Isolation and Characterization of Antifungal Agents Produced by Wood Decaying Fungi From Ghana

Abstract

Human systemic fungal infections have increased in the past decade due to the dramatic increase in immunocompromised patients hence the emergence of resistant fungal strains. It is therefore necessary to discover new antifungal compounds with novel mode of action. This study was aimed at isolating and characterizing antifungal agents from wood decaying fungi (WDF). The growth conditions for maximum production of bioactive agents from WDF were first tested. It was observed that mineral supplements from soil extract supported the growth and metabolite production of WDF. Media richness, culture volume and mineral supplementation were identified as the critical factors that influence the batch to batch consistency of metabolite production in WDF. Collections of 189 WDF were partially screened for their antifungal activity against Candida albicans. They were further screened against Saccharomyces cerevisiae in this project. Based on this screening, 33 of WDF were selected for mycelium isolation. The mycelia of 31 out of the 33 were successfully isolated on agar plates and stored called Plate Mycelium (PM). This served as a continuous fungal inoculum source. The 31 isolated WDF mycelia were then grown in broth and their metabolites were extracted with ethyl acetate. The antifungal activity of each WDF extracts was validated through a phenotypic assay screening using media conditions and mutant S. cerevisaie strains. In the chemical phenotypic array, the sensitivity of the C. albicans and S. cerevisiae cells to the WDF extracts was altered by chemical modifications in the YPD agar plates. This was used as a read out for validating the antifungal activities of the extracts. From the phenotypic screening, the best 6 WDF candidates with highly potent antifungal activity were selected. The mode of action of this top 6 WDF was examined by the antifungal activity pattern displayed against the mutant S. cereviaise cell.