Department of Bacteriology I, National Institute of Infectious Diseases (NIID), Tokyo 162-8640, Japan.
Department of Microbiology, Faculty of Medicine, Kagawa University, Kagawa 761-0793, Japan.
Sci Rep. 2017 Feb 23;7:43136. doi: 10.1038/srep43136.
Enterohemorrhagic Escherichia coli (EHEC) O26 infections cause severe human diseases such as hemolytic uremic syndrome and encephalopathy, and is the predominant serogroup among non-O157 EHEC in many countries. Shiga toxin (Stx), which consists of two distinct types (Stx1 and Stx2), plays a central role in EHEC pathogenesis. The major stx gene type in EHEC O26 strains is stx1, although isolates with only stx2 have emerged in Japan since 2012 and have been reported in Europe. In this study, we selected 27 EHEC O26 strains isolated in Japan and identified a distinct genetic clade within sequence type (ST) 29, designated ST29C1, that carried only stx2 and had the plasmid gene profile ehxA+/katP-/espP+/etpD-. We showed that ST29C1 strains produced higher Stx2a levels, and greater virulence in Vero cells and in germ-free mice than other lineages. We also showed that ST29C1 was a distinct phylogenetic clade by SNP analysis using whole genome sequences and clearly differed from the major European EHEC O26 virulent clone, which was designated ST29C2 in this study. The combination of toxin production analysis, virulence analysis in Vero cells and germ-free mice, and phylogenetic analysis identified a newly emerging virulent EHEC clade.
肠出血性大肠杆菌（EHEC）O26 感染可引起严重的人类疾病，如溶血尿毒综合征和脑炎，并且是许多国家中除 O157 之外的 EHEC 的主要血清群。志贺毒素（Stx）由两种不同类型（Stx1 和 Stx2）组成，在 EHEC 发病机制中起核心作用。EHEC O26 菌株中的主要 stx 基因类型是 stx1，尽管自 2012 年以来日本已出现仅携带 stx2 的分离株，并在欧洲有报道。在这项研究中，我们选择了日本分离的 27 株 EHEC O26 菌株，并在序列型（ST）29 内鉴定出一个独特的遗传分支，命名为 ST29C1，该分支仅携带 stx2，并且具有质粒基因谱 ehxA+/katP-/espP+/etpD-。我们表明 ST29C1 菌株产生更高水平的 Stx2a，并且在 Vero 细胞和无菌小鼠中比其他谱系具有更高的毒力。我们还通过使用全基因组序列的 SNP 分析表明，ST29C1 是一个独特的系统发育分支，与本研究中指定为 ST29C2 的主要欧洲 EHEC O26 毒力克隆明显不同。毒素产生分析、Vero 细胞和无菌小鼠中的毒力分析以及系统发育分析相结合，确定了一个新出现的具有毒力的 EHEC 分支。
