Synergistic antifungal activity of tea tree (Melaleuca alternifolia) and lavender (Lavandula angustifolia) essential oils against dermatophyte infection

The antifungal potential of tea tree and lavender essential oils alone and in combination, against common causes of tinea infection in humans was investigated via in-vitro investigations, in order to determine a suitable dosage for use in clinical trials. The concept of synergy was considered, in the microbiological environment, and as a chemical phenomenon. Trichophyton rubrum and T. mentagrophytes var. interdigitale were studied, as the most prevalent causes of tinea and onychomycosis. Possible chemical interactions between essential oils were examined using gas chromatography-mass spectrometry (GC-MS) infra-red (IR) spectroscopy and polarimetry. There was a clear antifungal action by both tea tree and lavender essential oils on these organisms grown in culture. In combination, appropriate blends demonstrated synergistic action. No changes in retention times or identified compounds were observed by GC-MS. Alterations were found using IR spectroscopy in some combinations of the essential oils. The inconsistency in findings between the two analytical techniques may in part be due to a difference in sensitivities of the techniques or the conditions used in the GC-MS equipment; different column parameters have yet to be trialled. These were time dependent and affected by changing temperature. The measurement of optical rotation was determined to be an inappropriate technique for the study of synergy in essential oil mixtures. The data from this study confirm that synergistic action does occur between these two commonly used essential oils in effecting antifungal activity. GC-MS analysis demonstrated that there was no chemical interaction resulting in a new compound that could be identified using the analytical equipment in this study. IR analysis supports the suggestion that synergistic action may be dependent upon reaction involving the numerous organic substances present in essential oils. These changes may be due to as yet unidentified transient chemical interactions between functional groups within the essential oil mixtures.