Antibacterial activity of some African medicinal plants used traditionally against infectious diseases

Context: Plants are known to play a crucial role in African traditional medicine for the treatment of infection diseases. Objectives: To investigate the claimed antimicrobial properties of plants traditionally used in African countries, providing scientific validation for their use. Materials and methods: Eighty-three polar and non-polar extracts from 22 medicinal plants were screened for their antibacterial activity against Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) and Mycobacterium smegmatis using the broth microdilution method. Results and Discussion: In vitro antibacterial activity against one or more tested bacteria was shown by 83% of the extracts. The highest activity was obtained with the methanol extracts of the aerial parts of Acacia karroo Hayne (Fabaceae) and Anacardium occidentale L. (Anacardiaceae) and the roots of Bridelia cathartica G. Bertol (Euphorbiaceae), against S. aureus (minimum inhibitory concentration (MIC) = 7.5 mu g/mL). The same MIC values were exhibited against E. faecalis by the methanol extract of A. occidentale, the dichloromethane and methanol extracts of B. cathartica and the ethyl acetate extract of Momordica balsamina L. (Curcubitaceae) leaves. Gram-negative bacteria were less sensitive; the growth of P. aeruginosa was significantly inhibited (MIC = 31 mu g/mL) by the n-hexane and methanol extracts of Gomphocarpus fruticosus (L) Ait. (Asclepiadaceae) fruits and by the dichloromethane extract of Trichilia emetica Vahl (Meliaceae) seeds. Most of the active extracts were rich in fenols/flavonoids. Conclusion: This study supports the use of most of the studied plants in traditional medicine, for the treatment of infectious diseases. Some of them are worthy of further investigation.