Characterization of Shiga-toxin producing Escherichia coli (STEC) isolated from retail raw meats in Southeast China

Abstract

Shiga toxin-producing Escherichia coli (STEC) is an important zoonotic foodborne pathogen that can induce acute gastrointestinal symptoms related to human infection. In this study, we characterized 49 STEC strains isolated from 816 retail raw meats from 2010 to 2016 in Southeast China for their serotype, virulence-associated genes, phylogenetic group, antibiotic resistance, and biofilm-forming ability. These isolates belonged to 33 divergent O: H serotypes, among which O157: H7 (12.24%, 6/49) was the most common serotype. Moreover, 22.45% (11/49) isolates belonged to the “top six” serotypes most frequently implicated in human infections. Among the 11 virulence-associated genes studied, stx2 (71.43%, 35/49) was the most prevalent virulence factor, with 87.76% (43/49) of isolates carrying two or more types of virulence factors. The B1 (55.10%, 27/49) and D (28.57%, 14/49) phylogenetic groups were predominant among isolates, whereas no strain belonged to group B2. A total of 59.18% (29/49) of isolates were resistant to 13 out of 16 tested antimicrobials, with resistance rate ranging from 4.08% (2/49) for both ceftazidime and chloramphenicol to 46.94% (23/49) for streptomycin. We detected eight out of 30 antibiotic-resistance genes (tetA, tetB, strA, strB, gyrA, floR, sulI, and sulII), with obvious mismatch between the phenotypes and genotypes of these isolates. Most strains (87.76%, 43/49) produced biofilms and 23.26% (10/43) were categorized as high producers. In conclusion, raw meats retailed in Southeast China contain STEC with multifarious serotypes, virulence-associated genes, antimicrobial resistance and biofilm-forming ability, some of which pose potential health risks to consumers.