Candida auris is an emergent yeast pathogen responsible for many invasive fungal infections due to its multidrug-resistant character and its huge transmission ability. Essential oils (EOs) obtained from several aromatic plants have been regarded as an alternative treatment upon to fungal infections. For example, Thymus spp. are known by their antifungal effect due to the presence of some volatile compounds in their EOs, such as carvacrol, thymol, linalool and γ-terpinene. So, the main goal of this work was to compare the effect of several EOs from Thymus spp. on C. auris biofilm.

The antifungal activity of Thymus vulgaris, Thymus zygis, Thymus satureioides and Thymus mastichina against planktonic cells of C. auris NCPF 8971 was assessed by agar disk diffusion method. The effect of these EOs with direct or vapour phases on preformed biofilms was evaluated by colony-forming units’ enumeration. Importantly it was noticed a completely different range of action between the EOs from the same genus. While T. vulgaris showed the biggest antifungal effect with a halo of 59.75 ± 15.75 mm, T. mastichina for the other side, presented a halo of 13.13 ± 1.36 mm, showing a very low activity. In addition, the direct application of T. vulgaris and T. zygis EOs demonstrated higher antifungal activity against C. auris biofilms than vapour phase application. However, T. vulgaris also showed significant action in the vapour phase mode. The chemical composition of Thymus EOs was analysed by GC and GC-MS, and was demonstrated that they have different chemical profiles, namely in the amount of phenolic compounds, which justify the different antifungal actions.

In conclusion, T. vulgaris and T. zygis oils, can be pointed out as a great contribution to the treatment of C. auris infections, being promising alternatives to conventional therapy. However, the efficiency of the EOs differs substantially between the four species of Thymus. Therefore, the selection of natural therapies should always have in account EOs composition.