The in-vitro activity of moxifloxacin against Legionella species and the effects of medium on susceptibility test results.

The in-vitro activities of moxifloxacin, ciprofloxacin, erythromycin and rifampicin against 49 Legionella spp. isolates were determined by an agar dilution method with buffered charcoal yeast extract agar containing alpha-ketoglutarate. Because the inhibitory effects of charcoal in the test media were pronounced (92% for quinolones, 90.5% for rifampicin and 92.5% for erythromycin), the MICs were corrected for the charcoal-bound fraction of the antibiotics. The corrected geometric mean MICs were 0.018 mg/L for moxifloxacin, 0.02 mg/L for ciprofloxacin, 0.27 mg/L for erythromycin and 0.005 mg/L for rifampicin.