Influence on Pseudomonas aeruginosa elastase, proteinase and alginate by supra-inhibitory and supra-subinhibitory concentrations of quinolones

Suppression of elastase, proteinase and alginate of Pseudomonas aeruginosa after the exposure of a bacterial suspension (30 min) to supra-inhibitory concentrations (2x or 4x MIC) of norfloxacin was found. The norfloxacin at 4x MIC was more effective, and this concentration depressed elastase to 13.0%, proteinase to 14.6% and alginate to 0% of the control values. Enoxacin at 2x MIC did not affect the virulence factors studied, and at a concentration of 4x MIC only elastase was effectively reduced to 61% of the control value. Supra-subinhibitory concentrations of the quinolones tested (2x or 4x MIC + sub-MICs) severely diminished all of the activities tested compared with supra-inhibitory concentrations alone. Combinations of 4x MIC + sub-MICs were more effective in the majority of cases.