Phytochemical analysis and antibacterial evaluation of the leaf stem bark and root of the African locust bean (Parkia biglobosa)

Abstract

Antibacterial evaluation of the methanolic extract and aqueous fractions of the Leaf, Stem Bark and root of the African locust bean tree, Parkia biglobosa was carried out using the agar- well diffusion method. The extracts and their fractions were tested against two gram positive organisms – Staphylococcus aureus ATCC 25923 and Bacillus subtilis NCTC 8326B76 and two gram negative organisms–Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC-27853. Results obtained confirmed a broad spectrum of activity as all the organisms used were inhibited by the extracts and their aqueous fractions at concentrations between 2.5 – 20 mg. Zones of clearing observed against S.aureus were more pronounced, distinct and wider than those against other organisms tested. It was closely followed by P. aeruginosa. Results of the Minimum Inhibitory Concentrations (MIC) test using the aqueous fractions showed that the MIC ranged from 1.562 - 25mg/ml. This confirms the high activity of the aqueous fraction of the methanolic extract of the stem bark (WS) against S.aureus ATCC 25923 and P. aeruginosa ATCC 27853. The WS showed higher activity than the aqueous fraction of the methanolic extract of the leaf (WL) and the aqueous fraction of the methanolic extract of the root (WR). When the extracts were screened for secondary metabolites, tannins, flavonoids and saponins were detected among others. This was further confirmed by the aqueous fractions. These secondary metabolites are most likely responsible for the observed activity of the plant parts. Results obtained in this work justify the medicinal uses to whichP. biglobosa parts have been employed traditionally in recipes for infection. Key words: Antibacterial evaluation, parkia biglobosa, aqueous fraction, minimum inhibitory concentration, secondary metabolite.