CYTOLETHAL DISTENDING TOXIN (CDT): GENETIC DIVERSITY, STRUCTURE AND ROLE IN DIARRHEAL DISEASE

Detection of prolong excretion of Escherichia albertii in stool specimens of a 7-year-old child by a newly developed Eacdt gene-based quantitative real-time PCR method and molecular characterization of the isolates

Escherichia albertii is an emerging zoonotic foodborne pathogen. The clinical significance of this bacterium has increasingly been recognized worldwide. However, diagnostic method has not yet been established and its clinical manifestations are not fully understood. Here, we show that an Eacdt gene-based quantitative real-time PCR (qRT-PCR) developed in this study is 100% specific and sensitive when tested with 39 E. albertii and 36 non-E. albertii strains, respectively. Detection limit of the real-time PCR was 10 colony forming unit (CFU) and 1 pg of genomic DNA per PCR tube. When E. albertii was spiked with 4 × 100-106 CFU per mL to stool of healthy person, detection limit was 4.0 × 103 and 4.0 CFU per mL before and after enrichment culture, respectively. Moreover, the qRT-PCR was able to detect E. albertii in five children out of 246 (2%) but none from 142 adults suffering from gastroenteritis. All five E. albertii strains isolated carried eae and paa genes, however, only one strain harbored stx2f genes. Long-term shedding of stx2f gene-positive E. albertii in a child stool could be detected because of the qRT-PCR developed in this study which might have been missed if only conventional PCR and culture methods were employed. Furthermore, E. albertii isolated from siblings with diarrhea showed clonality by PFGE analysis. Taken together, these data suggest that the Eacdt gene-based qRT-PCR developed for the detection of E. albertii is useful and will assist in determining the real burden and clinical manifestation of E. albertii infections.

Presence of Functionally Active Cytolethal Distending Toxin Genes on a Conjugative Plasmid in a Clinical Isolate of Providencia rustigianii

Providencia rustigianii is potentially enteropathogenic in humans. Recently, we identified a P. rustigianii strain carrying a part of the cdtB gene homologous to that of Providencia alcalifacines that produces an exotoxin called cytolethal distending toxin (CDT), encoded by three subunit genes (cdtA, cdtB, and cdtC). In this study, we analyzed the P. rustigianii strain for possible presence of the entire cdt gene cluster and its organization, location, and mobility, as well as expression of the toxin as a putative virulence factor of P. rustigianii. Nucleotide sequence analysis revealed the presence of the three cdt subunit genes in tandem, and over 94% homology to the corresponding genes carried by P. alcalifaciens both at nucleotide and amino acid sequence levels. The P. rustigianii strain produced biologically active CDT, which caused distension of eukaryotic cell lines with characteristic tropism of CHO and Caco-2 cells but not of Vero cells. S1-nuclease digested pulsed-field gel electrophoresis followed by Southern hybridization analysis demonstrated that the cdt genes in both P. rustigianii and P. alcalifaciens strains are located on large plasmids (140 to 170 kb). Subsequently, conjugation assays using a genetically marked derivative of the P. rustigianii strain showed that the plasmid carrying cdt genes in the P. rustigianii was transferable to cdt gene-negative recipient strains of P. rustigianii, Providencia rettgeri, and Escherichia coli. Our results demonstrated the presence of cdt genes in P. rustigianii for the first time, and further showed that the genes are located on a transferable plasmid, which can potentially spread to other bacterial species.

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.

Microbiology and Epidemiology of Escherichia albertii—An Emerging Elusive Foodborne Pathogen

Escherichia albertii, a close relative of E. coli, is an emerging zoonotic foodborne pathogen associated with watery diarrhea mainly in children and immunocompromised individuals. E. albertii was initially classified as eae-positive Hafnia alvei, however, as more genetic and biochemical information became available it was reassigned to its current novel taxonomy. Its infections are common under conditions of poor hygiene with confirmed transmission via contaminated water and food, mainly poultry-based products. This pathogen has been isolated from various domestic and wild animals, with most isolates being derived from birds, implying that birds among other wild animals might act as its reservoir. Due to the absence of standardized isolation and identification protocols, E. albertii can be misidentified as other Enterobacteriaceae. Exploiting phenotypes such as its inability to ferment rhamnose and xylose and PCR assays targeting E. albertii-specific genes such as the cytolethal distending toxin and the DNA-binding transcriptional activator of cysteine biosynthesis encoding genes can be used to accurately identify this pathogen. Several gaps exist in our knowledge of E. albertii and need to be bridged. A deeper understanding of E. albertii epidemiology and physiology is required to allow the development of effective measures to control its transmission and infections. Overall, current data suggest that E. albertii might play a more significant role in global infectious diarrhea cases than previously assumed and is often overlooked or misidentified. Therefore, simple, and efficient diagnostic tools that cover E. albertii biodiversity are required for effective isolation and identification of this elusive agent of diarrhea.

