Copper Resistance in Enterococcus faecium , Mediated by the tcrB Gene, Is Selected by Supplementation of Pig Feed with Copper Sulfate

Thetcr gene cluster mediates in vitro copper resistance inEnterococcus faecium . Here we describe the selection oftcr -mediated copper resistance inE. faecium in an animal feeding experiment with young pigs fed 175 mg copper/kg feed (ppm), which is the concentration commonly used for piglets in European pig production.tcr -mediated copper resistance was not selected for in a control group fed low levels of copper (6 ppm). We also show coselection of macrolide- and glycopeptide-resistantE. faecium in the animal group fed the high level of copper. Finally, we identify thetcr genes in the enterococcal speciesE. mundtii ,E. casseliflavus , andE. gallinarum for the first time.