Antimicrobial Activities of Some Constituents Isolated from a Kenyan Medicinal Plant, Capparis fascicularis DC

Abstract

Capparis fascicularis DC. is an indigenous medicinal plant belonging to the family Capparaceae found in Nyandarua County, Nairobi, Kenya, and many parts of Africa. It is a shrub whose roots are used traditionally to treat colds. Aim. The aim of the present study is to carry out antimicrobial activities of solvent extracts of different parts of Capparis fascicularis, characterize the phytochemical constituents of the most active extract, and identify the most active compounds. Place and Duration of the Study. All the experiments were carried out in the departments of Chemistry and Microbiology, Kenyatta University, Nairobi, Kenya. Methodology. Petroleum ether, ethyl acetate, methanol, and water extracts from the leaves, stem bark, and root bark of C. fascicularis were screened against selected strains of both Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Salmonella typhimurium and Escherichia coli) bacteria using disc diffusion and tube dilution methods. Fractionation of the most active crude extract was carried out by column chromatography, and the fractions together with the most active crude extract were screened against the selected bacterial strains. The most active fraction was further fractionated, and the subfractions were screened against the bacterial strains to test for possible synergistic effects between the subfractions and their constituents. The most active fraction was then analysed by GC-MS and LC-ESI-MS methods to identify the major constituents. Results. The ethyl acetate extract of C. fascicularis root bark (CFR2) showed a significant in vitro antibacterial activity. From the seven fractions of CFR2 obtained, fraction 2 (F2) had the lowest MIC value and was thus most active. Moreover, F2 was found to be more active compared to the four subfractions obtained from it. This suggested that constituents of F2 worked in synergy. Fraction 2 contained phenols, terpenes, and flavonoids. Two compounds were identified by GC-MS as 2,4-di-tert-butylphenol and (E,E)-2,4-decadienal, while three compounds were identified by LC-ESI-MS as tanshinone II A, cryptotanshinone, and danshensu. Conclusion. The study revealed that CFR2 is the most active extract on bacteria, suggesting that most antimicrobial compounds are concentrated in the roots of C. fascicularis. A follow-up study is directed towards chromatographic separations to obtain the other chemical constituents and screen them against various strains of bacteria.