Prevalence and whole-genome sequence analysis of Campylobacter spp. strains isolated from wild deer and boar in Japan

As a part of risk analysis for consumption of meat from wild animals, the prevalence of Campylobacter spp. in wild deer and boar in Japan was investigated. C. hyointestinalis subsp. hyointestinalis (C. hyointestinalis) was isolated from 2.8% (7/253) of the wild deer and 22.1% (71/321) of the wild boar examined. All 23 wild deer isolates and 141 (72.7%) wild boar isolates carried both chcdt-I and chcdt-II genes. The remaining 53 (27.3%) wild boar isolates had only the chcdt-II gene. By whole-genome sequence analysis, we detected 38-40 virulence- and survival-associated genes (motility, chemotactic, adhesion, invasion, toxin, glycosylation, iron uptake, drug resistance, and stress response), which had been identified in C. jejuni and C. coli. In conclusion, our study highlights C. hyointestinalis as a possible cause of food-borne disease in humans and emphasizes the importance of food hygiene in the processing of wild meats for human consumption.

Genomic Characterization of Fluoroquinolone-Resistant Thermophilic Campylobacter Strains Isolated from Layer Chicken Feces in Gangneung, South Korea by Whole-Genome Sequencing

Thermophilic Campylobacter species of poultry origin have been associated with up to 80% of human campylobacteriosis cases. Layer chickens have received less attention as possible reservoirs of Campylobacter species. Initially, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of two archived Campylobacter isolates (Campylobacter jejuni strain 200605 and Campylobacter coli strain 200606) from layer chickens to five antimicrobials (ciprofloxacin, nalidixic acid, erythromycin, tetracycline, and gentamicin) were determined using broth microdilution while the presence of selected antimicrobial resistance genes was performed by polymerase chain reaction (PCR) using specific primers. Whole-genome sequencing (WGS) was performed by the Illumina HiSeq X platform. The analysis involved antimicrobial resistance genes, virulome, multilocus sequence typing (MLST), and phylogeny. Both isolates were phenotypically resistant to ciprofloxacin (MIC: 32 vs. 32 µg/mL), nalidixic acid (MIC: 128 vs. 64 µg/mL), and tetracycline (MIC: 64 vs. 64 µg/mL), but sensitive to erythromycin (MIC: 1 vs. 2 µg/mL) and gentamicin (MIC: 0.25 vs. 1 µg/mL) for C. jejuni strain 200605 and C. coli strain 200606, respectively. WGS confirmed C257T mutation in the gyrA gene and the presence of cmeABC complex conferring resistance to FQs in both strains. Both strains also exhibited tet(O) genes associated with tetracycline resistance. Various virulence genes associated with motility, chemotaxis, and capsule formation were found in both isolates. However, the analysis of virulence genes showed that C. jejuni strain 200605 is more virulent than C. coli strain 200606. The MLST showed that C. jejuni strain 200605 belongs to sequence type ST-5229 while C. coli strain 200606 belongs to ST-5935, and both STs are less common. The phylogenetic analysis clustered C. jejuni strain 200605 along with other strains reported in Korea (CP028933 from chicken and CP014344 from human) while C. coli strain 200606 formed a separate cluster with C. coli (CP007181) from turkey. The WGS confirmed FQ-resistance in both strains and showed potential virulence of both strains. Further studies are recommended to understand the reasons behind the regional distribution (Korea, China, and Vietnam) of such rare STs.

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.

Risk of multi-drug resistant Campylobacter spp. and residual antimicrobials at poultry farms and live bird markets in Bangladesh

BACKGROUND

Understanding potential risks of multi-drug resistant (MDR) pathogens from the booming poultry sector is a crucial public health concern. Campylobacter spp. are among the most important zoonotic pathogens associated with MDR infections in poultry and human. This study systematically examined potential risks and associated socio-environmental factors of MDR Campylobacter spp. in poultry farms and live bird markets (LBMs) of Bangladesh.

METHODS

Microbial culture and PCR-based methods were applied to examine the occurrence and MDR patterns of Campylobacter spp. in potential sources (n = 224) at 7 hatcheries, 9 broiler farms and 4 LBMs in three sub-districts. Antimicrobial residues in broiler meat and liver samples (n = 50) were detected by advanced chromatographic techniques. A questionnaire based cross-sectional survey was conducted on socio-environmental factors.

