AQUEOUS EXTRACTS FROM THE BULBS OF TULBAGHIA VIOLACEA ARE ANTIFUNGAL AGAINST ASPERGILLUS FLAVUS

Aspergillus flavus is a cosmopolitan fungal pathogen that is often implicated in food spoilage and in aspergillosis infections in immunocompromised individuals. The current study was undertaken to assess the effect of aqueous bulb extracts of Tulbaghia violacea on A. flavus spore survival. The broth dilution assay was used to determine that the minimum inhibitory concentration (MIC) of the extract against A. flavus was 15 mg/mL and that the minimum fungicidal concentration (MFC) was 20 mg/mL. During well diffusion assays A. flavus was inhibited by a minimal extract concentration of 60 mg/mL. As expected, inhibition zones during well diffusion assays increased with increasing extract concentrations. The 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-([phenylamino] carbonyl)-2H-tetrazolium hydroxide (XTT) assay showed a direct proportional decrease in metabolic activity of A. flavus with an increase in extract concentration. Inhibition of metabolic activity was quantifiable as early as 12 h after spore inoculation. This was in contrast to the broth dilution assay where inhibition only became clearly observable 48 h after spore inoculation. The antifungal nature of T. violacea aqueous bulb extracts against A. flavus 2527 shown here for the first time indicates a potential use of this extract as an effective antifungal agent against Aspergillus species. The extract could possibly be used in the future for reducing Aspergillus contamination of plant-derived foods.