الفهرس 
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Abstract
S.agalactiae caused streptococcosis and is probably the most important fish production disease in the world, it is crucial to avoid infection and the disease of this pathogen, and it should be handled not only for commercial reasons but also for public health issues in a short time. This study was designed to investigate the isolation and characterization of S.agalactieae from diseased tilapia (Oreochromis niloticus) and sea bass (Dicentrarchus labrax) fishes from farms. And the evaluation of the relative level of protection to locally prepared bacterin and a commercial probiotic Sanolife PRO-F ® against a virulent strain of S. agalactiae in O.niloticus.
In our study , a total number of 50 of tilapia (Oreochromis niloticus) of different body weight (100 ±10 gm) and 50 sea bass (Dicentrarchus labrax) with average bodyweight (600 ± 50 gm) were collected from a private farm at Borg El-Arab, Alexandria governorate Egypt, fishes were collected showing clinical signs and subjected to gross and postmortem examination.
Water qualities were measured parallel to the fish sample. S.agalactiae isolates were identified by phenotypic and biochemical VITEK II methods. Also an overall number of 190 apparently healthy O. niloticus with an average body weight of (40 ± 5 grams) collected from private farm in Baltim region, Kafr-Elshikh governorate from private farm at Borg El-arab region in large plastic bags containing enriched oxygen (2/3) water and transported to the private lab at Borg El-Arab, Alexandria governorate Egypt as soon as possible 70 were collected for determination of LD50, and 120 fish were collected for the evaluation of the relative level of protection in locally prepared killed bacterin and a commercial probiotic Sanolife PRO-F® against a virulent strain of S. agalactiae in O.niloticus fingerlings by I/P inoculation respectively. Moreover, tissue samples were taken from liver, kidney,Spleen, eye and heart for histopathological examination.