Department of Bacteriology, National Veterinary Institute, Uppsala, Sweden.
J Appl Microbiol. 2011 Jan;110(1):323-32. doi: 10.1111/j.1365-2672.2010.04887.x. Epub 2010 Nov 15.
To establish whether investigated subtyping methods could identify any specific characteristics that distinguish Swedish VTEC O157:H7 strains isolated from cattle farms associated with human enterohaemorrhagic Escherichia coli (EHEC) cases from cattle strains isolated in prevalence studies.
Strains (n = 32) isolated in a dairy herd prevalence study and strains isolated from farms associated with human cases (n = 13) were subjected to typing. Partial sequencing of the vtx(2) genes could not identify any unique variants of vtx(2) or vtx(2c) in strains associated with human cases. A specific variant of VTEC O157:H7, which was overrepresented among farms associated with human cases (P = 0·01), was by two different single-nucleotide-polymorphism (SNP) assays identified as clade 8, a subgroup of VTEC O157:H7 strains considered to be putatively hypervirulent. Multi-locus variable number tandem repeat analysis (MLVA) typing of all strains produced similar results as pulsed-field gel electrophoresis (PFGE) typing regarding clustering of the strains, but MLVA distinguished slightly better among strains than PFGE.
In Sweden, VTEC O157:H7 strains from the putatively hypervirulent clade 8 are overrepresented among isolates from cattle farms associated with human cases compared with VTEC O157:H7 strains isolated in prevalence studies.
Real-time PCR SNP typing for clade 8 can be used to identify cattle farms that are at higher risk of causing EHEC infections in humans.
确定所研究的分型方法是否能够识别出从与人类肠出血性大肠杆菌（EHEC）病例相关的牛场中分离出的瑞典产志贺样毒素大肠杆菌（VTEC）O157：H7 菌株与流行研究中分离出的牛株之间存在的任何特定特征。
对来自乳牛群流行研究的菌株（n=32）和来自与人类病例相关农场的菌株（n=13）进行了分型。vtx(2)基因的部分测序无法确定与人类病例相关的菌株中 vtx(2)或 vtx(2c)的任何独特变体。通过两种不同的单核苷酸多态性（SNP）检测，在与人类病例相关的农场中发现了一种 VTEC O157：H7 的特定变体，该变体在与人类病例相关的农场中所占比例过高（P=0.01），被鉴定为 8 型簇，这是一种被认为具有潜在高致病性的 VTEC O157：H7 菌株亚群。对所有菌株进行多位点可变数串联重复分析（MLVA）分型的结果与脉冲场凝胶电泳（PFGE）分型相似，均显示菌株聚类，但 MLVA 比 PFGE 更能区分菌株。
在瑞典，与流行研究中分离出的 VTEC O157：H7 菌株相比，来自与人类病例相关的牛场的、假定具有潜在高致病性的 8 型簇 VTEC O157：H7 菌株所占比例过高。
实时 PCR SNP 分型用于 clade 8 可用于识别具有更高风险引发人类 EHEC 感染的牛场。
