Thymol-Induced Alterations in Candida albicans Imaged by Atomic Force Microscopy

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 and this activity has been investigated by means of atomic force microscopy (AFM). 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 h, the envelopes of 100 cells in each of five randomly chosen fields were analysed by means of 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, and collapsed cells and ghosts. Thymol is an amphipathic 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. 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.