Enzymatic quorum quenching increases antibiotic susceptibility of multidrug resistant pseudomonas aeruginosa

ABSTRACT

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. 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. 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. Lactonase treatment increased antibiotic susceptibility of the biofilms of MDRPA isolates underscoring the potential of quorum quenching in antimicrobial therapeutics