Thymol-induced morphological changes in candida albicans : an atomic force microscopy study

The aim of this study was to investigate whether thymol, a constituent of thyme essential oil that has been credited with interesting antimicrobial and antifungal effects, acts by interfering with the envelope of Candida albicans. Candida culture samples incubated with 1, 1/2 and 1/4 MIC of thymol or vehicle were taken at time 0, and after 1,2 and 4 hours, and the envelopes of 100 cells in each of five randomly chosen fields were analysed by means of atomic force microscopy (AFM). Our AFM findings show that thymol affects the envelope of C.albicans cells. The cells showed major morphostructural deformities with envelope damage becoming greater at increasing thymol concentrations and longer times of incubation, including the number of flattened cells with surface folds, cells with holes, collapsed cells and ghosts. Thymol is an amphipatic monoterpene, which suggests that it affects cell membrane structure by generating asymmetries and membrane tensions. This is confirmed by the fact that terpenes alter cell permeability by entering between the fatty acyl chains making up the membrane lipid bilayers, disrupting lipid packing, and changing membrane fluidity. Terpenes also inhibit Candida respiration, thus suggesting adverse mitochondrial effects. All of these phenomena lead to major surface alterations and deformities that also reduce the ability of fungi to adhere to mucosal cells, and decrease their virulence and infectiousness.