الفهرس 
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Abstract
This study aimed to determine the prevalence, phenotypic, genotypic character and antibiotic resistance of Aeromonas spp. isolated from Oreochromis niloticus, Mugil cephalus and water samples from Manzala Lake and Sea water in PortSaid Governorate referring to enterotoxin genes and antibiotic resistance genes. Out of 200 fish samples (100 Oreochromis niloticus and 100 Mugil cephalus) and 50 Water samples were collected from Manzala Lake and Sea water in Port-Said Governorate, 69%, 44%, 80% and 36%, respectively were detected positive by cultural method. The isolates of fish samples were biochemically identified as A. hydrophila which was the most dominant species with total prevalence 54.31% (107/197) followed by A. sobria 26.4% (52/197) , A. caviae 16.24% (32/197) and A. schubertii 3.05% (6/197) while the isolates of water samples were biochemically identified as A. hydrophila which was the most dominant species with total prevalence 52.73% (29/55) followed by A. sobria 29.09% (16/55) , A. caviae 16.36% (9/55) and A. schubertii 1.82% (1/55). Results of antimicrobial showed that antibiotic resistance pattern varied between strains. In general, all isolates showed highly sensitive to Cefotamixe 75/75 (100%) and sensitive to Norfloxacin 63/75 (84%), Gentamycin 62/75 (82.67%), Chloramphenicol 61/75 (81.33%), Amikacin 60/75 (80%) and Nalidixic acid 58/75 (77.33%). While all isolates show resistant to Ampicillin, Pencillin and Trimethoprim – sulfamethazole 75/75 (100%) and highly resistant to Oxytetracycline and Streptomycin with 68/75 (90.67%) and 46/75 (61.33%), respectively. PCR assay of 16 representatives, biochemically confirmed Aeromonas spp. isolates were genetically confirmed belonging to genus Aeromonas based on 16S rRNA gene sequence. Virulence gene (enterotoxin genes) properties of 16 representative strains showed that presence of (act) with 100% (16/16) and (alt) with 25% (4/16). Otherwise, (ast) gene not detected in any examined Aeromonas isolates. While antibiotic resistance genes which encoded as (blaTEM, sul1, tetA(A) and aadA1 were detected in 16 examined Aeromonas isolates with 100% at 516 bp, 100% at 433 bp., 100% at 576 bp. and 6.25% at 484 bp., respectively.