Antibacterial activity of leaf extracts from combretum micranthum and guiera senegalensis (Combretaceae)

African ethnopharmacology relays on the use of plants as a treatment of a wide spectrum of pathologies. The collaboration with Gruppo Solidarietà Africa (GSA onlus) allowed the selection of plants specifically used in West Africa as a traditional remedy for a number of diseases. Guiera senegalensis and Combretum micranthum (Combretaceae) leaves were selected and studied for the presence of antibacterial compounds. Plant material was sequentially extracted with a series of five solvents with an increasing polarity. Antibacterial activity against Escherichia coli Cla and Staphylococcus aureus MSSA (Methicillin sensible S. aureus) (ATCC 25293) was determined for the crude extracts and more purified fractions by means of agar disk and well diffusion assays. Moreover a novel bioautographic method was developed to follow the antibacterial activity throughout the purification steps, at the same time allowing to assess the ongoing fractions purification efficacy. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of the most purified and active products were evaluated at the end of the procedure. The ethanolic extract of C. micranthum (Cm4) and the toluene extract from G. senegalensis (Gs2) showed the most relevant antibacterial activity. Two purified fractions, indicated as Cm4-P and Gs2-P, have been isolated from the most active crude extracts and their antibacterial efficacy was further studied against a panel of nine clinically relevant bacterial strains. Cm4-P resulted effective against both Gram positive and Gram negative strains, whereas Gs2-P was found active only against the Gram positive strains at very low concentrations (particularly MIC of 18.7 μg mL-1 and MBC of 75 μg mL-1 against C. difficile and S. aureus).