Abstract

Edwardsiella septicemia is a systemic bacterial disease caused by Edwardsiella tarda that is considered one of the most important bacterial microorganisms causing severe economic losses due to morbidity and mortality among wide fish species in many countries. In this study Edwardsiella tarda (E. tarda) was isolated and identified from Oreochromis niloticus fish farms using traditional and molecular PCR techniques using E. tarda specific primers. Fifty-six isolates of E. tarda were isolated from 300 fish samples during spring, summer and autumn. While in winter it couldn’t be isolated from 100 samples. The summer season showed the highest prevalence with 28% then the spring season with 18% finally autamn10%. Experimental infection using the isolated E. tarda was performed to determine the pathogenicity in O. niloticus through mortality rate, clinical sings, post mortem lesions and histopathological changes that were observed in the liver, spleen, kidney and gills of the infected fish. The result also showed that there is no significant difference between in vivo and in vitro effect of antibiotic on E. tarda. Norfloxacin showed the highest protection in vivo with 90% survival while Ampicillin showed no protection. These results indicated that the antibiotic of choice for treatment of E. tarda was Norfloxacin.

Key words: Edwardsiella tarda, Oreochromis niloticus, antibiotics, histopathology