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

Abstract

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 carry stx₂ or its variants and the stx_2c was the dominant subtype; for the prevalence of stx_2c in stx₂-positive isolates was 89.6% (42/47). All stx₂ and stx_2c harboring isolates obtained from humans had caused diarrhea or hemolytic-uremic syndrome. Three strains isolated from a piglet and two cattle carried the stx_2c 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 stx_2c gene. The corresponding positions in the stx_2c 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.