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The in vitro activity of daptomycin against Staphylococcus aureus and Enterococcus species
S S Richter1, D E Kealey, C T Murray
1Department of Pathology, C606 GH, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa 52242-1009, USA. sandra-richter@uiowa.edu
Objective:
The purpose of this study was to examine the in vitro activity of daptomycin using an optimal calcium (Ca2+) concentration (50 mg/L) against a diverse collection of enterococcal and Staphylococcus aureus clinical isolates, including glycopeptide-resistant enterococci (GRE) and methicillin-resistant S. aureus (MRSA).
Methods:
The activity of daptomycin was compared with the activities of seven other agents against 1483 enterococcal and S. aureus clinical isolates, including 303 GRE and 193 methicillin-resistant S. aureus (MRSA) strains. Susceptibility testing was performed by the NCCLS broth microdilution method, with one exception: Mueller-Hinton (MH) broth was supplemented to a physiological level of 50 mg/L Ca2+ when testing daptomycin. Daptomycin zone diameters were determined by disc diffusion with MH agar plates containing Ca2+ 50 mg/L.
Results:
All staphylococcal isolates tested, and the majority of enterococcal isolates (96.5%), would be considered susceptible to daptomycin if the breakpoint previously proposed of or = 20 mm, and all of the enterococcal isolates had daptomycin zone diameters > or = 17 mm.
Conclusions:
Overall, daptomycin showed potent activity against S. aureus and enterococcal isolates, comparable to quinupristin-dalfopristin and linezolid.