Antimicrobial activities of two investigational fluoroquinolones (CI-960 and E4695) against over 100 Legionella sp. isolates.

The antimicrobial activities of two investigational fluoroquinolones (CI-960 and E4695) were compared with those of five similar compounds and four comparison drugs against 103 strains of Legionella pneumophila and five other Legionella species type strains. When concentrations inhibiting 90% of strains tested (MIC90s) for L. pneumophila were determined, CI-960 and temafloxacin emerged as the most active (0.015 microgram/ml) and were followed in potency by E4695 (0.03 microgram/ml). This activity was two- to fourfold greater than that of the reference drug, ciprofloxacin, and approached that of rifampin (MIC90, 0.008 microgram/ml). All fluoroquinolones studied were more active than erythromycin (MIC90, 0.5 microgram/ml). These two investigational fluoroquinolones appear well suited for further in vivo study of legionellosis therapy.