Evaluation of anti-quorum sensing activity of indigenous dietary plants against Pseudomonas aeruginosa

Increasing antibiotic resistance in Pseudomonas aeruginosa has encouraged the search for alternative means which can aid in reducing the virulence of the pathogen. Quorum sensing (QS) is considered to be an attractive target to limit infections caused by this bacterium. The limited reports on the screening of anti-QS activity from locally available vegetables and spices against P. aeruginosa prompted us to take up the present investigation. Initial screening of antibacterial activity against P. aeruginosa was carried out by agar well diffusion method. Assessment of anti-QS activity was performed against C. violaceum MTCC 2656. Virulence assays against P. aeruginosa ATCC 15692 were accomplished in the presence of sub-MIC values of the crude extracts. Of the 95 samples initially screened, only 11 extracts with a significant antibacterial activity were selected for MIC determination against P. aeruginosa and C. violaceum. 6 extracts with a MIC value in the range of 0.5–1.0 mg/ml were picked for anti-QS screening. The highest violacein inhibition (70.5%) and inhibition of elastase (81.41%), pyocyanin (94%), swarming motility (71%) and biofilm formation (80.3%) was found in Cinnamomum verum leaf extract. The present investigation reveals the anti-QS activity in the indigenous vegetables and spices in effectively reducing the virulence factor production in P. aeruginosa. It also emphasizes the importance of evaluating the anti-QS property of un-explored locally available vegetables and spices for isolating novel anti-QS compounds which might lead to new therapeutic strategies.