RESULTS

Overall, 32% (71/ 224) samples were found contaminated with Campylobacter spp. In poultry farms, Campylobacter spp. was primarily found in cloacal swab (21/49, 43%), followed by drinking water (8/24, 33%), and meat (8/28, 29%) samples of broilers. Remarkably, at LBMs, Campylobacter spp. was detected in higher prevalence (p < 0.05) in broiler meat (14/26, 54%), which could be related (p < 0.01) to bacterial contamination of drinking water (11/21, 52%) and floor (9/21, 43%). Campylobacter isolates, one from each of 71 positive samples, were differentiated into Campylobacter jejuni (66%) and Campylobacter coli (34%). Alarmingly, 49 and 42% strains of C. jejuni and C. coli, respectively, were observed as MDR, i.e., resistant to three or more antimicrobials, including, tetracycline, amoxicillin, streptomycin, fluoroquinolones, and macrolides. Residual antimicrobials (oxytetracycline, ciprofloxacin and enrofloxacin) were detected in majority of broiler liver (79%) and meat (62%) samples, among which 33 and 19%, respectively, had concentration above acceptable limit. Inadequate personal and environmental hygiene, unscrupulously use of antimicrobials, improper waste disposal, and lack of health surveillance were distinguishable risk factors, with local diversity and compound influences on MDR pathogens.

CONCLUSION

Potential contamination sources and anthropogenic factors associated with the alarming occurrence of MDR Campylobacter, noted in this study, would aid in developing interventions to minimize the increasing risks of poultry-associated MDR pathogens under 'One Health' banner that includes poultry, human and environment perspectives.

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.

Epidemiology and Pathogenesis of Providencia alcalifaciens Infections

Providencia alcalifaciens is a member of the family Enterobacteriaceae that has been commonly implicated as a causative agent of diarrheal infection in humans and animals. Recent outbreaks of P. alcalifaciens in both developing and developed countries have raised public health concerns. Several studies have suggested that P. alcalifaciens can cause diarrhea by invading the intestinal mucosa, although its pathogenicity has not been well established. Often routine laboratory investigations that seek etiological agents of diarrhea do not actively pursue P. alcalifaciens detection. Therefore, routine laboratory diagnosis should be given more attention for better understanding the epidemiology and pathogenicity of P. alcalifaciens.

Development of a specific cytolethal distending toxin (cdt) gene (Eacdt)-based PCR assay for the detection of Escherichia albertii

Many Escherichia albertii isolates, an emerging pathogen of human and birds, might have been misidentified due to the difficulty of differentiating this bacterium from Escherichia coli and Shigella spp. by routine biochemical tests, resulting in underestimation of E. albertii infections. We have developed a polymerase chain reaction (PCR) assay that targets E. albertii cytolethal distending toxin (Eacdt) genes, which include the genes previously identified as Escherichia coli cdt-II. This assay could generate a single 449-bp PCR product in each of 67 confirmed E. albertii strains but failed to produce PCR product from any of the tested non-E. albertii enteric strains belonging to 37 different species, indicating 100% sensitivity and specificity of the PCR assay. The detection limit was 10 CFU per PCR tube and could detect 10⁵ CFU E. albertii per gram of spiked healthy human stool. The Eacdt gene-based PCR could be useful for simple, rapid, and accurate detection and identification of E. albertii.

Development of a multiplex PCR targeting eae, stx and cdt genes in genus Escherichia and detection of a novel cdtB gene in Providencia rustigianii

This study was aimed to develop a multiplex PCR (m-PCR) for the detection of Escherichia coli attaching and effacing (eae), Shiga toxin (stx) and cytolethal distending toxin (cdt) genes encoding important virulence factors of diarrheagenic E. coli such as EPEC, STEC, and Escherichia albertii. For this purpose, the m-PCR was designed to detect eae, all the subtypes of stx (stx1, stx2a-g except stx2f) and cdt (I-V) genes. The m-PCR was validated with 58 and 55 target gene-positive and negative strains of different sources, respectively. Sensitivity and specificity of the m-PCR were 100%. The m-PCR could also detect the eae, stx and cdt genes in bacteria spiked into stool specimens with or without enrichment culture. Clinical specimens collected from children with diarrhea were tested by the m-PCR, and 27 eae and 32 cdt genes were detected. Among them, three cdt-II and one untypable cdt gene-positive bacteria were isolated and identified as E. albertii and Providencia rustigianii, respectively. This is the first report demonstrating the presence of cdtB gene in P. rustigianii. These results indicate that the m-PCR is useful for surveillance of eae, stx and cdt gene-positive bacteria, not only EPEC, STEC and E. albertii but also P. rustigianii.

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.

Antibiotic Susceptibility, Genetic Diversity, and the Presence of Toxin Producing Genes in Campylobacter Isolates from Poultry

This study examined antibiotic susceptibility, genetic diversity, and characteristics of virulence genes in Campylobacter isolates from poultry. Chicken (n = 152) and duck (n = 154) samples were collected from 18 wet markets in Korea. Campylobacter spp. isolated from the carcasses were identified by PCR. The isolated colonies were analyzed for antibiotic susceptibility to chloramphenicol, amikacin, erythromycin, tetracycline, ciprofloxacin, nalidixic acid, and enrofloxacin. The isolates were also used to analyze genetic diversity using the DiversiLab^TM system and were tested for the presence of cytolethal distending toxin (cdt) genes. Campylobacter spp. were isolated from 45 poultry samples out of 306 poultry samples (14.7%) and the average levels of Campylobacter contamination were 22.0 CFU/g and 366.1 CFU/g in chicken and duck samples, respectively. Moreover, more than 90% of the isolates showed resistance to nalidixic acid and ciprofloxacin. Genetic correlation analysis showed greater than 95% similarity between 84.4% of the isolates, and three cdt genes (cdtA, cdtB, and cdtC) were present in 71.1% of Campylobacter isolates. These results indicate that Campylobacter contamination should be decreased to prevent and treat Campylobacter foodborne illness.

