Identification of a Shiga-toxin type I variant containing an IS1203-like element, from Shiga-toxin producing Escherichia coli O157:H7.

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.