Enterohemorrhagic Escherichia coli O157 subclade 8b strains in Chiba Prefecture, Japan, produced larger amounts of Shiga toxin 2 than strains in subclade 8a and other clades

PLOS ONE, Nov 2019

Enterohemorrhagic Escherichia coli O157 (O157) strains can be classified into clades (one of several phylogenetic groups) by single nucleotide polymorphisms (SNPs): these are clade 1, clade 2, clade 3, descendant and ancestral clades 4/5, clade 6, clade 7, clade 8, clade 9, and clade 12. Some recent studies showed that some O157 strains in clade 8 produced a larger amount of Shiga toxin (Stx) 2 than other strains. In this study, 1121 epidemiologically unlinked strains of O157 isolated in Chiba Prefecture, Japan were classified into clades during 1996–2014. Clade 8 strains were further classified into subclade 8a (67 strains) and subclade 8b (48 strains) using SNP analysis. In the absence of mitomycin C (MMC), subclade 8a strains in this study produced significantly greater amounts of Stx2 than subclade 8b strains. However, in the presence of MMC, the levels of Stx2 production in subclade 8b strains were significantly greater than subclade 8a strains. On the other hand, a recent study reported that the Stx2 production level in O157 strains was determined mainly by the subtypes of Stx2a phage (ϕStx2_α, β, γ, δ, ε, and ζ). Using O157 strains in this study, the Stx2a phages were classified into these subtypes. In this study, all strains of subclades 8a and 8b carried ϕStx2a_γ and ϕStx2a_δ, respectively. Some strains in clade 6 also carried ϕStx2a_δ. In the presence of MMC, subclade 8b strains produced significantly greater amounts of Stx2 than clade 6 strains carrying ϕStx2_δ. In this study, we propose that Stx2 production in subclade 8b strains in the presence of MMC might be enhanced due to genetic factors other than ϕStx2_δ.

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Enterohemorrhagic Escherichia coli O157 subclade 8b strains in Chiba Prefecture, Japan, produced larger amounts of Shiga toxin 2 than strains in subclade 8a and other clades

January Enterohemorrhagic Escherichia coli O157 subclade 8b strains in Chiba Prefecture, Japan, produced larger amounts of Shiga toxin 2 than strains in subclade 8a and other clades Shinichiro Hirai 0 1 Eiji Yokoyama 0 1 Taku Wakui 1 Taichiro Ishige 1 Masaki Nakamura 0 1 0 Division of Bacteriology, Chiba Prefectural Institute of Public Health , Chiba , Japan , 2 Division of Epidemiology, Chiba Prefectural Institute of Public Health , Chiba , Japan , 3 Genome Research Center, NODAI Research Institute, Tokyo University of Agriculture , Tokyo , Japan 1 Editor: Pina Fratamico, USDA-ARS Eastern Regional Research Center , UNITED STATES Enterohemorrhagic Escherichia coli O157 (O157) strains can be classified into clades (one of several phylogenetic groups) by single nucleotide polymorphisms (SNPs): these are clade 1, clade 2, clade 3, descendant and ancestral clades 4/5, clade 6, clade 7, clade 8, clade 9, and clade 12. Some recent studies showed that some O157 strains in clade 8 produced a larger amount of Shiga toxin (Stx) 2 than other strains. In this study, 1121 epidemiologically unlinked strains of O157 isolated in Chiba Prefecture, Japan were classified into clades during 1996±2014. Clade 8 strains were further classified into subclade 8a (67 strains) and subclade 8b (48 strains) using SNP analysis. In the absence of mitomycin C (MMC), subclade 8a strains in this study produced significantly greater amounts of Stx2 than subclade 8b strains. However, in the presence of MMC, the levels of Stx2 production in subclade 8b strains were significantly greater than subclade 8a strains. On the other hand, a recent study reported that the Stx2 production level in O157 strains was determined mainly by the subtypes of Stx2a phage (ϕStx2_α, β, γ, δ, ε, and ζ). Using O157 strains in this study, the Stx2a phages were classified into these subtypes. In this study, all strains of subclades 8a and 8b carried ϕStx2a_γ and ϕStx2a_δ, respectively. Some strains in clade 6 also carried ϕStx2a_δ. In the presence of MMC, subclade 8b strains produced significantly greater amounts of Stx2 than clade 6 strains carrying ϕStx2_δ. In this study, we propose that Stx2 production in subclade 8b strains in the presence of MMC might be enhanced due to genetic factors other than ϕStx2_δ. - Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: Part of this study was supported by a Grant from the Daido Life Welfare Foundation for Regional Health and Welfare Research in fiscal 2016 (Grant Number: None, URL: http://www. daido-life-welfare.or.jp/subsidize/welfare/index. htm, and Receiver: SH), by the Cooperative Research Grant of the Genome Research for Introduction Phylogenetic groups are groups of bacterial strains originating from a common ancestral clone [ 1, 2 ]. Since bacteria reproduce asexually, the strains in the same phylogenetic group possess similar or common genetic features e.g., biochemical properties [3], polymorphisms in the BioResource, NODAI Genome Research Center, Tokyo University of Agriculture in fiscal 2014 (Grant Number: 14A-18, URL: http://www.nodaigenome.org/gabase/index.html?lang=ja, and Receiver: EY), and by JSPS KAKENHI (Grant Number: 26460540, URL: http://www.jsps.go.jp/jgrantsinaid/index.html, and Receiver: EY). All funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. genome [ 4 ], and possession of pathogenic factors [ 5 ]. Recent studies have shown that enterohemorrhagic Escherichia coli O157 (O157) strains can be divided into several phylogenetic groups i.e., lineages [ 6 ], subgroups and clusters [ 7 ], and clades [ 8 ]. Yokoyama et al. [ 9 ] showed that the hierarchical relationship of the O157 phylogenetic groups was, in descending order, lineage, subgroup, cluster, and clade. In addition, Yokoyama et al. [ 9 ] suggested a paraphyletic model for O157 evolution based on these hierarchical relationships. This model has been further modified with new clade designations based on lineage analysis data (S1 Table) [ 10 ]. It has been reported that the pathogenicity of O157 strains varied between different clades. A higher percentage of clade 8 strains caused hemolytic uremic syndrome (HUS) than strains in other clades, suggesting strong pathogenicity of clade 8 strains [ 8, 11 ]. The strong pathogenicity of those O157 strains was due to Shiga toxin (Stx) 2 subtypes and the level of Stx2 production [12]. Stx2 were classified into several subtypes (i.e., Stx2a, Stx2b, Stx2c, Stx2d, Stx2e, Stx2f and Stx2g) [ 13 ]. Enterohemorrhagic Escherichia coli strains with Stx2a were more frequently isolated from HUS patients than the strains with the other Stx2 subtypes [ 14, 15 ]. Most clade 8 strains carry a stx2a gene and produce more Stx2 than strains in other clades [ 9, 16 ]. However, some O157 clade 8 strains produce less Stx2 than other clade 8 strains [ 17 ], ind (...truncated)


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Shinichiro Hirai, Eiji Yokoyama, Taku Wakui, Taichiro Ishige, Masaki Nakamura. Enterohemorrhagic Escherichia coli O157 subclade 8b strains in Chiba Prefecture, Japan, produced larger amounts of Shiga toxin 2 than strains in subclade 8a and other clades, PLOS ONE, 2018, Volume 13, Issue 1, DOI: 10.1371/journal.pone.0191834