Essential oils and their active compounds potentially useful in the fight against Candida auris

The anti-fungal activity of 15 EOs (Pranarom International, Belgique) was tested against 10 clinical fluconazole-resistant strains of C. auris. Micro-broth dilution (MBD) test, according to EUCAST guidelines, was performed to select the most active EOs by identifying the Minimal Inhibitory Concentration 90 (MIC90) and Minimal Fungicidal Concentration 90 (MFC90). Both Cinnamomum zeylanicum (CZ) from bark and Coriandrum sativum (CS) EOs were first chemically characterized by using gas-chromatography/mass-spectrometry (GC/MS) and then fractionated with petroleum ether/ethyl acetate and petroleum ether/methanol with different ratios, respectively, to obtain 3 fractions/EO. The chemical quality and the antimicrobial activity of each fraction were evaluated using the aforementioned GC-MS and MBD tests. Once identified the active fraction of each EO, MBD tests were repeated by using the chemical compounds (linalool, cinnamaldheyde, eugenol and camphor isolated from vegetables) of each active fraction. Finally, the synergy between fluconazole and the CZ-OE was evaluated using the checkerboard test. The EOs of CZ and CS showed the lowest values of MIC90 (0.25 % v/v and 0.015% v/v respectively) and MFC90 (0.5% v/v and 0.06% v/v respectively) (fig.1). CZ-EO was mainly composed of cinnamaldheyde (66.0%), while CS-EO of linalool (31.2%) and 2-decenal (18.8%). For both EOs, the second fraction was the most active, and that of CZ-EO was composed of 4 compounds (linalool, cinnamaldheyde, eugenol and cynnamil acetate), while that of CS-EO of only two compounds (linalool and camphor). Cinnamaldehyde and linalool were the active compounds of CZ-EO and CS-EO respectively; they show the same MIC90 and MFC90 values as their corresponding EOs. Fluconazole at a concentration of 8 ug/ml showed synergy with CZOE (concentration of 0.03% v/v).