title: Antibiotic resistance in Escherichia coll and Enterococcus spp. isolates from commercial broiler chickens receiving growth-promoting doses of bacitracin or virginiamycin.
abstract: Antibacterial agents such as zinc bacitracin (ZB) and virginiamycin (VG) are used as growth promoting agents (GP) in broiler chicken production. The objective of this study was to evaluate the effect of the use of ZB and VG on the emergence of antibacterial resistance in a commercial broiler chicken farm. Three trials were conducted using 3 different diets: one without antibacterial agents, one containing VG, and one with ZB. Escherichia coli and Enterococcus spp. strains were isolated and tested for their susceptibility to various antibacterial agents. The occurrence of the resistance genes vatD, ermB, and bcrR in Enterococcus spp. isolates was determined by polymerase chain reaction (PCR). Comparative quantification of vatD and bcrR genes in total deoxyribonucleic acid (DNA) extracts from litter was done by SYBR Green Real-Time PCR (QPCR). Escherichia coli and Enterococcus spp. isolates from diet groups had different levels of resistance to various antibacterial agents over time. These GPs did not select for specific antibacterial agent resistance (AAR) in Enterococcus spp. The use of GPs seemed to lower the percentage of E. coli isolates resistant to some antibacterial agents. The presence of the bcrR gene could not explain all resistant phenotypes to ZB. Genes other than vatD and ermB might be involved in the resistance to VG in Enterococcus spp. Use of GPs was not associated with presence of the bcrR gene in DNA extracts from litter, but use of VG was associated with vatD presence.
authors.affiliation: University of Montreal, Faculty of Veterinary Medicine, 3200 rue Sicotte, Saint-Hyacinthe, Quebec J2S 2M2.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Thibodeau
authors.forename: Sylvain
authors.initials: S
authors.lastname: Quessy
authors.forename: Evelyne
authors.initials: E
authors.lastname: Guévremont
authors.forename: Alain
authors.initials: A
authors.lastname: Houde
authors.forename: Edward
authors.initials: E
authors.lastname: Topp
authors.forename: Moussa Sory
authors.initials: MS
authors.lastname: Diarra
authors.forename: Ann
authors.initials: A
authors.lastname: Letellier
mesh_terms: D000821:Animal Feed; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D001414:Bacitracin / Q000008:administration & dosage; D002645:Chickens / Q000254:growth & development / Q000382:microbiology*; D015169:Colony Count, Microbial; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D016983:Enterococcus / Q000187:drug effects*; D004926:Escherichia coli / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction / Q000379:methods / Q000662:veterinary; D011897:Random Allocation; D014769:Virginiamycin / Q000008:administration & dosage
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D014769:Virginiamycin; D001414:Bacitracin