Tarr Cheryl L, Large Teresa M, Moeller Chris L, Lacher David W, Tarr Phillip I, Acheson David W, Whittam Thomas S
Microbial Evolution Laboratory, National Food Safety and Toxicology Center, Michigan State University, East Lansing 48824, USA.
Infect Immun. 2002 Dec;70(12):6853-9. doi: 10.1128/IAI.70.12.6853-6859.2002.
Most illnesses caused by Shiga toxin-producing Escherichia coli (STEC) have been attributed to E. coli serotype O157:H7, but non-O157 STEC infections are now increasingly recognized as public health problems worldwide. The O121:H19 serotype is being isolated more frequently from clinical specimens and has been implicated in one waterborne outbreak. We used multilocus virulence gene profiling, a PCR-based assay, to characterize the virulence gene content of 24 isolates of serotype O121:H19 and nonmotile variants. We also performed multilocus enzyme electrophoresis and multilocus sequencing to establish the clonal relatedness of O121 isolates and to elucidate the relationship of O121 to common STEC clones. The 24 isolates were found to represent a single bacterial clone, as there was no allelic variation across 18 enzyme loci among the isolates. The complete nucleotide sequence of the intimin gene differed by four substitutions from that of the epsilon (Int- epsilon ) allele of O103:H2 strain PMK5. The typical O121 virulence gene profile was similar to the profiles of enterohemorrhagic E. coli (EHEC) clones of E. coli: it included a Shiga toxin 2 gene (stx(2)), two genes on the EHEC plasmid (toxB and ehxA), and the gene encoding intimin (eae). Despite the similarities, putative virulence genes distributed on O islands-large chromosomal DNA segments present in the O157:H7 genome-were useful for discriminating among STEC serotypes and the O121:H19 clone had a composite profile that was distinct from the profiles of the other major EHEC clones of pathogenic E. coli. On the basis of sequencing analysis with 13 housekeeping genes, the O121:H19 clone did not fall into any of the four classical EHEC and enteropathogenic E. coli groups but instead was closely related to two eae-negative STEC strains.
大多数由产志贺毒素大肠杆菌（STEC）引起的疾病都归因于O157:H7血清型大肠杆菌，但非O157 STEC感染如今在全球范围内日益被视为公共卫生问题。O121:H19血清型越来越频繁地从临床标本中分离出来，并且与一次水源性暴发有关。我们使用多位点毒力基因分析（一种基于PCR的检测方法）来鉴定24株O121:H19血清型菌株和无动力变体的毒力基因组成。我们还进行了多位点酶电泳和多位点测序，以确定O121菌株的克隆相关性，并阐明O121与常见STEC克隆的关系。发现这24株菌株代表单个细菌克隆，因为这些菌株在18个酶位点上没有等位基因变异。紧密黏附素基因的完整核苷酸序列与O103:H2菌株PMK5的ε（Int-ε）等位基因相比有四处替换差异。典型的O121毒力基因图谱与大肠杆菌肠出血性大肠杆菌（EHEC）克隆的图谱相似：它包括一个志贺毒素2基因（stx(2)）、EHEC质粒上的两个基因（toxB和ehxA）以及编码紧密黏附素的基因（eae）。尽管存在相似性，但分布在O岛（O157:H7基因组中存在的大染色体DNA片段）上的假定毒力基因有助于区分STEC血清型，并且O121:H19克隆具有与致病性大肠杆菌其他主要EHEC克隆的图谱不同的复合图谱。基于对13个管家基因的测序分析，O121:H19克隆不属于四个经典的EHEC和肠致病性大肠杆菌组中的任何一组，而是与两株eae阴性STEC菌株密切相关。
