The isolation, identification and antimicrobial activities of endophytic fungi from Azadirachta indica

Endophytic microorganisms are the storehouse of novel secondary metabolites that can serve as an excellent source of drugs for different ailment. In this study, we isolated endophytic fungi associated with Azadirachta indica collected from Agulu, Awka, Anambra State, South Eastern Nigeria, identified some of their bioactive secondary metabolites and evaluated their antimicrobial properties. The endophytic fungi were isolated following standard method and the pure culture of the isolates identified morphologically and molecularly. The fungi were subjected to solid-state fermentation on rice medium and the metabolites were extracted using ethyl acetate. The fungal crude extracts were screened for antimicrobial activity. The extracts were further subjected to high-performance liquid chromatography-diode-array detection (HPLC-DAD) analysis for the identification of the bioactive compounds. A total of four endophytic fungi identified as Aureobasidium sp. (AIL1), Sodaria sp. (AIL3), Aspergillus sp. (AIS1) and Penicillium sp. (AIS2) were isolated from the Azadirachta indica. The crude extracts at 1 mg/mL, showed varying degrees of antimicrobial activity against the test fungi and bacteria Iinhibtion zone diameter (IZD) ranged from 2 to 11 mm. The minimum inhibitory concentrations (MICs) of the fungal extracts ranged from 0.0625 to 0.25 mg/mL. The HPLC-DAD analysis revealed the presence Glucobrassicin, Ferulic acid, 4-methoxybenzaldehyde, 12-Hydroxy-16-scalaren, 12-O-deacetyl-12-epi-scalarin, Ixoside, Citreodrimene F, and Cytosporin D, some of which has been reported to have shown antimicrobial activity. Azadirachta indica possess sundry groups of fungal endophytes that contain secondary metabolites with interesting antimicrobial properties that could be explored in drug discovery.