Isolation, Antimicrobial properties and characterization of endophytic secondary metabolites obtained from Azadirachta indica

Abstract

Phytochemicals of endophytes have generated significant interest in drug discovery programs due to their immense potential towards contributing to the discovery of new biologically active molecules. Reports have shown that endophytes of Azadirachta indica are been used in the treatment of many human disease conditions. The study was aimed to evaluate the antimicrobial properties and chemical characterization of endophytic extracts isolated from A. indica. Endophytic extract was isolated from A. indica leaves using standard extraction protocols. The extracts were screened for their potential antimicrobial activities using the agar diffusion well method. Phytochemical analyses for the identification of secondary metabolites were done using HPLC-DAD, GC-FID, GC-MS, and FTIR methods. The endophytic fungi (MR3) screened for antimicrobial activity, showed quantifiable activity. At 1.0 mg/mL, inhibition of bacterial by the endophytic fungal extract was observed in Pseudomonas aeruginosa, Escherichia coli, Bacillus subtilis, and Candida albicans with zones of inhibition diameters of 6, 5, 4, and 4 mm respectively.  HPLC-DAD analysis revealed the presence of 2-carboxymethyl-3-n-hexylmaleic acid anhydride and aspernigin A. GC-FID analysis showed remarkably high concentrations of flavanones and catechins. The results of GC-MS analysis also showed the presence of trans-13-octadecenoic acid (282.5g/mol), hexadecanoic acid (114.14g/mol), and 1,6-Anhydro-beta-D-glucopyranose (162.14g/mol). FTIR results established the existence of functional groups like carboxylic acids, which may be associated with some of the detected compounds. Endophytic fungal extracts of A. indica have a potent antimicrobial activity which is related to a high content of flavonoids and alkaloids.