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.

Clinical relevance of infections with zoonotic and human oral species of Campylobacter

Genus Campylobacter has been recognized as a causative bacterial agent of animal and human diseases. Human Campylobacter infections have caused more concern. Campylobacters can be classified into two groups in terms of their original host: zoonotic and human oral species. The major zoonotic species are Campylobacter jejuni and Campylobacter coli, which mostly reside in the intestines of avian species and are transmitted to humans via consumption of contaminated poultry products, thus causing human gastroenteritis and other diseases as sequelae. The other campylobacters, human oral species, include C. concisus, C. showae, C. gracilis, C. ureolyticus, C. curvus, and C. rectus. These species are isolated from the oral cavity, natural colonization site, but have potential clinical relevance in the periodontal region to varying extent. Two species, C. jejuni and C. coli, are believed to be mainly associated with intestinal diseases, but recent studies suggested that oral Campylobacter species also play a significant role in intestinal diseases. This review offers an outline of the two Campylobacter groups (zoonotic and human oral), their virulence traits, and the associated illnesses including gastroenteritis.

Caracterização de estirpes de Campylobacter coli isoladas de carcaças de ovinos e de efluentes de abatedouro do estado de São Paulo

Doença bacteriana zoonótica, a campilobacteriose é responsável mundialmente por frequentes casos de gastroenterite humana. Campylobacter spp. apresenta fator de virulência associado à diarreia, denominado toxina citoletal distensiva (CDT), sendo codificado pelos genes do complexo cdt. Os objetivos do presente estudo foram: 1) isolar e identificar estirpes de Campylobacter spp. de 102 suabes de carcaças e 102 suabes retais de ovinos (Ovis aries) e de sete amostras de água dos efluentes, antes e depois do tratamento de desinfecção de abatedouro localizado no estado de São Paulo; e 2) detectar, pela técnica de multiplex-PCR, a presença do complexo de genes cdt. Foram isoladas e identificadas, por métodos fenotípicos e genotípicos, sete estirpes de Campylobacter coli provenientes de 4/102 (3,92%) das amostras de suabes retais, 1/102 (0,98%) de suabes de carcaças e 2/7 (28,5%) das águas dos efluentes. Dos isolados de suabes retais, em 2/7 (28,6%) estirpes foi detectada a presença dos genes cdt. Trata-se do primeiro relato de isolamento de estirpes de Campylobacter coli provenientes de abatedouro de ovinos e das estirpes portadoras do complexo de genes cdt nessa espécie animal no Brasil.

Prevalence and pathogenic potential of Escherichia coli isolates from raw milk and raw milk cheese in Egypt

The objectives of this study were to investigate prevalence and pathogenic potential of Escherichia coli contaminating raw milk and its products in Egypt. Out of 187 dairy products including 72 raw milk samples, 55 Karish cheese and 60 Ras cheese, 222 E. coli isolates including 111, 89 and 22 were obtained from 55 raw milk samples (76.4%), 41 Karish cheese (74.5%), and 13 Ras cheese (21.7%), respectively. Isolated E. coli strains were examined for 24 representative virulence genes present in diarrheagenic E. coli (DEC) and extraintestinal pathogenic E. coli (ExPEC). Among DEC and ExPEC virulence factors, genes for enteropathogenic E. coli (eaeA, bfpA, EAF), enterohemorrhagic E. coli (stx1, stx2, eaeA), enterotoxigenic E. coli (elt, est), enteroinvasive E. coli (invE), enteroaggregative E. coli (Eagg, astA), diffusely adherent E. coli (daaD), ExPEC (cdt-I to cdt-V, cnf1, cnf2, hlyA) and putative adhesins (efa1, iha, ehaA, saa, and lpfAO113) were screened by colony hybridization assay. Out of 222 E. coli strains, 104 (46.8%) isolated from 69 (36.9%) samples carried one or more virulence genes. The most prevalent gene detected was lpfAO113 (40.5%), followed by ehaA (32.4%,), astA (3.15%,), iha (1.80%), hlyA (1.35%), stx1 (0.90%), stx2 (0.90%), eaeA (0.45%), cdt-III (0.45%) and cnf2 (0.45%). Two strains isolated from Karish cheese harbored 5 virulence genes (stx1, stx2, iha, ehaA, lpfAO113). Stx subtype was determined to be stx1 (not stx1c or stx1d) and stx2d. Indeed, expression of hemolysin A, CDT-III, CNF-II, Stx1 and Stx2d was confirmed by blood agar plate, cytotoxicity assay and Western blotting, respectively. Among the 222 E. coli strains, 54 (48.6%), 38 (42.6%) and 12 (54.7%) isolated from raw milk, Karish cheese and Ras cheese were potentially virulent, respectively. O-genotyping indicated that most of the potentially virulent E. coli isolates did not belong to clinically important O serogroups except O75, O91 and O166, which have been associated with human diseases. Phylogenetic grouping revealed that 150 (67.6%), 67 (30.2%) and 5 (2.30%) strains were clustered into A, B1 and D groups, respectively, which are considered to be associated with intestinal infection, indicating that these E. coli strains might have a potential to cause gastroenteritis. To the best of our knowledge, this is the first comprehensive study regarding prevalence and pathogenic potential of E. coli in dairy products in Egypt. Raw milk, Karish cheese and Ras cheese in Egypt are highly contaminated with E. coli including potentially pathogenic strains, which may impose a public health threat.

