Cinnamon Leaf and Clove Essential Oils Are Potent Inhibitors of Candida albicans Virulence Traits

Plant-based essential oils are promising anti-virulence agents against the multidrug-resistant opportunistic pathogen Candida albicans. Gas chromatography-mass spectrometry of Cinnamomum zeylanicum (cinnamon) leaf and Eugenia caryophyllus (clove) flower bud essential oils revealed eugenol (73 and 75%, respectively) as their major component, with beta-caryophyllene, eugenyl acetate, and alpha-humulene as common minor components. Cinnamon leaf and clove essential oils had minimum inhibitory concentrations of 600 and 500 mu g/mL, respectively against the C. albicans RSY150 reference strain and 1000 and 750 mu g/mL, respectively for the clinical reference strain ATCC 10231. The combined oils are additive (FICI = 0.72 +/- 0.16) and synergistic (0.5 +/- 0.0) against RSY150 and the clinical reference strain, respectively. Mycelial growth was inhibited by sublethal concentrations of either essential oil, which abolished colony growth. At half of the lowest combined lethal concentration for the two oils, the yeast-to-hyphal transition and mycelial growth was potently inhibited. Mutant strains als1 Delta/Delta, als3 Delta/Delta, hwp1 Delta/HWP1+, and efg1 Delta/Delta were sensitive to either or both oils, especially efg1 Delta/Delta. In conclusion, oils of cinnamon leaf and clove and their combination significantly impact C. albicans virulence by inhibiting hyphal and mycelial growth.