Abstract
Pathogenesis of Aspergillus flavus on important agricultural products is a key concern on human health due to the synthesis and secretion of the hazardous secondary metabolite, aflatoxin. This study identified and further characterized aflatoxigenic A. flavus from groundnuts sampled from sundry shops in Kenya using integrated morphological and molecular approaches. The groundnuts were plated on potato dextrose agar for isolation and morphological observation of A. flavus based on macroscopic and microscopic features. Molecular characterization was done through amplification and comparison of the partial sequence of the ITS1-5.8S-ITS2 region. The expression analysis of aflR, aflS, aflD, aflP, and aflQ genes in the aflatoxin biosynthesis pathways was conducted to confirm the positive identification of A. flavus. The gene expression also aided to delineate toxigenic isolates of A. flavus from atoxigenic ones. Morphologically, 18 isolates suspected to be A. flavus were identified. Out of these, 14 isolates successfully amplified the 500 bp ITS region of A. flavus or Aspergillus oryzae, while 4 isolates were not amplified. All the remaining 14 isolates expressed at least one of the aflatoxigenic genes but only 5 had all the genes expressed. Partial sequencing revealed that isolates 5, 11, 12, 13, and 15 had 99.2%, 97.6%, 98.4%, 97.5%, and 100% homology, respectively, to the A. flavus isolate LUOHE, ITS-5.8S-ITS2, obtained from the NCBI database. The five isolates were accurate identification of atoxigenic A. flavus. Precise identification of toxigenic strains of A. flavus will be useful in establishing control strategies of the fungus in food products.
Highlights
Aspergillus flavus is a facultative pathogen capable of existing in diverse ecological niches [1]
A. flavus does synthesize and release a plethora of secondary metabolites such as aflatoxin B1 and aflatoxin B2, aspergillic acid, aflam, nitropropionic acid, and kojic acid [4]. ese metabolites act as virulence factors during pathogenicity, as communication signals, and for ecological adjustments to suit their existence [5]
The reported high incidences of A. flavus on groundnuts (Arachis hypogea) in Western Kenya [9] underscore the need for greater vigilance and surveillance of other foodstuffs other than maize. e current study is one such effort targeting groundnut which is a nonstaple foodstuff that is a delicacy to many Kenyan communities especially in Western Kenya region
Summary
Aspergillus flavus is a facultative pathogen capable of existing in diverse ecological niches [1]. It survives optimally in the tropics at relatively high temperature of about 28°C to 37°C and high relative humidity of about 95% [2]. In Kenya, the outbreak of aflatoxin contamination in the years 2004 and 2005 focused most of the aflatoxin research efforts on maize [7, 8]. E current study is one such effort targeting groundnut which is a nonstaple foodstuff that is a delicacy to many Kenyan communities especially in Western Kenya region The reported high incidences of A. flavus on groundnuts (Arachis hypogea) in Western Kenya [9] underscore the need for greater vigilance and surveillance of other foodstuffs other than maize. e current study is one such effort targeting groundnut which is a nonstaple foodstuff that is a delicacy to many Kenyan communities especially in Western Kenya region
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