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Appl Environ Microbiol, April 1998, p. 1390-1399, Vol. 64, No. 4
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Longitudinal Study of Escherichia coli O157:H7 Dissemination on Four Dairy Farms in Wisconsin

J. A. Shere,1,2 K. J. Bartlett,1 and C. W. Kaspar1,*

Department of Food Microbiology and Toxicology, Food Research Institute, University of Wisconsin, Madison, Wisconsin 53706,1 and Veterinary Services, Animal, Plant Health Inspection Service, U.S. Department of Agriculture, Madison, Wisconsin 537192

Received 14 October 1997/Accepted 15 January 1998

A 14-month longitudinal study was conducted on four dairy farms (C, H, R, and X) in Wisconsin to ascertain the source(s) and dissemination of Escherichia coli O157:H7. A cohort of 15 heifer calves from each farm were sampled weekly by digital rectal retrieval from birth to a minimum of 7 months of age (range, 7 to 13 months). Over the 14 months of the study, the cohort heifers and other randomly selected cattle from farms C and H tested negative. Farm R had two separate periods of E. coli O157:H7 shedding lasting 4 months (November 1995 to February 1996) and 1 month (July to August 1996), while farm X had at least one positive cohort animal for a 5-month period (May to October 1996). Heifers shed O157:H7 strains in feces for 1 to 16 weeks at levels ranging from 2.0 × 102 to 8.7 × 104 CFU per g. E. coli O157:H7 was also isolated from other noncohort cattle, feed, flies, a pigeon, and water associated with the cohort heifers on farms R and/or X. When present in animal drinking water, E. coli O157:H7 disseminated through the cohort cattle and other cattle that used the water source. E. coli O157:H7 was found in water at <1 to 23 CFU/ml. Genomic subtyping by pulsed-field gel electrophoresis demonstrated that a single O157:H7 strain comprised a majority of the isolates from cohort and noncohort cattle, water, and other positive samples (i.e., from feed, flies, and a pigeon, etc.) on a farm. The isolates from farm R displayed two predominant XbaI restriction endonuclease digestion profiles (REDP), REDP 3 and REDP 7, during the first and second periods of shedding, respectively. Six additional REDP that were >= 89% similar to REDP 3 or REDP 7 were identified among the farm R isolates. Additionally, the REDP of an O157:H7 isolate from a heifer on farm R in 1994 was indistinguishable from REDP 3. Farm X had one O157:H7 strain that predominated (96% of positive samples had strains with REDP 9), and the REDP of an isolate from a heifer in 1994 was indistinguishable from REDP 9. These results suggest that E. coli O157:H7 is disseminated from a common source on farms and that strains can persist in a herd for a 2-year period.

* Corresponding author. Mailing address: Food Research Institute, University of Wisconsin, 1925 Willow Dr., Madison, WI 53706-1187. Phone: (608) 263-6936. Fax: (608) 263-1114. E-mail: cwkaspar{at}facstaff.wisc.edu.




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Copyright © 1998 by the American Society for Microbiology. All rights reserved.