Copyright C) 1991, American Society for Microbiology Synergistic Killing of Vancomycin-Resistant Enterococci of Classes

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 (>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. Enterococci resistant to various glycopeptide antibiotics have been described recently (4). These include Enterococ-cus faecalis, E. faecium, E. avium, and E. gallinarum (4, 12). The resistant strains are readily divided into three classes, VanA, VanB, and VanC, on the basis of the level of resistance to vancomycin and teicoplanin and whether the resistance is inducible (9, 13). VanA strains have inducible, high-level resistance to all the glycopeptides we have tested (11), while VanB strains show inducible, moderate levels o