Screening of Aflatoxin-producing mould isolates based on fluorescence production on a specific medium under ultraviolet light

Abstract

Aflatoxin contamination of food and feedstuffs is a serious economic and health hazard. Over a period of two years, 35 samples of raw pistachio nuts collected from different parts of Iran were analysed for the presence of aflatoxigenic strains of the Aspergillus flavus group. Eighty-five isolates of A.flavus and A.parasiticuswere identified based on specific yello-orange pigment production in the reverse of the colonies on Aspergillus flavus and parasiticus agar (AFPA) medium and microscopic criteria. These isolates were present in 65.71% of the samples and their aflatoxin-producting ability was examined. At first , 12 out ot the 15 aflatoxin-producing isolates were selected based on bright blue fluorescence colour on aflatoxin-producing ability (APA) medium. Later, all of the isolates were identifid after culturing on sucrose-low salts (SLS) medium. Furthermore, aflatoxin production on APA and SLS media was confirmed when the mycelia and media were extracte and analysed fo aflatoxins on TLC plates. A.flavus strions produced mainly aflatoxin B1 with concentrations rangiong from 0.21 to 1.49 µg/g of APA medium, where as A.parasiticus strain produced all four aflatoxins (B1, B2, G1 and G2) with 3.71 µg aflatoxin B1/g of the medium. Isolates other than A.flavus and A.parasiticus grown on this specific culture medium failed to produce a characteristic fluorescence under UV light. Evidences from this study indicate that fluorescent production on APA medium is a reliable screening test for distinguishing potential aflatoxin-producing strains of A.parasiticus from nontoxigenic strains.