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We found two Shiga toxin producing Escherichia coli O157:H7 strains isolated from humans carrying the stx(1) gene with an IS1203-like element (designated as IS1203v(1)). The IS1203v(1) was inserted into the coding region of the A subunit 7 bp upstream from the TGA termination codon, resulting in a loss of two amino acid residues (Ser-Ser) from its C terminus. Toxicity of the Stx1 was confirmed by Vero cell assay. IS1203v(1) hardly affected the stx(1) gene in either its expression or the toxicity of its product.

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 stx1and 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.