The impact of farnesol in combination with fluconazole on Candida albicans biofilm: regulation of ERG20, ERG9, and ERG11 genes.

Farnesol (FAR) has already demonstrated an inhibitory effect on Candida albicans biofilm. The aim of this work was to determine the effectiveness of externally added FAR in combination with fluconazole (FLC) on Candida albicans biofilm and on regulation of the ergosterol genes ERG20, ERG9, and ERG11. The effectiveness of compounds was determined by MTT assay and evaluated by the minimal inhibitory concentrations reducing a sessile biofilm to 50% activity (0.5 μg/mL and 200 μmol/L for FLC and FAR, respectively). These concentrations as well as 30 and 100 μmol/L FAR were selected for a study of the effectiveness of the FAR/FLC combination. The reduction in biofilm robustness mainly caused by the presence of 200 μmol/L FAR-alone or in combination with FLC-was accompanied by a significant inhibition of the yeast-to-hyphae transition that was observed by light microscopy and CLSM. Results from qRT-PCR indicated that while 30 μmol/L FAR only slightly regulated the expression of all 3 genes in the 48-h biofilm, the presence of 200 μmol/L FAR downregulated all the tested genes. However, the addition of 0.5 μg/mL of FLC to the samples with 200 μmol/L FAR restored the downregulation of the ERG20 and ERG11 genes to the control level. Moreover, the gene ERG9 was slightly upregulated. In summary, FAR acted via multiple effects on the C. albicans biofilm, but only a higher concentration of FAR proved to be effective.