Effect of Satureja montana L. essential oil and thymol on growth and biofilm production of Pseudomonas aeruginosa

Background: Opportunistic and nosocomial pathogen Pseudomonas aeruginosa in planktonic form causes acute infection, and in biofilm form causes chronic persistent infections, common in patients with cystic fibrosis and diabetic chronic wounds. Multiple resistance mechanisms compromise the choice of effective treatment. Essential oils and their components have a wide range of antimicrobial properties and some of them have recently been shown to have antibiofilm activity. Objectives: The aim of this study was to investigate the effect of Satureja montana L. essential oil and thymol as the predominant component of the oil (56.5%) on the planktonic growth and biofilm of P. aeruginosa ATCC 27853, alone and in combination with tobramycin. Methods: The effect on planktonic growth was determined by measuring OD570. The amount of formed biofilm was determined by crystal violet staining and the effect on biofilm was defined as biofilm index. Results: Essential oil and thymol in subinhibitory concentrations could effectively inhibit the planktonic growth of P. aeruginosa, both alone, and in combination with tobramycin. On the other hand, the effect on the biofilm may be opposite and completely independent of antibacterial effect. Essential oil and thymol in subinhibitory concentrations promoted biofilm formation. Essential oil antagonized the promotional effect of tobramycin on preformed biofilm in concentration corresponding to its MIC value. Depending on the concentration, thymol in subinhibitory concentrations either antagonized tobramycin or synergises with it to promoted biofilm survival. Results of this work will support future studies to find new and preserve existing therapies of P. aeruginosa infections.