Mode of Antifungal Action of Daito-Gettou (Alpinia zerumbet var. exelsa) Essential Oil against Aspergillus brasiliensis

Plant-derived essential oils (EOs) are used in medicines, disinfectants, and aromatherapy products. Information on the antifungal activity of EO of <i>Alpinia zerumbet</i> var. <i>exelsa</i> (known as Daito-<i>gettou</i>) found in Kitadaito Island, Okinawa, is limited. Therefore, we aimed to evaluate the antifungal activity of EOs obtained via steam distillation of leaves of Daito-<i>gettou</i>, which is a hybrid of <i>A. zerumbet</i> and <i>A. uraiensis</i>. Daito-<i>gettou</i> EO showed antifungal activity (minimum inhibitory concentration = 0.4%) against <i>Aspergillus brasiliensis</i> NBRC 9455, which was comparable to that of <i>A. zerumbet</i> found in the Okinawa main island. Gas chromatography/mass spectrometry revealed that the main components of Daito-<i>gettou</i> EOs are γ-terpinene, terpinen-4-ol, 1,8-cineole, 3-carene, and <i>p</i>-cymene. Terpinen-4-ol content (MIC = 0.075%) was 17.24%, suggesting that the antifungal activity of Daito-<i>gettou</i> EO was mainly attributable to this component. Daito-<i>gettou</i> EO and terpinen-4-ol inhibited mycelial growth. Moreover, calorimetric observations of fungal growth in the presence of Daito-<i>gettou</i> EO showed a characteristic pattern with no change in the initial growth rate and only a delay in growth. As this pattern is similar to that of amphotericin B, it implies that the action mode of Daito-<i>gettou</i> EO and terpinen-4-ol may be fungicidal. Further studies on the molecular mechanisms of action are needed for validation.