Selection of fecal enterococci exhibiting tcrB-mediated copper resistance in pigs fed diets supplemented with copper. Academic Article uri icon


  • 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.

published proceedings

  • Appl Environ Microbiol

altmetric score

  • 3

author list (cited authors)

  • Amachawadi, R. G., Shelton, N. W., Shi, X., Vinasco, J., Dritz, S. S., Tokach, M. D., ... Nagaraja, T. G.

citation count

  • 53

complete list of authors

  • Amachawadi, RG||Shelton, NW||Shi, X||Vinasco, J||Dritz, SS||Tokach, MD||Nelssen, JL||Scott, HM||Nagaraja, TG

publication date

  • August 2011