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 antimicrobial agents against 71 clinical isolates (39 of Enterococcus faecalis and 32 of Enterococcus faecium) by means of the agar dilution method. Resistance was determined on the basis of the minimum inhibitory 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 β-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 μg/mL; MIC₉₀, 128 vs 8 μg/mL; susceptibility rates, 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 quinupristin/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 μg/mL; MIC₉₀, 64 vs 4 μg/mL). Our data suggest the potential of teicoplanin and quinupristin/dalfopristin as appropriate antimicrobial agents in the treatment of infections caused by vanB phenotype E. faecium. Penicillin, ampicillin, and rifampin alone, or preferably in combination with other agents, appear to be the most appropriate agents for the treatment of vancomycin-resistant E. faecalis infections in Taiwan.