title: Risk factors for antimicrobial resistance in fecal Escherichia coli from preweaned dairy calves.
abstract: The primary objective of this study was to investigate calf and farm factors associated with antimicrobial-resistant Escherichia coli in the feces of preweaned dairy calves in Sweden. In particular, we investigated the effects of feeding calves colostrum and milk from cows treated with antimicrobials. The secondary objective was to describe the prevalence of resistant E. coli in feces of preweaned dairy calves in Sweden. Fecal samples from 3 calves, aged 7 to 28d, from 243 farms were analyzed for the within-sample prevalence of E. coli resistant to nalidixic acid, streptomycin, and cefotaxime using selective agars supplemented with antimicrobials. In addition, resistance to 12 antimicrobials was tested in one randomly selected E. coli isolate per calf. Information was collected from the farmers via questionnaires regarding the use of colostrum and milk from cows treated with antimicrobials as calf feed and other uses of antimicrobials in the herd. Multivariable zero-inflated negative binomial and logistic regression models were used to assess the effect of various risk factors for shedding of resistant E. coli. Escherichia coli resistant to streptomycin, nalidixic acid, or cefotaxime were isolated from 90, 49, and 11% of the calves, respectively. Resistance to at least one antimicrobial was found in a random isolate of E. coli from 48% of the calves. Feeding colostrum from cows treated with antimicrobials at drying off did not affect the prevalence of resistant E. coli. In contrast, feeding milk from cows treated with antimicrobials during lactation resulted in significantly more nalidixic acid- and streptomycin-resistant E. coli than when such milk was discarded; no significant effect was seen for other resistance traits. Furthermore, an interaction was found between feeding milk from cows treated with antimicrobials and use of fluoroquinolones in cows. In general, the prevalence of resistance was lower for older calves and calves on small farms. Other factors that were associated with the shedding of resistant E. coli were administration of oral dihydrostreptomycin to calves, administration of systemic tetracycline and ceftiofur to cows and calves, housing of the calves, predominant breed of the herd, and geographic location of the farm. The presence of resistant E. coli in calves was clearly due to multiple factors, but minimizing the feeding of milk from cows treated with antimicrobials during lactation should lower the prevalence of resistant E. coli in the gastrointestinal tract of the calves.
authors.affiliation: Department of Animal Health and Antimicrobial Strategies, National Veterinary Institute, SE-751 89 Uppsala, Sweden; Department of Clinical Sciences, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden. Electronic address: anna.duse@sva.se.
authors.forename: Anna
authors.initials: A
authors.lastname: Duse
authors.affiliation: Department of Animal Health and Antimicrobial Strategies, National Veterinary Institute, SE-751 89 Uppsala, Sweden; Department of Clinical Sciences, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden.
authors.forename: Karin Persson
authors.initials: KP
authors.lastname: Waller
authors.affiliation: Department of Clinical Sciences, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Emanuelson
authors.affiliation: Department of Animal Health and Antimicrobial Strategies, National Veterinary Institute, SE-751 89 Uppsala, Sweden.
authors.forename: Helle Ericsson
authors.initials: HE
authors.lastname: Unnerstad
authors.affiliation: Department of Animal Health and Antimicrobial Strategies, National Veterinary Institute, SE-751 89 Uppsala, Sweden; Växa Sverige, SE-751 05 Uppsala, Sweden.
authors.forename: Ylva
authors.initials: Y
authors.lastname: Persson
authors.affiliation: Department of Animal Health and Antimicrobial Strategies, National Veterinary Institute, SE-751 89 Uppsala, Sweden.
authors.forename: Björn
authors.initials: B
authors.lastname: Bengtsson
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D057138:Bacterial Shedding; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000382:microbiology*; D003126:Colostrum / Q000378:metabolism; D004032:Diet / Q000662:veterinary; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005243:Feces / Q000382:microbiology; D008892:Milk / Q000378:metabolism; D015995:Prevalence; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D014886:Weaning
chemical_list: D000890:Anti-Infective Agents
keywords: antibiotic resistance; dairy calf; risk factor; waste milk