Prevalence, species distribution and antimicrobial resistance of enterococci isolated from US dairy cattle

Aims: To estimate prevalence and antimicrobial susceptibility of enterococci in faeces collected in 2007 from U.S. dairy cattle. Methods and Results: A total of 718 faecal samples from 122 dairy cattle operations from 17 US States were collected and cultured for the presence of enterococci. One hundred and eighteen of the 122 operations (96 center dot 7%) had at least one dairy cow positive for enterococci and 88 center dot 7% (637 of 718) of the faecal samples were positive. At least ten different enterococcal species were found on the dairy operations and 90 center dot 7% (107 of 118) of the operations were positive for Enterococcus hirae followed by E. faecalis (40 center dot 7%; 48 of 118) and E. faecium (39%; 46 of 118). The highest percentage of resistant isolates were to lincomycin (92 center dot 3%; 587 of 636), flavomycin (71 center dot 9%; 457 of 636) and tetracycline (24 center dot 5%; 156 of 636). Multi-drug resistance (MDR) (resistance >= 2 antimicrobials) was observed to as many as seven antimicrobials regardless of class. Conclusion: In contrast to previous studies, faecal shedding of enterococci in dairy cattle occurred in almost 90% of cows sampled and represented a variety of enterococcal species. Significance and Impact of Study: Although this study demonstrated a high prevalence of antimicrobial-resistant enterococci from dairy cattle faeces in the United States, the contribution of dairy cattle as a source of antimicrobial-resistant enterococci that can be transmitted to humans remains unclear.