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

Plant-based essential oils are promising anti-virulence agents against the multidrug-resistant opportunistic pathogen . Gas chromatography-mass spectrometry of (cinnamon) leaf and (clove) flower bud essential oils revealed eugenol (73 and 75%, respectively) as their major component, with β-caryophyllene, eugenyl acetate, and α-humulene as common minor components. Cinnamon leaf and clove essential oils had minimum inhibitory concentrations of 600 and 500 µg/mL, respectively against the RSY150 reference strain and 1000 and 750 µg/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 Δ/Δ, Δ/Δ, Δ/+, and Δ/Δ were sensitive to either or both oils, especially Δ/Δ. In conclusion, oils of cinnamon leaf and clove and their combination significantly impact virulence by inhibiting hyphal and mycelial growth.