SOUTH AFRICAN ETHNOVETERINARY PLANT EXTRACTS WITH ANTIMICROBIAL AND ANTIVIRAL POTENTIAL

Abstract

In South Africa, medicinal plants used for treating various disorders in animals may have useful biological activities, particularly if the cause of the disease is linked to infectious microorganisms. The acetone extracts of leaves of sixteen plant species commonly applied in ethnoveterinary medicine were tested in several in vitro bioactivity assays. Antibacterial and antifungal serial microdilution assays were performed against two Gram-positive (Enterococcus faecalis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria, and against Cryptococcus neoformans and Candida albicans. Antibacterial minimum inhibitory concentrations (MIC) reached as low as 0.039 mg/ml, and 62.5% of extracts inhibited the Gram-positive bacteria. Average antifungal MICs were 0.56 and 0.59 against C. neoformans and C. albicans respectively. Some extracts showed simultaneous antimicrobial activity and cytotoxicity against Vero cells using a colorimetric cell viability assay while others had higher selective activity. Antiviral assays against the sensitive feline herspesvirus type 1 identified six ineffective plant extracts (37.5%), including Ziziphus mucronata, Rhus lancea and Leonotis leonurus, while three extracts (19%, Pouzolzia mixta, Pterocarpus angolensis and Hippobromus pauciflorus) showed a 1 log reduction in viral growth. A 2 log reduction in viral growth was shown by Pittosporum viridiflorum and Cussonia spicata extracts (12.5%). A quarter of the extracts, Combretum caffrum, Ricinus communis, Schotia brachypetala and Sclerocarya birrea, resulted in a promising 3 log reduction in viral cytopathic effect. We are targeting plant extracts with low cytotoxicity and high biological activity for isolation of active compounds, and development of active standardized extracts.