title: Emergence of enterohemorrhagic Escherichia coli serovar O157 strains in clade 8 with highly similar pulsed-field gel electrophoresis patterns.
abstract: Enterohemorrhagic Escherichia coli serovar O157 (O157) strains with highly similar pulsed-field gel electrophoresis (PFGE) patterns were isolated in Japan during 2007 and 2008. Several genetic features related to O157 evolution were investigated to indicate whether homoplasy might have contributed to the highly similar PFGE patterns in these strains. The O157 strains were classified in lineage I/II, as defined by a lineage-specific polymorphism assay-6 with an atypical allele in Z5935 (code: 231111). Analysis of the insertion sites of stx(2) phage in these strains showed that the sites were "occupied" in yehV and "intact" in wrbA, indicating that the strains were derived from "Cluster 1" of "Subgroup C." When a specific single-nucleotide polymorphism in ECs2357 in clade 8 strains was investigated, all of the strains in the present study were confirmed to be clade 8 strains. These results indicated that the O157 strains in this study had common genetic features, suggesting that the highly similar PFGE patterns of these strains were not due to homoplasy. Because no common source of these strains could be identified in 2007 to 2008 in Japan, these strains may have emerged from a unique O157 clade 8 clone and then spread by dissemination in Japan.
authors.affiliation: Division of Bacteriology, Chiba Prefectural Institute of Public Health, 666-2, Chuo, Chiba City, Chiba 260-8715, Japan. e.ykym@ma.pref.chiba.lg.jp
authors.forename: Eiji
authors.initials: E
authors.lastname: Yokoyama
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Etoh
authors.forename: Sachiko
authors.initials: S
authors.lastname: Ichihara
authors.forename: Kazumi
authors.initials: K
authors.lastname: Horikawa
authors.forename: Noriko
authors.initials: N
authors.lastname: Konishi
authors.forename: Akemi
authors.initials: A
authors.lastname: Kai
authors.forename: Yuko
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Morito
authors.initials: M
authors.lastname: Kurosaki
authors.forename: Hitomi
authors.initials: H
authors.lastname: Kasahara
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kurazono
authors.forename: Kiyoe
authors.initials: K
authors.lastname: Yoda
mesh_terms: D015373:Bacterial Typing Techniques; D004269:DNA, Bacterial / Q000032:analysis*; D016521:Electrophoresis, Gel, Pulsed-Field; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000145:classification* / Q000235:genetics*; D005516:Food Microbiology; D005798:Genes, Bacterial; D006801:Humans; D007564:Japan / Q000453:epidemiology; D015810:Linkage Disequilibrium; D020641:Polymorphism, Single Nucleotide
chemical_list: D004269:DNA, Bacterial