CHARACTERIZATION OF VANCOMYCIN-RESISTANT ENTEROCOCCUS-FAECIUM ISOLATES FROM THE UNITED-STATES AND THEIR SUSCEPTIBILITY IN-VITRO TO DALFOPRISTIN-QUINUPRISTIN

In the course of clinical studies with the investigational streptogram in antimicrobial dalfopristin-quinupristin, isolates of vancomycin-res istant Enterococcus faecium were referred to our laboratory from acros s the United States. Seventy-two percent of the strains were of the Va nA type, phenotypically and genotypically, while 28% were of the VanB type. High-level resistance to streptomycin or gentamicin was observed in 86 and 81%, respectively, of the VanA strains but in only 69 and 6 6%, respectively, of the VanB strains. These enterococci were resistan t to ampicillin (MIC for 50% of the isolates tested [MIC50] and MIC90, 128 and 256 mu g/ml, respectively) and to the other approved agents t ested, with the exception of chloramphenicol (MIC90, 8 mu g/ml) and no vobiocin (MIC90, 1 mu g/ml). Considering all of tie isolates submitted , dalfopristin-quinupristin inhibited 86.4% of them at concentrations of less than or equal to 1 mu g/ml and 95.1% of them at less than or e qual to 2 mu g/ml. However, for the data set comprised of only the fir st isolate submitted for each patient, 94.3% of the strains mere inhib ited at concentrations of less than or equal to 1 mu g/ml and 98.9% me re inhibited at concentrations of less than or equal to 2 mu g/ml. Mul tiple drug resistance was very common among these isolates of vancomyc in-resistant E. faecium, while dalfopristin-quinupristin inhibited the majority at concentrations that are likely to he clinically relevant.