Clonal structure of Shiga toxin (Stx)-producing and β-d-glucuronidase-positive Escherichia coli O157:H7 strains isolated from outbreaks and sporadic cases in Hokkaido, Japan

A total of 22 clonal phenotypic variants of Shiga toxin (Stx)-producing Escherichia coli (STEC) O157:H7 was isolated from six different locations in Hokkaido, Japan. These isolates were negative for sorbitol fermentation but positive for β-d-glucuronidase (GUD+). They carried eaeA, EHEC-hlyA, pas and etpD genes like typical E. coli O157:H7 and, in addition, stx1 and stx2 genes. However, they were shown to lack katP and espP genes that are present in typical STEC O157:H7. All these atypical GUD+ STEC O157:H7 isolates had very similar antimicrobial susceptibilities. Pulsed-field gel electrophoresis analysis with XbaI, SfiI, SwaI, SpeI and NotI indicated that they were identical or closely related to one another. From their phenotypic and genotypic features, these GUD+ STEC O157:H7 isolates may represent a distinct clone among STEC O157.