Chemical composition and antifungal activity of the essential oil of Thymbra capitata

The composition and the antifungal activity of the essential oil of Thymbra capitata on Candida, Aspergillus and dermatophyte strains were studied. Twenty-two samples of the essential oils from the aerial parts of the plant were obtained by hydrodistillation and analysed by GC and GC-MS. All samples are of the carvacrol type, with a high content of carvacrol (60.0 - 65.8 %) and its biogenetic precursors, gamma-terpinene (8.2 - 9.5 %) and p-cymene (6.0 - 7.5 %). The minimal inhibitory concentration (MIC) and the minimal lethal concentration (MLC) were used to evaluate the antifungal activity against Candida (7 clinical isolates and 3 ATCC type strains), Aspergillus (5 clinical isolates, 2 CECT and 2 ATCC type strains) and 5 dermatophyte clinical strains. To clarify its mechanism of action on Candida strains, the inhibition of germ tube and a flow cytometry assay with propidium iodide (PI) were used. The oil exhibited antifungal activity for all the tested strains, particularly for dermatophytes, with MIC values ranging from 0.08 to 0.32 microL/mL. Regarding Candida, concentrations lower than the MIC values prevented germ tube formation. After a short incubation time the cells incorporated quickly PI, meaning that the fungicidal effect is mainly due to direct lesion of the membrane.