Location: Produce Safety and Microbiology ResearchTitle: Prevalence and molecular characterization of Escherichia coli O157:H7 by multiple locus variable number tandem repeat analysis and pulsed field gel electrophoresis in three sheep farming operations in California.) Author
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2011
Publication Date: 9/12/2011
Publication URL: doi:10.4315/0362-028XJFP-10-529
Citation: Kilonzo, C., Atwill, R.R., Mandrell, R.E., Garrick, M., Villanueva, V., Hoar, B.R. 2011. Prevalence and molecular characterization of Escherichia coli O157:H7 by multiple locus variable number tandem repeat analysis and pulsed field gel electrophoresis in three sheep farming operations in California.. Journal of Food Protection. 74(9):1413-1421. Interpretive Summary: Escherichia coli O157:H7, the major STEC serotype isolated from food has been recognized as the primary cause of various human diseases including bloody diarrhea, abdominal pain, hemorrhagic colitis, thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. Outbreaks have been associated with consumption of a variety of foods including beef products, milk, apple cider and sprouts, and leafy greens. Sheep are an integral part of the US agricultural economy and useful in converting renewable resources from rangelands, pasture and crop residues into humanly edible food, a feature that can potentially result in deleterious consequences associated with contamination of agricultural produce. Little is known about the epidemiology of E. coli O157:H7 in sheep. The aims of this study were to determine the prevalence of E. coli O157:H7 in fecal samples, identify potential factors associated with presence of E. coli O157:H7 and determine the diversity and temporal transition of E. coli O157:H7 strains using MLVA and PFGE. This analysis revealed the diversity and persistence of E. coli O157:H7 strains present in the feedlot farming operation, and the persistence of some strains circulating in the U.S sheep population.
Technical Abstract: A yearlong study was conducted to determine the fecal prevalence of Escherichia coli O157:H7 in three sheep ranches. Strain diversity and persistence was compared using multiple locus variable number tandem repeat analysis and pulsed field gel electrophoresis. Ranch C, a feedlot, consisted of young sheep raised predominantly on a high grain diet. The other two sites consisted of sheep raised on native pasture and a combination of native and irrigated pasture. Forty fecal samples were collected every month from each ranch. Samples were examined for E. coli O157:H7 by immunomagnetic separation and culture of the magnetic beads onto selective media. Detection of virulence markers in positive isolates was determined by PCR. E. coli O157:H7 was isolated from 100/440 (22.7%) fecal samples collected from Ranch C. In Ranch B, 9/480 (1.9%) of the fecal samples were positive for the pathogenwhilenone was isolated from Ranch A. In Ranch C, the odds of detecting E. coli O157:H7 was 3.2 times greater during the warmer months compared to the cooler months of the year. There was no association between days spent in the feedlot and fecal prevalence of the pathogen (p=0.62). Most MLVA types were isolated only once from Ranch C (14/23), but several strains were isolated across 4-6 months, often in many intervening negative months. This study revealed that the prevalence of E. coli O157:H7 can be high in some sheep ranches in California, especially in feedlots where young sheep are fed predominantly on high grain rations.