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Appl. Environ. Microbiol., 05 1996, 1519-1525, Vol 62, No. 5
NG Faith, JA Shere, R Brosch, KW Arnold, SE Ansay, MS Lee, JB Luchansky and CW Kaspar
A survey was conducted between March and October of 1994 to determine the
prevalence and identify the sources of serotype O157:H7 isolates of
Escherichia coli in Wisconsin dairy herds. A stratified sample of 400 farms
was identified, and 70 farms with weaned calves less than 4 months old were
included in the study. During the prevalence study, 5 of the 70 farms (herd
prevalence, 7.1 +/- 4.5%) and fecal samples from 10 of 560 calves (animal
prevalence, 1.8%) tested positive for serotype O157:H7. In a follow-up
study, the five O157:H7-positive farms and seven of the O157:H7-negative
farms identified in the prevalence study were visited again. An additional
517 fecal samples from cattle of various ages were tested, and a total of
15 animals from four of the five herds that were previously positive and 4
animals from two of seven herds that were previously negative tested
positive for E. coli O157:H7. Observations made during the follow-up study
suggested that horizontal transmission was an important means of E. coli
O157:H7 dissemination on the farms. A total of 302 environmental samples,
were examined, and 2 animal drinking water samples from one previously
negative farm and 1 animal drinking water sample from a previously positive
farm contained E. coli O157:H7. Analyses by the pulsed-field gel
electrophoresis technique of contour-clamped homogeneous electric field
electrophoresis revealed that isolates from the same farm displayed
identical or very similar XbaI restriction endonuclease digestion profiles
(REDP), whereas isolates from different farms typically displayed different
REDP. However, more than one REDP was usually observed for a given herd
over the 8-month sampling period. Analyses of multiple isolates from an
animal revealed that some animals harbored O157:H7 strains that had
different REDP, although the REDP of isolates obtained from the same fecal
sample were very similar. Collectively, 160 bovine isolates obtained from
29 different animals and three water isolates displayed 20 distinct XbaI
REDP. Our data revealed that there are several clonal types of serotype
O157:H7 isolates in Wisconsin and indicated that there is probably more
than one source of this pathogen on the dairy farms studied. However,
animal drinking water was identified as one source of E. coli O157:H7 on
one farm.
Copyright © 1996, American Society for Microbiology
Prevalence and clonal nature of Escherichia coli O157:H7 on dairy farms in Wisconsin
Food Research Institute, Department of Food Microbiology and Toxicology, Madison, WI 53706-1187, USA.
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