Synergistic killing of vancomycin-resistant enterococci of classes A, B, and C by combinations of vancomycin, penicillin, and gentamicin.

Using both high and low inocula for time-kill curves, we examined the antibiotic killing of clinical isolates of glycopeptide-resistant enterococci (Enterococcus faecium, E. faecalis, and E. gallinarum) belonging to phenotypic resistance classes A, B, and C. None were resistant to high levels (greater than 500 mg/liter) of gentamicin. Vancomycin-penicillin-gentamicin resulted in 2 or more logs of killing above that of the most effective two-antibiotic combination for all strains except two of three E. gallinarum (VanC) strains and a constitutive mutant of a VanB strain. This strategy may be useful clinically.