title: Effect of antimicrobial dosage regimen on Salmonella and Escherichia coli isolates from feeder swine.
abstract: A body of evidence exists that suggests that antimicrobial use in food animals leads to resistance in both pathogenic and commensal bacteria. This study focused on the impact of three different antimicrobial regimes (low-level continuous, pulse, and no antimicrobial) for two antimicrobials (chlortetracycline and tylosin) on the presence of Salmonella spp. and on the prevalence of antimicrobial resistance of both Salmonella spp. and nonspecific Escherichia coli in fecal samples from feeder swine. The prevalence of fecal samples positive for Salmonella spp. significantly decreased between the samples taken at feeder placement compared to samples taken when the animals were close to market weight. Differences in resistance of Salmonella spp. did not appear to be influenced by dosing treatment including the control. Analysis of antimicrobial resistance examining both susceptibility and resistance, as well as MIC outcomes, demonstrated that only resistance to cephalothin increased in E. coli under the pulse chlortetracycline treatment. These results suggest that the dosing regimes examined in this study did not lead to an increase in either the prevalence of Salmonella spp. or the prevalence of antimicrobial resistance in isolates of Salmonella spp. or E. coli.
authors.affiliation: Centers for Epidemiology and Animal Health, Animal and Plant Health Inspection Service, U.S. Department of Agriculture, 2150 Centre Avenue, Bldg. B, Fort Collins, CO 80526, USA. bruce.a.wagner@aphis.usda.gov
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Wagner
authors.forename: Barbara E
authors.initials: BE
authors.lastname: Straw
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Fedorka-Cray
authors.forename: David A
authors.initials: DA
authors.lastname: Dargatz
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002512:Cephalothin / Q000494:pharmacology; D002751:Chlortetracycline / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D012475:Salmonella / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D013552:Swine; D015645:Tylosin / Q000494:pharmacology
chemical_list: D000890:Anti-Infective Agents; D002512:Cephalothin; D002751:Chlortetracycline; D015645:Tylosin