Thesis (Ph.D.) - Cairo University - Faculty of Veterinary Medicine - Department of Microbiology

A total of one hundred feed samples were collected from Cairo and Giza Governorates and screened for aflatoxin producing and ochratoxin producing fungal isolates. A total of 106 fungal isolate comprising, Aspergillus flavus, A. ochraceus and A. niger were recovered from feed samples and tested for aflatoxins and ochratoxin A (OTA) production. The most predominant isolate was A. flavus, which was recovered at the range of (40-55%), followed by A. niger (30-50 %) and A. ochraceus (15-20%). Thirty three of 47 A. flavus isolates produced aflatoxin B1 and B2 at an average levels of (170-750 ppb), while, 22 of 44 tested isolates of A. niger produced OTA with an average levels of (100-550 ppb), whereas 12 of 15 A. ochraceus isolates produced OTA at average levels of (300-700 ppb). Molecular identification of 16 toxigenic fungal isolates (5 A. flavus, 6 A. ochraceus and 5 A. niger) was carried out by PCR. The results of PCR of the DNA extracted from these isolates using ITS primer confirmed the identification of A. flavus, A. ochraceous and A. niger. The application of real-time PCR (RT-PCR) system directed against the nor-1 gene of the aflatoxins biosynthetic pathway was applied on the DNA extracted from the 5 selected strains of A. flavus. The amplification plot of the DNA samples indicated the presence of nor-1 gene in all aflatoxins-producing A. flavus isolates and in only one isolate of the negative aflatoxins-producing A. flavus. On the other hand, the use of primer set for amplification of omtB gene responsible for AF production amplified 611 bp fragments bands in all aflatoxigenic A. flavus, while, no band was detected in all negative aflatoxigenic isolates. All the sequenced A. flavus isolates were confirmed to belong to A. flavus species and were 100% similar to the reference isolates of A. flavus

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