الفهرس 
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Abstract
This study investigated the in vitro and in vivo antimicrobial activity of Cichoriumintybus(C.intybus)leaves extract in Orechromisniloticus (O.niloticus) challenged with Aeromonas hydrophila (A. hydrophila). Fingerlings were divided into four groups (60fish/group). The control group (C) was fed a basal diet with no plant extraction. In the groups 2, 3, 4 were fed a basal diet contain 0.5, 1.0, 1.5 % (T1, T2, T3) C.intybus extraction respectively. In vitro, C.intybus extract showed 25 mm inhibition zone. In vivo, The haematocrite level was increased in T1, T2 and T3 groups fed on diets supplemented with different levels of C.intybus extract with advancing the experimental time till fourth week (44.67±2.60, 70.67±3.48 and 82.33±1.45, respectively) and subsequently decreased at sixth week (36.67±0.88, 51.67±0.88 and 63.00±1.53, respectively). The serum total protein, albumin, globulin were significantly increased in fish fed on diets supplemented with C.intybusleaves extract in a dose dependent manner compared to control till fourth week then was decreased. The respiratory burst activity and lysozyme activity of the O.niloticus that fed diet supplemented with 1.5% C.intybus extract (T3) were significantly higher after four weeks of feeding (7.23±0.10 and 4.27±0.06, respectively) than other groups. Fish that were fed on C.intybus extract exhibited better relative level of protection than the controls when challenged by A.hydrophila. Dietary supplementation with C.intybus extract improves immune status and disease resistance in Nile tilapia.Two different phages active against these bacteria were isolated in this study. Phages ΦZH1and ΦZH2 were active against Aeromonashydrophila. These phages formed plaques with an average diameter of 3.0±1.0 mm after 24hrs of incubation at 37°C in its morphology and measured using Transmission electron microscope JEOL(JEM-1400cx), showed that these two phages related to the family podoviridae,with typical icosahedral heads and contractile tails, showed that the two phages were composed of icosahedralheads measured 100 &50 nm with very short tail measured 30 &7 nm for ZH1&ZH2, respectively. Phages (ZH1&ZH2) adsorbed on cell wall and no receptor on flagella was found. Phages (ZH1&ZH2)were reached the maximum adsorbed rate after 20 and 30 min and the latent period was about 20 min while rise period was60 min, and the mean brust size were about 113 and 114 pfu per infected cell for ZH1&ZH2.Both phages were inactivated by exposure to temperature at 70°C for 10 min and to Ultraviolet for 2 hrs.These phages may have a potential to be used as antibacterial agents to control pathogenic Aeromonashydrophila bacteria in Nile water.