Abstract
M.Tech. (Biomedical Technology)
Aflatoxins (AFs) are naturally occurring secondary metabolites produced principally by Aspergillus flavus and Aspergillus parasiticus in food and feed commodities worldwide. Contaminations of compound feeds by AFs do not only affect animal health, but the economy as well. It is for this purpose that a study was carried out to establish the quality of South African feeds with respect to AF-producing fungi, establish a correlation between levels of AFs and determinant gene (nor-1) responsible for producing these toxins. To this end, compound feeds (n=92) from various feed manufacturers in South Africa were sampled and analysed for aflatoxigenic fungi (Aspergillus flavus and Aspergillus parasiticus) and nor~1 genes using the conventional identification and real time- polymerize reaction (RT-PCR) methods, respectively. Data obtained revealed that 66.5 and 53.1% of samples were positive for A. flavus and A. parasiticus, respectively. Aflatoxins levels in similar samples were estimated by high performance liquid chromatography (HPLC) following an immune-affinity clean-up and multi mycotoxin extraction procedures. Accordingly, levels established ranged from 0.06 – 77.97 ppb (mean: 16.8 ppb) with feeds for poultry being the main contaminating substrate and no correlation (overall R2=0.093) was established between the concentrations of AFs and those of nor~1. The cytotoxic effect of some selected AF extracts from these feeds on human lymphocyte cells was performed in comparison to that of AFB1 standard. Data obtained from the cytotoxic assay revealed that cell viability was affected significantly (P<0.001) by both the dose and duration of exposure, which was much more noticeable when cells were exposed to AFB1 standard than for individual extracts. In conclusion, even though none of the feeds analysed contained levels of AFs above regulatory limits established in South Africa, such feeds when consumed on a continuous basis may pose some serious health problems especially when AFs is found in co-contamination with such significant mycotoxins as ochratoxins (OTs) and fumonisins (FBs). Thus, the continuous need to limit AFs levels in feed commodities from South Africa is imperative.