title: Development of an experimental model to assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder within a feedlot environment.
abstract: This study was conducted to develop an experimental model that could assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder (>10(4) CFU/g of feces) within a feedlot environment. The day before the study began, 48 steers that had been negative for E. coli O157:H7 in feces for three consecutive weeks were sorted into three treatment groups, with two replicate pens per treatment and 8 steers per pen. Steers within the pens (20.50 by 10.75 m) were exposed to control feces or feces inoculated with two levels of a mixture of five strains of nalidixic acid-resistant E. coli O157:H7 (low level, 10(2) CFU/g; high level, 10(5) CFU/g). Five 300-g fecal pats were introduced into the pens twice daily (10:00 a.m. and 2:30 p.m.) on days 0 through 6 and days 14 through 20. Pats were placed in the pen at random locations to mimic defecation of a steer within the pen. Fecal grab samples, hide swab samples (500-cm2 area of the rump), natural fecal pat samples (freshly voided), and rope samples (1.22-m-long manila rope) where obtained at multiple times during the 49-day trial to evaluate the spread of nalidixic acid-resistant E. coli O157:H7 throughout the feedlot environment and among penmates. Immunomagnetic separation and selective media were used to detect E. coli O157:H7. Nalidixic acid-resistant E. coli O157:H7 was detected in 13 high-level treatment fecal grab samples, 7 high-level treatment hide swab samples, 1 low-level hide swab sample, and 2 high-level rope samples. For both fecal grab and hide swab samples, the overall prevalence of E. coli O157:H7 in the high-level group was greater (P < 0.01) than that for the pooled low-level and control groups. Addition of inoculated fecal pats to pens increased transmission of E. coli O157:H7 among penmates, but cattle that acquired E. coli O157:H7 shed the bacterium for only a short time at low levels. Transmission of E. coli O157:H7 from the feces of super shedders to naive penmates may contribute to the observed transient nature of shedding of E. coli O157:H7 among feedlot cattle.
authors.affiliation: Alberta Agriculture and Food, Lethbridge, Alberta, Canada.
authors.forename: T P
authors.initials: TP
authors.lastname: Stephens
authors.forename: T A
authors.initials: TA
authors.lastname: McAllister
authors.forename: K
authors.initials: K
authors.lastname: Stanford
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology / Q000635:transmission*; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D004927:Escherichia coli Infections / Q000382:microbiology / Q000635:transmission / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D005506:Food Contamination / Q000517:prevention & control; D005516:Food Microbiology; D018189:Immunomagnetic Separation / Q000379:methods; D008297:Male; D008954:Models, Biological; D011897:Random Allocation
chemical_list: D003470:Culture Media