Journal of Dental Research, Vol 75, 816-822, Copyright © 1996 by International & American Associations for Dental Research Online Journals
The inhibiting effect of aqueous Azadirachta indica (Neem) extract upon bacterial properties influencing in vitro plaque formation
L. E. Wolinsky, S. Mania, S. Nachnani and S. Ling
Section of Oral Biology, University of California, School of Dentistry, Los Angeles 90095-1668, USA.
The purpose of this investigation was to examine the inhibitory effects of
aqueous extracts derived from the bark-containing sticks (Neem stick) of
Azadirachta indica upon bacterial aggregation, growth, adhesion to
hydroxyapatite, and production of insoluble glucan, which may affect in
vitro plaque formation. Neem stick extracts were screened for minimal
bacterial growth inhibition (MIC) against a panel of streptococci by means
of a broth dilution assay. Initial bacterial attachment was quantified by
the measurement of the adhesion of 3H-labeled Streptococcus sanguis to
saliva-conditioned synthetic hydroxyapatite. The effect of the Neem stick
extract upon insoluble glucan synthesis was measured by the uptake of
radiolabeled glucose from 14C-sucrose. Aggregating activity of the Neem
stick extracts upon a panel of streptococci was also examined. No
inhibition of bacterial growth was observed among the streptococcal strains
tested in the presence of < or = 320 micrograms/mL of the Neem stick
extract. The pre-treatment of S. sanguis with the Neem stick extract or the
gallotannin-enriched extract from Melaphis chinensis at 250 micrograms/mL
resulted in a significant inhibition of the bacterial adhesion to
saliva-conditioned hydroxyapatite. Pre-treatment of saliva-conditioned
hydroxyapatite with the Neem stick or gallotannin-rich extract prior to
exposure to bacteria yielded significant reductions in bacterial adhesion.
The Neem stick extract and the gallotannin-enriched extract from Melaphis
chinensis inhibited insoluble glucan synthesis. Incubation of oral
streptococci with the Neem stick extract resulted in a microscopically
observable bacteria aggregation. These data suggest that Neem stick extract
can reduce the ability of some streptococci to colonize tooth surfaces.
