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Diosquinone and plumbagin isolated from the root of Diospyros rnespiliforrnis (Hostch), a common ingredient in several folk medicines and foods, have been shown to have antibacterial activity against a wide range of organisms. The minimum inhibitory concentrations (MICs) of diosquinone against Staphylococcus aureus NCTC 6571 and S. aureus E3T ranged from 3 to 30 pglmL, while those against Escherichia coli KL16 and Pseudomoms aeruginosa NCTC 6750 ranged from 15 to 16pglmL. MICs were found to increase with the concentration of cells used in the inaculum. Bacterial studies showed that S. aureus NCTC 6571 exhibited a paradoxical biphasic response to dioquinone in nutrient broth, whereas bacterial activity against E . coli KL16 increased with concentration up to the highest concentration of dioquinone tested. Activity against E . coli KL16 was more pronounced in phosphate-buffered saline than in nutrient broth.The other active compound isolated, the naphthoquinone plumbagin, gave MIC values between 400 and 600 pg/mL.

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Two known compounds, friedelin and epifriedelinol were isolated from Euphorbia kamerunica Pax. The compound's structures were established on the basis of spectral analysis. The antibacterial activities of these compounds and the ethyl acetate extract were established on Pseudomonas aeruginosa, Salmonella typhii and Staphylococcus aureus. The extract displayed higher inhibition activities on the bacteria than the isolated compounds. The zones of inhibition of the extracts were between 9.0 and 30.5 mm, with the highest extract activity on Staphylococcus aureus. The minimum inhibition concentration (MIC) values of the isolated triterpenes were between 7.5 -10 µg/ml.