Background

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.

Methods

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.

Results

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 0.08 mg/ml), Escherichia coli (MIC 0.08 mg/ml) and Staphylococcus aureus (MIC 0.08 mg/ml). The extract ofB. fistulosa had significant antifungal activity against Cryptococcus neoformans with an MIC of 0.08 mg/ml. Other extracts had moderate to poor antimicrobial activities with the MIC ranging from 0.16 to 2.50 mg/ml. The isolated compounds were generally more active against bacteria (MIC ranging from 16 to 250 μg/ml) than fungi (MIC between 31 and 250 μg/ml). Moderate antibacterial activity was obtained with compound 3 againstE. faecalis and E. coli (MIC of 16 μg/ml in both cases), compounds 6 and 10 against E. faecalis (MIC of 16 μg/ml), and compound 9 against E. faecalis (MIC 31 μg/ml) and S. aureus (MIC 31 μg/ml). The B. fistulosaextract had the greatest radical scavenging activity (IC₅₀ 100.16 μg/ml) followed by extracts of D. perkinsiae(IC₅₀ 130.66 μg/ml), and A. mannii (IC₅₀ 361.30 μg/ml). Compounds 3 and 5 had significant antioxidant activities with the IC₅₀of 9.84 and 9.99 μg/ml as compared to that of ascorbic acid (IC₅₀ 2.41 μg/ml).

Conclusion

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 isolated compounds could be useful in development of antimicrobial agents. We are currently investigating the toxicity and other pharmacological activities with the potential use as topical antimicrobial agents.

Keywords: Cameroon; Dissotis perkinsiae; Adenocarpus mannii; Barteria fistulosa; Constituents; Antimicrobial; Antioxidant.