Comparative in-vitro activity of quinupristin/dalfopristin against Enterococcus spp

The in-vitro activity of quinupristin/dalfopristin against Enterococcus spp. was compared with that of amoxycillin, vancomycin, telcoplanin and erythromycin. The susceptibility of 106 vancomycin-susceptible Enterococcus faecalis, 92 vancomycin-susceptible Enterococcus faecium and 14 vancomycin-resistant enterococci (VRE) was tested. Only one strain of vancomycin-susceptible E. faecium was not susceptible to < or = 0.5 mg/L quinupristin/dalfopristin; this strain required 4 mg/L. All strains of E. faecalis were inhibited by < or = 8 mg/L quinupristin/dalfopristin and all VRE strains were inhibited by < or = 2 mg/L. In contrast, teicoplanin and vancomycin showed inhibitory activity against E. faecalis and E. faecium but not against VRE. Amoxycillin was active against E. faecalis but not usually against E. faecium and showed variable activity against VRE; 38% of E. faecalis, 84% of E. faecium and 80% of VRE strains were resistant to erythromycin. The bactericidal activity of quinupristin/dalfopristin against E. faecium exceeded that of the comparator drugs as judged by MIC:MBC ratios and killing curves. The MBC99 of quinupristin/dalfopristin determined by a microdilution broth technique was < or = 1 mg/L for E. faecium. Four of the five strains of vancomycin-susceptible E. faecium and three of the five VRE strains tested with time-kill curves showed a > or = 2 log reduction in viable count after exposure to quinupristin/dalfopristin for 6 h.