Antifungal activity of silver ion on ultrastructure and production of aflatoxin B1 and patulin by two mycotoxigenic strains, Aspergillus flavus OC1 and Penicillium vulpinum CM1

Objective - The antifungal activity of silver ion from silver nitrate solution was tested against two pathogenic and toxigenic fungal strains. The first was Aspergillus flavus OC1, a clinical aflatoxigenic strain that causes fungal keratitis and the second was Penicillium vulpinum CM1, a maize-pathogenic strain that is positive for patulin (PAT) producing ability. Materials and methods - Agar well diffusion assays on yeast sucrose (YES) agar were applied for determination of the antifungal activity of silver ions either filter- or autoclaved-sterilized. Transmission electron microscopy was used to analyze the cellular effects of silver ion. The mycotoxins AFB1 and PAT were analyzed in the fungal strains cultures treated with silver ion. Results - Filter-sterilized ions have a greater potential for growth inhibition of both fungal strains than autoclaved-sterilized ions. The minimal inhibitory concentration of the filter-sterilized ions against A. flavus OC1 was 70 mu g mL(-1) and against P vulpinum CM1 was 60 mu g mL(-1) and that the minimum fungicidal concentration was 120 mu g mL(-1) against the first strain and 80 mu g mL(-1) against the second strain. Hyphal cells treated with silver ion showed considerable changes in the nature of cell membranes and cytoplasmic organelles. Silver applied to YES broth inhibited mycelial growth and AFB1 and PAT formation of both strains. Growth and mycotoxin production appeared to be correlated processes. Conclusion - These findings indicate the future possibility to use silver ion as substitute for synthetic fungicides to control the growth of pathogenic fungi and their mycotoxin production. (C) 2014 Elsevier Masson SAS. All rights reserved.