Comparative evaluation of in vitro antifungal activity of major essential oil terpenes against non-dermatophyte fungal strains causing onychomycosis

Onychomycosis caused by non-dermatophyte filamentous fungi has increased in frequency. Among the most relevant etiological agents are Fusarium spp. , Neoscytalidium dimidiatum, Aspergillus section Versicolores, Scopulariopsis spp. and Paecilomyces spp. Their treatment represents a clinical challenge because these fungi are resistant to conventional antifungals. In this context, the main components of essential oils represent a novel alternative due to their antifungal activity. Thus, the aim of this study was to evaluate the in vitro inhibitory activity of major components of essential oil terpenes on the growth of non-dermatophyte filamentous fungi, isolated in Costa Rica, that cause onychomycosis. Thus, an experimental study was carried out using 73 clinical isolates preserved in the Fungal Collection of the School of Microbiology of the Universidad de Costa Rica; obtained between 2007 and 2022. Isolates of N. dimidiatum (n=20), A. s ection Versicolores (n=18), F. solani (n=15), Scopulariopsis brevecaulis (n=10), and Paecilomyces spp. (n=10) were included. The inhibitory activity of eucalyptol, limonene, linalool, pinene, and terpineol was evaluated by the broth microdilution method according to CLSI M38-A2. Minimum inhibitory concentrations (MICs) were determined, and statistical analysis was performed using Kruskal-Wallis test with a Dunn’s Post Hoc test. Statistically significant differences were observed between the compounds evaluated for all the genera studied (p < 0.05). Terpineol and linalool showed the highest inhibitory activity against most isolates and pinene the least. Therefore, the results show the in vitro antifungal potential of various terpene components of essential oils against clinically relevant non-dermatophyte filamentous fungi which could represent promising therapeutic alternatives in the face of growing antifungal resistance.