Activity of Selected Essential Oils against Candida spp. strains. Evaluation of New Aspects of their Specific Pharmacological Properties, with Special Reference to Lemon Balm

The aim was to investigate the antifungal effectiveness and some of pharmacological properties of essential oils (EOs), which had not yet been thoroughly studied in the planned scope. We first evaluated MIC/MFC of sixteen EOs against C. albicans ATCC 10231. Then, five most active EOs were tested, using 50 clinical Candida spp. strains and additional reference C. albicans ATCC 90028 strain. The time-kill curve, carryover, post-antifungal effects (PAFE), mutant prevention concentrations, the susceptibility of reference strains to the cell wall disrupting agents and tolerance to oxidative stress, were evaluated. For these detailed studies, we chose the following four essential oils. Clove oil, Geranium oil, Lemon balm and Citronella oil, with MICs of 0.097% (v/v), resulted concentrationand time-dependent killing and may be therapeutically safe, because they do not generate resistance. The best one was Lemon balm, which caused most extended PAFE, significantly reduced tolerance to oxidative stress and increased susceptibility to Calcofluor White, Congo Red and SDS. Phytochemical analysis of these four EOs has been performed and compared; looking for the reason that Lemon balm was the best.