Isolation and Antimycobacterial Evaluation of Compounds from Combretum micranthum Used in North East Nigerian Ethnomedicine

Tuberculosis remains a major infectious disease burden in Nigeria, particularly in North East states where the disease prevalence is high and traditional plant medicine remains a first-line resource for many affected communities. Combretum micranthum, known as kinkeliba, is used by traditional healers in Borno and Adamawa States specifically for respiratory conditions, and the antimycobacterial potential of its chemical constituents has not been systematically investigated. This study undertook bioassay-guided isolation of antimycobacterial compounds from root extracts of Combretum micranthum. Roots collected from Adamawa State were extracted and the extract was tested for preliminary antimycobacterial activity against Mycobacterium smegmatis and Mycobacterium bovis BCG using the resazurin microplate assay. Active fractions were subjected to repeated column chromatography to isolate pure compounds characterised by nuclear magnetic resonance, mass spectrometry, and infrared spectroscopy. Bioactivity-guided fractionation ultimately isolated five compounds exhibiting antimycobacterial activity. The most active compound, identified as combretastatin A-related flavonoid based on spectral data, showed a minimum inhibitory concentration of 8 micrograms per millilitre against Mycobacterium smegmatis. Two terpene compounds showed MIC values of 16 and 32 micrograms per millilitre. Selectivity indices greater than 10 were calculated by comparing antibacterial MICs against Staphylococcus aureus with cytotoxicity values against Vero cells. These results represent the first report of antimycobacterial compounds from Combretum micranthum and provide important leads for the development of plant-derived anti-tuberculosis agents from North East Nigerian botanical resources.

Keywords: Combretum micranthum, antimycobacterial activity, bioassay-guided isolation, tuberculosis, Adamawa State