Hallewell Jennyka, Reuter Tim, Stanford Kim, Topp Ed, Alexander Trevor W
1 Agriculture and Agri-Food Canada, Lethbridge Research Centre , Lethbridge, Canada .
2 Alberta Agriculture and Forestry, Agriculture Centre , Lethbridge, Canada .
Foodborne Pathog Dis. 2016 Dec;13(12):661-667. doi: 10.1089/fpd.2016.2164. Epub 2016 Oct 25.
The goal of this study was to monitor Shiga toxin-producing Escherichia coli (STEC) serogroups and virulence genes in cattle (n = 30) originating from a closed herd. Fecal samples were collected (1) at weaning, (2) upon arrival to a feedlot, (3) after 30 days on feed (DOF), and (4) after 135 DOF. DNA was extracted from feces for detection of virulence and serogroup genes by polymerase chain reaction (PCR) and immunomagnetic separation and pulsed-field gel electrophoresis (PFGE) were performed to collect and subtype STEC isolates. The prevalence of each serogroup measured by PCR from weaning to 135 DOF was 23.3-80.0% for O26, 33.3-46.7% for O45, 70.0-73.3% for O103, 36.7-86.7% for O111, 56.7-6.7% for O121, 26.7-66.7% for O145, and 66.7-90.0% for O157. Total fecal samples positive for virulence genes were 87.5% for ehxA, 85.8% for stx, 60.0% for stx, 52.5% for eae, and 44.2% for the autoagglutinating adhesion gene, saa. The prevalence of each serogroup and virulence gene tended to increase by 135 DOF, with the exception of O121, stx, and saa. The frequency of detection of some virulence genes was largely affected over time, most notably with saa and stx decreasing, and eae increasing when cattle were transitioned to concentrate-based diets. PFGE analysis of O157 and O103 fecal isolates revealed dominant pulsotypes, but the presence of identical O103 isolates, which differed in virulence profiles. Overall, this study showed that fecal shedding of E. coli serogroups and virulence-associated genes are highly variable over time as cattle move from ranch to feedlot. To mitigate STEC, it is important to understand the factors affecting both prevalence of individual serogroups and the presence of virulence factors.
本研究的目的是监测来自封闭牛群的30头牛中产生志贺毒素的大肠杆菌（STEC）血清群和毒力基因。在（1）断奶时、（2）到达饲养场时、（3）采食30天后（DOF）以及（4）采食135天后采集粪便样本。从粪便中提取DNA，通过聚合酶链反应（PCR）检测毒力和血清群基因，并进行免疫磁珠分离和脉冲场凝胶电泳（PFGE）以收集STEC分离株并进行亚型分析。从断奶到135 DOF，通过PCR检测的各血清群患病率分别为：O26为23.3 - 80.0%，O45为33.3 - 46.7%，O103为70.0 - 73.3%，O111为36.7 - 86.7%，O121为56.7 - 6.7%，O145为26.7 - 66.7%，O157为66.7 - 90.0%。毒力基因检测呈阳性的粪便样本总数中，ehxA为87.5%，stx为85.8%，stx为60.0%，eae为52.5%，自凝集黏附基因saa为44.2%。除O121、stx和saa外，各血清群及毒力基因的患病率在135 DOF时均有上升趋势。随着时间推移，一些毒力基因的检测频率受到很大影响，最显著的是当牛转换为以精饲料为主的日粮时，saa和stx减少，而eae增加。对O157和O103粪便分离株的PFGE分析揭示了主要的脉冲型，但存在毒力谱不同的相同O103分离株。总体而言，本研究表明，随着牛从牧场转移到饲养场，大肠杆菌血清群的粪便排泄和毒力相关基因随时间变化差异很大。为减轻STEC感染，了解影响个体血清群患病率和毒力因子存在的因素很重要。
