Influence of reduced susceptibility to glycopeptides on activities of vancomycin and teicoplanin against Staphylococcus aureus in experimental endocarditis

Abstract

The influence of reduced susceptibilities to glycopeptides on the activities of vancomycin and teicoplanin against an isogenic pair of clinical Staphylococcus aureus strains in experimental endocarditis was investigated. While vancomycin was similarly active against both strains, teicoplanin was approximately 100-fold less active against the resistant strain and selected for the emergence of more resistant subpopulations.

FIG. 1.

In vitro population analysis of S. aureus Lim-1 and Lim-2 on vancomycin (A) and teicoplanin (B) agar. Population analyses were performed with overnight cultures (∼10⁸ to 10⁹ CFU/ml) that were serially diluted and plated onto BHI agar containing increasing concentrations of vancomycin (0 to 10 μg/ml) or teicoplanin (0 to 40 μg/ml) and incubated for 48 h at 37°C before enumeration of the CFU.

FIG. 2.

Time-kill curve studies with vancomycin (Vm) (A) and teicoplanin (Tc) (B) at various concentrations against S. aureus Lim-1 and Lim-2.

FIG. 3.

Ex vivo population analysis of S. aureus Lim-1 (A) and Lim-2 (B) on vancomycin agar. The two strains were from the vegetations of six different infected rabbits sampled at the start of therapy.