Comparison of Etest, agar dilution, broth microdilution and disk diffusion methods for testing in vitro activity of levofloxacin against Staphylococcus spp. isolated from neutropenic cancer patients.

The susceptibility to levofloxacin of 194 consecutive staphylococcal (45 Staphylococcus aureus and 149 coagulase-negative staphylococci) isolates from neutropenic patients was determined by Etest and the results compared with those obtained using NCCLS-methods (broth microdilution, agar dilution and disk diffusion). Overall agreement at +/- 1log(2) dilution for Etest compared with broth microdilution and agar dilution was 99.0 and 83.5%, respectively. The Etest category agreement with broth microdilution and disk diffusion was 95.9 and 89.7%, respectively. Comparison of categories with Etest and agar dilution method gave only 67.0% absolute categorical agreement, with 29.9% minor errors and 10.7% major errors. No very major errors occurred by the four methods tested. Our results show that Etest is a valid alternative to the reference NCCLS-methods for monitoring the clinical usefulness of levofloxacin against staphylococci isolates from neutropenic patients.