Genotypic and Cytotoxicity Analysis of Non-O157 Shiga Toxin-producing Escherichia coli Isolates from Humans, Animals and Food

Introduction: Non-O157 Shiga toxin-producing Escherichia coli(STEC) have become increasingly important to public health and food safety. Better understanding of non-O157 STEC is important for development of measures.

Purpose: To analyze the diversity of virulence factors among non-O157 STEC isolates from human, animal and food isolates.

Methods: A total of 311 STEC isolates (73 human, 139 animal and 99 food) were examined for the Shiga toxin gene (stx) variants, intimin gene (eae) variants and enterohaemolysin gene (hlyA) using PCR and PCR-RFLP. They were also classified into seropathotypes based on serotypes. Vero cytotoxicity of selected isolates from different sources was also determined.

Results: Most human and animal isolates belonged to seropathotype B, whereas food isolates were mainly seropathotypes C, D and E. Virulence gene profiles differed significantly among the isolates. Most human and animal isolates were positive for stx1a (76% and 97%), eae (82% and 92%) and hlyA (81% and 81%), respectively. The virulence gene distribution in food isolates was stx1a (27%), stx2a (35%), stx2dact (36%), eae (1%), hlyA(45%) and other minor virulence factors. Food isolates had a greater variety of virulence factor combinations (20) compared to human (11) and animal isolates (10). As expected, the human isolates exhibited the greatest cell cytotoxicity, whereas cytotoxicity varied among the food isolates.

Significance: STEC isolates from food significantly differed from human isolates in serotypes, virulence factors and vero cell cytotoxicity. Some food isolates, however, belonged to important serotypes, carried important virulence factors and exhibited elevated cell cytotoxicity, thereby have the potential to cause severe diseases in humans.