Son Insook, Van Kessel Jo Ann S, Karns Jeffrey S
Environmental Microbial Safety Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705, USA.
Foodborne Pathog Dis. 2009 Sep;6(7):837-47. doi: 10.1089/fpd.2008.0201.
Dairy cattle are known reservoirs of pathogenic Escherichia coli, but little is known about the dynamics of E. coli in dairy cows or within the dairy farm environment. This study was conducted to evaluate the diversity and distribution of E. coli strains in a dairy farm using pulsed-field gel electrophoresis and to determine the relationships between E. coli isolated from feces and throughout the farm environment. Water from watering troughs, feces from cows, manure composites, milk, and milk filters were collected on December 2005 and December 2006. Isolates were analyzed by PCR for phylogenetic grouping (A, B1, B2, and D) and for the presence of virulence genes associated with enteropathogenic E. coli and enterohemorrhagic E. coli strains. Most of the isolates were in groups A (22%) and B1 (64%), while 4% and 11% of the isolates were within groups B2 and D, respectively. Enterohemorrhagic E. coli and enteropathogenic E. coli virulence genes were detected in strains from the feces of three cows and in one manure composite, and E. coli O157:H7 was present in one manure composite. Pulsed-field gel electrophoresis analysis resulted in 155 unique restriction digestion patterns (RDPs) among 570 isolates. E. coli isolates from water, manure composites, feces, milk, and milk filters grouped into 34, 65, 76, 4, and 6 clusters (identical RDPs), respectively. There was little diversity of isolates within individual fecal samples; however, high diversity was observed between fecal samples. Diversity was high within the water and composite samples. Some RDPs were common to multiple sample types. Although there were common RDPs between the 2005 and 2006 samplings, the E. coli populations were quite distinct between these two sampling times. These results demonstrate a high degree of diversity for E. coli within a dairy farm and that assigning a single environmental isolate to a particular farming operation would require the testing of an impractical number of isolates.
奶牛是致病性大肠杆菌已知的宿主，但对于奶牛体内或奶牛场环境中大肠杆菌的动态变化了解甚少。本研究旨在利用脉冲场凝胶电泳评估奶牛场中大肠杆菌菌株的多样性和分布，并确定从粪便及整个农场环境中分离出的大肠杆菌之间的关系。于2005年12月和2006年12月收集了来自饮水槽的水、奶牛粪便、粪便混合物、牛奶及牛奶过滤器。通过PCR分析分离株的系统发育分组（A、B1、B2和D）以及与肠致病性大肠杆菌和肠出血性大肠杆菌菌株相关的毒力基因的存在情况。大多数分离株属于A组（22%）和B1组（64%），而分别有4%和11%的分离株属于B2组和D组。在三头奶牛的粪便菌株及一份粪便混合物中检测到了肠出血性大肠杆菌和肠致病性大肠杆菌的毒力基因，并且在一份粪便混合物中存在大肠杆菌O157:H7。脉冲场凝胶电泳分析在570个分离株中产生了155种独特的限制性消化模式（RDPs）。从水、粪便混合物、粪便、牛奶及牛奶过滤器中分离出的大肠杆菌分别聚为34、65、76、4和6个簇（相同的RDPs）。单个粪便样本内分离株的多样性较低；然而，粪便样本之间观察到高度的多样性。水和混合物样本中的多样性较高。一些RDPs在多种样本类型中是常见的。尽管在2005年和2006年的采样之间存在共同的RDPs，但这两个采样时间的大肠杆菌群体截然不同。这些结果表明奶牛场内大肠杆菌具有高度的多样性，并且将单个环境分离株归因于特定的养殖操作需要检测数量不切实际的分离株。