Quantitative Microbial Risk Assessment for Campylobacter spp. on Ham in Korea

The objective of this study was to evaluate the risk of illness from Campylobacter spp. on ham. To identify the hazards of Campylobacter spp. on ham, the general characteristics and microbial criteria for Campylobacter spp., and campylobacteriosis outbreaks were investigated. In the exposure assessment, the prevalence of Campylobacter spp. on ham was evaluated, and the probabilistic distributions for the temperature of ham surfaces in retail markets and home refrigerators were prepared. In addition, the raw data from the Korea National Health and Nutrition Examination Survey (KNHNES) 2012 were used to estimate the consumption amount and frequency of ham. In the hazard characterization, the Beta-Poisson model for Campylobacter spp. infection was used. For risk characterization, a simulation model was developed using the collected data, and the risk of Campylobacter spp. on ham was estimated with @RISK. The Campylobacter spp. cell counts on ham samples were below the detection limit (<0.70 Log CFU/g). The daily consumption of ham was 23.93 g per person, and the consumption frequency was 11.57%. The simulated mean value of the initial contamination level of Campylobacter spp. on ham was -3.95 Log CFU/g, and the mean value of ham for probable risk per person per day was 2.20×10(-12). It is considered that the risk of foodborne illness for Campylobacter spp. was low. Furthermore, these results indicate that the microbial risk assessment of Campylobacter spp. in this study should be useful in providing scientific evidence to set up the criteria of Campylobacter spp..

Campylobacter hyointestinalis Isolated from Pigs Produces Multiple Variants of Biologically Active Cytolethal Distending Toxin

Campylobacter hyointestinalis isolated from swine with proliferative enteritis often is considered to be pathogenic. While the precise virulence mechanisms of this species remain unclear, we have recently identified a cytolethal distending toxin (cdt) gene cluster in C. hyointestinalis isolated from a patient with diarrhea (W. Samosornsuk et al., J Med Microbiol, 27 July 2015, http://dx.doi.org/10.1099/jmm.0.000145). However, the sequences of the cdt genes in C. hyointestinalis were found to be significantly different and the gene products are immunologically distinct from those of other Campylobacter species. In this study, we demonstrate the presence of a second variant of the cdt gene cluster in C. hyointestinalis, designated cdt-II, while the former is named cdt-I. Sequencing of the cdt-II gene cluster and deduced amino acid sequences revealed that homologies between the subunits CdtA, CdtB, and CdtC of ChCDT-I and ChCDT-II are 25.0, 56.0, and 24.8%, respectively. Furthermore, the CdtB subunit of ChCDT-II was found to be immunologically unrelated to that of ChCDT-I by Ouchterlony double gel diffusion test. Recombinant ChCDT-II also induced cell distention and death of HeLa cells by blocking the cell cycle at G2/M phase. Interestingly, the cdt-II genes were detected in all 23 animal isolates and in 1 human isolate of C. hyointestinalis, and 21 of these strains carried both cdt-I and cdt-II gene clusters. Altogether, our results indicate that ChCDT-II is an important virulence factor of C. hyointestinalis in animals.

A Cytolethal Distending Toxin Gene-Based Multiplex PCR Assay for Campylobacter jejuni, C. fetus, C. coli, C. upsaliensis, C. hyointestinalis, and C. lari

In this study, we devised a multiplex PCR assay based on the gene of cytolethal distending toxin (cdt) B subunit to simultaneously detect and discriminate Campylobacter jejuni, C. fetus, C. coli, C. upsaliensis, C. hyointestinalis, and C. lari. Species-specific PCR products were successfully obtained from all 38 C. jejuni, 12 C. fetus, 39 C. coli, 22 C. upsaliensis, 24 C. hyointestinalis, and 7 C. lari strains tested. On the other hand, no specific PCR products were obtained from other campylobacters and bacterial species tested (41 strains in total). The proposed multiplex PCR assay is a valuable tool for detection and descrimination of 6 major Campylobacter species, that are associated with gastrointestinal diseases in humans.

