A large insertion in the Shiga-like toxin 2 gene (stx(2)) of an Escherichia coli O157 : H7 clinical isolate

Six clinical Escherichia coli O157:H7 isolates were epidemiologically linke d as part of an outbreak in which the most likely source was undercooked gr ound beef or cross-contamination from the ground beef to other food product s at a Mexican-style restaurant. These cultures were analyzed using molecul ar genetic, immunological and cytotoxicity procedures. All six isolates wer e confirmed as E. coli O157:H7 and were indistinguishable by pulsed-field g el electrophoresis using XbaI. The results of polymerase chain reaction (PC R) tests, non-isotopic gene probing, reversed passive latex agglutination ( RPLA) kit results and Vero cell assays were consistent for the presence of a functional Shiga-like toxin 1 (Stx 1) protein. All six strains produced a stx(2) PCR amplicon product; five strains produced a product which was con sistent with the predicted amplicon size and one (SEA 6414) produced a much larger PCR product. The SEA 6414 isolate produced a protein reactive with the RPLA kit anti-Stx 2 antibody but was not cytotoxic to Vero cells. Seque ncing of this region revealed that this 1310 bp insertion was very similar to a previously identified IS 1203 sequence and the insertion interrupted t he carboxyl end of the coding region of the stx(2) gene 'A' subunit. Publis hed by Elsevier Science B.V.