Inhibitory effects of the essential oils α-longipinene and linalool on biofilm formation and hyphal growth of <i>Candida albicans</i>

<i>Candida albicans</i> is one of the most common fungal pathogens, and causes systemic and invasive infections in humans. <i>C. albicans</i> biofilms are composed of yeast and hyphal and pseudohyphal elements, and the transition of yeast to the hyphal stage could be a virulence factor. In this study, diverse essential oils were initially investigated for anti-biofilm activity against <i>C. albicans</i> strains, and cascarilla bark oil and helichrysum oil and their components α-longipinene (a major constituent of both) and linalool were found to markedly inhibit biofilm formation without affecting planktonic cell growth. Moreover, α-longipinene and linalool were found to synergistically reduce biofilm formation. Notably, treatments with cascarilla bark oil, helichrysum oil, α-longipinene, or linalool clearly inhibited hyphal formation, and this appeared to be largely responsible for their anti-biofilm effect. Furthermore, the two essential oils, α-longipinene and linalool, reduced <i>C. albicans</i> virulence in <i>Caenorhabditis elegans</i>.