Molecular characterization of cytolethal distending toxin gene-positive Escherichia coli from healthy cattle and swine in Nara, Japan

BACKGROUND

Cytolethal distending toxin (CDT)-producing Escherichia coli (CTEC) has been isolated from patients with gastrointestinal or urinary tract infection, and sepsis. However, the source of human infection remains unknown. In this study, we attempted to detect and isolate CTEC strains from fecal specimens of healthy farm animals and characterized them phenotypically and genotypically.

RESULTS

By PCR analysis, the cdtB gene was detected in 90 and 14 out of 102 and 45 stool specimens of healthy cattle and swine, respectively, and none from 45 chicken samples. Subtypes of the cdtB genes (I to V) were further examined by restriction fragment length polymorphism analysis of the amplicons and by type-specific PCRs for the cdt-III and cdt-V genes. Of the 90 cdtB gene-positive cattle samples, 2 cdt-I, 25 cdt-III, 1 cdt-IV, 52 cdt-V and 1 both cdt-III and cdt-V gene-positive strains were isolated while 1 cdt-II and 6 cdt-V gene-positive were isolated from 14 cdtB positive swine samples. Serotypes of some isolates were identical to those of human isolates. Interestingly, a cdt-II gene-positive strain isolated from swine was for the first time identified as Escherichia albertii. Phylogenetic analysis grouped 87 E. coli strains into 77 phylogroup B1, 6 B2, and 4 D, respectively. Most of the B1 strains harbored both lpfAO113 and ehaA. Three and twenty-two cdt-V gene-positive strains harbored eaeA and stx genes, respectively, and seven possessed cdt-V, stx and subAB genes. The cnf2 gene, normally present in cdt-III gene-positive strains, was also detected in cdt-V gene-positive strains.

CONCLUSIONS

Our results suggest that healthy cattle and swine could be the reservoir of CTEC, and they could be a potential source of human infections.

A PCR-RFLP assay for the detection and differentiation of Campylobacter jejuni, C. coli, C. fetus, C. hyointestinalis, C. lari, C. helveticus and C. upsaliensis

Although Campylobacter jejuni and Campylobacter coli are the most common bacterial causes of human gastrointestinal diseases, other Campylobacter species are also involved in human and animal infections. In this study, we developed a cytolethal distending toxin (cdt) gene-based PCR-RFLP assay for the detection and differentiation of C. jejuni, C. coli, C. fetus, C. hyointestinalis, C. lari, C. helveticus and C. upsaliensis. Previously designed common primers, which can amplify the cdtB gene of C. jejuni, C. coli and C. fetus, were used for detecting seven Campylobacter species and differentiating between them by restriction digestion. The PCR-RFLP assay was validated with 277 strains, including 35 C. jejuni, 19 C. coli, 20 C. fetus, 24 C. hyointestinalis, 13 C. lari, 2 C. helveticus, 22 C. upsaliensis, 3 other Campylobacter spp. and 17 other species associated with human diseases. Sensitivity and specificity of the PCR-RFLP assay were 100 % except for C. hyointestinalis (88 % sensitivity). Furthermore, the PCR-RFLP assay successfully detected and differentiated C. jejuni, C. coli and C. fetus in clinical and animal samples. The results indicate that the PCR-RFLP assay is useful for the detection and differentiation of seven Campylobacter species important for human and animal diseases.

Molecular characterizations of cytolethal distending toxin produced by Providencia alcalifaciens strains isolated from patients with diarrhea

Cytolethal distending toxins (CDTs), which block eukaryotic cell proliferation by acting as inhibitory cyclomodulins, are produced by diverse groups of Gram-negative bacteria. Active CDT is composed of three polypeptides--CdtA, CdtB, and CdtC--encoded by the genes cdtA, cdtB, and cdtC, respectively. We developed a PCR-restriction fragment length polymorphism assay for the detection and differentiation of five alleles of cdtB (Cdt-I through Cdt-V) in Escherichia coli and used the assay to investigate the prevalence and characteristic of CDT-producing E. coli in children with diarrhea (A. Hinenoya et al., Microbiol. Immunol. 53:206-215, 2009). In these assays, two untypable cdtB genes were detected and the organisms harboring the cdtB gene were identified as Providencia alcalifaciens (strains AH-31 and AS-1). Nucleotide sequence analysis of the cdt gene cluster revealed that the cdtA, cdtB, and cdtC genes of P. alcalifaciens are of 750, 810, and 549 bp, respectively. To understand the possible horizontal transfer of the cdt genes among closely related species, the presence of cdt genes was screened in various Providencia spp. by colony hybridization assay, and the cdt gene cluster was found in only limited strains of P. alcalifaciens. Genome walking revealed that the cdt gene cluster of P. alcalifaciens is located adjacent to a putative transposase gene, suggesting the locus might be horizontally transferable. Interestingly, the CDT of P. alcalifaciens (PaCDT) showed some homology with the CDT of Shigella boydii. Whereas filter-sterilized lysates of strains AH-31 and AS-1 showed distention of CHO but not of HeLa cells, E. coli CDT-I exhibited distention of both cells. This activity of PaCDT was confirmed by generating recombinant PaCDT protein, which could also be neutralized by rabbit anti-PaCdtB antibody. Furthermore, recombinant PaCDT was found to induce G(2)/M cell cycle arrest and phosphorylation of host histone H2AX, a sensitive marker of DNA double-strand breaks. To our knowledge, this is the first report showing that certain clinical P. alcalifaciens strains could produce variants of the CDTs compared.

