Comparative In vitro activities of daptomycin and vancomycin against resistant gram-positive pathogens

Abstract

The in vitro activity of daptomycin against 224 current gram-positive clinical isolates including vancomycin-resistant Enterococcus faecium (VREF), methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus spp. (MRSS), and penicillin-resistant Streptococcus pneumoniae (PRSP) was evaluated. The MICs at which 90% of isolates are inhibited for daptomycin and vancomycin, respectively, were as follows: MRSA, 1 and 2 microg/ml; MRSS, 1 and 4 microg/ml; PRSP, 1 and 0.5 microg/ml; and VREF, 2 and >64 microg/ml. Daptomycin was bactericidal against 82% of 17 VREF isolates. The antibacterial activity of daptomycin was strongly dependent on the calcium concentration of the medium. Daptomycin was active against all gram-positive cocci tested.

FIG. 1

Effect of daptomycin concentration on in vitro time-kill kinetics for E. faecium SSL 110 (VRE) in MH II broth (25 μg of Ca²⁺/ml).

FIG. 2

Effect of calcium concentration in the test medium (MH broth) on activity of daptomycin against S. aureus SSL 50 (MRSA). (A) Daptomycin concentration equivalent to 1× the MIC (1 μg/ml). (B) Daptomycin concentration equivalent to 4× the MIC (4 μg/ml).