Pharmacodynamics of ciprofloxacin against Pseudomonas aeruginosa planktonic and biofilm-derived cells.

The influence of growth phase and state on survival and recovery of Pseudomonas aeruginosa exposed to ciprofloxacin was investigated using batch culture grown planktonic cells and disaggregated biofilm populations. Biofilms were either non-antibiotic exposed or previously exposed to ciprofloxacin before disaggregation and subsequent challenge with ciprofloxacin. Viable counts showed that late stationary phase cells were tolerant to ciprofloxacin over 24 h exposure, whilst all other populations presented a biphasic killing pattern. In contrast, the metabolic activity of planktonic and biofilm-derived cells remained similar to controls during the initial 6 h of ciprofloxacin exposure, despite a significant reduction in viable cell numbers. A similar effect was observed when assessing the PAE of 1 h ciprofloxacin exposure. Thus, although cell reduction occured, the metabolic status of the cells remained unchanged. The recovery of disaggregated biofilm cells previously exposed to ciprofloxacin was significantly quicker than naïve biofilm cells, and this latter population's recovery was significantly slower than all planktonic populations. Results from this work have implications for our understanding of biofilm-related infections and their resilience to antimicrobial treatment. This article is protected by copyright. All rights reserved.