Toxigenic Potential of Aspergillus Species Occurring on Maize Kernels from Two Agro-Ecological Zones in Kenya

Abstract

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.

Postharvest Practices of Maize Farmers in Kaiti District, Kenya and the Impact of Hermetic Storage on Populations of Aspergillus Spp. and Aflatoxin Contamination

“…The current findings on the abundance of A. flavus L-strain contradict those of Okoth et al (2012) who reported that A. flavus S-strain was the most predominant in maize obtained from Makueni region of Kenya. A previous study in Eastern Kenya by Probst, Njapau and Cotty (2007) observed a higher incidence of A. flavus S-strain (71.8%), followed by A. flavus L -strain (28.2%) and lastly A. parasiticus (2.1%).…”

“…Predominance of A. flavus L-strain in the current study could be attributed to the fact that the climatic conditions during the study period were not harsh to favour A. flavus S-strain over other members of Aspergillus section Flavi. The high occurrence of Aspergillus section Flavi in this study indicates a risk of aflatoxin poisoning when conditions are favorable as observed by Probst et al (2007) since Aspergillus section Flavi, have been reported as the main contaminants of maize from Eastern regions, Kenya (Okoth et al, 2012).…”

“…The high population of Aspergillus spp. in maize sampled at harvest could be attributed to the dry weather conditions associated with high temperatures in Makueni County which predispose maize to the fungi at pre-harvest stages in the field (Okoth et al, 2012). Also, improper harvest practices such as delayed harvesting and throwing cobs on the ground during and after harvesting might have contributed to Aspergillus spp.…”

Aflatoxin B1 occurrence in millet, sorghum and maize from four agro-ecological zones in Kenya

“…This could be attributed to unfavourable climatic conditions for the fungal growth and, to a lesser extent, presence of lowaflatoxin-producing L strains of Aspergillus found in their soils [20]. A survey of maize collected from local mills in Bungoma and Kisii found a low proportion of samples contaminated above legal limits, with only 2% and 8%, respectively, exceeding the limit [21], results that were much lower than in the present study.…”

Assessing Genotype-By-Environment Interactions in Aspergillus Ear Rot and Pre-Harvest Aflatoxin Accumulation in Maize Inbred Lines

“…These isolates are known to produce high levels of aflatoxins in maize grain [19,20]. For inoculation of the field trials in South Africa, three toxigenic strains of A. flavus (MRC 3951, MRC 3952, and MRC 3954) were obtained from the Medical Research Council's Programme on Mycotoxins and Experimental Carcinogenesis unit (MRC-PROMEC, Tygerberg, South Africa).…”