Eugenol: a potent quorum sensing inhibitor to restrict Pseudomonas aeruginosa pathogenicity

Bacterium Pseudomonas aeruginosa is an opportunistic human pathogen and one of the most important causes of nosocomial infections in a wide range of immunocompromised patients including those with malignancies, cystic fibrosis, and burns. This bacterium produces many virulence factors and is highly resistant to lots of common antibiotics due to its biofilm formation. The production of many virulence factors in this bacterium is under the control of quorum sensing systems (QS). The QS is an attractive target for the development of novel therapeutics. Eugenol is the major component of clove (Eugenia caryophylata) oil. The previous studies have shown its antibacterial activities. This study aimed to determine the in vitro anti-QS activity of eugenol on QS-regulatedbiofilm formation and virulence factors production in P. aeruginosa strains. The minimum inhibitory concentration (MIC) of eugenol was determined against two strains of this bacterium ATCC 27853 and PAO1, and three clinical isolates. Then the effect of eugenol on bacterial proliferation was determined by monitoring the growth curve. The biofilm formation, the production of exopolysaccharide (EPS), pyocyanins, rhamnolipids, the motility of swimming, swarming, and twitching were evaluated after the eugenol treatment. The MICs against two strains of the bacterium ATCC 27853 and PAO1 were obtained 0.3% and 0.6% (v/v), respectively. Different concentrations of eugenol (≤0.15%) significantly reduced the production of virulence factors including pyocyanin and rhamnolipid. The biofilm formation, EPS production, and swarming, swimming, and twitching motility were also reduced after the eugenol treatment. In general, according to the results of this study, the use of eugenol, as a potent QS inhibitor and anti-biofilm agent, could be an effective therapeutic strategy against P. aeruginosa infections.