Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 3 1 2011 03 15 1 12 EN P Sharma Departments of Microbiology, Panjab University, Chandigarh S Kiran Departments of Biotechnology and, Panjab University, Chandigarh K Harjai Departments of Microbiology, Panjab University, Chandigarh N Capalash Departments of Biotechnology and, Panjab University, Chandigarh 2015 10 01 Background and Objectives: There is increasing emergence of multidrug resistant Pseudomonas aeruginosa (MDRPA) strains and drug resistance is positively-correlated with biofilm-forming ability. Since about 10% of P. aeruginosa genome is controlled by quorum sensing (QS), alteration in its antibiotic susceptibility by targeting QS was the focus of the present study. Materials and Methods: One day biofilms of PAO1 and three urinary tract infection MDRPA isolates (PA2, PA8 and PA18) were formed in 96-well microtiter plate. Biofilms were exposed to concentration gradient of ciprofloxacin and gentamicin to obtain Minimum Biofilm Eradication Concentration (MBEC) by direct enumeration method. Susceptibility of 24 h biofilms was evaluated by treatment with ciprofloxacin and gentamicin per se and in combination with lactonase. The effect was also examined on 72 h biofilms by Scanning Electron Microscopy. Results: Lactonase treatment did not have any effect on growth of the selected strains but 73.42, 69.1, 77.34 and 72.5% reduction of biofilm was observed after lactonase (1 unit) treatment, respectively. Antibiotics in combination with lactonase (0.3 units) resulted in an increased susceptibility of the biofilm forms by > 3.3, 4, 5 and 1.5 folds of MBEC, for ciprofloxacin and > 6.67, 12.5, 6 and > 2.5 folds, for gentamicin respectively, which could be due to the disruption of biofilm by lactonase treatment as shown by scanning electron microscopy. Also there was significant reduction (p < 0.001) in virulence factor production by the strains. Conclusion: Lactonase treatment increased antibiotic susceptibility of the biofilms of MDRPA isolates underscoring the potential of quorum quenching in antimicrobial therapeutics. https://ijm.tums.ac.ir/index.php/ijm/article/view/78 https://ijm.tums.ac.ir/index.php/ijm/article/download/78/78