Antimicrobial Efficacy of Origanum syriacum L. and Origanum onites L. Essential Oils against Pseudomonas aeruginosa and Their Effects on Biofilm Formation

In this study, we aimed to search the components and antimicrobial activity of Origanum syriacum and Origanum onites essential oils against Pseudomonas aeruginosa and also investigated the effects of these two plants essential oils on biofilm formation of Pseudomonas aeruginosa. Seventeen essential oil components, representing 98,76 %, were detected in the essential oil of Origanum syriacum L. and the major essential oil constituents were thymol (42,18 %), carvacrol (33,95 %), cymene (8,87 %) and γ-terpinene (8,21%). Thirty-four essential oil components, representing 98,62 %, were detected in the essential oil of Origanum onites L. with major essential oil constituents were thymol (68,28 %), γ-terpinene (5,50 %), p-cymene (5,47 %) and linalool (4,40%). In the study, Origanum onites essential oils were found to be more effective against both amikacin-resistant Pseudomonas aeruginosa strains and amikacin susceptible strains. In addition, the combination of Origanum syriacum and Origanum onites essential oils showed stronger efficacy against both amikacin-resistant and susceptible strains of Pseudomonas aeruginosa. The combined use of Origanum syriacum and Origanum onites essential oils showed stronger biofilm inhibition activity in all Pseudomonas strains. In the present study, the remarkable efficacy of Origanum syriacum and Origanum onites essential oils against both drug-resistant and drug-sensitive Pseudomonas aeruginosa strains was determined. More importantly, it has been found that the ability of these bacteria to form biofilms was inhibited by increasing concentrations of essential oils of these plants.