Research on anti-infective agents
We focus on investigating plant species that can be of value against infective diseases because this is a major need in developing countries. The value of the plant extracts may be either by killing or at least inhibiting the growth of microorganisms or parasites and/or by stimulating the immune system of the infected animal. Therefore, we investigate antibacterial, antifungal, antiviral, antiparasitic and antioxidant activity of plant extracts and isolated compounds. Within this focus our aim is not primarily to isolate compounds that will enter the pharmaceutical industry as a new lead compound, but rather to use isolated compounds or extracts in the herbal medicine industry in its widest sense and to promote and support the primary health care of people and animals in rural communities. We are also interested in developing extracts that can be used to protect plants against fungal pathogens. Several patents have been registered or are under preparation and two commercial products are already in the market.
Research on using plants to promote animal and plant productivity
Our focus up to 2003 was mainly on antibacterial activity, but we now have students investigating antifungal, antiviral, antiparasitic, antioxidant and insecticidal activities of plant extracts.
Due to an apparent gap in international research and our own strengths with many collaborators in our Faculty of Veterinary Medicine we are focussing more on the use of plant extracts in animal health and production. Our group is collaborating with a consortium of a European Union Framework project to replace antibiotic feed additives with plant extracts.
Research on aspects related to the herbal medicine industry
We have developed methods that can be applied in the quality control of herbal medicines because there is an urgent need for this aspect in terms of pending South African legislation on complementary medicines.
Our Programme has played a leading role in establishing AAMPS, the Association for African Medicinal Plant Standards [see www.aamps.org], registered in Mauritius with Eloff as the first Chairman of the AAMPS Board.
Our expertise is used to address problems experienced in the complementary medicine industry.
We have expertise in developing extracts with high activity using a laboratory scale pilot plant in our unit to resolve scaling up challenges.
Selection of plants
Instead of doing grasshopper research on different plant species, we initially decided to work mainly on the Combretaceae plant family for the following reasons:
The species in this family are used for many medicinal purposes. These include treating abdominal disorders, abdominal pains, backache, bilharziasis, chest coughs, colds, conjunctivitis, diarrhoea, dysmenorrhoea, earache, fattening babies, fever, headache, hookworm, infertility in women, leprosy, pneumonia, scorpion bite, snake bite, swelling caused by mumps, syphilis, toothache and general weakness.
A number of activities have been proven in vitro such as antibacterial, antifungal, antiviral, anticancer, anti-inflammatory, anti-schistosomal, anti-ulcer, anthelminthic and molluscicidal efficacy. Some of the compounds isolated have been patented and are now in phase II clinical trials.
The members of the family have a very complex chemistry, containing triterpenoids, flavonoids, stilbenes, tannins and many other compounds.
We have selected the most promising species to work on by screening close to 30 different taxa for chemical composition, antibacterial activity and diversity of antibacterial compounds present. We have isolated 25 different antimicrobial compounds from different species; in most cases the compounds were known, but the biological activity was not known. (For a review of some of this work see Eloff et al., 2008)
Plants used in Ethnoveterinary Medicine for treating infections
In addition to research on the Combretaceae we are investigating different plant species used in ethnoveterinary medicine. This work was done in collaboration with the Onderstepoort Veterinary Institute that handles the communication with rural farmers that use medicinal plants. (For a review of some of this work see McGaw and Eloff 2008)
Screening of tree leaves for several biological activities
Based on our work, it became clear that as far as anti-infective agents are concerned, there is not a good correlation between traditional use of plants and in vitro antimicrobial activity. This is probably because hardly any of the c. 50 antibacterial compounds that we have isolated from plants to date extracted from plants are polar and few aqueous plant leaf extracts have any antibacterial activity. Because non-polar extractants are not readily available to poor rural people the correlation between ethnomedicinal use for infections and in vitro antimicrobial activity is low. Because so many people have investigated plants from ethnobotanical leads, it may explain the lack of success in developing antimicrobial pharmaceutical products from plants. Consequently we have started a screening programme of acetone extracts of leaves of trees occurring in southern Africa using validated quantitative methods.
We investigated the antibacterial activity of the first 100 species within a period of two months using only two pathogens. Approximately 10% of the species examined had MIC values below 0.04 mg/ml against Staphylococcus aureus and another 10% had MIC values below 0.08 mg/ml. For Escherichia coli, the percentages were 2% and 5% with the same MIC values. Many of these plants have not been known to have antibacterial activity. These results demonstrated the viability of the project. To date more than 700 tree species have been investigated against the following pathogens: Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Staphylococcus aureus, methycillin resistant Staphylococcus aureus, Mycobacterium smegmatis, Candida albicans, and Cryptococcus neoformans. The results of these assays have been used to identify MSc and PhD projects.