TheInhibiting Effect ofAqueous Azadirachta indica (Neem)Extract UponBacterial Properties Influencing invitro Plaque Formation

Thepurpose ofthis investigation wastoexamine theinhibitory effects ofaqueous extracts derived fromthe bark-containing sticks (Neemstick) ofAzadirachta indica uponbacterial aggregation, growth,adhesionto hydroxyapatite, andproduction ofinsoluble glucan, which mayaffect invitro plaque formation. Neemstick extracts werescreened forminimal bacterial growthinhibition (MIC) against apanel ofstreptococci bymeansofabroth dilution assay. Initial bacterial attachment wasquantified bythemeasurementoftheadhesion of3H-labeled Streptococcus sanguis tosaliva-conditioned synthetic hydroxyapatite. Theeffect oftheNeemstick extract upon insoluble glucan synthesis wasmeasured bytheuptake of radiolabeled glucose from14C-sucrose. Aggregating activity oftheNeem stick extracts uponapanelof streptococci wasalso examined. Noinhibition ofbacterial growthwasobserved amongthestreptococcal strains tested inthepresence of<320pg/mLoftheNeemstick extract. Thepre-treatment ofS.sanguis withtheNeemstick extract orthegallotannin-enri ched extract fromMelaphis chinensis at250Vg/mL resulted inasignificant inhibition of the bacterial adhesionto saliva-conditioned hydroxyapatite. Pre-treatment ofsaliva-conditioned hydroxyapatite withtheNeemstick orgallotannin-rich extract prior toexposure tobacteria yielded significant reductions inbacterial adhesion. TheNeemstick extract andthegallotannin-enriched extract fromMelaphis chinensis inhibited insoluble glucan synthesis. Incubation oforal streptococci withtheNeemstick extract resulted ina microscopically observable bacterial aggregation. These datasuggest thatNeemstick extract canreduce theability ofsomestreptococci tocolonize tooth surfaces.