AVOPARCIN, A GLYCOPEPTIDE USED IN ANIMAL FOODS - ANTIMICROBIAL SPECTRUM AND POTENCY TESTED AGAINST HUMAN ISOLATES FROM THE UNITED-STATES

Avoparcin is a glycopeptide antimicrobial that is widely used as a gro wth promoter in animal feeds in portions of Western Europe. Recently, concern has emerged about the possible contribution of avoparcin use t o the emergence of glycopeptide resistance in enterococci. Relatively little information exists on the spectrum of activity and potency of a voparcin. We studied the activity of avoparcin compared to vancomycin, teicoplanin, and 3 other antimicrobials against 814 recent human clin ical isolates, including Staphylococcus spp. (240 strains), Streptococ cus spp. (90 strains), and Enterococcus spp. (60 strains), using refer ence susceptibility test methods. Our results indicate that avoparcin was less potent than either vancomycin or teichoplanin against staphyl ococci (MIC50, 4 mu g/mL). There was a good correlation of avoparcin M ICs with the MICs for vancomycin and teichoplanin for most species; ho wever, the avoparcin MICs for Enterococcus spp. of the vanB phenotype were quite variable (MIG range, 2 to >16 mu g/mL). For Staphylococcus haemolyticus, high avoparcin MICs (greater than or equal to 16 mu g/mL ) were associated with oxacillin resistance. These results are relevan t to the debate concerning the appropriateness of continued use of avo parcin as a growth promoter in animal husbandry. In particular, avopar cin as a glycopeptide with limited potency against some staphylococci seems to represent a theoretically greater risk for selecting glycopep tide resistance among staphylococci, but may not represent any greater threat for the selection of resistance in enterococci. (C) 1997 Elsev ier Science Inc.