In-vitro activity of fleroxacin against Chlamydia trachomatis

The in-vitro activities of fleroxacin, tetracycline, erythromycin and clindamycin against two clinical isolates of Chlamydia trachomatis were compared. The MIC of fleroxacin (4.0 mg/l) was comparable to that of clindamycin (2.0 mg/l), but was higher than the MICs of both tetracycline (0.4 mg/l) and erythromycin (0.2-0.4 mg/l). Repeated passaging of C. trachomatis in the presence of sub MIC concentrations of fleroxacin did not affect the MIC and resulted in a rapid and complete loss of inclusions. The effect of combining fleroxacin with the other antibiotics was investigated by chequerboard titrations of pairs of antibiotics. The mean fractional inhibitory concentration index was calculated for each combination. Results showed indifference for the combinations fleroxacin/tetracycline, fleroxacin/erythromycin and fleroxacin/clindamycin and synergism for the combination tetracycline/clindamycin.