inhibition of quorum sensing-controlled virulence factor production in pseudomonas aeruginosa by quercus infectoria gall extracts

background and objectives: this study was designed to evaluate the activity of quercus infectoria galls extract (qifge) on virulence factor production and inhibition of quorum sensing (qs) in pseudomonas aeruginosa. materials and methods: minimum inhibitory concentration (mic) of qifge against 5 strains of p. aeruginosa was determined. the extract at sub-mic was used to determine biofilm formation, level of protease lasa, lasb, swarming and twitching motility and qs using chromobacterium violaceum cv026 as a biosensor. effect of the extract on expression levels of lasr gene was determined by real time pcr. results: qifge inhibited the qs and all other tested virulence factors compared with the control grown in the absence of the extract (p=0.001). real time pcr showed 2 to 8-fold reduction in lasr gene expression in presence of the extracts compared with the control. qifge significantly inhibited the virulence factor production, had inhibitory effect on qs, and resulted in the lower expression of lasr gene. conclusion: qifge showed novel inhibitory effect against qs related virulence factor production, which was unrelated to antimicrobial effect. the extract can down regulate the production of virulence factor and should be evaluated as a candidate for alternative treatment of pseudomonad infections in future. keywords: pseudomonas aeruginosa , quercus infectoria , virulence factor, quorum sensing, lasr gene, chromobacterium violaceum