Inhibition of biofilm formation by the solubilized TTO and LS-TTO

Objectives: Antimicrobial activity of Tea Tree Oil (TTO) and Lemon Scented Tea Tree Oil (LS-TTO) against oral microorganisms has been reported previously. The TTO and LS-TTO are natural essential oil and water insoluble fluids. Despite this, the TTO and LS-TTO have been used without solubilization in the previous studies. In this study, we attemped to establish a condition for solubilization of TTO and LS-TTO, and examined the antimicrobial activity and the effects on biofilm formation by the solubilized TTO and LS-TTO. Method: Non-ionic surfactant, Tween 20 and decaglycerol esters of lauric acids (L-7D) were used as solubilizer. Bacterial cells of Streptococcus mutans Ingbritt, Actinomyces viscosus ATCC 19246, Porphylomonas gingivalis ATCC 33277, Fusobacterium nucleatum JCM 6328 were suspended as 10⁶ CFU/ml in phosphate-buffered saline, and treated with the solubilized TTO and LS-TTO for 5 minutes. After washing (3 times), the bacterial suspensions were diluted and inoculated on BHI blood agar plate to estimate bactericidal activity. Biofilm formation was quantified with the method by using crystal violet solution. Result: Tween 20 has no antimicrobial activity in the concentration used in this experiment. The solubilized TTO and LS-TTO with Tween 20 have inhibited biofilm formation in S. mutans, and reduced the viability of oral bacteria. The solubilized TTO and LS-TTO with L-7D have inhibited biofilm formation significantly more than solubilized them with Tween 20. Conclusion: In this study, we established the suitable condition for solubilization of TTO and LS-TTO. These solubilized TTO and LS-TTO have bactericidal activity, and have inhibited biofilm formation in the oral bacteria. The present study may suggest a effectiveness of the solubilized TTO and LS-TTO when they are used for clinical application in dental cares.