Antimicrobial potential of extracts and fractions of the African walnut – Tetracarpidium conophorum

Abstract

Antibacterial and antifungal evaluation of the leaf, stem bark, kernel and root methanol extracts as well as the hexane, chloroform, ethyl acetate and methanol fractions of the leaf of Tetracarpidium conophorum, the African walnut, were investigated using the agar cup diffusion and agar broth dilution techniques. Extracts and fractions were tested against four clinical strains of 2 Gram positive, 2 Gram negative bacteria and two of fungi. They exhibited concentration-dependent antimicrobial properties. The extracts displayed higher activities to the Gram positive organisms. The edible nut was devoid of any antimicrobial property. The leaf extract was most active and it inhibited the growth of all the microorganisms used in the study. This led to the bioassay-guided fractionation of the leaf methanol extract and the ethyl acetate fraction of the leaf extract, displayed higher activities with the bacteria and fungi used in the assay, at the five test concentrations (100 mg – 10 mg/ml). Pseudomomas aeruginosa and Candida albicans were most sensitive to the extracts. Ampicillin and tioconazole were used as positive control, and methanol, used as negative control. The plant materials were also screened for secondary metabolites and this indicated the presence of alkaloids, saponins and tannins and absence of cardiac glycosides. The thin layer chromatographic analysis of the ethyl acetate fraction of the leaf crude extract confirmed the presence of alkaloids and tannis. These could be responsible for observed activity in the leaf of the plant; thus justifying its traditional uses especially in the treatment of dysentery.