Comparative bactericidal activities of daptomycin and vancomycin against glycopeptide-intermediate Staphylococcus aureus (GISA) and heterogeneous GISA isolates

Staphylococcus aureus strains from the U.S. SENTRY Antimicrobial Surveillance Program, 2002-2003, glycopeptide-intermediate S. aureus (GISA) strains, and heterogeneous GISA (hGISA) strains were used to compare bactericidal activities of daptomycin and vancomycin using MICs and minimum bactericidal concentrations. Glycopeptide-susceptible S. aureus and hGISA strains were further studied by using time-kill curves. For all isolates, the daptomycin MIC50 and MIC90 are four times lower and the log drops in viable counts at 6 h and 24 h are significantly greater than those for vancomycin.