Dental plaque is the community of microorganisms found on a tooth surface as a biofilm, embedded in a matrix of polymers of host and bacterial origin. Over 400 microbial
species can be found in the typical adolescent human mouth. The most virulent of these species is Streptococcus mutans, which has been found to be the initiator of most dental caries. As a result, dental caries can be considered one of the most widespread and common infectious disease.
The aim of this study was to isolate pathogens in dental caries and to evaluate the biofilm inhibition and antibacterial properties of methanol and aqueous extracts of 6 selected plants: Eclipta alba, Spilanthes acmella, Murraya koenigii, Hemigraphi scolorata, Piper nigrum and Psidium guajava over the inital colonizers of teeth, predominently Streptococcus mutans. Antibacterial activity of the plant extracts was performed by well diffusion method. Minimum inhibitory concentration (MIC) of the plant extracts was determined using broth micro-dilution assay. To determine effects of the extracts on the virulence factors of S. mutans, acid tolerance assays were performed at sub-MIC levels. Anti-adherence effects of the plant extracts were performed using Microplate biofilm assay.
Methanolic extracts of the six selected plants, showed antibacterial activity against S. mutans. Maximum zone of inhibition was observed with Methanolic extracts of Piper nigrum root at concentrations of 400 μg/ml . Aqueous extracts of Piper nigrum root, and Eclipta albashowed antibacterial activity (400μg/ml ).Minimum inhibitory concentration (MIC) of of the extracts tested showed an antibacterial rangeof 100—400 μg/ml. Methanolic extracts of Piper nigrum root at concentrations of (100-200μg/ml ) inhibited the acid tolerance in S.mutans, thereby confirming the effects on virulence factors of the organism. In biofilm inhibition studies methanol extract of Eclipta alba and aqueous extract of Piper nigrum showed significant activity at 100μg/ml concentrations. The data indicate inhibitory effects on bacterial viability suggesting the use of these plant extract formulations as potent anti plaque agents.