INTRAPHAGOCYTIC KILLING OF GRAM-POSITIVE BACTERIA BY CIPROFLOXACIN

The intraphagocytic killing of Staphylococcus aureus, Streptococcus py ogenes, and Corynebacterium group D2 by ciprofloxacin (0.1, 1 and 5 mg /L) within human neutrophils was determined. The organisms showed diff erent susceptibility to neutrophil killing mechanisms. The neutrophils with intact and impaired (by phenylbutazone treatment) O-2-dependent killing mechanisms were studied. The minimum concentrations of ciprofl oxacin to kill 90% of phagocytosed bacteria within untreated neutrophi ls after 2 h were 1 mg/L for S. aureus and Corynebacterium group D2, a nd 0.1 mg/L for S. pyogenes. In contrast, exposure for 3 h was require d to achieve similar cidal effects within phenylbutazone treated neutr ophils. Synergic interaction between ciprofloxacin and the O-2-depende nt mechanisms of phagocytes was found. The reactive oxygen metabolites produced in the respiratory burst did not affect the intraphagocytic activity of ciprofloxacin. Phenylbutazone treatment of phagocytes woul d be a good experimental model to study intraphagocytic killing by dru gs in situations where the oxidative mechanisms of neutrophils are imp aired (for example AIDS and chronic granulomatous disease).