Lavandula angustifolia Essential Oils as Effective Enhancers of Fluconazole Antifungal Activity against Candida albicans

The increasing prevalence of Candida albicans resistance to commercial antifungal agents in recent decades has prompted modern medicine and veterinary medicine to search for combined treatment options. The aim of the study was to determine the activity of essential oils from different cultivars and morphological parts of the medicinal lavender (Lavandula angustifolia) in combination with fluconazole against Candida albicans ATCC 10231 strain. The effect of the combination of lavender essential oil with fluconazole was tested using the checkerboard method, and the obtained results were interpreted on the basis of fractional inhibitory concentration indices (FICIs). A synergistic interaction was found for all combinations of fluconazole with essential oils isolated both from flowers and leafy stalks of two tested lavender cultivars: ‘Blue River’ and ‘Ellagance Purple’. The observed enhancement effect of fluconazole antifungal activity was significantly stronger in the case of essential oils obtained from flowers and leafy stalks of ‘Blue River’ cultivar. Analogous studies were performed for linalool, one of the main components of lavender essential oils, and a similar synergistic interaction with fluconazole was found.