Oral candidiasis is caused by Candida albicans. The symptoms including pain in the oral cavity affect our eating function. While some antifungal agents are commonly used for the treatment of candidiasis, occasional consumption of the effective dose cannot be tolerated due to side effects. There is also a possibility of induction of antifungal resistance, thus the development of replacement agents has been awaited. We aim to explore antimicrobial activities of essential oils. We evaluated the antifungal activities against C. albicans of essential oils from seven aromatic plants from three manufacturers, and of three chemotype essential oils from rosemary (Rosmarinus officinalis). As a result, we found that the antifungal activity was increased several times by the addition of Tween 80. All the tested essential oils showed stable antifungal activity, however, the variation was observed among the manufacturers of rosemary and eucalyptus. Rosemary has three chemotypes; CINEOL, CAMPHOR and VERBENON. They derived from a same plant species, but contain different chemical components. The CINEOL, dose-dependently decreased the number of C. albicans in the time-kill assay. Hence we concluded that the components of rosemary essential oil would have an effect on its antifungal activity. A chemotype is the first to consider in measuring antifungal activities of rosemary oil.

Oral candidiasis causes pain in oral cavity or tongue. Antifungal drugs are commonly used for the treatment of candidiasis, however, there could be several problems such as side effects, drug resistance, or contraindication to concomitant use with drugs already taken. The development of substituting antimicrobial agents, which could be used internally or as gargling agents, is expected. Some essential oils have been known for the activities against microbes. We focused on the three chemotype essential oils from rosemary and five essential oils from Lamiaceae plants including rosemary, and examined their antifungal activity against Candida albicans by broth microdilution method. The activity with or without addition of Tween 80 or Tween 20 was statistically analyzed. Minimal inhibitory concentration (MIC) values of the essential oils were significantly decreased when either of the two surfactants was added. Among the tested oils, only CAMPHOR, a rosemary chemotype, showed a significantly lower MIC with addition of Tween 20 than Tween 80. It is inferred that the antifungal activity of essential oils is influenced by the type of surfactants. Some of the essential oils showed the same values of MIC and the minimal fungicidal concentration (MFC) when surfactant was added. Peppermint showed the same MICs and MFCs in most cases, and its low MFC indicated potent fungicidal activity against C. albicans, as observed in CINEOL. We will * Corresponding author. Y. Matsuzaki et al. 59discuss peppermint oil as one of the potential candidates for antifungal agents against C. albicans.