Molecular characterization of quinolone-insensitive Streptococcus pneumoniae isolates from Japanese patients

Fluoroquinolone resistance in Streptococcus pneumoniae has become a growing concern. Using S. pneumoniae isolates (n = 61) for which the minimum inhibitory concentration (MIC) of levofloxacin was not less than 1 μg/ml, we investigated the susceptibility of S. pneumoniae isolates to other fluoroquinolones (ciprofloxacin, pazufloxacin, moxifloxacin, garenoxacin, and sitafloxacin) and sequenced the quinolone resistance-determining regions of two topoisomerase genes, parC and gyrA, in these isolates to identify mutations. As the number of missense mutations increased, the MIC values for each drug increased. However, moxifloxacin, garenoxacin, and sitafloxacin showed potent activities against the isolates, while the MICs of ciprofloxacin and pazufloxacin were higher than the MICs of levofloxacin.