Activity of quercetin and kaemferol against Streptococcus mutans biofilm

Nidus Vespae (NV) is the honeycomb of Polistes Olivaceous, P. Japonicus Saussure, and Parapolybiavaria Fabricius. Previously, we have shown the extract and chemical fractions from NV demonstrated remarkable capacities of inhibiting the acid production of oral bacteria at sub-minimum inhibitory concentration (MIC) concentrations. In searching the most potent anti-caries compounds in NV, we further separated the NV Chl/MeOH fraction and obtained two purified compounds: quercetin and kaemferol. The objective of this study was to assess the effectiveness of quercetin and kaemferol against S. mutans biofilm formation. The MIC, minimum biofilm inhibition concentration (MBIC50) and minimum biofilm reduction concentration (MBRC50) against Streptococcus mutans were examined for NV-derived of quercetin and kaemferol. The effectiveness of inhibiting S. mutans biofilm formation was further examined using in vitro biofilm model. Both quercetin and kaemferol compounds demonstrated anti-biofilm activities when compared to the negative control. They are capable of reducing biofilm dry-weight, total protein, viable cells measured by colony forming unit (CFU), insoluble and soluble glucans formation. The in situ culture pH was less acidic when the biofilms were treated by quercetin and kaemferol. The quercetin and kaemferol demonstrated comparable capability of S. mutans killing in biofilms, compared to chlorhexidine. The results of this study showed inhibitory activity of quercetin and kaemferol against S. mutans biofilms, suggesting that quercetin and kaemferol might be considered as alternative anti-caries agents in searching novel anti-caries therapeutics.