Abstract
This study aimed at morphologically identifying Aspergillus flavus in soil and maize and at determining their aflatoxin-producing potentials. Five hundred and fourteen isolates obtained from maize and soil in Kenya were cultivated on Czapeck Dox Agar, Malt Extract Agar, Sabouraud Dextrose Agar, Potato Dextrose Agar, and Rose-Bengal Chloramphenicol Agar. Isolates were identified using macro-morphological characteristics. Micromorphological characteristics were determined using slide cultures. Aflatoxin production was determined by direct visual determination of the UV fluorescence of colonies on Coconut Agar Medium, Yeast Extract Sucrose agar, and Yeast Extract Cyclodextrin Sodium Deoxycholate agar and by Thin Layer Chromatography. Forty-three presumptive A. flavus isolates were identified; aflatoxin was detected in 23% of the isolates by UV fluorescence screening and in 30% by Thin-Layer Chromatography (TLC). The aflatoxins produced were: aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), and aflatoxin G1 (AFG1); some isolates produced only AFB1, whereas others produced either AFB1 and AFB2 or AFB1 and AFG1. The highest incidence of A. flavus (63%) and aflatoxin production (28%) was recorded in samples from Makueni District. Isolates from Uasin Gishu (21%) and Nyeri (5%) were non-aflatoxigenic. Bungoma District recorded 11% positive isolates of which 2% were aflatoxin producers. The occurrence of aflatoxin-producing A. flavus emphasises the need for measures to eliminate their presence in food crops.
Highlights
Aspergillus flavus is a ubiquitous and cosmopolitan filamentous fungus known to proliferate in a wide range of environmental conditions [1]
Forty-three A. flavus isolates were identified from the fungal cultures previously isolated from
Bungoma and was not detected in the isolates from Nyeri and Uasin Gishu (Figure 4). These findings suggest that the inocula of the aflatoxin-producing A. flavus are more prevalent in Eastern Kenya and that the conditions in the semi-arid region of the Eastern Province are more conducive for aflatoxin formation than the conditions in the humid regions of the Central, Rift Valley, and Western Provinces
Summary
Aspergillus flavus is a ubiquitous and cosmopolitan filamentous fungus known to proliferate in a wide range of environmental conditions [1]. It is both a saprophytic and an opportunistic pathogen and thrives abundantly on many organic nutrient sources with monosaccharides and disaccharides [2]. According to Hell and Mutegi [3] and Yu [4], species of the Aspergillus section Flavi have the ability to survive temperatures ranging from 12 ◦ C to 48 ◦ C, with the optimal growth temperature ranging from 28 ◦ C to 37 ◦ C, with a high humidity of above 80%. Members of the genus Aspergillus, the taxonomy of which is complex and continuously evolving, are characterized by vesicle-bearing conidiophore [6].
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