Inhibition of Candida albicans yeast-hyphal transition and biofilm formation by Solidago virgaurea water extracts

Xerostomia is a decrease of saliva secretion, which can unbalance the oral microflora, mainly to the benefit of Candida albicans. The aim of the present study was to find a plant extract that could create an unfavourable environment for Candida, and would, therefore, be appropriate for use in a dry-mouth daily-care mouthwash. Water extract from the herbaceous plant Solidago virgaurea (Goldenrod) was selected due to its saponin content (plant detergents). Saponin concentrations reached 0.7 and 0.95 mg ml(-1) in S. virgaurea subsp. virgaurea and S. virgaurea subsp. alpestris extracts, respectively. C. albicans was grown in liquid medium and cells were counted by microscopic examination after 0, 4 and 24 h of incubation. Solidago extracts did not inhibit the growth of C. albicans (four strains), Escherichia Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus mutans, Streptococcus salivarius or Enterococcus faecalis. When inocula were incubated with Solidago extract for 4 and 24 h, we observed a decrease in Candida yeasth-yphal transition. Candida biofilms were then prepared in microtitre plates and treated with plant extracts at 0 h, to estimate biofilm formation, or at 18 h to estimate the effect of the saponin on pre-formed biofilms. Biofilm formation and pre-formed biofilms were both strongly inhibited. In conclusion, the S. virgaurea extract was efficient against two key virulence factors of C. albicans: the yeast-hyphal transition phase and biofilm formation.