Antibacterial Activities of Three Medicinal Plants on Organisms Associated with Dental Plaque

Abstract

The antimicrobial properties of plants have shown promise for development of new drugs which might aid to overcome the increasing challenge of resistance and also the toxicity of the currently available antibiotics. Hence, the aim of the study was to investigate the antibacterial activities of Sida acuta, Anthocleista nobilis, and Zanthozylum leprieurii on clinical isolates of Streptococcus mutans and Streptococcus sanguis and two reference strains: Streptococcus mutans (ATCC 700610) and Streptococcus sanguis (ATCC 10556) which are known to cause dental caries and periodontal diseases. The plants were selected based on existing traditional medicine knowledge, usage and interaction with herbal healers. The antibacterial activity of aqueous and ethanol extract was determined by agar-well diffusion method. Subsequently, Minimum Inhibitory Concentration (MIC) was determined by using macro broth dilution method at a concentration ranging between 200mg/ml and 3.125 mg/ml. Minimum Bactericidal Concentration (MBC) was obtained by sub-culturing the test dilution which showed no visible turbidity. Standard antibiotic penicillin (1.5i.u) and gentamicin (10μg) were used for comparison. Both the aqueous and ethanolic extract of the selected medicinal plants showed inhibition zones which did not differ significantly (P>0.05) against each tested bacteria. Among the plant parts tried on the microorganisms, the leaves of Sida acuta proved to be more potent than the stem bark of Anthocleista nobilis, followed by the stem bark of Zanthozylum leprieurii. The ethanolic extract of Anthocleista nobilis was more efficient in its antibacterial activity as compared to its aqueous extract. The inhibitory activity of Anthocleista nobilis stem bark against Streptococcus mutans was comparatively more than that of gentamicin (10μg) but less than penicillin (1.5i.u). The aqueous and ethanolic extract of Zanthozylum leprieurii did not have inhibitory activity on Streptococcus sanguis strains. The ethanolic extract of Zanthozylum leprieurii showed better results as compared to the aqueous ones. The antibacterial activity of all the plant extracts were concentration dependent, increasing with increasing concentration (P<0.05). The results from the study support the ethnomedicinal use of the plants and suggest that the plants extracts have compounds with antibacterial properties that can be used, as phytotherapeutic agents in the developments of new drugs. Sida acuta and Anthocleista nobilis showed promising antibacterial activities and thus can be employed as an effective anti-plaque agent and can be used in the prevention of dental caries.