DETECTION OF ANTIMICROBIAL COMPOUNDS BY DIRECT BIOAUTOGRAPHY IN SOME SOUTH AFRICAN PLANTS

Abstract

The hexane, acetone, dichloromethane and methanol extract of Commiphora harveyi (Engl.) Engl. (Burseraceae), Combretum vendae (A.E. van Wyk) (Combretaceae), Khaya anthotheca (Welm.) (Meliaceae), Kirkia wilmsii (Engl.) (Kirkiaceae), Loxostylis alata (A.Spreng. ex Rchb) (Anarcardiaceae), Ochna natalitia (Meisn.) (Walp.) (Ochnaceae) and Protorhus longifolia (Bernh.) Engl. (Anarcardiaceae) were screened for their antimicrobial activity against bacteria (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis), and fungi (Aspergillus fumigatus, Sporothrix schenckii, Microsporum canis, Cryptococcus neoformans and Candida albicans) using simple bioautographic procedure on thin layer chromatographic (TLC) plates developed in solvents of varying polarities. All the extracts showed varied levels of antimicrobial activity against at least one of the tested pathogen. This activity was denoted by white spots against a red-purple background on the TLC plates. L. alata is the most active plant; it showed the highest inhibition zones against bacteria and fungi. Of the bacteria tested, S. aureus is the most susceptible organism having been inhibited by most of the compounds contained in the plants. Similarly, C. neoformans depicted the highest susceptibility among fungal organisms. This study clearly shows that the South African flora offers great potential in the search for natural compounds with antimicrobial activity. Isolation and characterisation of active compounds from extracts that showed good antimicrobial activity is presently in progress in our laboratory. Moreover, we are also carrying out toxicological and pharmacological evaluations on the active plant extracts.