Two agro-ecological zones in Kenya were selected to compare the distribution in maize of Aspergillus spp. and their toxigenicity. These were Nandi County, which is the main maize growing region in the country but where no human aflatoxicoses have been reported, and Makueni County where most of the aflatoxicosis cases have occurred. Two hundred and fifty-five households were sampled in Nandi and 258 in Makueni, and Aspergillus was isolated from maize. Aspergillus flavus and A. parasiticus isolates were tested for the presence of aflD and aflQ genes. Positive strains were induced to produce aflatoxins on yeast extract sucrose and quantified using liquid chromatography-tandem mass spectrometry (LCMSMS). Aspergillus flavus was the most common contaminant, and the incidence of occurrence in Nandi and Makueni was not significantly different (82.33% and 73.26%, respectively). Toxigenic strains were more prevalent than non-toxigenic strains. All the toxigenic strains from Makueni were of the S-type while those from Nandi belonged to the L-type. Quantitative differences in aflatoxin production in vitro between isolates and between strains were detected with S strains producing relatively larger amounts of total aflatoxins, B toxins and lower values for G toxins. This was in accord with the frequent aflatoxicosis outbreaks in Makueni. However some L strains produced considerable amounts of B toxins. Given the widespread distribution of toxigenic strains in both regions, the risk of aflatoxin poisoning is high when favorable conditions for toxin production occur.

The aim of this study was to identify Aspergillus species isolated from maize kernels and soils of maize fields of Nandi County using macro and micro morphological characteristics. A cross sectional research design was used in the study and purposive sampling was employed to determine districts of Nandi County and sub locations where sampling was done. This study was part of a larger project whose aim was to survey aflatoxin exposure in the maize value chain. Aspergillus species were isolated from maize and soil samples using quarter strength potato dextrose agar and modified Rose Bengal agar respectively. Pure cultures of the isolates were sub cultured and transferred onto differential media; malt extract agar, czapek yeast extract agar and czapek dox agar for species identification using macro morphological characteristics. Fungal slides were prepared from pure cultures on potato dextrose agar media after three days to identify micro morphological characteristics. Based on morphological characteristics, seven sections of Aspergillus namely: Flavi, Fumigati, Nigri, Circumdati, Clavati, Nidulantes and Candidi were identified. Aspergillus section Flavi was the most predominant with 57% followed by section Nigri with 27% from maize and 58% of section Flavi followed by 26% of section Nigri from the soil across the three locations. Aspergillus sections Nidulantes and Candidi were rare and only recovered from the soil samples of Kaptumo location. All the Aspergillius flavus that formed sclerotia both from the soils or maize kernels were of the L strains. In conclusion Aspergillus section Flavi was most frequent during the isolation process and dominated with Aspergillus flavus from both the maize and soil. Morphological characteristics remain the primary tool for detection and identification of Aspergillus species. The significance for high incidence of Aspergillus section Flavi is in regard to their aflatoxin production profiles that poses a health threat to the community and it is of public health concern. Morphological characteristics as a primary tool for Aspergillus identification should be embraced and more personnel with the knowledge are required since modern and faster techniques are scarce and expensive.

We studied the relationship between sclerotia formation and aflatoxin production by Aspergillusflavus strains isolated from maize kernels from Nandi County. Isolates recovered from maize kernels were tested for their ability to form sclerotia on different growth media. PCR analysis was done on the isolates to detect 2 structural genes, aflD and aflQ, involved in aflatoxin biosynthesis pathway. Positive A. flavus isolates for one or both genes were grown on Yeast Extract Sucrose Agar medium and aflatoxins quantified using LCMSMS. All the isolates formed large sclerotia and their formation was influenced by media type but could not be related to amount of aflatoxins produced both in vivo and in vitro. Though sclerotia are perennating structures and so contribute to survival index of a fungus, their initiation is regulated by external factors though ability to form is genetic. This brings ambiguity of their presence or abundance as a measure of toxicity.