Impact of the quorum-sensing molecule farnesol on biofilm formation by Candida albicans and Streptococcus mutans

Objectives: The aim of this study was to evaluate the effect of different concentrations of farnesol on single and mixed biofilm formation of Candida albicans ATCC 10231 and Streptococcus mutans ATCC 25175.
Methods: The inoculum of each strain in single and mixed cultures was added to wells of 96-well plates, and plates were then incubated for 2 hours to allow cell adhesion. Next, farnesol (diluted in artificial saliva) at 3.12 and 12.5 mM was pipetted within the wells containing the adhered cells and the plates were incubated for 48 hours. The effect of farnesol was assessed through total biomass quantification, evaluation of metabolic activity and counting of colony forming units (CFUs). The composition of extracellular matrix (proteins and carbohydrates) and the structure of biofilms (scanning electron microscopy (SEM)) were also evaluated. Chlorhexidine gluconate (CHG; 0.37mM) was used as positive control. Data were analyzed by ANOVA followed by Holm-Sidak test (α = 0.05).
Results: It was observed that the farnesol decreased the formation of single and mixed biofilms, with significant reductions of 60 % to 90 % and 80 % to 95%, respectively for total biomass and metabolic activity. With regard to cell viability, the treatments with farnesol promoted significant decreases in the number of CFUs ranging from 1.3-3.8log₁₀ and 1.37-4.17log₁₀, respectively for single and mixed biofilms. In general, only the content of proteins of the extracellular matrix was reduced in the presence of farnesol. By SEM, it was noted a significant disruption of biofilms exposed to farnesol.
Conclusions: In conclusion, these findings highlight the role of farnesol as an alternative agent which aims to reduce the formation of pathogenic biofilms.