title: Longitudinal study of Escherichia coli O157:H7 dissemination on four dairy farms in Wisconsin.
abstract: 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 x 10(2) to 8.7 x 10(4) 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 > or = 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.
authors.affiliation: Department of Food Microbiology and Toxicology, University of Wisconsin, Madison 53706, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Shere
authors.forename: K J
authors.initials: KJ
authors.lastname: Bartlett
authors.forename: C W
authors.initials: CW
authors.lastname: Kaspar
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D002417:Cattle / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D003612:Dairying; D004197:Disease Reservoirs; D004352:Drug Resistance, Microbial; D019453:Escherichia coli O157 / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity; D005260:Female; D005516:Food Microbiology; D008137:Longitudinal Studies; D008297:Male; D010641:Phenotype; D014871:Water Microbiology; D014922:Wisconsin
chemical_list: D004269:DNA, Bacterial