Isolation of endophytic fungi from South African plants and their medicinal significance

The growing resistance of pathogenic microorganisms to antibiotics has resulted in an increasing need worldwide for new candidate drugs to combat antibiotic resistance. It is widely acknowledged that microorganisms are a prolific source of highly potent antibacterial, antifungal and anticancer compounds, owing to their capacity for producing interesting natural products [1]. Endophytes residing in medicinal plants have excellent bioprospecting potential, particularly when combined with the remarkable pharmacological properties of many South African medicinal plants. These are highly under-investigated sources of potentially useful endophytic microbes. In this research project several endophytic fungi were obtained from the leaves of South African medicinal plants, including Cotyledon orbiculata L, Gomphocarpus fruticosus (L.) W.T.Aiton, Podranea ricasoliana (Tanfani) Sprague, Ficus elastica Roxb. ex Hornem, Catha edulis (Vahl) Endl. and Psychotria zombamontana (Kuntze) E.M.A.Petit. In preliminary microbial inhibition investigation, the isolated endophytes displayed promising antifungal activity against Cryptococcus neoformans and Candida albicans. Two endophytic fungi, named zom-gr and zom-cot obtained from Psychotria zombamontana, showed similar minimum inhibitory concentration (MIC) values of 0.625 to 1.25 mg/ml against Cryptococcus neoformans and Candida albicans. Catha edulis also afforded endophytic fungal strains with activity against Cryptococcus neoformans and Candida albicans with MIC values in the same range. In the antibacterial assays, endophytic fungi from Catha edulis had antibacterial activity against Staphylococcus aureus and Salmonella Typhimurium with MIC = 1.25 mg/ml. Moreover they exhibited moderate activity against Enterococcus faecalis and Escherichia coli. Further experiments are in progress to identify the isolated fungal strains and to study their anticancer activity against different cancer cell lines. It is worth considering further investigation of their bioactive secondary metabolites [2], which will be the future focus of this study.

[1] Abdalla MA, Helmke E, Laatsch H. Nat Prod Comm 2010; 5: 1917 – 1920

[2] Abdalla MA, Matasyoh JC. Nat Prod Bioprospect 2014; 4: 257 – 270