Daptomycin activity tested against linezolid-nonsusceptible gram-positive clinical isolates

Staphylococcus aureus, coagulase-negative staphylococci, and Enterococcus spp. represent the most frequently recovered organisms from bloodstream infections. As a treatment option, daptomycin has been recently approved for the treatment of S. aureus bacteremia and right-sided endocarditis. We evaluated the spectrum of activity and potency of daptomycin and other antibiotics against 142 linezolid-nonsusceptible clinical strains. The isolates were tested for susceptibility by reference broth microdilution methods utilizing physiologic free calcium ions levels (50 mg/L) when testing daptomycin. Staphylococcus spp. and Enterococcus spp. were selected and screened for 23S rRNA, L4 and L22 mutations, and the cfr gene. Daptomycin was potent against all linezolid-nonsusceptible staphylococci (minimal inhibitory concentrations [MIC](90), 0.5 microg/ml) and enterococci (MIC(90), 1 microg/ml) isolates at the respective breakpoints of