Activity of daptomycin against recent North American isolates of Streptococcus pneumoniae.

Daptomycin MICs at which 50% of isolates were inhibited (MIC(50)s) and MIC(90)s determined by the NCCLS broth microdilution method were both 0.25 microg/ml (range, 0.06 to 2 microg/ml) for 350 pneumococcal isolates. MICs determined by E test strips on commercially prepared Mueller-Hinton sheep blood agars with different calcium contents were 2 to 3 dilutions higher than those determined by strips that contained daptomycin plus calcium. Daptomycin zone diameters varied little on the same media.