Occurrence of Escherichia coli carrying Shiga toxin-producing genes in buffaloes on smallholdings in Bangladesh

Prevalence and Molecular Characterization of Shiga Toxin-Producing Escherichia coli from Food and Clinical Samples

Shiga toxin-producing Escherichia coli (STEC) is one of the most prominent food-borne pathogens in humans. The current study aims to detect and to analyze the virulence factors, antibiotic resistance, and plasmid profiles for forty-six STEC strains, isolated from clinical and food strains. Pulsed-field gel electrophoresis (PFGE) was used to determine the genetic relatedness between different serotypes and sources of samples. The clinical samples were found to be resistant to Nb (100%), Tet (100%), Amp (20%), SXT (15%), and Kan (15%) antibiotics. In contrast, the food strains were found to be resistant to Nb (100%), Tet (33%), Amp (16.6%), and SXT (16.6%) antibiotics. The PFGE typing of the forty-six isolates was grouped into more than ten clusters, each with a similarity between 30% and 70%. Most of the isolates were found positive for more than five virulence genes (eae, hlyA, stx1, stx2, stx2f, stx2c, stx2e, stx2, nelB, pagC, sen, toxB, irp, efa, and efa1). All the isolates carried different sizes of the plasmids. The isolates were analyzed for plasmid replicon type by PCR, and 72.5% of the clinical isolates were found to contain X replicon-type plasmid, 50% of the clinical isolates contained FIB replicon-type plasmid, and 17.5% of the clinical isolates contained Y replicon-type plasmid. Three clinical isolates contained both I1 and Hi1 replicon-type plasmid. Only two food isolates contained B/O and W replicon-type plasmid. These results indicate that STEC strains have diverse clonal populations among food and clinical strains that are resistant to several antimicrobials. In conclusion, our findings indicate that food isolates of STEC strains harbor virulence, antimicrobial resistance, plasmid replicon typing determinants like those of other STEC strains from clinical strains. These results suggest that these strains are unique and may contribute to the virulence of the isolates. Therefore, surveillance and characterization of STEC strains can provide useful information about the prevalence of STEC in food and clinical sources. Furthermore, it will help to identify STEC serotypes that are highly pathogenic to humans and may emerge as a threat to public health.

High Prevalence and Persistence of Escherichia coli Strains Producing Shiga Toxin Subtype 2k in Goat Herds

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a zoonotic pathogen with the ability to cause severe diseases like hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). Shiga toxin (Stx) is the key virulence factor in STEC and can be classified into two types, Stx1 and Stx2, and different subtypes. Stx2k is a newly reported Stx2 subtype in E. coli strains from diarrheal patients, animals, and raw meats exclusively in China so far. To understand the reservoir of Stx2k-producing E. coli (Stx2k-STEC), we investigated Stx2k-STEC strains in goat herds and examined their genetic characteristics using whole-genome sequencing. A total of 448 STEC strains were recovered from 2,896 goat fecal samples, and 37.95% (170/448) were Stx2k-STEC. Stx2k-STEC strains of serotype O93:H28 and sequence type 4038 (ST4038) were the most predominant and were detected over several years. Notably, 55% of Stx2k-STEC strains carried the heat-labile toxin (LT)-encoding gene (elt) defining enterotoxigenic E. coli (ETEC), thereby exhibiting the hybrid STEC/ETEC pathotype. Stx2k-converting prophage genomes clustered into four groups and exhibited high similarity within each group. Strains from patients, raw meat, sheep, and goats were intermixed distributed in the phylogenetic tree, indicating the risk for cross-species spread of Stx2k-STEC and pathogenic potential for humans. Further studies are required to investigate the Stx2k-STEC strains in other reservoirs and to understand the mechanism of persistence in these hosts.

IMPORTANCE Strains of the recently reported Stx2k-STEC have been circulating in a variety of sources over time in China. Here, we show a high prevalence of Stx2k-STEC in goat herds. More than half of the strains were of the hybrid STEC/ETEC pathotype. Stx2k-STEC strains of predominant serotypes have been widespread in the goat herds over several years. Stx2k-converting prophages have exhibited a high level of similarity across geographical regions and time and might be maintained and transmitted horizontally. Given that goat-derived Stx2k-STEC strains share similar genetic backbones with patient-derived strains, the high prevalence of Stx2k-STEC in goats suggests that there is a risk of cross-species spread and that these strains may pose pathogenetic potential to humans. Our study thus highlights the need to monitor human Stx2k-STEC infections in this region and, by extension, in other geographic locations.

Molecular detection of Shiga toxin-producing and antibiotic-resistant Escherichia coli isolates from buffaloes in southwest of Iran

Three hundred fifteen bacteriological samples were obtained from feces and both external and visceral cavity surfaces of carcasses of 105 healthy buffalo slaughtered in southwest of Iran. Confirmed Escherichia coli isolates were examined for antimicrobial resistance phenotypically and were screened for stx₁, stx₂, and eae genes and their subtypes and assessment of antimicrobial resistance genes by regular PCR and RFLP techniques. One hundred forty-five E. coli were isolated from feces (96 isolates) and external (37) and internal (12) surfaces of carcasses. Results showed that the prevalence of STEC, EPEC, and EHEC pathotypes was 2.8%, 0.7%, and 0.7% respectively. Among 6 (4.13%) positive isolates for examined genes, 4 (2.8%) isolates were positive for stx1, 3 (2.1%) for stx2, and 2 (1.4%) for eae gene. The detected genes were classified into stx₁a (4 isolates), stx₂a, stx₂b, stx₂c, eae-β, and unknown subtypes. The most prevalent antibiotic resistance gene was sulII (11.03%). The tetB, qnrB, floR, bla_TEM, bla_SHV, and aad_A genes were found to a lesser extent, and all isolates were negative for bla_CTX-15, bla_OXA, aac(3)-I, tetA, cat1, qnrA, sulI, dhfrI, and dhfrV genes. Twelve combination patterns of antibiotic-resistant genes were observed. Maximum phenotypically resistance rate was against doxycycline (91.83%), and the minimum was against ceftazidime and florfenicol (2.75%). E. coli isolates from feces and carcasses of slaughtered buffalo can be considered a mild reservoir for stx and eae genes. However, healthy buffaloes could be considered a potential reservoir of multiple antibiotic resistance genes in E. coli isolates.