Antimycobacterial activities, cytotoxicity and phytochemical screening of extracts for three medicinal plants growing in Kenya

Tuberculosis (TB), an airborne disease, is among the ten leading deadly diseases worldwide. Despite the efforts of WHO and its partners to eradicate it, it is still a public health issue especially with the rise of multi-drug resistant tuberculosis (MDR-TB) and extensively drug- resistant tuberculosis (XDR-TB). Commiphora species (Burseraceae family) are known in the Kenyan traditional medicine to treat respiratory diseases including TB. In the search of new anti-TB alternative drugs, plant materials from Commiphora mildbraedii Engl. (root bark and stem bark), Commiphora edulis (Klotzsch) Engl. (stem bark and leaves) and C. ellenbeckii Engl. (Stem bark and leaves) were tested for antimycobacterial activity, cytotoxicity and phytochemistry. 100 g of the powdered plant materials were macerated using the serial method with solvents of increasing polarity. Aqueous extraction was carried out by decoction. The microbroth dilution method was used to determine the antimycobacterial activity (MIC) against a model Mycobacterium smegmatis ATCC607 while the cytotoxicity evaluation (CC50) was carried out using the MTT assay. The most active extract was fractionated using preparative TLC and fractions were analysed by GC-MS. Thirty extracts were obtained from the 6 different plant materials and eleven of them exhibited the antimycobacterial activity with the methanolic extracts of the stem and root bark of C. mildbraedii, and the aqueous extract of the C. ellenbeckii leaves exhibiting high activities (MIC= 0.39, 0.78 and 0.78 mg/L respectively). The MTT assay showed no or low cytotoxicity. The GC-MS analysis of the preparative TLC fractions from the methanolic extract of C. mildbraedii revealed the presence of 42 compounds belonging to 10 different classes of phytochemicals. Lup-20(29)-en-3-one and o-xylene were the most abundant. Except o-xylene and α-terpineol, all the compounds were detected for the first time in the Commiphora genus. These findings justify the ethnomedicinal uses of Commiphora species in TB treatment.