Prevalence and molecular characterization of shiga toxin-producing Escherichia coli in animal source foods and green leafy vegetables

Shiga toxin-producing Escherichia coli (STEC) has emerged as important enteric foodborne zoonotic pathogens of considerable public health significance worldwide. The aim of this study was to determine the prevalence of the top seven STEC serotypes and to identify these serotypes in samples of animal source foods and vegetables. A total of 294 samples including 84 meat samples, 135 milk and dairy product samples and 75 green leafy vegetable samples were tested. The samples were harvested in mTSB-broth pre-enriched with novobiocin and then were tested by amplifying 16S shiga toxin (stx1/2), and eae genes using multiplex polymerase chain reaction (m-PCR) assay. A total of 260 (88.4%) samples were positive for E. coli and 29 (11.1%) of them were positive for shiga toxin, and eae genes. The positive samples were cultivated on CHROMAgar STEC and the colonies were evaluated for top seven STEC by m-PCR. The top seven STEC serotypes were detected in 27 (93.1%) of the samples: the STEC O111 serotype in 11 (40.7%) beef samples, STEC O45 in 3 (11.1%) chicken, STEC O145 in 6 (22.2%) parsley, 3 (11.1%) lettuce, 1 (3.7%) spinach, and 1 (3.7%) cheese, and STEC O103 in 2 (7.4%) lettuce samples. None of the samples was found positive for STEC O26, O121, and O157 serotypes. This study highlights the fact that the top seven STEC group poses a great risk in terms of food safety and public health in both animal source foods and vegetables.