In vitro susceptibility of Enterococcus faecium isolated from food to growth-promoting and therapeutic antibiotics

A total of 76 E. faecium strains, isolated at retail level from raw poultry meat, cheese, raw pork, and preparations of cheese and raw pork, were tested for their susceptibility and resistance to growth-promoting antibacterials used in animals and antibiotics used therapeutically in humans. All strains were uniformly susceptible to the growth promoters bambermycin and avilamycin. Resistance against bacitracin, virginiamycin and narasin was high among strains from poultry meat. With tylosin, a macrolide antibiotic used therapeutically and for growth promotion, resistance was mainly detected in strains originating from poultry meat, though also in some strains from pork and from pork and cheese preparations. The therapeutic antibiotic dalfopristin/quinupristin did not show full cross-resistance with the growth-promoting antibiotic virginiamycin. With dalfopristin/quinupristin two different levels of resistance were found. Only one E. faecium strain isolated from poultry was resistant to the glycopeptides avoparcin and vancomycin. Only one poultry meat strain was highly resistant to ampicillin. However, nearly all poultry meat strains showed decreased sensitivity. Only 3 out of 24 poultry strains were susceptible to minocycline, while all strains from other origins were susceptible to this tetracycline antibiotic. High-level streptomycin resistance was seen in strains of all origins, though infrequently. High-level gentamicin resistance was not found.