The preliminary isolation of several antibacterial compounds from Combretum erythrophyllum (Combretaceae)

Freeze dried ground leaves of Combretum erythrophyllum were extracted with different extractants to determine if they contain inhibitors of pathogenic bacteria. Acetone yielded the most compounds inhibiting the growth of Staphylococcus aureus using bioautography of thin layer chromatography plates. Acetone also extracted many different compounds and group separation was attempted by solid phase extraction on reverse and normal phase silica gel. Both techniques separated the bioactive components to a degree. The best group separation results, however, were obtained using liquid/liquid extraction. The six fractions obtained inhibited the four test organisms to different degrees. S. aureus was the most sensitive (100%) followed by Enterococcus faecalis (36%), Escherichia coli (11%) and Pseudomonas aeruginosa (3%). With S. aureus as test organism, the chloroform soluble fraction contained by far the largest quantity of inhibiting components (100%), followed by the fractions soluble in water (23%), 35% methanol in water (18%), butanol (5%), carbon tetrachloride (2%) and hexane (traces). The lowest minimum inhibitory concentration for S. aureus was 0.05 mg/ml at this stage of purification compared to MIC values of 0.08 and 0.16 mg/ml for ampicillin and chloramphenicol. There were at least 14 different inhibitors with a wide range of polarities present in the different fractions. The polar components apparently did not contain polysaccharides and were probably basic according to the chromatographic behaviour.