Activity of teicoplanin compared with vancomycin alone, and combined with gentamicin, against penicillin tolerant viridans streptococci and enterococci causing endocarditis

Abstract

Teicoplanin had greater inhibitory activity than vancomycin against most of 22 penicillin tolerant strains of streptococci, but both drugs failed to kill 99.9% of the inoculum when tested alone at concentrations less than 16mg 1(-1). Bactericidal synergy between teicoplanin combined with gentamicin and vancomycin combined with gentamicin was always demonstrated in further tests with 16 penicillin tolerant strains. Teicoplanin had greater bactericidal activity than vancomycin against five of seven strains of viridans streptococci and five of nine strains of enterococci in MBC experiments, where each drug was combined with gentamicin. Killing curve experiments with five penicillin tolerant streptococci showed teicoplanin and vancomycin to have similar bactericidal activity within 24 h when tested at 5 mg 1(-1) with 2 mg 1(-1) gentamicin. However, at 0.5 mg 1(-1) only teicoplanin had a bactericidal synergic effect with gentamicin.