The antimicrobial screening of four South African Asteraceae species and the preliminary structural investigation of an antipseudomonal compound from Arctotis auriculata

Abstract

Infectious diseases represent one of the main causes of morbidity and mortality in developing countries, like South Africa. The indiscriminate use of antibiotics has also resulted in the emergence of a number of resistant bacterial strains. Four plants belonging to the Asteraceae (Daisy) Family, which forms part of the Fynbos Biome, were screened for their phytochemical composition and antimicrobial activity. The plants investigated were: Helichrysum crispum, Felicia erigeroides, Eriocephalus africanzs and Arctotis auriculata. The plants were selected on the basis of their ethnobotanical use in various infectious diseases. The results from the phytochemical identification showed that all the plants tested positive for tannins. Flavonoids were detected in the leaves and stems of A. auriculata and F. erigeroides and the stems of E. africanus. Saponins were present in the leaves of H. crispum and the leaves and roots of F. erigeroides. Triterpene steroids were found in the stems of E. africanus and F. erigeroides. Akaloids were only detected in the leaves of A. auriculata and cyanogenic glucosides were in the stems of H. crispum and the leaves of A. auricula/a. None of the plants tested positive for quinones. The disc diffirsion method was used to determine the antimicrobial potential of the selected plant species. The results from this initial study showed that the organic extracts of A. auriculata and H. crispum inhibited the growth of Mycobacterium smegmatis. The same extracts, together with the organic extracts of F. erigeroides, were active against Pseudomonas aeruginosa. Antifungal activities against Candida albicans were exhibited by the organic extracts of E. africanus, F. erigeroide^s and H. crispum. Organic extracts of A. auriculata and E. africanus, as well as the aqueous extract of the latter plant, were active against Staphylococcus aureus. Hereafter, the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), minimum fungicidal concentration (MFC) and minimum mycobactericidal concentration (MMC) of the most active solvent extracts of selected organs of the four plants were done.