Antibacterial effects of essential oils on oral pathogens

Essential oils are plant derived substances that have been shown to have antimicrobial activity. However, limited evidence of activity against oral bacteria is available. Objective: The present study was designed to ascertain if a composite formulation of three essential oils had antimicrobial activity against a panel of Gram positive and Gram negative oral bacteria. ORA MD is a commercially available composite of peppermint, spearmint, and almond oils and has been reported to be effective in the treatment of periodontal infection and inflammation. However, no objective studies are available to support these clinical observations. Methods: The antibacterial activity of the essential oils was assessed in triplicate against a panel of early, intermediate, and late plaque colonizers including S. sanguis, S. oralis, S. gordonii, A. naeslundii, F. nucleatum, A. actinomycetemcomitans, and P. gingivalis strains 381 and W83 with S. aureus as a non-oral control. A spectrophotometric assessment of inhibition of planktonic growth and a growth inhibition zone assay on agar plates using filter paper discs were used for each species and strain. Results: The composite of essential oils effectively inhibited the growth of all species and strains tested using either the spectrophotometric assay at 2µl essential oils/ml media or the plate assay at 1µl/mm of filter paper disc. The essential oils were more effective against the Gram negative species and strains than against the Gram positive species and least effective against S. aureus. Conclusions: The composite mixture of peppermint, spearmint, and almond oils has effective antibacterial activity against Gram positive and Gram negative oral bacteria although asppars to be most effective against Gram negative species. This suggests that the beneficial clinical effects in reducing periodontal inflammation may be due to the antibacterial effects of the oils. Further studies are needed to elucidate the relative antibacterial activities of each oil independently.