Secondary metabolites from endophytic fungi of moringa oleifera: antimicrobial and antioxidant properties

Abstract

The exponential increase in antimicrobial resistance among several microbes, now more than ever, poses a tremendous challenge to the health system. This has created an urgency to look outside the “norm” for antimicrobial agents that would be useful in tackling the various disease-causing microorganisms. Endophytes are microorganisms that not only have a niche within the plant tissues but also produce bioactive compounds which could be a significant breakthrough in the pharmaceutical industry, especially with the manufacture of novel drugs having an impactful effect on these disease-causing microbes. The study examined the secondary metabolites produced by endophytic fungi associated with Moringa oleifera as well as the antioxidant and antimicrobial activities of the crude extracts of these secondary metabolites against microbes of medical importance. To achieve this, the fresh leaves of moringa (Moringa oleifera) were collected from Ngwo in Enugu’s north local government area, Enugu State. Isolation of endophytic fungi was done using the protocol described by.13 The fungus was cultured by placing agar blocks of actively growing pure culture (3 mm in diameter) in a 500 ml Erlenmeyer flask containing 100 g of rice medium. Incubation was done at room temperature for 3 weeks. Afterward, the fermentation was stopped by introducing 500 ml of ethyl acetate into the flask. Whatman No. 1 filter paper was used to separate the fermentation mixture. Cultures of the bacteria and fungi were maintained on nutrient and Sabouraud dextrose agar respectively at 4 ºC. After the extraction had been done, antimicrobial activity was determined by agar well diffusion assay by Kirby-Bauer’s method. The result of the DPPH antioxidant assay of the endophytic fungal extract revealed that at a concentration of 100 µg/ml, Two Endophytic fungi, MA and MB showed antioxidant activity with % Inhibition of 55.1 and 48.3% respectively. The result of HPLC analysis of the fungal endophytic fungal metabolites revealed the presence of active compounds in the extracts. It was concluded that Moringa oleifera leaves harbor endophytic fungi. These endophytes could be exploited in medicine as novel metabolites.