title: Escherichia coli O157:H7 in a cohort of weaned, preconditioned range beef calves.
abstract: Escherichia coli O157:H7 (EC O157) is an important cause of foodborne disease. Cattle are reservoirs for the bacteria and are implicated in transmission to humans. Prevalence data in prefeedlot calves are limited. With the use of sensitive methods, a cohort of weaned beef calves (n = 408) was sampled before and after preconditioning to estimate fecal point prevalence and describe changes in EC O157 fecal shedding. EC O157 isolates were confirmed and characterized by PCR and pulsed-field gel electrophoresis. Calves from 29 cow-calf farms were commingled at three preconditioning sites and placed on a transition ration containing oxytetracycline (200 g/ton) for 45 days. Initial animal-level fecal point prevalence was 2.5% (95% confidence interval, 1 to 5) with a herd-level prevalence of 17.2% (95% confidence interval, 6 to 36). Point prevalence following the preconditioning feeding period was 0%. An unexpected finding in our study was EC O157 isolates that were Shiga toxin-deficient. Pulsed-field gel electrophoresis subtypes of EC O157 were unique in epidemiologically unlinked herds, except one herd that had two unique subtypes. We expected, but observed, neither increased fecal shedding in the cohort nor horizontal transmission of unique EC O157 subtypes. The absence of fecal shedding following the 45-day feeding period might be attributable to seasonal influences, inhibitory concentrations of oxytetracycline in the transition ration, or transient colonization that ended before sampling. EC O157 is apparently widely dispersed at low prevalence in U.S. prefeedlot, weaned calves.
authors.affiliation: Louisiana State University, School of Veterinary Medicine, Skip Bertman Drive, Baton Rouge, Louisiana 70803, USA. jp_dunn@msn.com
authors.forename: John R
authors.initials: JR
authors.lastname: Dunn
authors.forename: James E
authors.initials: JE
authors.lastname: Keen
authors.forename: Ron
authors.initials: R
authors.lastname: Del Vecchio
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Wittum
authors.forename: R Alex
authors.initials: RA
authors.lastname: Thompson
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy / Q000453:epidemiology* / Q000635:transmission; D015331:Cohort Studies; D004197:Disease Reservoirs / Q000662:veterinary*; D016521:Electrophoresis, Gel, Pulsed-Field / Q000662:veterinary; D004927:Escherichia coli Infections / Q000188:drug therapy / Q000453:epidemiology / Q000635:transmission / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D010118:Oxytetracycline / Q000008:administration & dosage / Q000627:therapeutic use; D016133:Polymerase Chain Reaction / Q000662:veterinary; D015995:Prevalence; D012703:Serotyping / Q000662:veterinary; D014481:United States / Q000453:epidemiology; D014886:Weaning
chemical_list: D000900:Anti-Bacterial Agents; D010118:Oxytetracycline