Putative classification of clades of enterohemorrhagic Escherichia coli O157 using an IS‐printing system

Enterohemorrhagic Escherichia coli O157 (O157) strains can be classified in clades by single nucleotide polymorphisms (SNPs), but this analysis requires significant laboratory effort. As the distribution of insertion sequence (IS) 629 insertions has been reported to be biased among different clades, O157 isolates can be putatively classified in clades by comparison with an IS629 distribution database. A database of the IS629 distribution in O157 strains isolated in Chiba Prefecture and their classification in clades was determined by SNP analysis and IS‐printing, an easy and quick analytical tool for IS629 in the O157 genome. The IS629 distribution in O157 strains isolated in Fukuoka and Yamagata Prefectures was determined by IS‐printing. These strains were putatively classified in clades by Relative Likelihood calculations that compared the IS‐printing data and the IS629 distribution database. Concordance Ratios were calculated, which compared the number of strains putatively classified in a clade by Relative Likelihood to the number of strains classified in that clade by SNP analysis. For the Fukuoka and Yamagata strains, the Concordance Ratios for clades 3, 6 and 8 were 97–100%, for clade 7 about 88%, and for clades 2 and 12 over 90%. In conclusion, O157 clade 2, 3, 6, 7, 8 and 12 strains could be putatively classified by IS‐printing. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated that enterohemorrhagic E. coli O157 (O157) strains could be putatively classified in clades using an IS‐printing system. IS‐printing was previously developed as a relatively quick and easy tool for analysis of insertion sequence 629 in the O157 genome. Since most local government public health institutes in Japan carry out IS‐printing for early detection of O157 outbreaks, these data should be useful for putative classification of O157 strains in each area.