Extraction of antibacterial active compounds from dry leaves of African plants of the Combretaceae family

The dry leaves of two African plants of the Combretaceae family, furnished by the botanist of the St. Jean de Dieu hospital of Tangueità (Benin, central Africa),were extracted with a sequence of 5 solvents with increasing polarity (from cyclohexane to water).The raw materials, obtained from these extractions following solvent evaporations, were tested for antibiotic activity against gram negative and gram positive bacterial strains. According to the results of a modified Kirby-Bauer test, no promising effect was obtained against Gram negative bacteria while interesting dose-effect activities were observed against Gram positive strains. In particular, from G. senegalensis active compounds were found in the low polarity extract (dichloromethane) which, at a concentration of 800 μg/disk (13 mm diameter disk), resulted in a grow inhibition crown of 4.7 mm and 2.6 mm on Enterococcus faecalis and Staphylococcus aureus MSSA, respectively. An higher amount of the aqueous extract (4760 μg/disk) also produced a good result as 5.7 mm and 5.0 mm crowns were observed. The extracts from C. micranthum showed an inhibiting effect in the more polar extracts (i.e. from ethanol and water) which gave 1 mm of grow inhibition crown on both strains at a concentration of 1000 μg/disk. The most promising extract from each plant was partially purified and then tested on some clinical relevant bacterial strains: S. aureus MRSA, Clostridium difficile, Streptococcus pyogenes, Streptococcus pneumoniae, Corynebacterium striatum, Neisseria gonorrhoeae, Haemophylus influenzae, Escherichia coli, obtaining a good killing effects on the Gram positive bacteria of the panel.