Campylobacter jejuni infection and virulence-associated genes in children with moderate to severe diarrhoea admitted to emergency rooms in northeastern Brazil

Campylobacter is an important cause of foodborne gastroenteritis. We determined the occurrence of Campylobacter jejuni and Campylobacter coli, using culture-based methods and PCRs targeting virulence-associated genes (VAGs) among children aged ≤14 years who were treated for diarrhoea at emergency rooms in northeastern Brazil. Genomic DNA was extracted directly from stool samples collected from 366 children. A questionnaire was also applied to qualify the clinical conditions presented by each child at the time of admission. C. jejuni and C. coli were detected in 16.4 % (60/366) and 1.4 % (5/366) of the diarrhoeal samples, respectively, by PCR, a much higher proportion than that detected by conventional methods. C. jejuni VAGs were detected in the following proportions of hipO-positive samples: ciaB, 95 % (57/60); dnaJ, 86.7 % (52/60); racR, 98.3 % (59/60); flaA, 80 % (48/60); pldA, 45 % (27/60); cdtABC, 95 % (57/60); and pVir 0 % (0/60). Particular symptoms, such as blood in faeces, vomiting, fever, and/or abdominal pain, were not associated with detection of C. jejuni nor were they associated with any particular VAG or combination of VAGs (P>0.05). C. jejuni and its VAGs were detected in a substantial proportion of the children admitted. Further efforts shall be directed towards elucidating whether these genetic factors or their expressed proteins play a role in Campylobacter pathogenesis.

Comparative studies of Campylobacter jejuni genomic diversity reveal the importance of core and dispensable genes in the biology of this enigmatic food-borne pathogen

MLST, DNA microarrays, and genome sequencing has allowed for a greater understanding of the metabolic capacity and epidemiology of Campylobacter jejuni. While strain-specific genes may provide an isolate a selective advantage in environments and contribute to the organism's pathogenicity, recent work indicates that C. jejuni pathogenicity is dictated by variations in the nucleotide sequence of core genes. Challenges facing C. jejuni researchers include determining (a) the degree to which genomic diversity enables this bacterium to persist in particular environments; (b) if C. jejuni virulence and disease severity can be predicted on the basis of genotype; (c) the set of core and variable genes whose products contribute to virulence; and (d) the genes in which nucleotide changes can affect a strain's pathogenicity.

Evaluation of a cytolethal distending toxin (cdt) gene-based species-specific multiplex PCR assay for the identification of Campylobacter strains isolated from poultry in Thailand

We have recently developed a cytolethal distending toxin (cdt) gene-based species-specific multiplex PCR assay for identifying Campylobacter jejuni, C. coli and C. fetus. In the present study, the applicability of this assay was evaluated with 34 Campylobacter-like organisms isolated from poultry in Thailand for species identification and was compared with other assays including API Campy, 16S rRNA gene sequence, and hippuricase (hipO) gene detection. Of the 34 strains analyzed, 20, 10 and 1 were identified as C. jejuni, C. coli, and Arcobacter cryaerophilus, respectively, and 3 could not be identified by API Campy. However, 16S rRNA gene analysis, showed that all 34 strains are C. jejuni/coli. To discriminate between these 2 species, the hipO gene, which is specifically present in C. jejuni, was examined by PCR and was detected in 20 strains, which were identified as C. jejuni by API Campy but not in the remaining 14 strains. Collective results indicated that 20 strains were C. jejuni whereas the 14 strains were C. coli. When the cdt gene-based multiplex PCR was employed, however, 19, 20 and 19 strains were identified as C. jejuni while 13, 14 and 13 were identified as C. coli by the cdtA, cdtB and cdtC gene-based multiplex PCR, respectively. Pulsed-field gel electrophoresis revealed that C. jejuni and C. coli strains analyzed are genetically diverse. Taken together, these data suggest that the cdt gene-based multiplex PCR, particularly cdtB gene-based multiplex PCR, is a simple, rapid and reliable method for identifying the species of Campylobacter strains.

