Postantibiotic effect and virulence factors depression induced by ciprofloxacin and by aminoglycosides in a clinical isolate of Pseudomonas aeruginosa.

The postantibiotic effect (PAE) was induced in Pseudomonas aeruginosa by ciprofloxacin, tobramycin and netilmicin (2x or 4x MIC). A longer PAE was evoked by a higher concentration of antibiotics. The evaluation of Pseudomonas aeruginosa virulence factors after treatment with suprainhibitory concentrations of the antibiotics tested showed that a higher suppression of elastase activity was associated with a longer PAE. Elastase was suppressed more effectively than proteinase. The highest reduction of elastase and proteinase activity (to 24.9% and 76.4% of the control values) was observed after treatment with ciprofloxacin.