Characterization of stx2 and its variants in Escherichia coli O157:H7 isolated from patients and animals

In this study, we investigated 72 Escherichia coli O157:H7 strains from humans and animals to determine stx2 and its variants by polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism. Most isolates were found to carrystx2 or its variants and the stx2c was the dominant subtype; for the prevalence ofstx2c in stx2-positive isolates was 89.6% (42/47). All stx2 and stx2c harboring isolates obtained from humans had caused diarrhea or hemolytic-uremic syndrome. Three strains isolated from a piglet and two cattle carried the stx2c gene with an IS1203v inserted sequence. Sequencing of this region revealed that, this 1.3 kb insertion was very similar to a previously identified IS 1203v sequence and the insertion interrupted the carboxyl end of the B subunit coding region of stx2c gene. The corresponding positions in the stx2c gene sequence in which the IS 1203v sequence was inserted was varied. The isolates possessing IS1203v were inactive in the Vero cell toxicity assay. Key words: Shiga toxin-producing Escherichia coli; stx2; PCR-RFLP; insertion sequence; cytotoxicity.