Antimicrobial and phytochemical properties of some medicinal plants used by the Luo community of Kenya

Abstract

The Luo community of Kenya have traditionally used plants for treatment of various disease conditions, some of which we now know to be caused by microbial infections. Some of these plants, namely Lannea stuhlmanii, Carissa edulis, Combretum fragrans, Conyza sumatrensis, Ormocarpum trichocarpum, Sida cuneifolia, Plumbago zeylanica, and Rhoicissus revoilii, were studied. Their ethanol extracts were screened for their antimicrobial activity against Candida albicans, Escherichia coli, Staphylococcus aureus and Bacillus pumulus. Ethanolic root extract of C sumatrensis had good antibacterial activity against E. coli, while extracts of C fragrans root bark, C edulis root, S. cuneifolia whole plant, R. revoilii tubers and leaf extract of C sumatrensis in the same solvent had good activity against it. Activity against B. pumulus was observed in all extracts except those of L. stuhlmanii bark and R. revoilii tubers. Good activity against S. aureus was observed for C fragrans, S. cuneifolia and L. stuhlmanii. R. revoihi, L. stuhlmanii, C fragrans and C edulis exhibited good antifungal activity against Candida albicans. Combretum fragrans bark extract had the highest overall antimicrobial activity of all the different plant extracts examined and was subsequently chosen for further studies. All its ethanol, methanol, ethyl acetate and chloroform extracts were found to have significant antimicrobial activity. Combretum fragrans bark powder was found to contain saponins, cardiac glycosides, free anthraquinones (anthracene glycosides), tannins and flavonoids. However, it had no starch nor alkaloids. The chloroform extract of C fragrans was subjected to column chromatographic separation and sitosterol (with stigmasterol as a minor compound) was isolated and identified. Sitosterol was shown to have antifungal activity against C albicans and antibacterial activity against Escherichia coli. The results of this work would therefore appear to lend support to the traditional use of Lannea stuhlmanii, Combretum fragrans, Conyza sumatrensis (tineasis), Plumbago zeylanica, and Rhoicissus revoilii in disease conditions where microbial infections may be a factor. Use of growth enhancers like Carissa edulis in combination therapy may be justified on the basis of their immune boosting activity.