Antimicrobial susceptibilities of clinical isolates of vancomycin-resistant enterococci in Taiwan

To understand the antimicrobial resistance patterns of vancomycin-resistant enterococci in Taiwan, we tested the in vitro activities of 10 antimicrobi al agents against 71 clinical isolates (39 of Enterococcus faecalis and 32 of Enterococcus faecium) by means of the agar dilution method. Resistance w as determined on the basis of the minimum inhibitor) concentration (MIC) of each antimicrobial agent-MIC50 and MIC90 (minimum concentrations required to inhibit growth of 50% and 90% of isolates, respectively) were determined . No beta-lactamase producers were identified with the cefinase test. All E . faecalis isolates were susceptible to penicillin and ampicillin, and 97% of these isolates were resistant to teicoplanin (vanA phenotype). Of the E. faecium isolates, 75% were susceptible to teicoplanin (vanB phenotype) and most were resistant to penicillin (94%) and ampicillin (94%). Quinupristin / dalfopristin was markedly less active against E. faecalis than E. faecium isolates (MIC50, 64 vs 2 mu g/mL; MIC90 128 vs 8 mu g/mL; susceptibility r ates, 3% vs 81%). Five of the eight vanA phenotype E. faecium isolates and one of the 24 vanB phenotype E. faecium isolates were resistant to quinupri stin/dalfopristin. The activity of rifampin was also species-specific, with E. faecium being markedly less susceptible to this agent than E. faecalis (MIC50 16 vs 1 mu g/mL; MIC90, 64 vs 4 mu g/mL). Our data suggest the poten tial of teicoplanin and quinupristin/dalfopristin as appropriate antimicrob ial agents in the treatment of infections caused by vanB phenotype E. faeci um. Penicillin, ampicillin, and rifampin alone, or preferably in combinatio n with other agents, appear to be the most appropriate agents for the treat ment of vancomycin-resistant E. faecalis infections in Taiwan.