ANTIPNEUMOCOCCAL ACTIVITIES OF LEVOFLOXACIN AND CLARITHROMYCIN AS DETERMINED BY AGAR DILUTION, MICRODILUTION, E-TEST, AND DISK DIFFUSION METHODOLOGIES

The activities of levofloxacin and clarithromycin against 199 penicill in- and macrolide-susceptible and -resistant pneumococci were tested b y agar and microdilution methods in air and by disk diffusion and E-te st methods in air and CO2. For levofloxacin, greater than or equal to 99.0% of strains were susceptible at less than or equal to 2.0 mu g/ml with zone diameters of greater than or equal to 17 mm, regardless of incubation in air or CO2. Although zone sizes were smaller and E-test MICs were higher for clarithromycin in CO2 than those in air, category differences were minor, and susceptibility rates for clarithromycin w ere similar to those obtained by agar and microdilution in air (range, 76.9 to 80.9% by all methods). For clarithromycin, adjustment of brea kpoints based upon distribution of results resulted in susceptibility rates which were similar by all methods (75.8 to 76.9% susceptible, 0 to 1.5% intermediate, 22.6 to 23.1% resistant). Minor discrepancies we re obtained with levofloxacin for one strain (0.5%) by microdilution a nd two strains (1.0%) by disk diffusion in CO2. For clarithromycin, mi nor discrepancies were found in three strains (1.5%) by microdilution, seven strains (3.5%) by agar dilution, four strains (2.0%) by E-test in air, six strains (3.0%) by disk diffusion in air, and five strains (2.5%) by disk diffusion in CO2. Major discrepancies occurred with lev ofloxacin in one strain (0.5%) by microdilution but were not found wit h clarithromycin. Very major discrepancies were not seen with levoflox acin, but occurred with clarithromycin in five strains (2.5%) by micro dilution, three strains (1.5%) by agar dilution, two strains (1.0%) by E-test in air, eight strains (4.0%) by disk diffusion in air, and one strain (0.5%) by disk diffusion in CO2.