Use of medicinal plant extracts and light sensitization to inhibit conidia growth in aflatoxin producing Aspergillus flavus

Fungal proliferation causing aflatoxin contamination has been on the rise in Africa due to the adverse changes in climate. Deaths and diseases like cancers have been detected in human beings and animals due to consumption of these toxigenic mycotoxins. Chemical, cultural and biological means have been used to manage aflatoxins but they have failed to eliminate them fully. Medicinal plant extracts traditionally used to cure various ailments are safe in nature and they offer a promising remedy for the control of aflatoxin contamination. Inhibition activity of six aqueous and organic medicinal plant extracts was tested against aflatoxin producing Aspergillus flavus. Antifungal activities, photosensitization and phytochemical composition of aqueous and organic extracts of fruits from Solanum aculeastrum, bark from Syzygium cordatum, and leaves from Prunus africana, Ocimum lamiifolium, Lippia kituensis, and Spinacia oleracea were tested. Spores from four-day-old cultures of previously identified toxigenic fungi, UONV017 and UONV003, were used. Disc diffusion and broth dilution methods were used to test antifungal activity. The spores were suspended in 2 ml of each extract separately and treated with visible light (420 nm) for varying periods. Organic extracts displayed species and concentration dependent antifungal activity. Solanum aculeastrum had the highest zones of inhibition diameters in both strains: UONV017 (mean = 18.50 ± 0.71 mm) and UONV003 (mean = 11.92 ± 0.94 mm) at 600 mg/ml. Aqueous extracts had no antifungal activity (mean = < 8 mm). Solanum aculeastrum had the lowest minimum inhibitory concentration at 25 mg/ml against A. flavus UONV017. All the plant extracts in combination with light reduced the viability of fungal conidia compared with the controls without light, without extracts, and without both extracts and light. Six bioactive compounds were analyzed in the plant extracts. Medicinal plant extracts in this study can control conidia viability and hence with further development can control toxigenic fungal spread.