Distribution of IS629 and stx genotypes among enterohemorrhagic Escherichia coli O157 isolates in Yamaguchi Prefecture, Japan, 2004–2013

Patterns of insertion sequence (IS)629, norV genotype, and Shiga toxin (Stx) genotype distribution were investigated amongst 203 enterohemorrhagic Escherichia coli O157 isolates collected in Yamaguchi Prefecture, Japan, between 2004 and 2013. A total of 114 IS629 patterns were identified; these were divided into eight IS groups (A–H). Ninety isolates carried an intact norV gene, whereas 113 isolates carried a norV with a 204-bp deletion. Other than one isolate from IS group G, all isolates with an intact norV belonged to groups A–F, whereas isolates with a mutant norV belonged to IS groups G and H. Seven stx genotypes were identified, and of those, stx1a/stx2a was predominant (n=105), followed by stx2c (n=32) and stx2a (n=27). The stx1a/stx2a genotype was associated with the mutant norV isolates, whereas isolates with an intact norV had the stx2c genotype. Therefore, certain combinations of IS type and stx genotype appear to be more frequent among O157 clades which may be useful for detection of predominant subtypes in the interest of public health.