Virulence characteristics of Shiga toxin-producing Escherichia coli from raw meats and clinical samples

Shiga toxin producing Escherichia coli (STEC) are dangerous foodborne pathogens. Foods are considered as important sources for STEC infection in human. In this study, STEC contamination of raw meats was investigated and the virulence factors of 120 clinical STEC strains characterized. STEC was detected in 4.4% of tested samples. Among 25 STEC strains from meats, five strains (20%) were positive for the eae gene, which encodes intimin, an important binding protein of pathogenic STEC. The remaining strains (80%) were eae-negative. However, 28% of them possessed the saa gene, which encodes STEC agglutinating adhesin. The ehxA gene encoding for enterohemolysin was found in 75% of the meat strains and the subAB gene, the product is of which subtilase cytotoxin, was found in 32% of these strains. The stx2a gene, a subtype of Shiga toxin gene (stx), was the most prevalent subtype among the identified meat STEC bacteria. None of the meat STEC was O157:H7 serotype. Nevertheless, 92% of them produced Shiga toxin (Stx). Among 120 clinical STEC strains, 30% and 70% strains harbored single and multiple stx subtypes, respectively. Most clinical STEC bacteria possessed eae (90.8%) and ehxA (96.7%) genes and 92.5% of them showed Stx productivity. Our study shows that some raw meat samples contain non-O157 STEC bacteria and some strains have virulence factors similar to those of clinical strains.