Background: Dental caries is considered to be a preventable disease, and various antimicrobial
agents have been developed for the prevention of dental diseases; however, many bacteria
show resistance to existing agents. In this study, 14 medicinal herbs were evaluated for
antimicrobial activity against five common oral bacteria as a screen for potential candidates
for the development of natural antibiotics.
Methods: Aqueous extracts of medicinal herbs were tested for activity against Enterococcus
faecalis, Actinomyces viscosus, Streptococcus salivarius, Streptococcus mutans, and Streptococcus
sanguis grown in brain heart infusion (BHI) broth. A broth microdilution assay was used to
determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration
(MBC). A disk diffusion assay was performed by inoculating bacterial cultures on BHI
agar plates with paper disks soaked in each of the medicinal herb extracts. Inhibition of the
synthesis of water-insoluble glucans by S. mutans was also investigated.
Results: The aqueous extracts of many of the 14 medicinal herbs demonstrated antimicrobial
activity against the five types of pathogenic oral bacteria. The extracts of Sappan Lignum,
Coptidis Rhizoma, and Psoraleae Semen effectively inhibited the growth of oral bacteria
and showed distinct bactericidal activity. The extracts of Notoginseng Radix, Perillae Herba,
and Psoraleae Semen decreased the synthesis of water-insoluble glucans by the S. mutans
enzyme glucosyltransferase (GTase). The present study is the first to confirm the antimicrobial
activity of the extract of Sappan Lignum against all five species of oral bacteria
strains.
Conclusion: These results suggest that certain herbal medicines with proven antimicrobial
effects, such as Sappan Lignum and Psoraleae Semen, may be useful for the treatment of
dental diseases.