title: Evolutionary model of the divergence of enterohemorrhagic Escherichia coli O157 lineage I/II clades reconstructed from high resolution melting and Shiga-like toxin 2 analyses.
abstract: We have studied 167 epidemiologically unlinked strains of enterohemorrhagic Escherichia coli O157 (O157) isolated from patients with hemorrhagic colitis (HC), 87 strains from patients not with HC and 35 asymptomatic carriers (the not HC group), and differentiated these strains into clades using high resolution melting analysis. In addition, lineage analysis was carried out using lineage-specific polymorphism assay-6 and analysis of the distribution of IS629 insertion sites was carried out using IS-printing. Most strains were correctly clustered by minimum spanning tree analysis, and strains in the major clades showed linkage disequilibrium, confirming the clade differentiation in this study. The number of O157 strains in the different clades isolated from HC patients and the not HC group was significantly different (Chi square test, P<0.05), indicating that strains in different clades had different pathogenicities for hemorrhagic colitis. Pairwise comparison of the number of strains in different clades isolated from HC patients indicated that clade 12 strains were weakly pathogenic for HC. Stx2 titers and the number of strains carrying an stx2 gene were significantly different for different clades (Kruscal-Wallis test and Chi square test, P<0.05). Pairwise comparison of the Stx2 titer and the number of strains with an stx2 gene in different clades showed that the weak HC pathogenicity of clade 12 strains would be related to the low number of clade 12 strains with an stx2 gene and the low Stx2 production in those strains. Interestingly, the Stx2 titer and the prevalence of strains with an stx2 gene were significantly higher among clade 6 and 8 strains compared to clade 7 strains, although clades 6, 7, and 8 were all in lineage I/II. These results were discordant with the O157 evolutionary model, suggesting that insertion of an stx2 gene in lineage I/II strains after divergence of each clade.
authors.affiliation: Division of Pathology and Bacteriology, Fukuoka Institute of Health and Environmental Sciences, Fukuoka, Japan. Electronic address: etoh@fihes.pref.fukuoka.jp.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Etoh
authors.affiliation: Division of Bacteriology, Chiba Prefectural Institute of Public Health, Chiba, Japan; Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Science, Chiba University, Chiba, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Hirai
authors.affiliation: Division of Pathology and Bacteriology, Fukuoka Institute of Health and Environmental Sciences, Fukuoka, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Ichihara
authors.affiliation: Division of Pathology and Bacteriology, Fukuoka Institute of Health and Environmental Sciences, Fukuoka, Japan.
authors.forename: Eriko
authors.initials: E
authors.lastname: Maeda
authors.affiliation: Division of Bacteriology, Chiba Prefectural Institute of Public Health, Chiba, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Yokoyama
authors.affiliation: Division of Pathology and Bacteriology, Fukuoka Institute of Health and Environmental Sciences, Fukuoka, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Sera
authors.affiliation: Division of Pathology and Bacteriology, Fukuoka Institute of Health and Environmental Sciences, Fukuoka, Japan.
authors.forename: Kazumi
authors.initials: K
authors.lastname: Horikawa
authors.affiliation: Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Science, Chiba University, Chiba, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Yamamoto
mesh_terms: D005075:Biological Evolution; D003092:Colitis / Q000382:microbiology*; D054324:Enterohemorrhagic Escherichia coli / Q000145:classification / Q000235:genetics*; D004927:Escherichia coli Infections / Q000382:microbiology; D019453:Escherichia coli O157 / Q000145:classification* / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics; D022641:Shiga Toxin 2 / Q000235:genetics*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D022641:Shiga Toxin 2; D037521:Virulence Factors
keywords: Clade; Enterohemorrhagic Escherichia coli O157; Evolutionary model; High resolution melting; Stx2