Mechanism of anti-biofilm thymol activity in oral Candida albicans strains – phenotypic and genotypic level

Background Recently, the incidences of superficial infections caused by Candida albicans has been increasing. In turn, the limited number of available antimycotics has led to the search for new antifungals.Objective The purpose of this study was to evaluate the antifungal activity, especially the anti-biofilm effect, of thymol (THY) towards oral C. albicans isolates from hemato-oncological patients.Design The studies included: (1) the evaluation of the minimum inhibitory concentration and minimum fungicidal concentration of THY against C. albicans as found using the broth microdilution method; (2) its effect on biofilm inhibition and reduction, as assessed by way of a similar technique with crystal violet staining; (3) the interactions of THY with yeast cellular structures, as brought to light via sorbitol and ergosterol tests; (4) its influence on the filamentation as revealed through the use of an optical microscope and (5) the impact on the expression of selected biofilm genes, as determined by quantitative real-time PCR.Results THY showed good or moderate anticandidal activity with fungicidal effect. The concentrations required to inhibit the formation or eradication of mature biofilm were higher. These results suggest that THY may likely have an effect on the cell membrane and filamentation at C. albicans. Exploratory RT-qPCR analysis indicated a directional increase in BCR1 expression under biofilm-forming conditions (unadjusted p = 0.010), but this result did not remain statistically significant after Benjamini‒Hochberg correction (q = 0.080). ALS3, HWP1 and NRG1 showed non-significant directional trends, and no gene revealed a statistically significant change under planktonic conditions.Conclusion THY demonstrated a multidirectional mechanism of anticandidal action, which may suggest its promising effect in the prevention and treatment of oral infections.