الفهرس 
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Abstract
Bacterial diseases are responsible for heavy morality of cultured sea bass and sea bream and one of the most important factors of economic loss . Therefore, the present study aimed to isolation and identification of bacterial isolates encountered in cultured sea bass (Dicentrachus Labrax L.) and sea bream (Sparus aurata L.) and try to control and treatment of these bacterial disease by application of antimicrobial sensitivity test as well as recording the best concentration of NaCl for growth of these bacterial serotypes .
In our study, total number of (400) cage and pen cultured diseased sea bass and sea bream (200 fish from each) were collected from Wadi Mariut at Borg El-Arab City at Alexandria Governorate, Egypt .
1. The collected fishes were examined for parasitological and fungal infection firstly to ensure the real cause of signs and mortalities, the results showed no parasitic infection or fungal infection .
2. After that the fishes subject to bacteriological examination as the following :
• Culturing on different ordinary and specific laboratory media .
• Morphological identification of bacterial isolates .
• Biochemical characterization of these isolates .
• Serotyping of bacterial isolates .
• API 20E system for serotyping of Pseudomonas species isolates .
• Slide-agglutination test for serotyping of all bacterial isolates .
The obtained results showed that :
a. The total number of bacterial isolates (290) divided as (136) from sea bass and (154) isolates from sea bream .
b. The prevalence of bacterial species isolates in sea bass were (47%) vibrio, (27.3%) Pseudomonas and (25.7%) T. maritimum, while in sea bass were (53%) vibrio, (28%) Pseudomonas and (19%) T. maritimum .
c. The most highly incidence bacterial isolates serotypes in sea bass and sea bream were V. anguillarum, T. maritimum, V. alginolyticus and Ps. Fluroscence .
3. NaCl tolerance test :
Different concentration of NaCl used on pleat count ager media 2, 3, 4, 5, 6, 8% for different bacterial serotypes, incubate for 24 hours after that count the total bacterial colonies, the results revealed that the best NaCl concentration for Pseudomonas species growth was 2%, but T. maritimum grow well in 3% NaCl and best growth recorded at 4% NaCl concentration .
Antimicrobial susceptibility test :
4. For control and treatment of these bacterial infections, applying Antimicrobial susceptibility test by using disc diffusion technique and reading the zone of inhibition .
The results revealed that most Pseudomonas species serotypes were sensitive to Ciproflexacin and intermediate sensitive to flumequine enroflexacin and gentamycin, but in T. maritimum isolates were resist to all antimicrobial except Ciproflexacin, enroflexacin and doxycyline . In regards to vibrio species susceptibility, this study noticed that all serotypes of vibrio were sensitive to all antimicrobial except amoxycilline, sulphamethoxale/Trimethoprim were resist and intermediate sensitive to erythromycin and oxytetracyline in some serotypes. PCR method used for detection of one of the most prevalent bacterial serotypes T. maritimum which used in experimental infection .
The results revealed that the primer sequence showed maximum identify with the sequence of T. maritimum with 100% hemology and the PCR amplified the correctly sized products (400 pb) for the isolates identified as virulent strain of five .
5. Experimental infection :
A total number of (60) Mugil Capito (45 + 10 gm) obtained from floating cages at Rashid area, El-Behera Governorate, Egypt, were transported to the laboratory of fish disease department, Faculty of veterinary medicine, Alexandria University in oxygenated water, and acclimated for two weeks .