Antimicrobial Activity of Kenyan Laikipia County Leonotis mollissima Plant Extract

Abstract

The use of herbal medicine is expanding rapidly across the world due to the high bills involved in the importation of modern medicinal drugs. About 80 percent of the African population use traditional medicine from plants to treat common infectious diseases caused by microorganisms. The main objective of this research was to determine the antimicrobial activity of crude extracts and isolated compounds of Laikipia University Leonotis mollissima (Lion’s ear) from the Lamiaceae family. The plant was studied in this research due to its wide use by local communities of Kenya for medicinal remedies. Its decoction is used by the Marakwets of Kenya to treat microbial diseases. The plant was sampled from Laikipia University Kenya, identified, air dried and voucher specimen kept for reference in the Biological Department of Egerton University in Kenya. Crude extracts from dry powder of the leaves were successively extracted with hexane, dichloromethane, ethyl acetate and methanol for seventy-two hours. With repeated column chromatography, Leonotis mollissima dichloromethane leaves (79.69 g) crude extract yielded compounds 1 (Sederin), 2 (20-hydroxylucidenicacid D2) and 3 (labdane). Identification of pure compounds was achieved by 1H and 13C NMR (500 MHz) spectroscopy. Chemical shifts (δ) were expressed in ppm relative to tetramethylsilane (TMS) as internal standard and coupling (J) in Hz. On screening for antimicrobial activity, all crude extracts showed an MIC (Minimum Inhibition Concentration) of < 0.1 mg/mL to > 0.5 mg/mL on all test microorganism (Bacillus cereus, Staphylococcus aureus, Escherichia coli, Salmonella typhimurium and Candidas albican. Compounds 1 and 3 had an MIC of > 0.16 mg/mL on all test microorganisms while 2 compound had an MIC of 0.10 mg/mL. The IC50 (Inhibition Concentration that reduces the effect of microorganisms by 50%) for all crude extracts and isolated compounds was less than that of Amoxil® and Doxycycline® antibiotics on all test micro-organisms on calculation with Graphpad Prism 8 free download computer program at different concentrations. This is a confirmation that Leonotis mollissima contains compounds that can be isolated and used as drugs to treat various diseases including microbial infectious diseases. Keywords: Kenya, Laikipia County, leonotis mollissima, minimum inhibition concentration (MIC)