Reliability of the chemical, metabolic, and molecular methods in discriminating aflatoxigenic from non-aflatoxigenic Aspergillus isolates

Abstract

Aflatoxins, potent carcinogens produced by Aspergillus species (A. flavus and A. parasiticus), are primarily consumed through dietary sources. Aflatoxin management using non-aflatoxigenic Aspergillus to outcompete their aflatoxigenic congeneric to achieve low residual toxin levels is a promising biological control (BC) field intervention. A prerequisite for the BC program is the accurate delineation of aflatoxigenic fungi from their non-aflatoxigenic relatives. In this study, we use three methods: Chemical (Dichlorvos-ammonia), Metabolic (ELISA coupled live cultures), and Molecular (10 aflatoxin biosynthetic genes) to determine the aflatoxigenicity of Aspergillus spp. previously collected from Eastern Kenya, an aflatoxin hotspot. Thirty-six different Aspergillus isolates were identified and studied microscopically from a total of 314 fungal cultures. The chemical method reported 21 aflatoxigenic and 15 non-aflatoxigenic isolates, while the metabolic technique distinguished 20 aflatoxigenic and 16 non-aflatoxigenic isolates. A large proportion (97.22 %) of the isolates harboured the aflR, aflO, and aflM genes, while 91.67 % of the isolates possessed the aflS gene. All isolates (100 %) harboured the aflD, aflQ, aflP, and aflK genes. ELISA-coupled live cultures positively correlated with Dichlorvos-ammonia (p > 0.01), only differing in one sample, indicating a strong concurrence between the two methods at segregating toxigenic A. flavus isolates. Cluster analysis based on Multiple Correspondence revealed that the non-aflatoxigenic group exhibited similar characteristics correlating with the absence of aflR, aflS, aflI, and aflO genes. These findings indicate the reliability of the Chemical and Metabolic methods and can function as confirmatory assays to complement the molecular detection approach in determining aflatoxigenicity among Aspergillus spp.