THE INHIBITING EFFECT OF AQUEOUS AZADIRACHTA-INDICA (NEEM) EXTRACT UPON BACTERIAL PROPERTIES INFLUENCING IN-VITRO PLAQUE-FORMATION

The purpose of this investigation was to examine the inhibitory effect s of aqueous extracts derived from the bark-containing sticks (Neem st ick) of Azadirachta indica upon bacterial aggregation, growth adhesion to hydroxyapatite, and production of insoluble glucan, which may affe ct in vitro plaque formation. Neem stick extracts were screened for mi nimal bacterial growth inhibition (MIG) against a panel of streptococc i by means of a broth dilution assay. Initial bacterial attachment was quantified by the measurement of the adhesion of H-3-labeled Streptoc occus sanguis to saliva-conditioned synthetic hydroxyapatite. The effe ct of the Neem stick extract upon insoluble glucan synthesis was measu red by the uptake of radiolabeled glucose from C-14-sucrose. Aggregati ng activity of the Neem stick extracts upon a panel of streptococci wa s also examined. No inhibition of bacterial growth was observed among the streptococcal strains tested in the presence of less than or equal to 320 mu g/mL of the Neem stick extract. The pre-treatment of S. san guis with the Neem stick extract or the gallotannin-enriched extract f rom Melaphis chinensis at 250 mu g/mL resulted in a significant inhibi tion of the bacterial adhesion to saliva-conditioned hydroxyapatite. P re-treatment of saliva-conditioned hydroxyapatite with the Neem stick or gallotannin-rich extract prior to exposure to bacteria yielded sign ificant reductions in bacterial adhesion. The Neem stick extract and t he gallotannin-enriched extract from Melaphis chinensis inhibited inso luble glucan synthesis. Incubation of oral streptococci with the Neem stick extract resulted in a microscopically observable bacterial aggre gation. These data suggest that Neem stick extract can reduce the abil ity of some streptococci to colonize tooth surfaces.