Nidus Vespae (honeycomb) is a kind of traditional Chinese medicine that has been demonstrated to inhibit the growth and acid-production of oral cariogenic bacteria. Subsequent studies showed that the chloroform/methanol (Chl/MeOH) chemical extraction of Nidus Vespae was the most effective inhibitor of growth and acidogenicity of Streptococcus mutans. In this study, we isolated the chemical compounds of the Nidus Vespae Chl/MeOH extraction, tested their antimicrobial activity against six cariogenic bacteria and further evaluated the acid inhibition properties, anti-F-ATPase activity and anti-LDH activity against S. mutans. The isolated flavonoids, quercetin and kaempferol, inhibited the growth of bacteria (S. mutans, Streptococcus sobrinus, Streptococcus sanguis, Actinomyces viscosus, Actinomyces naeslundii and Lactobacillus rhamnosus) with minimum inhibitory concentrations (MICs) ranging from 1 to 4 mg/ml and minimum bactericidal concentrations (MBCs) from 4 to 16 mg/ml. In addition, quercetin and kaempferol at sub-MIC levels significantly inhibited acidogenicity and acidurity of S. mutans cells. Treated with the test agents, the F-ATPase activity was reduced by 47.37% with 1mg/ml quercetin and by 49.66% with 0.5mg/ml kaempferol. The results showed that quercetin and kaempferol contained in Chl/MeOH extraction presented remarkably biological activity, suggesting that Nidus Vespae might be useful as a potential preventive and therapeutic agent in dental caries.
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