Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA.
Michigan Department of Agriculture and Rural Development, State of Michigan, East Lansing, Michigan, USA.
Appl Environ Microbiol. 2020 Oct 1;86(20). doi: 10.1128/AEM.01292-20.
Shiga toxin-producing (STEC) is a leading cause of foodborne infections. Cattle are an important STEC reservoir, although little is known about specific pathogen traits that impact persistence in the farm environment. Hence, we sought to evaluate STEC isolates recovered from beef cattle in a single herd in Michigan. To do this, we collected fecal grabs from 26 cattle and resampled 13 of these animals at 3 additional visits over a 3-month period. In all, 66 STEC isolates were recovered for genomics and biofilm quantification using crystal violet assays. The STEC population was diverse, representing seven serotypes, including O157:H7, O26:H11, and O103:H2, which are commonly associated with human infections. Although a core genome analysis of 2,933 genes grouped isolates into clusters based on serogroups, some isolates within each cluster had variable biofilm levels and virulence gene profiles. Most (77.8%; = 49) isolates harbored , while 38 (57.5%) isolates formed strong biofilms. Isolates belonging to the predominant serogroup O6 ( = 36; 54.5%) were more likely to form strong biofilms, persistently colonize multiple cattle, and be acquired over time. A high-quality single nucleotide polymorphism (SNP) analysis of 33 O6 isolates detected between 0 and 13 single nucleotide polymorphism (SNP) differences between strains, indicating that highly similar strain types were persisting in this herd. Similar findings were observed for other persistent serogroups, although key genes were found to differ among strong and weak biofilm producers. Together, these data highlight the diversity and persistent nature of some STEC types in this important food animal reservoir. Food animal reservoirs contribute to Shiga toxin-producing (STEC) evolution via the acquisition of horizontally acquired elements like Shiga toxin bacteriophages that enhance pathogenicity. In cattle, persistent fecal shedding of STEC contributes to contamination of beef and dairy products and to crops being exposed to contaminated water systems. Hence, identifying factors important for STEC persistence is critical. This longitudinal study enhances our understanding of the genetic diversity of STEC types circulating in a cattle herd and identifies genotypic and phenotypic traits associated with persistence. Key findings demonstrate that multiple STEC types readily persist in and are transmitted across cattle in a shared environment. These dynamics also enhance the persistence of virulence genes that can be transferred between bacterial hosts, resulting in the emergence of novel STEC strain types. Understanding how pathogens persist and diversify in reservoirs is important for guiding new preharvest prevention strategies aimed at reducing foodborne transmission to humans.
产志贺毒素大肠杆菌（STEC）是食源性感染的主要原因。牛是 STEC 的重要储存宿主，但对于影响其在农场环境中持久性的特定病原体特征知之甚少。因此，我们试图评估密歇根州一个单一牛群中回收的牛肉牛 STEC 分离株。为此，我们从 26 头牛中采集粪便样本，并在 3 个月的时间内另外 3 次访问时重新采样了其中 13 只动物。总共回收了 66 株 STEC 分离株，用于使用结晶紫测定法进行基因组学和生物膜定量。STEC 种群多样，代表了 7 种血清型，包括 O157:H7、O26:H11 和 O103:H2，这些血清型通常与人类感染有关。尽管对 2933 个基因的核心基因组分析根据血清群将分离株分为聚类，但每个聚类中的一些分离株具有不同的生物膜水平和毒力基因谱。大多数（77.8%；n=49）分离株携带，而 38 株（57.5%）分离株形成强生物膜。属于主要血清群 O6（n=36；54.5%）的分离株更有可能形成强生物膜，持续定植多只牛，并随时间推移而获得。对 33 株 O6 分离株进行高质量单核苷酸多态性（SNP）分析，在菌株之间检测到 0 到 13 个单核苷酸多态性（SNP）差异，表明该牛群中持续存在高度相似的菌株类型。在其他持久性血清群中也观察到类似的发现，尽管在强和弱生物膜生产者之间发现了关键基因的差异。这些数据共同强调了一些 STEC 类型在这种重要的食源动物储存库中的多样性和持久性。食源动物储存库通过获得水平获得的元素（如增强致病性的志贺毒素噬菌体）促进 STEC 的进化。在牛中，STEC 的持续粪便排出导致牛肉和奶制品污染，并使农作物暴露于受污染的水系统中。因此，确定 STEC 持久性的重要因素至关重要。这项纵向研究增强了我们对牛群中循环的 STEC 类型遗传多样性的理解，并确定了与持久性相关的基因型和表型特征。主要发现表明，多种 STEC 类型很容易在共享环境中在牛之间持续存在和传播。这些动态还增强了可在细菌宿主之间转移的毒力基因的持久性，导致新型 STEC 菌株类型的出现。了解病原体如何在储存库中持续存在和多样化对于指导旨在减少食源性传播给人类的新收获前预防策略非常重要。
