الفهرس 
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Abstract
In this study, diseased Oreochromis niloticus and sea bass (100 of each) were collected randomly from kafer El-shekh cultured fish farms and also from Dammitte province during the period from May 2016 till May 2017 .The samples were subjected to clinical and post-mortem examination then for bacteriological examination for liver, kidney and spleen. Some fishes showed hemorrhage all over the body surface including gills, fins and scales detachment accompanied by swelling of abdomen.The suspected isolateswere characterized by culture and morphological characters, biochemical tests including microbact 24 then by PCR assay. Total prevalence of Edwardsiella tarda isolates was (12%) among the examined fresh water fishes while (7%) in marine fishes.Invitro antibiotic sensitivity pattern of E. tarda isolates by disc diffusion method revealed that most of isolates were sensitive tociprofloxacin, streptomycin, chloramphenicoland gentamycin. Conversely most of isolates were resistant to tetracyclin, nalidixic acid, ampicillin and sulphamethaxazol. PCR was applied for detection of some virulence genes (etfA, etfD,gyrB genes) in E. tarda isolates and the obtained reslts indicate the presence of visible band appeared at 415bp and at 445 bp.