The antibacterial activity of 27 southern African members of the Combretaceae

Combretum erythrophyllum contains at least 14 antibacterial compounds and some of these have higher activity than currently used antibiotics. Other members of the Combretaceae were therefore examined to find the best source of antibacterial compounds. Leaves of 27 species of Combretum, Terminalia, Pteleopsis and Quisqualls were collected, dried, milled and extracted with acetone. The minimal inhibitory concentration (MIC) of extracts was determined by a microplate serial dilution technique using Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruglnosa and Escherichia coil as test organisms. All extracts inhibited the growth of the four test isolates, with MIC values generally from 0.1-6 mg ml-1 and an average of 2.01 mg ml-1. After storing extracts for six weeks at 7i?½C, there was a slight loss of activity, MICs increased from 1.75-2.24 mg ml-1. The Gram-positive strains were slightly more sensitive, with an average MIC of 1.8 mg ml-1, than the Gram-negative strains with a MIC of 2.22 mg ml-1. Based on MIC values and the total content of each plant, the seven species with the highest antibacterial activity were C. molle, C. petrophilum, C. moggli, C. erythrophyllum, C. padoides, C. paniculatum and C. mossambicense.