Vapour and Liquid-Phase Artemisia annua Essential Oil Activities against Several Clinical Strains of Candida

Candida spp. are often the cause of infection in immune-compromised individuals. They are characterized by a strong resistance to antimicrobial drugs and disinfectants. The activity of Artemisia annua essential oil against Candida spp. was determined by vapour contact and microdilution assay. The oil was characterized by the presence of oxygenated monoterpenes (more than 75 % of the constituents), mainly represented by the irregular monoterpene artemisia ketone (ca. 22 %), and the widespread monoterpenes 1,8 cineole (ca. 19 %) and camphor (ca. 17 %). Other representative constituents were artemisia alcohol (5.9 %), α-pinene (5.7 %), and pinocarvone (3.0 %). Thujone, a typical toxic constituent of the Artemisia species, was not detected. The results are reported as minimum inhibitory concentration, minimum fungicidal concentration, and diameter of inhibition zone obtained by the vapour diffusion assay. We tested 10 clinical Candida strains, coming from both clinical samples and international collections. The results show that the antifungal activity of A. annua is influenced by the type of method adopted. The inhibitory action of the essential oil was, in fact, higher in the vapour than in the liquid phase. Our results show an average minimum inhibitory concentration in the liquid phase of 11.88 µL/mL, while in the vapour phase, the growth of all Candida strains tested at a concentration of 2.13 µL/cm3 was inhibited. A strain of Candida glabrata was found to be less susceptible to the liquid medium than the vapour assay (50 µL/mL vs. 0.64 µL/cm3, respectively). Candida albicans and Candida dubliniensis were the most susceptible to the vapour test, while Candida parapsilosis was the most resistant.