Shiga toxin-producing Escherichia coli (STEC) are foodborne bacterial pathogens, with cattle a significant reservoir for human infection. This study evaluated environmental reservoirs, intermediate hosts and key pathways that could drive the presence of Top 7 STEC (O157:H7, O26, O45, O103, O111, O121 and O145) on pasture-based dairy herds, using molecular and culture-based methods. A total of 235 composite environmental samples (including soil, bedding, pasture, stock drinking water, bird droppings and flies and faecal samples of dairy animals) were collected from two dairy farms, with four sampling events on each farm. Molecular detection revealed O26, O45, O103 and O121 as the most common O-serogroups, with the greatest occurrence in dairy animal faeces (> 91%), environments freshly contaminated with faeces (> 73%) and birds and flies (> 71%). STEC (79 isolates) were a minor population within the target O-serogroups in all sample types but were widespread in the farm environment in the summer samplings. Phylogenetic analysis of whole genome sequence data targeting single nucleotide polymorphisms revealed the presence of several clonal strains on a farm; a single STEC clonal strain could be found in several sample types concurrently, indicating the existence of more than one possible route for transmission to dairy animals and a high rate of transmission of STEC between dairy animals and wildlife. Overall, the findings improved the understanding of the ecology of the Top 7 STEC in open farm environments, which is required to develop on-farm intervention strategies controlling these zoonoses.

产生志贺毒素的大肠杆菌（STEC）是食源性细菌病原体，牛是人类感染的重要储存库。这项研究使用基于分子和文化的方法，评估了可以驱动牧场型奶牛群中排名前7位的STEC（O157：H7，O26，O45，O103，O111，O121和O145）的环境储层，中间宿主和关键途径。方法。从两个奶牛场收集了总共235个复合环境样本（包括土壤，被褥，牧场，牲畜饮用水，鸟粪和苍蝇以及粪便的粪便样本），每个农场有四个采样事件。分子检测显示O26，O45，O103和O121是最常见的O血清群，在奶牛粪便（> 91％），新鲜被粪便污染的环境（> 73％）和鸟类和苍蝇（> 71％）中发生率最高。 ）。在所有样本类型中，STEC（79个分离株）在目标O血清群内都是少数，但在夏季采样中在农场环境中普遍存在。对针对单核苷酸多态性的全基因组序列数据进行的系统进化分析表明，农场中存在数个克隆菌株。可以同时在几种样本类型中发现单个STEC克隆菌株，这表明存在不止一种可能的途径传播给奶牛动物，并且STEC在奶牛动物和野生动物之间的传播率很高。总体而言，这些发现增进了人们对开放式农场环境中前7名STEC生态学的了解，这是制定控制这些人畜共患病的农场干预策略所必需的。