Synergistic effect between clove oil and its major compounds and antibiotics against oral bacteria

Background: Essential oils have been found to be antibacterial, antifungal, spasmolytic, and antiplasmodial activity and therapeutic effect in cancer treatment. Objective and design: In this study, clove oil and its major compounds, eugenol and beta-caryophyllene were evaluated against oral bacteria, either alone or in combination with ampicillin or gentamicin, via checkerboard and time kill assay. Results: The antibacterial activity of the clove oil was higher than beta-caryophyllene but was similar to eugenol against all tested oral bacteria. Furthermore, the MIC and MBC were reduced to one half-one sixteenth as a result of the combination of clove oil or eugenol with antibiotics. The synergistic interaction was verified by time kill studies using the clove oil or eugenol with antibiotics. 60 min of treatment with MIC of the clove oil or eugenol with ampicillin or gentamicin resulted in an increase in the rate of killing in units of CFU/mL to a greater degree than was observed with alone. Conclusion: The results suggest that the clove oil and eugenol could be employed as a natural antibacterial agent against cariogenic and periodontopathogenic bacteria. (C) 2011 Elsevier Ltd. All rights reserved.