Isolation and characterization of shiga toxin-producing Escherichia coli from meat and dairy products Original Research Article

Shiga toxin-producing Escherichia coli (STEC) strains were detected among 250 E. coli strains isolated from 204 food samples (meat and dairy products) obtained from butcher shops and retail stores in BEN AROUS (a Tunisian State/south east of the Tunisian capital). These 250 E. coli strains were isolated by applying culture techniques using sorbitol MacConkey (SMAC) agar after preenrichment of the homogenized food samples in buffered peptone water for 6 and 24 h, and violet red bile lactose (VRBL) agar. The highest percentage of E. coli recovery was from SMAC/6h preenrichment time and VRBL agar for meat and dairy products, respectively. Serotype O55:B5 was found to be the most prevalent type among E. coli isolates. E. coli isolates were screened for virulence factors: Shiga toxin 1 [stx1 (130 bp)], Shiga toxin 2 [stx2 (346 bp)], and eae gene [494 bp] by colony blot hybridization using three radioactively labelled DNA probes. Results obtained were confirmed by PCR. The three STEC isolates: one isolate-produced stx2, another isolate-produced stx1 and stx2, and the third isolate-expressed stx1, stx2, as well as eae genes. All three isolates produced EAST1. All Shiga toxin positive by PCR were found positive in the verocytotoxin test. In conclusion, this study indicates the presence of a possible bovine reservoir for STEC strains in Tunisia, signaling a potential risk for humans.