الفهرس 
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Abstract
Fish is the best animal protein due to its high nutritive value as well as its high quality. Also fish is rich in calcium, phosphorous and generous supply of B-complex vitamins as well as its lower content of cholesterol.Fish flesh is generally sterile immediately after catching; however it may become contaminated with different microorganisms during subsequent handling as these microorganisms can penetrate from skin and the gut into the flesh. Salmonellae act as a public health hazard if present, where it cause food poisoning. Also, E. coli may give rise to severe diarrhea in infants and young children as well as food poisoning and gastroenteritis among adult consumers.Therefore, the present study was carried out on 150 random samples of Nile fishes , Tilapia nilotica (O. niloticus), Bayad (B. bayad) and Cat fish (C. gariepinus), 50 of each were collected from different Markets and farms in Kalyobia Governorate to evaluate the bacterial quality of them and to evaluate the hygienic health hazard of Nile fish contaminated with some food borne pathogens as E. coli, Salmonella, Y. enterocolitica and other Enterobacteriaceae beside Staphylococcus aureus strains.The bacteriological examination of Tilapia nilotica (O. niloticus) revealed that, the mean values of APC, Enterobacteriaceae, Coliform and Staphylococcus aureus counts were 8.32 x105 ± 0.48 x105 , 2.65x103± 0.16 x103.,1.81 x103± 0.13 x103 and1.24 x103± 0.16 x103 respectively. While the mean values of APC, Enterobacteriaceae, Coliform and Staphylococcus aureus counts for Cat fish (C. gariepinus) were 9.74 x105 ± 0.42 x105, 3.25 x103 ± 0.14 x103, 2.35 x103 ± 0.15x103 and1.67 x103± 0.17x103respectively . Meanwhile, for Bayad (B. bayad) the mean values of APC, Enterobacteriaceae, Coliform and Staphylococcus aureus counts were 6.54 x105± 0.30 x105, 2.07x103± 0.13 x102,1.74 x103± 0.13 x102 and 0.71 x103± 0.01 x103 respectively. Regarding to the bacterial species isolated, the results appeared that, 22 isolates of E. coli were isolated from examined Nile fish represented as 7(14%) from O. niloticus with serotypes O27:H2 (8%), O63:H2 (2 %) and O158:H4 (4%) , 9(18%) from C. gariepinus with serotypes O27:H2(8%) ,O63:H2(2%),O158:H4(6%) and O159:H7(2%) and6(12%) from B. bayad with serotypes O27:H2 (6%), O63:H2 (2 %) and O158:H4 (4%). Also, 23 isolates of coagulase positive Staphylococcus aureus were isolated from examined Nile fish represented as7 (14%) from O. niloticus; 9(18%) C. gariepinus and 7(14%) from B. bayad samples. The results of Y. enterocolitica isolation revealed that, 7 isolates of Y. enterocolitica were isolated from examined Nile fish represented as 2(4%) O. niloticus and 5(10%) from C. gariepinus samples. Meanwhile, all examined samples of B. bayad fish were free from Y. enterocolitica. Meanwhile, the present study could not to be detected Salmonella serovars from examined O. niloticus and B. bayad samples but represented as 3(6%) from C. gariepinus with serotypes Salmonella Essen B O4,12 H g, m:-; Salmonella Saint Paul B O 1,4,5,12H e,h:1,2 and Salmonella Enteritidis D1O 1,9,12 H g, m:- with percentage of 2% of each .The most important Enterobacteriaceae isolated from fresh water fish are Citrobacter diversus , Citrobacter freundii, Enterobacter aerogenes, Enterobacter agglomerabs, Enterobacter cloacae, Klebsiella azanae, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris.The PCR results of isolated Enteropathogenic E. coli revealed that, the incidence of virulence genes in them were the Shiga-toxin 1 gene (stx1) that was amplified in E. coli isolates of O158: H4 and O63: H2; the Shiga-toxin 2 gene (stx2) was amplified in E. coli isolates of O27: H2, O63: H2 and O159: H7 and the Intimin gene (eaeA), was amplified in E. coli isolates of O159: H7 only.The PCR results of isolated Y. enterocolitica cleared that, the incidence of virulence genes of them were invasion gene (inv) that was amplified in five Y. enterocolitica strains and the Yersinia stable toxin gene (ystA) was amplified in seven Y. enterocolitica strains.Finally, the public health significance of contaminants and the possible sources of contamination of Nile fish with these organisms as well as suggestive hygienic measures to improve the quality of such fish were discussed.