title: Effects of In-Feed Copper, Chlortetracycline, and Tylosin on the Prevalence of Transferable Copper Resistance Gene, tcrB, Among Fecal Enterococci of Weaned Piglets.
abstract: Heavy metals, such as copper, are increasingly supplemented in swine diets as an alternative to antibiotics to promote growth. Enterococci, a common gut commensal, acquire plasmid-borne, transferable copper resistance (tcrB) gene-mediated resistance to copper. The plasmid also carried resistance genes to tetracyclines and macrolides. The potential genetic link between copper and antibiotic resistance suggests that copper supplementation may exert a selection pressure for antimicrobial resistance. Therefore, a longitudinal study was conducted to investigate the effects of in-feed copper, chlortetracycline, and tylosin alone or in combination on the selection and co-selection of antimicrobial-resistant enterococci. The study included 240 weaned piglets assigned randomly to 6 dietary treatment groups: control, copper, chlortetracycline, tylosin, copper and chlortetracycline, and copper and tylosin. Feces were collected before (day 0), during (days 7, 14, 21), and after (days 28 and 35) initiating treatment, and enterococcal isolates were obtained from each fecal sample and tested for genotypic and phenotypic resistance to copper and antibiotics. A total of 2592 enterococcal isolates were tested for tcrB by polymerase chain reaction. The overall prevalence of tcrB-positive enterococci was 14.3% (372/2592). Among the tcrB-positive isolates, 331 were Enterococcus faecium and 41 were E. faecalis. All tcrB-positive isolates contained both erm(B) and tet(M) genes. The median minimum inhibitory concentration of copper for tcrB-negative and tcrB-positive enterococci was 6 and 18 mM, respectively. The majority of isolates (95/100) were resistant to multiple antibiotics. In conclusion, supplementing copper or antibiotics alone did not increase copper-resistant enterococci; however, supplementing antibiotics with copper increased the prevalence of the tcrB gene among fecal enterococci of piglets.
authors.affiliation: 1 Departments of Diagnostic Medicine and Pathobiology, Kansas State University , Manhattan, Kansas.
authors.forename: Raghavendra G
authors.initials: RG
authors.lastname: Amachawadi
authors.affiliation: 1 Departments of Diagnostic Medicine and Pathobiology, Kansas State University , Manhattan, Kansas.|2 Department of Veterinary Pathobiology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University , College Station, Texas.
authors.forename: H Morgan
authors.initials: HM
authors.lastname: Scott
authors.affiliation: 3 Animal Sciences and Industry, Kansas State University , Manhattan, Kansas.
authors.forename: Javier
authors.initials: J
authors.lastname: Vinasco
authors.affiliation: 3 Animal Sciences and Industry, Kansas State University , Manhattan, Kansas.
authors.forename: Mike D
authors.initials: MD
authors.lastname: Tokach
authors.affiliation: 3 Animal Sciences and Industry, Kansas State University , Manhattan, Kansas.
authors.forename: Steve S
authors.initials: SS
authors.lastname: Dritz
authors.affiliation: 3 Animal Sciences and Industry, Kansas State University , Manhattan, Kansas.
authors.forename: Jim L
authors.initials: JL
authors.lastname: Nelssen
authors.affiliation: 1 Departments of Diagnostic Medicine and Pathobiology, Kansas State University , Manhattan, Kansas.
authors.forename: Tiruvoor G
authors.initials: TG
authors.lastname: Nagaraja
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017920:Antiporters / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002751:Chlortetracycline / Q000494:pharmacology*; D003300:Copper / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D016984:Enterococcus faecium / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification; D005243:Feces / Q000737:chemistry / Q000382:microbiology; D016015:Logistic Models; D008137:Longitudinal Studies; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D013552:Swine; D015645:Tylosin / Q000494:pharmacology*; D014886:Weaning
chemical_list: D000900:Anti-Bacterial Agents; D017920:Antiporters; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C461665:TcrB protein, Enterococcus faecium; C079051:tetA protein, Bacteria; D003300:Copper; D002751:Chlortetracycline; D015645:Tylosin