Activity of Gemifloxacin against Penicillin- and Ciprofloxacin-Resistant Streptococcus pneumoniae Displaying Topoisomerase- and Efflux-Mediated Resistance Mechanisms

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Abstract
Nine penicillin-resistant Streptococcus pneumoniae clinical isolates from Northern Ireland, resistant to ciprofloxacin (MICs, 2 to 64 μg/ml) through topoisomerase- and/or reserpine-sensitive efflux mechanisms, were highly susceptible to gemifloxacin (MICs, 0.03 to 0.12 μg/ml). Two strains (requiring a ciprofloxacin MIC of 64 μg/ml) carried known quinolone resistance mutations in parC , parE , and gyrB , resulting in S79F, D435V, and E474K changes, respectively. Thus, gemifloxacin is active against clinical strains exhibiting altered topoisomerase and efflux phenotypes.