Antibacterial activity of extracts of Vitex doniana (black plum) stem bark

Abstract

Bacteria are a leading cause of diarrhoea in humans and the use of orthodox drugs in its treatment has been found to possess certain side effects as well as economic burden. This study aimed at evaluating the antibacterial activity of aqueous, methanol, ethylacetate and n-hexane extracts of Vitex doniana (black plum) stem bark on some diarrhoeal causing organisms. Fresh samples of Vitex doniana stem bark were collected from Kontagora Local Government Area of Niger State, Nigeria. Preparation, extraction, secondary metabolite screening and antibacterial activities of the different extracts of Vitex doniana stem bark were carried out following standard procedures. The results revealed that all the extracts contained different concentrations of flavonoids, alkaloids, tannins and phenols. Aqueous extract contained a significantly (p < 0.05) lower concentration of flavonoids (20.40 ± 0.04 mg/g) when compared to other extracts. However, there was a significantly (p < 0.05) higher concentration of alkaloids in the aqueous extract (40.67mg/g) when compared to alkaloids concentration in the methanol (30.00 mg/g) extract. A significantly (p < 0.05) higher concentration of tannins was recorded in the methanol extract (0.99 mg/g) when compared to tannins concentration in ethylacetate (0.21 mg/g) extract. A significantly (p < 0.05) higher concentration of phenol was recorded in the aqueous extract (352.70 mg/g) as compared to the n-hexane (16.27 mg/g) extract. The result of the zone of inhibition for different extracts revealed that, at higher concentrations of 100% and 75%, the growth of Escherichia coli, Pseudomonas spp, Staphylococcus aureus and Salmonella spp were significantly (p < 0.05) inhibited, suggesting that the inhibitory activities of the extracts are dose-dependent. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the different extracts showed varying results across different extracts. In conclusion, the study demonstrated that both the aqueous and n-hexane extracts of Vitex doniana stem bark possess bacteriostatic effects whereas methanol and ethylacetate extracts exhibited bacteriocidal effects especially at higher concentrations.