Determining the frequency of resistance of Streptococcus pneumoniae to ciprofloxacin, levofloxacin, trovafloxacin, grepafloxacin, and gemifloxacin

Newer fluoroquinolones have good activity against Streptococcus pneumoniae and may be useful clinically for the treatment of pneumonia. Although resistance among Streptococcus pneumoniae has been reported, it is rare. The frequency of single-step resistance and the emergence of resistance were compared in serial transfer of 49 clinical isolates of penicillin-sensitive and -resistant Streptococcus pneumoniae to ciprofloxacin, levofloxacin, trovafloxacin, grepafloxacin, and gemifloxacin. Sin I-le-step resistance frequencies to four times the minimum inhibitory concentration were 2.73x10(-6) ( +/-8.46x10(-6),) for ciprofloxacin, 1.78x10(-7) (+/-4.62x10(-7)) for trovafloxacin, 5.45x10(-7) ( +/-1.24x10(-6)) for grepafloxacin, 6.78x10-(7) ( +/-1.38x10(-6)) for gemifloxacin, and 9.23x10-(8) (+/-4.47x10(-7)) for levofloxacin. In serial transfer experiments, all isolates became resistant to clinically relevant levels of all fluoroquinolones after eight passages. The resistance occurred most rapidly with ciprofloxacin followed by grepafloxacin, gemifloxacin, trovafloxacin, and levofloxacin. These results show that strains with decreased susceptibility to fluoroquinolones occur frequently in cultures of Streptococcus pneumoniae, and this organism can readily become resistant to clinically relevant concentrations of fluoroquinolones in vitro.