Antimicrobial activity of endophytic fungi isolated from Catharanthus roseus and Euphorbia hirta
Fungal endophytes of medicinal plants are important sources of secondary metabolites of pharmaceutical importance. The aim of this research was to investigate the endophytic fungi of Catharanthus roseus (L.) G. Don (Apocyanaceae) and Euphorbia hirta L. (Euphorbiaceae) for antimicrobial activity. A total of 10 fungi endophytes; 6 from C. roseus and 4 from E. hirta were isolated and subjected to solid state fermentation on rice media. The metabolites were extracted using ethyl acetate and the dried extracts tested for antimicrobial activity against Staphylococcus aureus, Escherichia coli, Salmonella typhi, Bacillus subtilis, Aspergillus fumigatus and Candida albicans using the agar well diffusion technique. The minimum inhibitory concentrations (MICs) of the extracts were also determined using the agar dilution method. The bioactive compounds of the extracts were detected using HPLC-DAD. At the concentrations evaluated (1 – 0.0625 mg/mL), antimicrobial activity was recorded by the extracts with inhibition zone diameters (IZDs) ranging from 0 – 16.33 mm (antibacterial) and 0 – 7.30 mm (antifungal). The MICs of the extract against the test organisms ranged from 0.125 – 0.5 mg/mL. Best antimicrobial activity was recorded by MR1B and MRB.2 with MIC of 0.125 mg/mL recorded against all test organisms. HPLC-DAD analysis of the extracts revealed the presence of some compounds with known antimicrobial property such as citreoisocoumarin, paxilline, nigricinol, fatty acid, sceptrin, cladosporin, desmethyldichlorodiaportin, desmethyldiaportinol and N-5(3-(5-Isopropyl-3,6-dioxo-pipperazin-2-yl)-propyl)-2-phenyl-acetamide. It can be concluded that these endophytic fungi could be a promising source of novel bioactive compounds, thus necessitating further studies.