SUSCEPTIBILITIES OF PENICILLIN-SUSCEPTIBLE AND PENICILLIN-RESISTANT STRAINS OF STREPTOCOCCUS-PNEUMONIAE TO RP-59500, VANCOMYCIN, ERYTHROMYCIN, PD-131628, SPARFLOXACIN, TEMAFLOXACIN, WIN-57273, OFLOXACIN, AND CIPROFLOXACIN

The MICs of four new quinolones, sparfloxacin (AT-4140, CI-978), PD 131628 (the active form of the prodrug CI-990), temafloxacin, and Win 57273, compared with those of ciprofloxacin and ofloxacin were tested against 53 penicillin-susceptible, 35 penicillin intermediate-resistant, and 51 penicillin-resistant pneumococci. Susceptibility to RP 59500, a new streptogramin, was also tested and compared with those to the quinolones, erythromycin, and vancomycin. All MICs were determined by a standardized agar dilution method by using Mueller-Hinton agar supplemented with sheep blood. Quinolone, vancomycin, and RP 59500 susceptibilities were not affected by susceptibility or resistance to penicillin. For Win 57273, the MICs for 50% (MIC50) and 90% (MIC90) of strains tested were 0.015 and 0.03-mu-g/ml. respectively. MIC50s of both sparfloxacin and PD 131628 were 0.25-mu-g/ml, and MIC90s were 0.5-mu-g/ml. The MIC50 of temafloxacin was 0.5-mu-g/ml, and the MIC90 was 1.0-mu-g/ml. By comparison, ofloxacin and ciprofloxacin both yielded MIC50s of 1.0-mu-g/ml and MIC90s of 2.0-mu-g/ml. RP 59500 yielded an MIC50 of 0.5-mu-g/ml and an MIC90 of 1.0-mu-g/ml and was only 1 doubling dilution less active against 17 erythromycin-resistant strains. Vancomycin was active against all strains (MIC50, 0.25-mu-g/ml; MIC90, 0.5-mu-g/ml). All four experimental quinolones as well as RP 59500 show promise for therapy of infections with penicillin-resistant and -susceptible pneumococci.