Isolation of vancomycin-re s i s t a n t e n t e rococci from animal feed i nU S A

1consistent with the hypothesis that VRE are being introduced into human populations from a number of sources. In Europe, chickens may be one such source: avoparcin (a vancomycin analogue) has been used subtherapeutically in animal feed, and VRE have been isolated from chicken carcasses. 2 In the USA (where avoparcin has not been used) there are, to our knowledge, no reports of isolation of VRE from chickens. However, gentamicin (to which VRE strains are generally also resistant) is at times given to chickens, and strains of enterococci with high-level gentamicin resistance have been isolated from chickens in this country. 3 As part of studies of a possible link between antimicrobial resistance in human beings and animals, we sampled commercially prepared chicken feed for the presence of resistant organisms. 1 g of pelleted feed taken under sterile conditions from a newly opened bag was added to tryptic soy broth and incubated for 48 hours at 35oC; 100 L of the broth was then plated onto colistin-naladixic acid agar (Becton Dickinson Microbiology Systems, Sparks, MD, USA) supplemented with vancomycin (10 g/mL), gentamicin ( 5 g/mL), and amphotericin (2 g/mL). Five colonies of Enterococcus faecium were isolated from the plate, with their species confirmed biochemically. On susceptibility testing (Etest, AB Biodisk, Solna, Sweden) all were resistant to vancomycin (MIC >256 g/mL), gentamicin (MIC >1024 g/mL), streptomycin (MIC >1024 g/mL), and ampicillin (MIC >256 g/ml); isolates were susceptible to teicoplanin and quinupristin/dalfopristin. All isolates had the vanB genotype (figure), 4 with identical banding