In Vitro Activity of Quinupristin/Dalfopristin against Clinical Isolates of Common Gram-Positive Bacteria in Taiwan

The MICs of quinupristin/dalfopristin against common Gram- positive bacteria isolated from various clinical specimens at a university hospital in Taiwan were determined by the agar dilution method. The tested bacteria included methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible S. aureus (MSSA), methicillin- resistant Staphylococcus epidermidis (MRSE), methicillin- susceptible S. epidermidis (MSSE), Streptococcus pyogenes, Streptococcus pneumoniae, and Enterococcus faecalis. With the exception off. faecalis all bacteria were susceptible to quinuprisin/dalfopristin. The MIC50 and MIC90 were, respectively, 0.25 mu g/mL and 0.5 mu g/mL for both MRSA and MSSA; 0.25 mu g/nL and 0.5 mu g/mL for MRSE; 0.25 mu g/mL and 0.25 mu g/mL for MSSE; 0. 125 mu g/mL and 0.125 mu g/mL or S. pyogenes; and less than or equal to 0. 03 mu g/mL and 0 .25 mu g/mL for S. pneumoniae. Eighty-two percent of the tested E. faecalis isolates were intermediately resistant or resistant to quinupristin/dalfopristin, with an MIC50 of 2 mu g/mL and an MIC90 of 4 mu g/mL. Quinupristin/dalfopristin seems to be a promising antimicrobial agent against common Gram-positive bacteria other than E. faecalis in Taiwan