Patrick F McDermott, Gregory H Tyson, Crystal Rice-Trujillo, Emily Crarey, Heather Tate, Claudine Kabera, Epiphanie Nyirabahizi, Claudia Lam
Bacteria of the genus Enterococcus are important human pathogens that are frequently resistant to a number of clinically important antibiotics. They are also used as a marker of animal fecal contamination of human foods, and are employed as sentinel organisms for tracking trends in resistance to antimicrobials with gram-positive activity. As part of the National Antimicrobial Resistance Monitoring System (NARMS), we evaluated several retail meat commodities for the presence of enterococci from 2002-2014, finding 92.0% to be contaminated. The majority of isolates were either E. faecalis (64.0%) or E. faecium (28.6%), and the antimicrobial resistance of each isolate was assessed by broth microdilution. The resistance prevalence for several drugs, including erythromycin and gentamicin, was significantly higher among poultry isolates, compared to retail beef or pork. None of the isolates was resistant to the clinically important human drug vancomycin, only one was resistant to linezolid, and resistance to tigecycline was below 1%. In contrast, a majority of both E. faecalis (67.5%) and E. faecium (53.7%) isolates were resistant to tetracycline. Overall, the robust NARMS testing system employed consistent sampling practices and methodology throughout the testing period, with the only significant trend in resistance prevalence being decreased E. faecium resistance to penicillin. These data provide excellent baseline levels of resistance that can be used to measure future changes in resistance prevalence that may result from alterations in the use of antimicrobials in food animal production.Importance Enterococci, including Enterococcus faecalis and E. faecium, are present in the gut of food-producing animals and are used as a measure of fecal contamination of meat. We used the large, consistent sampling methods of NARMS to assess the prevalence of Enterococcus strains isolated from retail meats, finding over 90% of meats to be contaminated with enterococci. We also assessed the resistance of the Enterococcus strains, commonly used as a measure of resistance to agents with gram-positive activity in foods. Resistance prevalence was over 25% for some antimicrobials and sample sources, but less than 1% for several of the most important therapeutics used in human medicine.