Development of a cytolethal distending toxin (cdt) gene-based species-specific multiplex PCR assay for the detection and identification of Campylobacter jejuni, Campylobacter coli and Campylobacter fetus

A cytolethal distending toxin (cdt) gene-based species-specific multiplex PCR assay for the detection of cdtA, cdtB or cdtC gene of Campylobacter jejuni, Campylobacter coli or Campylobacter fetus, respectively, was developed and evaluated with 76 Campylobacter strains belonging to seven different species and 131 other bacterial strains of eight different genera. The cdtA, cdtB or cdtC gene of C. jejuni, C. coli or C. fetus, respectively, could be successfully amplified using the corresponding set of primers in a highly species-specific manner. Furthermore, the specific primer set for the cdtA, cdtB or cdtC gene of a particular species could amplify the desired gene from a mixture of DNA templates of any of two or all three species. The detection limit of C. jejuni, C. coli or C. fetus was 10-100 CFU tube(-1) by the multiplex PCR assay on the basis of the presence of the cdtA, cdtB or cdtC gene. These data indicate that the cdt gene-based multiplex PCR assay may be useful for rapid and accurate detection as well as identification of Campylobacter strains in a species-specific manner.

Cytolethal distending toxin (Cdt)-producing escherichia coli isolated from a child with bloody diarrhea in Japan

In a retrospective analysis by PCR, the cdtI gene encoding the cytolethal distending toxin (Cdt) was detected in Escherichia coli O2:H12 strain isolated from the bloody diarrheal stool specimen of a child. To our knowledge, this is the first report showing the possible association of Cdt-producing E. coli in Japan, particularly in a child with bloody diarrhea.

An inducible lambdoid prophage encoding cytolethal distending toxin (Cdt-I) and a type III effector protein in enteropathogenic Escherichia coli

Cytolethal distending toxins (CDTs) are inhibitory cyclomodulins, which block eukaryotic cell proliferation and are produced by a diverse group of Gram-negative bacteria, including Escherichia coli strains associated with intestinal and extraintestinal infections. However, the mode of transmission of the toxin gene clusters among diverse bacterial pathogens is unclear. We found that Cdt-I produced by enteropathogenic E. coli strains associated with diarrhea is encoded by a lambdoid prophage, which is inducible and infectious. The genome of Cdt-I converting phage (CDT-1Phi) comprises 47,021 nucleotides with 60 predicted ORFs organized into six genomic regions encoding the head and tail, virulence, integrase, unknown functions, regulation, and lysis. The genomic organization of CDT-1Phi is similar to those of SfV, a serotype-converting phage of Shigella flexneri, and UTI89, a prophage identified in uropathogenic E. coli. Besides the cdtI gene cluster, the virulence region of CDT-1Phi genome contains sequences homologous to a truncated cycle inhibiting factor and a type 3 effector protein. Mutation analysis of susceptible E. coli strain C600 suggested that the outer membrane protein OmpC is a putative receptor for CDT-1Phi. CDT-1Phi genome was also found to integrate into the host bacterial chromosome forming lysogens, which produced biologically active Cdt-I. Furthermore, phage induction appeared to cause enhanced toxigenicity of the E. coli strains carrying lysogenic CDT-1Phi. Our results suggest that CDT-1Phi is the latest member of a growing family of lambdoid phages encoding bacterial cyclomodulins and that the phage may have a role in horizontal transfer of these virulence genes.

Comparative analysis of cytolethal distending toxin (cdt) genes among Campylobacter jejuni, C. coli and C. fetus strains

The cytolethal distending toxin (cdt) gene clusters of Campylobacter coli strain Co1-243 and C. fetus strain Col-187 were cloned and sequenced to understand the importance of Cdt as a virulence factor. The cdt genes of C. coli and C. fetus consist of three closely linked genes termed cdtA, cdtB, cdtC whose sizes are 774, 801, and 570 bp, and 702, 798, and 546 bp, respectively. The homologies of each subunit of cdt genes between C. jejuni and C. coli, C. jejuni and C. fetus, or C. coli and C. fetus are 59.6%, 40.3%, or 46.5% for cdtA, 70.2%, 62.4%, or 61.3% for cdtB, 61.3%, 52.3%, or 50.1% for cdtC, respectively. Colony hybridization assay revealed that the genes homologous to the cdtABC gene were distributed in all 27, 19, 20 strains of C. jejuni, C. coli, and C. fetus, respectively, isolated from patients and animals in species-specific manner. Furthermore, nucleotide sequence of the cdt operon, including flanking region, of 10 strains of each species indicated that though the size of the cdtB gene was conserved in each species, those of cdtA and cdtC genes varied particularly among C. coli strains. Amino acid residues demonstrated to be important for toxin activity in CdtB, corresponding to H152, D185, D222, D258, H259 in Cj-CdtB, were also conserved in Cc-CdtB and Cf-CdtB. The cdt gene cluster was located in different sites among different species but in the same site of genomes of the same species. Cdt activity produced by C. jejuni and C. fetus varied among strains, however, any C. coli strains exhibited Cdt activity on HeLa cells. These data indicate that the cdt gene may have a potential for virulence factor at least in C. jejuni and C. fetus.