Antimicrobial Activity and Constituents of the Root Bark of Loncocarpus Eriocalyx

Abstract

Conventional anti- infectives are expensive and in most cases unavailable to the target population. This has led to greater reliance on alternative medicine such as decoctions from plants. Lonchocarpus eriocalyx root bark, for example, has been used traditionally by many African communities for treatment of various ailments including microbial infections. This plant has previously been investigated for antibacterial and antiprotozooal activities. Lupeol, a triterpenoid, has been isolated from L. eriocalyx root bark in connection to the plant’s antiplasmodial activity. This study sought to investigate the antifungal and antibacterial activity of the root back extracts of L. eriocalyx and to isolate more compounds responsible for activity, with a view to giving scientific credence to the forklore use of the plant. Lonchocarpus eriocalyx root bark was collected from Makanyanga sub-location, Igamba- Ng’ombe division, Tharaka-Nithi County. The collected root bark was chopped into small pieces and dried at room temperature for 2 weeks. The dried plant material was ground to powder and stored at room temperature before use. Sequential extraction was carried out using methanol, chloroform and water. All the four extracts were screened for antibacterial activity against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, and for antifungal activity against Saccharomyces cerevisiae using agar diffusion method. Gentamicin and nystatin were used as positive controls for antibacterial and antifungal tests respectively. Four compounds were isolated by column chromatography in a gradient mode using silica gel 60-120 mesh, monitored by TLC. They were identified as β- sitosterol/stigmasterol mixture, lupenone, and lupeol using UV, IR, MS and NMR analysis. This is the first time that β- sitosterol, stigmasterol and lupenone have been isolated from L. eriocalyx. The four compounds exhibited antibacterial activity against S. aureus, E. coli and P. aeruginosa, and antifungal activity against S. cerevisiae. The greatest activity was against S. cerevisiae, with zones on inhibition of 1.1 cm, 1.2 cm and 1.3 cm for β-sitosterol/stigmasterol mixture, lupenone and lupeol respectively. This gives scientific credence to the forklore use of the root bark of Lonchocarpus eriocalyx in the treatment of bacterial and fungal infections.