Antifungal activity of thymol against clinical isolates of fluconazole-sensitive and -resistant Candida albicans

Thymol (THY) was found to have in vitro antifungal activity against 24 fluconazole (FLC)-resistant and 12 FLC-susceptible clinical isolates of Candida albicans , standard strain ATCC 10231 and one experimentally induced FLC-resistant C. albicans S-1. In addition, synergism was observed for clinical isolates of C. albicans with combinations of THY–FLC and THY–amphotericin B (AMB) evaluated by the chequerboard microdilution method. The interaction intensity was determined by spectrophotometry for the chequerboard assay, and the nature of the interactions was assessed using two non-parametric approaches [fractional inhibitory concentration index (FICI) and ΔE models]. The interaction between THY–FLC or THY–AMB in FLC-resistant and -susceptible strains of C. albicans showed a high percentage of synergism by the FICI method and the Δ E method. The ΔE model gave results consistent with FICI, and no antagonistic action was observed in the strains tested.