Characterisation of Shiga toxin-producing Escherichia coli (STEC) isolated from seafood and beef

Shiga toxin-producing Escherichia coli (STEC) strains isolated in Mangalore, India, were characterised by bead-enzyme-linked immunosorbent assay (bead-ELISA), Vero cell cytotoxicity assay, PCR and colony hybridisation for the detection of stx₁ and stx₂ genes. Four strains from seafood, six from beef and one from a clinical case of bloody diarrhoea were positive for Shiga toxins Stx1 and Stx2 and also for stx₁ and stx₂ genes. The seafood isolates produced either Stx2 alone or both Stx1 and Stx2, while the beef isolates produced Stx1 alone. The stx₁ gene of all the beef STEC was found to be of recently reported stx₁c type. All STEC strains and one non-STEC strain isolated from clam harboured EHEC-hlyA. Interestingly, though all STEC strains were negative for eae gene, two STEC strains isolated from seafood and one from a patient with bloody diarrhoea possessed STEC autoagglutinating adhesion (saa) gene, recently identified as a gene encoding a novel autoagglutinating adhesion.