الفهرس 
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Abstract
Our study is divided into two main parts; the first part was a survey for one year and
determination the prevalence rate of bacterial microorganisms affecting some fish
farms in El fayoum and El sharkia governorates. These farms showed signs of
septicemia with a history of 20 -25% recorded mortalities during the period from
autumn 2018 to summer 2019. In postmortem examination, the affected fish showed
loosed scales, ulceration in the dorsal part of the head, petechial hemorrhages on the
body surface, unilateral exophthalmia, and corneal opacity together with congested
blood vessels of nearly all fleshy portions of the body fins. Internal examination of the
viscera showed congestion of the blood vessels in the kidneys and brain together with
dark enlarged spleen while the liver was marbled in appearance. Ninety fish samples
(representing 10% of the fishes showing clinical signs) were collected from such fish
farms for histopathological and bacteriological examination. Aerococcus viridans was
isolated from El Fayoum and El Sharkia governorates in rates of 7.7% and 15.9%
respectively throughout the year while Enterococcus faecalis was isolated with a rate
of 34.6 and 39.02 respectively. The prevalence rate of Aeromonas hydrophila wasII
42.3% in El fayoum governorate and 13.4 % in El sharkia governorate while Vibrio
vulnificus was recorded 0 % in El fayoum governorate and 7.3 % in El sharkia
governorate, Proteus vulgaris was 3.8 in El fayoum governorate and 12.2% in El
sharkia governorate. Pseudomonas aeruginosa was 11.5% in El fayoum governorate
and 12.2% in El sharkia governorate. The seasonal prevalence rates were analyzed in
both locations throughout the year. In antibiotic sensitivity testing, the A.viridans and
E.faecalis showed resistance to ampicillin, oxolinic acid, nalidixic acid, amikacin, and
gentamicin but they were sensitive to amoxicillin and nitrofurantoin. E. faecalis
exhibited resistance to erythromycin and oxytetracycline while A. viridans was
sensitive to them. Experimental infection and re-isolation of both bacterial isolates in
O. niloticus was performed to confirm the field isolation and for studying the
pathogenicity of such microorganisms in this fish species. The Gram negative bacteria
were showing resistance against erythromycin except Vibrio vulnificus that showed
sensitivity. Aeromonas hydrophila and Proteus vulgaris showed resistance to colistin sulphate
and susceptibility to sulpha-trimethoprime. Vibrio vulnificus and Pseudomonas aeruginosa
showed resistance against sulpha-trimethoprime and sensitive against colistin sulphate. In last
decade, because of the bacterial diseases in egypatian farms were recorded ahighly
increase in Gram positive bacteria and a new isolates were admitted to aquaculture as
result of using agriculture drainage water, so part 2 of our study was directed to
experimental design to control newly admitted bacterial diseases by using of formalin
killed vaccine against the isolated Gram positive strain in our field study (A.viridans
and E.faecalis). This design were performed by using 84 fish divided in 7 groups
(control negative, vaccinated A.viridans, vaccinated E.faecalis, infected A.viridans,
infected E.faecalis, challenged A.viridans and challenged E.faecalis); 12 fish / each
group. The efficacy of vaccine was evaluated by making WBCs count and lysosome
activity which showed marked increase in vaccinated, challenged than in the infected
group. The statistical analysis for all parameters used for vaccine evaluation was
performed. The parameters included pathological changes, biochemical and
hematological aspects as well as immunological aspects to compare between naturally,
experimentally infected and vaccinated groups.