Inhibitory activity of thymol against the formation and viability of Candida albicans hyphae

As the capacity of Candida albicans to produce hyphae is considered an important virulence factor in the pathogenesis of candiasis, the aim of this study was to investigate whether thymol, the major component of thyme oil, can interfere with the filamentous forms of Candida albicans and their viability. The morphological transition from yeasts to filamentous forms was investigated by analysing the morphological index (MI), which classifies the differentiated forms and blastoconidia; viability was investigated by means of fluorescence microscopy using a new SYTO-9 and propidium iodide method previously used to stain only blastoconidia. Without thymol, there was an average of 94.00 +/- 3.06% hyphal forms. After 6 h of incubation with 1x MIC (125 microg ml(-1)), 1/2x MIC and 1/4x MIC of thymol, filamentation was, respectively, 14.33 +/- 8.25%, 28.33 +/- 7.17% and 45.67 +/- 8.09% in comparison with control (all statistically significant). In the absence of thymol, viable cells accounted for an average of 93.00 +/- 4.00% whereas, after 6 h of incubation with 1x MIC, 1/2x MIC and 1/4x MIC of thymol, the presence of 54.33 +/- 1.86%, 29.00 +/- 3.61% and 23.00 +/- 2.52% of yellow-orange coloured forms indicated damaged membranes and reduced viability. Our findings show that thymol interferes with the formation and viability of hyphae. This can be attributed to the characteristics of thymol disturbing Candida cell membranes and metabolism, probably by affecting fungal cell-wall synthesising enzymes.