Determination of aflatoxin-producing fungi strains and levels of aflatoxin b1 in some selected local grains

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Aflatoxins are bisfurans that are polyketide-derived, toxic, and carcinogenic secondary metabolites produced by some species of Aspergillus and other fungi on food crops and feed. The versatility of these fungi to different factors determine the infestation and colonization of the substrate, the type and amount of aflatoxin produced. Aflatoxin B1, is classified as the most toxic of the aflatoxins, responsible for not only causes great economic loss but also is the most potent naturally occurring chemical liver carcinogen known. Random and replicated samples of groundnut, maize, beans and rice were purchased from the Kumasi Central Market and analyzed for their aflatoxin levels using High Performance Liquid Chromatography (HPLC). The contamination levels found ranged from trace amount to 31.11ppb with groundnut registering the highest aflatoxin content. A further microbial culture examination revealed that most of the crop samples especially groundnut and maize were susceptible to various species of aflatogenic A. flavus, A. paracitius, A. tamarii, P. expansum, Mucor hiemalis, A. niger P. citrinum, Moniliella and other pathogenic fungi. Colony forming units per gram (CFU/g) from the microbial cultures ranged from 4.3×10 6 to 2.1×10 3 . However, a poor correlation existed between the aflatoxin contamination level and the CFU/g per sample. Furthermore, molecular assessment of aflatoxin producing fungi in the grains samples involving five pairs of universal and eight specific aflatoxin primers were carried out. A consistent correlation could not be made between the molecular analysis and microbial results. Just as in A. versicolor, four universal primers 0817F/1196R, U1/U2 and FF2/FR1 and ITS1/IST2 and one specific aflatoxin producing fungi primer Nor1/Nor2 was able to show positive bands on A. versicolor. Which means these particular fungi, have the gene to produce aflatoxin however it could not produce detectable aflatoxin by the HPLC.
A thesis submitted to the department of Biochemistry and Biotechnology, Kwame Nkrumah University of Science and Technology (KNUST), in partial fulfillment of the requirement for the award of Master of Philosophy (MPhil) degree in Biochemistry, 2015