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Research Article

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

NAGANO, HIDEKI, OKUI, TOYO, FUJIWARA, OSAMU, UCHIYAMA, YASUHIRO, TAMATE, NAOTO, KUMADA, HIROYUKI, MORIMOTO, YO, YANO, SHOKI

Journal of Medical Microbiology 2002; 51(5):405

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Summary auto-generated

This study characterized 22 clonal variants of Shiga toxin-producing Escherichia coli O157:H7 (STEC) isolated from two outbreaks and four sporadic cases in Hokkaido, Japan between 1996-1998. These isolates were unusual because they were positive for β-D-glucuronidase activity (GUD+), whereas typical STEC O157:H7 strains are GUD-negative. All isolates were negative for sorbitol fermentation and carried virulence genes stx1, stx2, eaeA, EHEC-hlyA, pas, and etpD, similar to typical strains. However, they lacked katP and espP genes normally present in typical STEC O157:H7. Pulsed-field gel electrophoresis (PFGE) analysis using multiple restriction enzymes showed all 22 isolates were identical or very closely related, indicating a single clonal origin. The GUD+ isolates displayed similar antimicrobial susceptibility patterns and produced Stx1, Stx2, and enterohaemolysin. Dendrogram analysis demonstrated that GUD+ STEC O157:H7 isolates formed a distinct cluster (>91.9% similarity within the group) separate from typical GUD- STEC O157 strains, supporting their classification as a unique clone within the STEC O157 complex.

Key findings

  • Twenty-two GUD+ STEC O157:H7 isolates from Hokkaido formed a single distinct clonal group with >91.9% genetic similarity by PFGE analysis
  • These atypical isolates lacked katP and espP genes present in typical STEC O157:H7 but retained stx1, stx2, and other major virulence genes
  • GUD+ and GUD- STEC O157 strains showed <60% similarity in PFGE patterns, confirming they represent separate clones within STEC O157
  • All 22 GUD+ isolates displayed nearly identical antimicrobial susceptibility patterns with minimal variation in MIC values
  • Most infected individuals (16/22) were asymptomatic or had mild non-bloody diarrhea, unlike typical STEC O157:H7 infections

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Abstract

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 ß-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.