Activity of gemifloxacin, a new broad-spectrum quinolone, against 200 pneumococci by four different susceptibility testing methods

Agar and microdilution (in air), Etest (in air and CO(2)) and disc diffusion (in air and CO(2)) susceptibility testing methods were used to investigate the activity of gemifloxacin against 200 pneumococci. MIC(50)s were 0.016-0.03 mg/L and MIC(90)s 0.125-0.25 mg/L for all methods. With agar dilution as reference, 187/200 strains gave essential agreement with microdilution and 196 with Etest (air and CO(2)). Disc zones were a few millimetres narrower in CO(2) than in air. With discs in CO(2), all ciprofloxacin-susceptible strains yielded zone diameters 26 mm; values in air were 28 mm. Zones for ciprofloxacin-resistant strains in CO(2) were mostly 21-26 mm; zones in air were a few millimetres wider, but mostly <31 mm.