Antimicrobial Activity of Thai Herbs Against Cariogenic Agents In vitro

Objectives: This study was conducted to investigate the antimicrobial effect of Thai herbs including Caesalpinia sappan (Fang), Cymbopogon citratus (Lemongrass), Clinacanthus nutans (Payayor) and Houttuynia cordata (Plukow) against planktonic Streptococcus mutans and lactobacilli as well as to test antiplaque effects against S. mutans biofilm. Methods: These four herbal extracts were dissolved and screened for their antimicrobial activity against those two cariogenic agents using agar disk diffusion method. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined by a broth micro-dilution method. Antimicrobial exhibiting extracts were further tested for their antiplaque effects. The biofilm-mass was quantitated by crystal violet staining method. Results: The extracts of Fang and Lemongrass exhibited potent antimicrobial activity against the tested microorganisms. The MICs and MBCs of Fang against S. mutans and lactobaccilli were 0.39 and 1.562 mg/ml, respectively. The MICs of Lemongrass were 1.562 and 0.781 mg/ml whereas their MBCs were 6.25 and 3.125 mg/ml. Payayor and Plukow extracts did not express such antimicrobial activity. Within 24 hr of exposure to 5% (w/v) of Fang, approximately 12.45% less biofilm was formed. Concomitantly, 31.46% reduction of established biofilm was observed after treated with the herb for 24 hr. Biofilm dislodgment was in exposure time dependent manner. The reduction ranged from 23.13%, 16.26%, and 14.43% when exposed to the tested agent for 4, 2, and 1 hr, respectively. Conclusion: Caesalpinia sappan (Fang) and Cymbopogon citratus (lemongrass) exhibited antimicrobial activity against planktonic S. mutans and lactobacilli. However, only Fang expressed antiplque effects on S. mutans biofilm.