LAMP-based group specific detection of aflatoxin producers within Aspergillus section Flavi in food raw materials, spices, and dried fruit using neutral red for visible-light signal detection

Aflatoxins can be produced by 21 species within sections Flavi (16 species), Ochraceorosei (2), and Nidulantes (3) of the fungal genus Aspergillus. They pose risks to human and animal health due to high toxicity and carcinogenicity. Detecting aflatoxin producers can help to assess toxicological risks associated with contaminated commodities. Species specific molecular assays (PCR and LAMP) are available for detection of major producers, but fail to detect species of minor importance. To enable rapid and sensitive detection of several aflatoxin producing species in a single analysis, a nor1 gene-specific LAMP assay was developed. Specificity testing showed that among 128 fungal species from 28 genera, 15 aflatoxigenic species in section Flavi were detected, including synonyms of A. flavus and A. parasiticus. No cross reactions were found with other tested species. The detection limit of the assay was 9.03 pg of A. parasiticus genomic DNA per reaction. Visual detection of positive LAMP reactions under daylight conditions was facilitated using neutral red to allow unambiguous distinction between positive and negative assay results. Application of the assay to the detection of A. parasiticus conidia revealed a detection limit of 211 conidia per reaction after minimal sample preparation. The usefulness of the assay was demonstrated in the analysis of aflatoxinogenic species in samples of rice, nuts, raisins, dried figs, as well as powdered spices. Comparison of LAMP results with presence/absence of aflatoxins and aflatoxin producing fungi in 50 rice samples showed good correlation between these parameters. Our study suggests that the developed LAMP assay is a rapid, sensitive and user-friendly tool for surveillance and quality control in our food industry.