Antifungal activity of endophytic <i>Fusarium oxysporum</i> from <i>Cola acuminata</i> against <i>Candida albicans</i> isolates from HIV-infected patients

Abstract

Background: The Human Immunodeficiency Virus (HIV) infection has exacerbated the occurrence of opportunistic diseases with Candida infection being the most prominent. Unfortunately, the growing ineffectiveness of the available antifungal drugs along with the emergence of new multi-resistant strains further worsen the matter. In the search for new active molecules, the present study aims at investigating the optimal growth conditions for the production of antifungal metabolites from the endophytic fungus Fusarium oxysporum.

Methods: Fusarium sp. isolated from Cola acuminata was identified using the ITS1-5.8S rRNA-ITS2 nucleotide sequence. For the production of various metabolites, the fungus was cultivated for ten days in various media supplemented with different sources of carbon, amino acids, nitrogen, ion and organic acids. All extracts were submitted to antifungal activity test against seven Candida albicans isolates using the broth microdilution method. The most active extract was evaluated for cytotoxic activity against the Vero cell line using the MTT assay.

Results: The endophytic fungal isolate Casb122 was identified as Fusarium oxysporum based on the ITS sequence. Extracellular extracts showed better activity against Candida albicans (MICs ranges 500-1000 μg/mL) compared to intracellular extracts (2000 μg/mL). The growth media supplemented with carbon, amino acids, nitrogen, ion and organic acids promoted mycelium growth and production of secondary metabolites. The MIC of extracts obtained from certain media supplemented with carbon, amino acids, nitrogen, ion and organic acids were 2 (500 μg/mL), 4 (250 μg/mL), 8 (125 μg/mL) and 16 (62.5 μg/mL) times lower than that of the control (extract obtained from unsupplemented media). Active extracts with a Cytotoxic concentration 50 (CC50) >200 μg/mL were not cytotoxic to Vero cell line.

Conclusion: The results from this study demonstrate that the culture of endophytic Fusarium oxysporum in supplemented media improves biomass production and antifungal activity against Candida albicans. This isolate could be an excellent source for the discovery of new antifungal compounds. Current investigations are ongoing to isolate and characterize potential antifungal metabolites.