EVALUATION OF THE ANTI-CARIES EFFECT OF LESPEDEZA CUNEATA EXTRACT AGAINST STREPTOCOCCUS MUTANS

The purpose of this study was to identify the antimicrobial activity of Lespedeza cuneata extract, a natural medicine, against a main causative bacterium of dental caries, Streptococcus mutans (S. mutans). Lespedeza cuneata purchased from Hwalim Natural Drug Co., Ltd. (Busan, South Korea) was immersed in 70% ethanol for 12 h, and concentrated Lespedeza cuneata extract was applied to S. mutans diluted to 6×105 CFU/mL at the concentrations of 0, 1.25, 2.5, 5, 10, 20, and 40 mg/ml. Then the colony-forming units (CFUs) were checked at 6 and 24 h to evaluate the antimicrobial activity of the extract. The CFUs and survival rate of S. mutans according to the concentration showed a higher mortality rate as the concentration of Lespedeza cuneata extract increased. In the time-dependent changes, the minimal inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) were 1.25 and 40 mg/mL or more, respectively, at 6 h, but they were 1.25 and 5 mg/mL, respectively, at 24 h. Therefore, Lespedeza cuneata extract is considered an excellent natural antibiotic for the prevention and treatment of dental caries, a typical oral disease, because it has excellent dental caries development suppression and bacteria extermination effects.