title: Selection of fecal enterococci exhibiting tcrB-mediated copper resistance in pigs fed diets supplemented with copper.
abstract: Copper, as copper sulfate, is increasingly used as an alternative to in-feed antibiotics for growth promotion in weaned piglets. Acquired copper resistance, conferred by a plasmid-borne, transferable copper resistance (tcrB) gene, has been reported in Enterococcus faecium and E. faecalis. A longitudinal field study was undertaken to determine the relationship between copper supplementation and the prevalence of tcrB-positive enterococci in piglets. The study was done with weaned piglets, housed in 10 pens with 6 piglets per pen, fed diets supplemented with a normal (16.5 ppm; control) or an elevated (125 ppm) level of copper. Fecal samples were randomly collected from three piglets per pen on days 0, 14, 28, and 42 and plated on M-Enterococcus agar, and three enterococcal isolates were obtained from each sample. The overall prevalence of tcrB-positive enterococci was 21.1% (38/180) in piglets fed elevated copper and 2.8% (5/180) in the control. Among the 43 tcrB-positive isolates, 35 were E. faecium and 8 were E. faecalis. The mean MICs of copper for tcrB-negative and tcrB-positive enterococci were 6.2 and 22.2 mM, respectively. The restriction digestion of the genomic DNA of E. faecium or E. faecalis with S1 nuclease yielded a band of ∼194-kbp size to which both tcrB and the erm(B) gene probes hybridized. A conjugation assay demonstrated cotransfer of tcrB and erm(B) genes between E. faecium and E. faecalis strains. The higher prevalence of tcrB-positive enterococci in piglets fed elevated copper compared to that in piglets fed normal copper suggests that supplementation of copper in swine diets selected for resistance.
authors.affiliation: Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS 66506-5606, USA.
authors.forename: R G
authors.initials: RG
authors.lastname: Amachawadi
authors.forename: N W
authors.initials: NW
authors.lastname: Shelton
authors.forename: X
authors.initials: X
authors.lastname: Shi
authors.forename: J
authors.initials: J
authors.lastname: Vinasco
authors.forename: S S
authors.initials: SS
authors.lastname: Dritz
authors.forename: M D
authors.initials: MD
authors.lastname: Tokach
authors.forename: J L
authors.initials: JL
authors.lastname: Nelssen
authors.forename: H M
authors.initials: HM
authors.lastname: Scott
authors.forename: T G
authors.initials: TG
authors.lastname: Nagaraja
mesh_terms: D000821:Animal Feed; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015373:Bacterial Typing Techniques; D019729:Carbon-Oxygen Ligases / Q000235:genetics / Q000378:metabolism; D003227:Conjugation, Genetic; D003300:Copper / Q000378:metabolism*; D019327:Copper Sulfate / Q000378:metabolism / Q000494:pharmacology; D004269:DNA, Bacterial / Q000235:genetics; D019587:Dietary Supplements; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D016983:Enterococcus / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D004917:Erythromycin / Q000494:pharmacology; D005243:Feces / Q000382:microbiology; D008137:Longitudinal Studies; D008826:Microbial Sensitivity Tests; D012641:Selection, Genetic; D013552:Swine / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C461665:TcrB protein, Enterococcus faecium; C071437:VanA ligase, Bacteria; D004917:Erythromycin; D003300:Copper; D019729:Carbon-Oxygen Ligases; D019327:Copper Sulfate