Antibacterial activity of Marula (Sclerocarya birrea (A. rich.) Hochst. subsp. caffra (Sond.) Kokwaro) (Anacardiaceae) bark and leaves

Marula bark is widely used for bacteria-related diseases by indigenous cultures in Africa. This study was undertaken to investigate whether the ethnobotanical use can be validated by laboratory studies. Bark and leaves were extracted with acetone and MIC values were determined using a microplate serial dilution technique with Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Enterococcus faecalis as test organisms. All extracts were active with MIC values from 0.15 to 3 mg/ml. Based on minimum inhibitory concentration values, inner bark extracts tended to be the most potent followed by outer bark and leaf extracts, but the differences were not statistically significant. There were two major bioactive components visible after bioautography of leaf extracts: one strongly polar and the other highly non-polar. The bioactive components could be separated from 92% of the non-active dry matter by solvent–solvent fractionation into the carbon tetrachloride, chloroform and n-butanol fractions; these fractions, however, still contained many different compounds. Using bark may be detrimental to the plant, but leaf material can also be used for antibacterial application.