Inhibitory effect of some herbal extracts on adherence of Streptococcus mutans

The objective of this study was to investigate the inhibitory effect of the crude extracts from some herbs on adherence of Streptococcus mutans (S. mutans) ATCC 25175 and TPF-1 in vitro. Six herbs, Andrographis paniculata; Cassia alata; Chinese black tea (Camellia sinensis); guava (Psidium guajava); Harrisonia perforata and Streblus asper, were extracted with 50 or 95% ethanol and dried. Herbal extracted solution at 0.5% concentration (w/v) was initially tested for bacterial adherence on glass surfaces. In order to identify type and effective concentration of the extracts, the extracts that showed the inhibition on glass surfaces were then tested on saliva-coated hydroxyapatite by the use of radiolabeled bacteria. To study the mechanism of action, the effect of the extracts at such concentration on glucosyltransferase and glucan-binding lectin activities were examined. It was found that all extracts, but Streblus asper, showed significant inhibitory effect on bacterial adherence to glass surfaces. For the saliva-coated hydroxyapatite adherence assay, Andrographis paniculata, Cassia alata, Chinese black tea and Harrisonia perforata could inhibit adherence of S. mutans ATCC 25175. Chinese black tea was the strongest inhibitor followed by Andrographis paniculata, Cassia alata and Harrisonia perforata, respectively. For S. mutans TPF-1, adherence inhibition was observed from Andrographis paniculata and Cassia alata at similar levels. The lowest concentrations of the extracts that inhibited the adherence at least 50% were 0.5% of Andrographis paniculata, 0.5% of Cassia alata, 0.3% of Chinese black tea and 0.5% of Harrisonia perforata for S. mutans ATCC 25175. For S. mutans TPF-1, the effective concentrations were 0.5% of Andrographis paniculata and 0.4% of Cassia alata. All extracts at such concentrations decreased the activity of glucosyltransferase from both strains. Only Andrographis paniculata and Cassia alata eliminated or decreased the activity of glucan-binding lectin from both strains. These findings suggested that Andrographis paniculata, Cassia alata, Chinese black tea and Harrisonia perforata could inhibit adherence of S. mutans ATCC 25175, while Andrographis paniculata and Cassia alata had an effect on S. mutans TPF-1 in vitro at the concentrations employed in this study.