Antimicrobial activity of Polygonum tinctorium Lour: extract against oral pathogenic bacteria

Extract of the leaves of the indigo plant (Polygonum tinctorium Lour.) was examined for antimicrobial activity against oral pathogenic bacteria. The indigo plant extract at concentrations of 1.74–3.48 mg/ml inhibited the growth of oral cariogenic and periodontopathic bacteria. Tryptanthrin, one of the components of indigo plant extract, showed the strongest antimicrobial effect at doses ranging from 3.13–25 μg/ml, indicating that this compound is one of the active ingredients. Furthermore, treatment of periodontopathic bacteria Porphyromonas gingivalis and Prevotella intermedia with the indigo plant extract for 3–8 h resulted in death of the bacteria in a dose-dependent manner, whereas Streptococcus mutans was not affected by the extract. Thus, for its antimicrobial and bactericidal effects on oral pathogens, indigo plant extract would provide useful material for preventing and treating periodontal diseases and dental caries.