Farnesol modulation of Rhodotorula mucilaginosa in biofilm and planktonic forms.

Biofilms are important to the virulence of human pathogenic fungi, and some molecules have been found to play key roles in the growth and regulation of fungal biofilms. Farnesol, one of these molecules, is well-described for some microorganisms but is still scarcely known for Rhodotorula spp. This study aimed to evaluate the influence of farnesol on the biofilm of R. mucilaginosa. Initially, screening with 0.2 mM to 2.1 mM of farnesol was evaluated against planktonic forms. A concentration of this compound was then chosen and evaluated for its effect on biofilm in formation and on preformed biofilm after 24, 48 and 72 hours. The impact of farnesol was evaluated by colony-forming units (CFU) counts, determination of metabolic activity and quantification of total biomass. In the presence of 0.9 mM, farnesol was able to decrease the CFU number, at 48 hours, when the biofilm was in formation, although it did not affect the preformed biofilms. Thus, our results show that farnesol exerts a modulating activity during biofilm formation for R. mucilaginosa, with this compound reducing the metabolic activity and total biomass of the biofilms.

Promising effect of propolis and a by-product on planktonic cells and biofilm formation by the main agents of human fungal infections.

Few antifungals available today are effective in treating biofilms. Thus, it is urgent to discover new compounds, such as natural products, that provide improvements to existing treatments or the development of new antifungal therapies. This study aimed to perform a comparative analysis between the green propolis extract (PE) and its by-product, a waste of propolis extract (WPE) through a screening with Candida sp., Fusarium sp. and Trichophyton sp. The antifungal property of PE and WPE was assessed by the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) determination in planktonic cells. The influence of both extracts on the inhibition of biofilm formation in these fungi was also tested. The WPE MIC and MFC values (68.75 to 275.0 µg/mL) were three to twelve times lower than the values obtained for PE (214.06 to 1712.5 µg/mL). PE was more efficient than WPE in inhibiting the biofilm initial phase, especially in C. albicans. Meanwhile, WPE had dose-dependent behavior for the three fungi, being more effective on filamentous ones. Both PE and WPE showed excellent antifungal activity on planktonic cells and demonstrated great efficacy for inhibiting biofilm formation in the three fungi evaluated.