Killing of Gram-Negative Bacteria by Ciprofloxacin within both Healthy Human Neutrophils and Neutrophils with Inactivated O₂-Dependent Bactericidal Mechanisms

Abstract

The intraphagocytic killing of Escherichia coli, Serratia marcescens, Pseudomonas aeruginosa, and Salmonella typhi by ciprofloxacin (0.1, 1 and 5 μg/ml) within human neutrophils with intact and impaired (by phenylbutazone treatment) O₂-dependent killing mechanisms was studied and compared with the extracellular killing in the same medium of the intraphagocytic killing, but omitting neutrophils. The MIC/MBC of ciprofloxacin in vitro (assays performed according to NCCLS specifications) were: 0.015/0.06 for E. coli, 0.12/32 for S. marcescens, 1/16 for P. aeruginosa, and 0.007/0.06 for S. typhi. Ciprofloxacin showed bactericidal activity both extracellular and within phenylbutazone-treated and untreated neutrophils. The minimum concentration of ciprofloxacin to kill 90% of phagocytosed bacteria within neutrophils with normal O₂-dependent killing power after 30 min was: 0.1 μg/ml for E. coli, and S. typhi, 1 μg/ml for P. aeruginosa, and 5 μg/ml for S. marcescens. In contrast, exposure for 60 min was required to reach this percentage within phenylbutazone treated neutrophils. The minimum concentration to kill 90% of extracellular bacteria after 30 min was: 0.1 μg/ml for E. coli, P. aeruginosa and S. typhi, and 5 μg/ml, for S. marcescens. A positive interaction between ciprofloxacin and the O₂-dependent 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 would be a good experimental model to study the intraphagocytic killing of drugs in situations such as AIDS and chronic granulomatous disease where inefficient oxidative mechanisms of neutrophils exist.

Antipseudomonal Agents Exhibit Differential Pharmacodynamic Interactions with Human Polymorphonuclear Leukocytes against Established Biofilms of Pseudomonas aeruginosa

“…The significant interactions we observed between CIP and PMNs are consistent with earlier reports showing that quinolones and in particular CIP kill P. aeruginosa either directly, by disrupting the regulatory mechanisms that control cell morphology and production of certain virulence factors (14,48), or indirectly, by entering PMNs and killing the bacteria intracellularly (49). However, biofilm-grown cells have shown variable results in this study and other reports: although we observed a concentration-dependent effect for P. aeruginosa biofilm cells exposed to CIP, the majority of the combinations of CIP and PMNs produced either nonsignificant or antagonistic interactions.…”

Case report: recovery from persistent septicemic melioidosis.

“…However, it is surprising that a quinolone antibiotic with good intracellular penetration and intracellular anti-pseudomonal activity should be disappointing in clinical use for patients with melioidosis. 16,17 Whatever the mechanism of functional resistance, conventional antibiotic susceptibility testing appears to be poor a predictor of intracellular antibacterial activity, as was seen in this case where breakpoint testing and e-test MIC did not explain treatment failure.…”

Modern management of chronic granulomatous disease

“…A course of oral ciprofloxacin may also be taken along as reserve on journeys or holidays. Being lipophilic, it is concentrated within neutrophils and reduces in vitro the survival of Serratia marcescens (Canton et al, 1999) and of intracellular S. aureus (Peman et al, 1994). Additional antistaphylococcal cover is provided by combining Ciprofloxacin with Teicoplanin.…”