Tetracycline- and Macrolide-Resistant Enterococcus Species Isolated from a Mink Farm in the United States

Enterococcus species are a normal flora of animals and humans. However, life-threatening opportunistic infections can be caused by antimicrobial resistant strains. Fecal (n = 42) and feed (n = 8) samples were obtained from a mink farm and cultured for the enumeration and detection of erythromycin-resistant (a macrolide; ERY^r)- and tetracycline-resistant (TET^r) enterococci. ERY^r and TET^r enterococci were detected from all fecal (mean concentrations = 6 and 7 logs, respectively) and feed (mean concentrations = 5 and 4 logs, respectively) samples. While Enterococcus faecalis and Enterococcus faecium were detected at equal proportions among the fecal TET^r isolates, E. faecium predominated among ERY^r fecal isolates. All ERY^r and 90% of the TET^r isolates (n = 50) were multidrug resistant (resistant to three or more antimicrobial classes). Among ERY^r isolates, while 83% of E. faecalis (n = 12) were positive for erm(B), 58% of E. faecium (n = 38) isolates were positive for msr(C). Among ERY^r isolates, tet(M) was detected from 92% of E. faecalis (n = 12) and 97% of E. faecium (n = 38) isolates. Conversely, however, erm(B) was detected in 18% of E. faecalis (n = 22) and 33% of E. faecium (n = 27) TET^r isolates. Our study provides a baseline for future efforts to reduce antimicrobial resistance and improve antimicrobial stewardship in commercial mink production facilities.