J. Dairy Sci. 88:4441–4451
American Dairy Science Association, 2005.
Ecology of Escherichia coli O157:H7 in Commercial Dairies
in Southern Alberta
K. Stanford,1 D. Croy,1 S. J. Bach,2 G. L. Wallins,1 H. Zahiroddini,1 and T. A. McAllister3
1Alberta Agriculture, Food and Rural Development, Agriculture Centre, Lethbridge, Alberta, Canada T1J 4V6
2Agriculture and Agri-Food Canada, Research Centre, Summerland, British Columbia, Canada V0H 1Z0
3Agriculture and Agri-Food Canada, Research Centre, Lethbridge, Alberta, Canada T1J 4B1
ABSTRACT
Shedding of Escherichia coli O157:H7 was monitored
monthly over a 1-yr period by collecting pooled fecal
pats (FECAL) and manila ropes orally accessed for 4 h
(ROPE) from multiple pens of cattle in 5 commercial
dairies in southern Alberta, Canada. Using immuno-
magnetic separation, E. coli O157:H7 was isolated from
cows on 4 of the dairies and from 13.5% of FECAL and
1.1% of ROPE samples. Pulsed-field gel electrophoresis
of XbaI- and SpeI-digested bacterial DNA of the 65
isolates produced 23 unique restriction endonuclease
digestion patterns, although 92% of the isolates be-
longed to 3 restriction endonuclease digestion pattern
clusters sharing a minimum 90% homology. Collection
of positive isolates was 15 times more likely from June
through September. Across dairies, peak somatic cell
count occurred in July, August, September, andNovem-
ber. The likelihood of positive isolates was 2.6 times
higher in calves and heifers compared with mature
cows. This study indicates that ROPE would be of little
value for the detection of E. coli O157:H7 in dairy herds
unless oral contact with ROPE could be increased in
mature animals. Additionally, mitigation strategies for
E. coli O157:H7 should be targeted to the months of
July, August, and September and toward immature
animals for maximum impact. All farms displayed
unique combinations of seasonality of shedding and di-
versity of E. coli O157:H7 subtypes. The fact that sea-
sonal prevalence of E. coli O157:H7 largely coincided
with peak somati