Characterization of aflatoxins and toxigenic aspergillus in maize and soil from the eastern region of Kenya

Abstract

Aflatoxin contamination is a major problem affecting cereal producers worldwide. Aspergillus species, which are known to produce these toxins, colonize cereals in the field, during post-harvest period through to storage. This study sought to establish variation in: (i) fungal species in maize and soil, (ii) their morphological diversity, (iii) the distribution of toxigenic Aspergillus species as well as, (iv) the seasonal variations of aflatoxins and (v) the predominant toxin type in Eastern Kenya. Maize and soil samples were collected from farmers’ grain stores and fields respectively (in May and December 2013), which corresponded to two months following the first and second harvesting seasons. Fungi of the genus Aspergillus were isolated from maize and soil samples by direct plate and dilution plate techniques respectively on Czapek Dox Agar and thereafter sub-cultured and purified on Potato Dextrose Agar (PDA). The total aflatoxins were determined using solid phase direct competitive Enzyme-Linked Immunosorbent Assay (ELISA), whereas the aflatoxin types were determined using thin layer chromatography (TLC). Aspergillus isolates were identified to species level based on cultural and morphological characteristics. A total of 229 pure Aspergillus spp. cultures were obtained (55% from maize and the remaining 45% from soil). Eleven species of Aspergillus were isolated in the following order of abundance: A. niger, A. flavus, A. clavatus, A. awamori, A. parasiticus, A. ochraceus, A. candidus, A. ustus, A. niveus, A. terreus, and A. wentii. Aspergillus niger was the predominant fungus of genus Aspergillus in both seasons. The seasonal variations of the Aspergillus isolates was not significant (P=0.544). However, more aflatoxins were obtained in maize from the short-rains season (269.2 ppb) than from the long-rains season (142.4 ppb). The difference in seasonal distribution of the total aflatoxins was significant (P=0.019) whereas 16% and 44% of maize samples from the long-rains and short-rains seasons respectively exceeded the maximum allowed limit (10 ppb). The predominant aflatoxin type in both planting seasons was aflatoxin B1. However, the short-rains season recorded the production of more types of aflatoxins with the production of aflatoxins B1, B2 and G2. This meant that maize from Eastern Kenya was susceptible to aflatoxin poisoning especially in the short rain seasons and that measures to curb this deserve attention.