Diversity of aflatoxin-producing fungi and their impact on food safety in sub-Saharan Africa
International Journal of Food Microbiology
The University of Arizona, School of Plant Sciences, Tucson 85721, United States; International Institute of Tropical Agriculture (IIITA), PMB 5320, Ibadan, Nigeria; USDA-ARS, The University of Arizona, School of Plant Sciences, Tucson 85721, United State
Crops frequently contaminated by aflatoxins are important sources of revenue and daily nourishment in many portions of sub-Saharan Africa. In recent years, reports have associated aflatoxins with diminished human health and export opportunities in many African Nations. Aflatoxins are highly carcinogenic metabolites mainly produced by members of Aspergillus sect. Flavi. The current study examined aflatoxin-producing fungi associated with maize grain intended for human consumption in 18 sub-Saharan African countries. 4469 Aspergillus sect. Flavi isolates were obtained from 339 samples. The majority (75%) of isolates belonged to the L strain morphotype of A. flavus. Minor percentages were A. tamarii (6%), A. parasiticus (1%), and isolates with S strain morphology (3%). No A. bombycis or A. nomius isolates were detected. Phylogenetic analyses of partial sequences of the nitrate reductase gene (niaD, 1.3kb) and the aflatoxin pathway transcription factor gene (aflR, 1.7kb) were used to verify isolate assignments into species and lineages. Phylogenetics resolved S strain isolates producing only B aflatoxins into two lineages fully supported by sizes of deletions in the gene region spanning the aflatoxin biosynthesis genes cypA (aflU) and norB (aflF). One lineage was the A. flavus S strain with either 0.9 or 1.5kb deletions. The second lineage, recently described from Kenya, has a 2.2kb deletion. Taxa with S strain morphology differed in distribution with strain SBG limited to West Africa and both A. minisclerotigenes and the new lineage from Kenya in Central and East Africa. African A. flavus L strain isolates formed a single clade with L strain isolates from other continents. The sampled maize frequently tested positive for aflatoxins (65%), fumonisins (81%), and deoxynivalenol (40%) indicating the presence of fungi capable of producing the respective toxins. Percentage of samples exceeding US limits for total aflatoxins (regulatory limit), fumonisins (advisory limit), and deoxynivalenol (advisory limit) were 47%, 49%, 4%, respectively. © 2013 Elsevier B.V.
aflatoxin; fumonisin; nitrate reductase; transcription factor; vomitoxin; Africa south of the Sahara; article; Aspergillus; cypa gene; enzyme linked immunosorbent assay; extraction; food intake; food safety; fungus; fungus isolation; gene; gene amplification; gene deletion; in vitro study; indel mutation; limit of detection; limit of quantitation; maize; microbial diversity; mycotoxin extraction; nonhuman; norb gene; parsimony analysis; phylogeny; plant structures; Aflatoxin; Africa; Aspergillus flavus; Food security; Maize; Mycotoxins; Aflatoxins; Africa South of the Sahara; Aspergillus; Base Sequence; Food Microbiology; Food Safety; Genes, Fungal; Humans; Phylogeny; Sequence Deletion; Zea mays