[Comparative activity of daptomycin against clinical isolates of methicillin-resistant Staphylococcus aureus and...

The objective of this study was to determine the in vitro activity of daptomycin and other agents against methicillin-resistant Staphylococcus aureus (MRSA) isolates from several sources and coagulase-negative staphylococci (CoNS) from clinically significant blood cultures.

We tested a total of 1186 staphylococci isolates (755 MRSA and 431 CoNS) collected as part of a multicenter surveillance program for antimicrobial resistance (VIRA study) from 40 medical centers throughout Spain between 2001 and 2006. Broth microdilution tests were performed according to the Clinical and Laboratory Standards Institute guidelines.

Most MRSA isolates were resistant to ciprofloxacin (96%) and erythromycin (79.7%). Daptomycin yielded a MIC(50)/MIC(90) of 0.5/1microg/mL in MRSA, compared with 1/2microg/mL for linezolid, vancomycin, and teicoplanin. Daptomycin MICs were in the range of < or =0.125-2microg/mL. Only 1 MRSA strain had a reproducible daptomycin MIC of 2microg/mL. Among CoNS isolates, the MIC range for daptomycin was < or =0.125-1microg/mL. Daptomycin was equally active against oxacillin-susceptible and oxacillin-resistant strains.

Daptomycin was highly active against the staphylococci isolates studied. The activity of this agent was not affected by resistance to other antibiotics such as oxacillin, teicoplanin, linezolid, ciprofloxacin, or gentamicin. These data suggest that daptomycin may be useful for the treatment of severe infection caused by MRSA or CoNS.