| Summary: | Abstract Quorum sensing (QS) inhibition by metal-antibiotic complexes is a promising strategy for the management and control of multidrug resistant Pseudomonas aeruginosa infections. We investigated the anti-quorum sensing activity of sub-minimum inhibitory concentration (sub-MIC) of copper(II) sulfate pentahydrate-ciprofloxacin (Cu-CIP) complex and free ciprofloxacin (free-CIP) against P. aeruginosa PAO1. Copper-CIP complex was synthesized and its characterization was assessed using spectroscopic methods and single crystal X-ray analysis. The effect of sub-MIC (1/4 and 1/16 MIC) concentrations of Cu-CIP and free-CIP on cell growth, biofilm formation, motility, alginate and pyocyanin production, H2O2 susceptibility and expression of QS circuit genes lasI and lasR in PAO1 was determined. Minimum inhibitory concentration of Cu-CIP complex and free-CIP was determined as 0.125 µg/ml. Copper-CIP complex did not show significant effect on the cell growth at concentrations of 1/4 and 1/16 MIC. However, sub-MIC concentrations (1/4 and 1/16 MIC) of Cu-CIP showed the significant reduction in violacein production, motility, biofilm formation, alginate and pyocyanin production and sensitivity to H2O2 in a concentration dependent manner (P < 0.001). Copper-CIP at the concentration of 1/4 MIC showed the greatest reduction in lasI and lasR transcriptional expression (89.5% and 96.2% respectively). Considering the biological effects of Cu-CIP complex and its inhibitory activity on QS related virulence traits at low concentrations (0.03 and 0.007 µg/ml), it may be used as an effective approach in the management of infections caused by P. aeruginosa.
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