. Average 3-day stool dry weights were similar in all 3 groups, but day-to-day variability in stool form and stool dry weight were significantly different in the C+ group vs both controls (P < 0.01) and the CDT- roup (P < 0.01), but were not different in the CDT- vs controls. Similarly, rectal lymphocytes were significantly higher after C. jejuni (C+) infection vs both controls (P < 0.01) and CDT-exposed rats (P < 0.05). The counts in the latter 2 groups were not significantly different. Finally, c-kit staining revealed that DMP-ICC were reduced only in rats exposed to wildtype C. jejuni.

CONCLUSIONS

In this rat model of PI-IBS, CDT appears to play a role in the development of chronic altered bowel patterns, mild chronic rectal inflammation and reduction in DMP-ICC.

Comparative analysis of Campylobacter lari cytolethal distending toxin (CDT) effect on HeLa cells

We aimed to clarify if Campylobacter lari exerts a cytolethal distending toxin (CDT) effect on HeLa cells. Campylobacter cell lysates (CCLys) from C. jejuni 81-176 and urease-positive thermophilic Campylobacter (UPTC) CF89-12 and UPTC NCTC12893 isolates were shown to exert a CDT effect on HeLa cells with morphological changes examined by Giemsa staining and microscopy. However, Campylobacter lari JCM2530(T) isolate showed no effect. In addition, Campylobacter cell culture supernatant wash gave low or absent toxic effects with both C. jejuni and C. lari organisms. When western blot analysis was carried out to clarify if there was a CDTB effect in the CCLys and soluble fractions from Campylobacter isolates, which had a CDT effect on HeLa cells or did not have any effect, anti-recombinant CjCDTB antibodies identified an immunoreactively positive signal at around approximately 25 kDa on all the C. lari isolates examined, as well as the C. jejuni 81116 strain. Thus, all the Campylobacter isolates including those without any CDT effect were shown to express CDTB at the translational level.

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.

Immunopathology and Th1/Th2 immune response of Campylobacter jejuni-induced paralysis resembling Guillain-Barré syndrome in chicken

Immunopathogenesis of Campylobacter jejuni-associated Guillain-Barré syndrome (GBS) is not yet well established probably due to lack of experimental model. Therefore, we studied the Th1/Th2 immune response and pathological changes in C. jejuni-induced chicken model for GBS. C. jejuni (5 × 10(9) CFU/ml) and placebo were fed to 30 chickens each. Stools of all birds were negative for C. jejuni by culture and PCR before experiment. The birds were regularly assessed for disease symptoms up to 30 days. Sciatic nerves from all chickens were examined at 5 days intervals by histopathology and immunohistochemistry, and also for the expression of Th1/Th2 cytokines. Twenty-two chickens (73.3%) developed diarrhea after C. jejuni infection; 18 (60.0%) experimental chickens developed GBS-like paralytic neuropathy. Pathology in the sciatic nerves of these chickens included perinodal and/or patchy demyelination, perivascular focal lymphocytic infiltration, myelin swelling and presence of macrophages within the nerve fibers on 10th-20th post-infection day (PID). Cytokines (IFN-γ, IL-1β, TNF-α, IL-6 and IL-2) were elevated in early phase (5th-15th PID) and TGF-β2, IL-10 and IL-4 in the recovery phase (25th-30th PID) of the disease. The study provides evidence that C. jejuni infection in the chicken can provide an experimental animal model of GBS.

Campylobacter spp. as a Foodborne Pathogen: A Review

Campylobacter is well recognized as the leading cause of bacterial foodborne diarrheal disease worldwide. Symptoms can range from mild to serious infections of the children and the elderly and permanent neurological symptoms. The organism is a cytochrome oxidase positive, microaerophilic, curved Gram-negative rod exhibiting corkscrew motility and is carried in the intestine of many wild and domestic animals, particularly avian species including poultry. Intestinal colonization results in healthy animals as carriers. In contrast with the most recent published reviews that cover specific aspects of Campylobacter/campylobacteriosis, this broad review aims at elucidating and discussing the (i) genus Campylobacter, growth and survival characteristics; (ii) detection, isolation and confirmation of Campylobacter; (iii) campylobacteriosis and presence of virulence factors; and (iv) colonization of poultry and control strategies.

The role of Campylobacter jejuni cytolethal distending toxin in gastroenteritis: toxin detection, antibody production, and clinical outcome

The role of Campylobacter jejuni cytolethal distending toxin (CDT) on clinical outcome after gastroenteritis was investigated. Clinical data, blood serum samples, and Campylobacter spp. isolated, from each of 30 patients were collected over a period of 6 months. The CDT encoding genes, cdtABC, characterized by PCR, revealed that all but one of the C. jejuni strains had the wild-type sequence. Sequencing of cdtABC from this strain showed two major deletions. From all of the strains, CDT titers were determined, and toxin neutralizing antibodies were documented using an in vitro assay. Three of the thirty clinical isolates, including the one with the mutant cdtABC coding genes, did not have a detectable CDT activity. Analyzing the relationship between CDT titer, serum neutralization of CDT, and the clinical outcome showed that campylobacteriosis caused by CDT-negative strains was clinically indistinguishable from that of patients infected with an isolate that produced high levels of CDT. These results suggest that CDT does not solely determine severity of infection and clinical outcome.