Frequency of selection of fluoroquinolone-resistant mutants of Neisseria gonorrhoeae exposed to gemifloxacin and four other quinolones

We studied the frequency of mutation of clinical isolates of Neisseria gono rrhoeae (two nalidixic acid susceptible and two nalidixic acid resistant), and the stability of the mutants obtained, in the presence of three differe nt concentrations of five fluoroquinolones. The frequency of mutation was l ow for all the quinolones. Only one N. gonorrhoeae mutant, obtained with tr ovafloxacin at 4 x MIC presented a stable increase in the MIC of this quino lone, not attributable to novel mutation(s), both in the gyrA and parC gene s, although not showing any increase in the MIC of the other quinolones tes ted. In summary, gemifloxacin was the only quinolone tested for which resis tant mutants were not obtained.