Public Health Microbiology, Forensic and Scientific Services, Queensland Department of Health, Queensland, Australia.
School of Biomedical Sciences, Institute of Health & Biomedical Innovation, Faculty of Health, Queensland University of Technology, Brisbane, Queensland, Australia.
J Clin Microbiol. 2018 Mar 26;56(4). doi: 10.1128/JCM.01906-17. Print 2018 Apr.
Shiga toxin-producing (STEC) is a foodborne pathogen, and serotype O157:H7 is typically associated with severe disease. Australia is unique in its STEC epidemiology, as severe cases are typically associated with non-O157 serogroups, and locally acquired O157 isolates are H-negative/nonmotile. The H-negative phenotype and reduced severity of disease compared to that associated with H7/motile strains are distinct features of Australian O157 strains, but the molecular mechanism behind this phenotype has not been reported. Accurate characterization of the H-negative phenotype is important in epidemiological surveillance of STEC. Serotyping is moving away from phenotype-based methods, as next generation sequencing allows rapid extrapolation of serotype through detection of the O-antigen processing genes, , , , and , and the H-antigen gene, The detection and genotyping of alone is unable to determine the motility of the strain. Typically, most Australian O157:H-negative strains carry an H7 genotype yet phenotypically are nonmotile; thus, many are mischaracterized as H7 strains by serotyping tools. Comparative genomic analysis of flagellar genes between Australian and international isolates was performed and an insertion at nucleotide (nt) 125 in the gene was identified in H-negative isolates. Chi-square results showed that this insertion was significantly associated with the H-negative phenotype ( < 0.0001). Phylogenetic analysis was also completed and showed that the Australian H-negative isolates with the insertion in represent a clade within the O157 serogroup, distinct from O157:H7 serotypes. This study provides a genetic target for inferring the nonmotile phenotype of Australian O157 STEC, which increases the predictive value of serotyping.
产志贺毒素（STEC）是一种食源性病原体，血清型 O157：H7 通常与严重疾病相关。澳大利亚在 STEC 流行病学方面具有独特性，因为严重病例通常与非 O157 血清群相关，并且本地获得的 O157 分离株呈 H-阴性/非运动性。与 H7/运动性菌株相关的疾病相比，H-阴性表型和疾病严重程度降低是澳大利亚 O157 菌株的显著特征，但这种表型的分子机制尚未报道。准确描述 H-阴性表型对于 STEC 的流行病学监测非常重要。血清分型正在从基于表型的方法转变，因为下一代测序允许通过检测 O-抗原加工基因 、 、 、 、 、和 H-抗原基因 来快速推断血清型。单独检测和基因分型 无法确定菌株的运动性。通常，大多数澳大利亚 O157：H-阴性菌株携带 H7 基因型，但表型上是非运动性的；因此，许多菌株被 血清分型工具错误地归类为 H7 菌株。对澳大利亚和国际分离株的鞭毛基因进行了比较基因组分析，发现 H-阴性分离株在 基因的核苷酸 125 处存在插入。卡方检验结果表明，该插入与 H-阴性表型显著相关（<0.0001）。还完成了系统发育分析，结果表明，澳大利亚 H-阴性分离株中 基因的插入代表了 O157 血清群内的一个分支，与 O157：H7 血清型不同。这项研究为推断澳大利亚 O157 STEC 的非运动性表型提供了一个遗传靶标，从而提高了 血清分型的预测价值。
