Antimicrobial and antioxidant activities of extracts and ten compounds from three Cameroonian medicinal plants: Dissotis perkinsiae (Melastomaceae), Adenocarpus mannii (Fabaceae) and Barteria fistulosa (Passifloraceae)

We decided to investigate the antimicrobial and the antioxidant activities of extracts and compounds isolated from Dissotis perkinsiae, Adenocarpus mannii and Barteria fistulosa, three Cameroonian medicinal plants used for the treatment of skin diseases, wounds, fever, rheumatism, malaria and/or infectious diseases. Standard chromatographic and spectroscopic methods were used to isolate and identify ten compounds from the three plant species [1–5 (from D. perkinsiae), 2, 6–8 (from A. mannii) and 2, 4, 9, and 10 (from B. fistulosa)]. A two-fold serial microdilution method was used to determine the minimum inhibitory concentration (MIC) against a panel of fungal and bacterial species. The radical scavenging capacity using 2,2-diphenyl-1-picryhydrazyl (DPPH) was determined to evaluate the antioxidant activity of the samples. The compounds isolated were: ursolic acid (1), oleanolic acid (2), quercetin 3-O-(6″-O-galloyl)-β-galactopyranoside (3), 3-O-β-d-glucopyranoside of sitosterol (4), ellagic acid (5), isoprunetin (6), chrysin 7-O-β-d-glucopyranoside (7), isovitexin (8), hederagenin (9) and shanzhiside methyl ester (10). The ethanol extract of D. perkinsiae had good antibacterial activity against Enterococcus faecalis (MICs 0.04 and 0.08mg/ml), Escherichia coli (MIC 0.08mg/ml) and Staphylococcus aureus (MIC 0.08mg/ml). The extract of B. fistulosa had significant antifungal activity against Cryptococcus neoformans with an MIC of 0.08mg/ml. Other extracts had moderate to poor antimicrobial activities with the MIC ranging from 0.16 to 2.50mg/ml. The isolated compounds were generally more active against bacteria (MIC ranging from 16 to 250μg/ml) than fungi (MIC between 31 and 250μg/ml). Moderate antibacterial activity was obtained with compound 3 against E. faecalis and E. coli (MIC of 16μg/ml in both cases), compounds 6 and 10 against E. faecalis (MIC of 16μg/ml), and compound 9 against E. faecalis (MIC 31μg/ml) and S. aureus (MIC 31μg/ml). The B. fistulosa extract had the greatest radical scavenging activity (IC50 100.16μg/ml) followed by extracts of D. perkinsiae (IC50 130.66μg/ml), and A. mannii (IC50 361.30μg/ml). Compounds 3 and 5 had significant antioxidant activities with the IC50 of 9.84 and 9.99μg/ml as compared to that of ascorbic acid (IC50 2.41μg/ml). The results obtained support the traditional use of the three plant species (D. perkinsiae, A. mannii and B. fistulosa) in traditional medicine for the treatment of infections. Some extracts and isolat