title: Antimicrobial resistance in fecal generic Escherichia coli and Salmonella spp. obtained from Ontario sheep flocks and associations between antimicrobial use and resistance.
abstract: The purpose of this study was to examine the prevalence and patterns of antimicrobial resistance (AMR) in enteric bacteria obtained from Ontario sheep flocks, and associations between antimicrobial use (AMU) and AMR. Forty-nine sheep producers participated for a 1-year interval between 2006 and 2008. Two-hundred and eighty-three pooled fecal samples were collected from the flocks during initial and final visits. Up to 3 isolates of Salmonella spp. and generic E. coli per pooled fecal sample were tested for susceptibility to 15 antimicrobials. Resistance was infrequent among Salmonella (0%, n = 7 isolates) and low among E. coli (13.1%; n = 849) isolates. A small number of isolates were resistant to antimicrobials classified as being of very high importance to human health. Tetracycline resistance was most frequently observed (12.0%). Logistic regression was used to model potential AMU (qualitative and quantitative) risk factors for tetracycline resistance in generic E. coli from final visits. Qualitative analysis indicated that the use of injectable sulfonamides [including trimethoprim-sulfonamide combinations (TMS)] and tetracycline in the feed and water were significantly associated with tetracycline resistance (OR = 2.6, P = 0.01; and OR = 4.8, P ≤ 0.01, respectively). Quantitative analysis also indicated that TMS exposure rate was significantly associated with tetracycline resistance, which varied depending on the exposure rate. The exposure rate of tetracycline in the feed and water was only significant after the removal of one influential flock, warranting further research examining flocks with higher tetracycline exposure rates. Although the prevalence of AMR in participating flocks was relatively low, risk factors for resistance were identified.
authors.affiliation: Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada. lisa.c.s@gmail.com
authors.forename: Lisa
authors.initials: L
authors.lastname: Scott
authors.forename: Paula
authors.initials: P
authors.lastname: Menzies
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Reid-Smith
authors.forename: Brent P
authors.initials: BP
authors.lastname: Avery
authors.forename: Scott A
authors.initials: SA
authors.lastname: McEwen
authors.forename: Catherine S
authors.initials: CS
authors.lastname: Moon
authors.forename: Olaf
authors.initials: O
authors.lastname: Berke
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000008:administration & dosage*; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000302:isolation & purification*; D004927:Escherichia coli Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005243:Feces / Q000382:microbiology; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D009864:Ontario / Q000453:epidemiology; D015995:Prevalence; D012475:Salmonella / Q000302:isolation & purification*; D012481:Salmonella Infections, Animal / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D018709:Statistics, Nonparametric; D011795:Surveys and Questionnaires
chemical_list: D000890:Anti-Infective Agents