Genotypic diversity of Escherichia coli in a dairy farm

Authors: Son, Insook; Van Kessel, Jo Ann; Karns, Jeffrey

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2009
Publication Date: 6/1/2009
Citation: Son, I., Van Kessel, J.S., Karns, J.S. 2009. Genotypic diversity of Escherichia coli in a dairy farm. Foodborne Pathogens and Disease. 6(7):837-847.

Interpretive Summary: Animal agriculture is often considered a significant source of E. coli and other bacteria in the environment. In addition, it is considered a source of pathogenic forms of E. coli such as O157:H7 which can cause severe disease in people who come in contact with it through food and water, or through direct contact with animals. This study uses a molecular tracking technique called pulsed field gel electrophoresis (PFGE) to examine the degree of diversity in E. coli populations on a dairy farm, and to examine the relationship between the E. coli found in cows to those found in dairy environmental samples such as manure and water and in the milk and milk filters. The results showed that there was a high degree of diversity in the E. coli populations on the dairy farm studied at the two times sampling was done and that few E. coli strains were found at both sampling times. The high degree of diversity found in this study indicates that attempts to utilize a method such as PFGE to track E. coli to determine the source of environmental contamination would require analysis of an impractical number of samples.

Technical Abstract: 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 (PFGE) to discriminate E. coli strains. Water from watering troughs, feces from cows, manure composites, milk and milk filters were collected on Dec., 2005 and Dec., 2006. Isolates were analyzed for phylogenetic grouping (A, B1, B2, and D) and for the presence of virulence genes associated with EPEC and EHEC strains by PCR. The bulk of the isolates were in the groups A (22%) and B1 (64%), while 4% and 11% of the isolates were within groups B2 and D, respectively. EHEC and EPEC virulence genes were detected in strains from the feces of 3 cows and in one composite manure. E. coli O157:H7 was present in one manure composite. PFGE analysis resulted in 155 unique restriction digestion patterns (RDPs). E. coli isolates from water, manure composite, fecal, milk and milk filters grouped into 34, 65, 76, 4, and 6 clusters, respectively. There was little diversity of isolates within a fecal sample 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.