Structure and biological activities of antimicrobial compounds recently isolated from southern African Combretum and Terminalia species

Combretum and Terminalia species have recently been identified as among the 50 most important medicinal plant species in Africa. These widely distributed species are traditionally used for a wide range of indications in Africa and Asia. By antibacterial and antifungal bioassay guided fractionation more than 20 terpenoids, flavonoids and bibenzyls have been isolated by our group during the last decade [MIC 16–50µg/mL]

Several biological activities of these compounds and of crude plant extracts against several bacteria, fungi, parasites and cell lines were determined in vitro [MIC some extracts against fungi 20µg/mL] and also in vivo in animal experiments. Toxicity and the application of some of these compounds or extracts in animal production systems were also evaluated.

The results support many of the ethnomedicinal uses of these genera, but there is a poor correlation between activities of extracts of different species and use against microbial infections. The reason is probably the relatively non-polar character of the antimicrobial compounds, making it difficult for poor rural people to extract. Many species with excellent antimicrobial activities growing widely are not used. It may be possible to use these species in primary health care. For example, leaf extracts of C. erythrophyllum growing widely along river banks have good activity against Vibrio cholera [MIC 25µg/mL] and may be used during cholera outbreaks.

There appears to be no correlation between sections of Combretum and chemical composition or biological activity. Some of the results indicate that at least in some of the species active speciation is still taking place.