الفهرس 
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Abstract
Aeromonas and Pseudomonas species are responsible for wide range spectrum of ulcer type diseases among fish, as ulcerative syndrome, Motile Aeromonas Septicemia (MAS) and Pseudomonas septicemia leading to high mortalities, high economic losses and decreases fish farm efficiencies, beside their role in gastrointestinal and extra intestinal infections in humans. Therefore, this study was planned for determination the prevalence of Aeromonas and Pseudomonas infection in 250 diseased Nile tilapia fish (O. niloticus) at Kaliobia Governorate, during the period from May (2017) to January (2019), and phenotypic characterization of Aeromonas and Pseudomonas species beside genotypic identification and detection of some virulence genes in some isolated strains. The samples were collected from apparently pathognomic lesions in muscle, liver, kidney, intestine and spleen of these fishes after clinical and postmortem examination.
The results of bacteriological examination revealed that, 128 out of 250 examined fish (51.2%) were positive for isolation of 161 Aeromonas and Pseudomonas species. For Aeromonas species, 118 strains (73.3 %) were isolated, 102 A. hydrophila strains (86.4%) and 16 A. caviae strains (13.6%). They were isolated mostly from muscle lesion samples 36 (30.5 %) [A. hydrophila 24.6% and A. caviae 5.9%], followed by liver samples 29 (24.6%) [A. hydrophila 21.2% and A. caviae 3.4%], then kidney samples 26 (22.0%) [A. hydrophila 19.5% and A. caviae 2.5%]; intestine24 (20.3 %) [A. hydrophila 18.6% and A. caviae 1.7%] and spleen samples 3 (2.5 %) that was A. hydrophila only. Meanwhile, for Pseudomonas species, 43 strains (26.7%) were isolated, 29 Ps. aeruginosa strains (67.4%) and 14 Ps. fluorescens strains (32.6%).They were mostly isolated from muscle lesion samples 14 (32.6%) [Ps. aeruginosa 25.6% and Ps. fluorescens7.0%] followed by liver samples 12 (27.9%) [Ps. aeruginosa 16.3% and Ps. fluorescens 11.6%] then kidney samples 9 (20.9%) [Ps. aeruginosa 11.6% and Ps. fluorescens 9.3% %] and 8 intestine lesion samples (18.6 %) [Ps. aeruginosa 13.9% and Ps. fluorescens 4.7%] but both Pseudomonas species were failed to be isolated from spleen samples.
The results of in- vitro sensitivity tests for 118 isolated Aeromonas strains revealed that, they were highly sensitive to meropenem followed by ciprofloxacin; norfloxacin; gentamycin and florphenicol. Meanwhile, they were highly resistant for ampicillin and methicillin followed by oxacillin; penicillin-G; amoxicillin; cefotaxime; oxytetracycline and streptomycin. Meanwhile, for 43 isolated Pseudomonas strains, they were highly sensitive to meropenem followed by gentamycin; norfloxacin; ciprofloxacin and florphenicol. In contrast, they were highly resistant for ampicillin; methicillin and penicillin-G followed by amoxicillin; oxacillin and cefotaxime.
The results of phenotypic virulence of Aeromonas and Pseudomonas strains cleared that, most isolated strains were enterotoxigenic ones, as they had haemolytic; amylase activity; proteolytic; lipolytic; Lecithinase activities and had the ability for biofilm production.
Moreover, the PCR results for A. hydrophila strains appeared that, 16SrRNA and fla genes was detected in all 8 studied strains; aero ; AHcytoen ; ast virulence genes were detected in 5; 3and 5 out of 8 A .hydrophila studied strains, respectively. In addition to Ps. aeruginosa strains, the 16SrRNA; oprL and fliC genes were detected in all 8 studied strains; exoS and toxA virulence gene were detected in 6 and 5 out of 8 studied strains, respectively.