Mohammed S.M Gado1; Refaat M.A Elgamal 2

and Marwa F. Abd El-Kader2

1Fish Diseases and Management Dept., Fac. Vet. Med., Kafrelsheikh Univ.

2Fish Health and Diseases Dept., Central Laboratory for Aquaculture Research, Agriculture Research Center, Ministry of Agriculture, Egypt.


Edwardsiella tarda is a serious bacterial pathogen especially under farm conditions; causing Edwardsiellosis disease, leading to mass mortalities in various fish species. Molecular identification provide rapid and accurate diagnosis of disease causes also, Gene sequencing have a rapid identification of the bacterial mutation and adaptation processes which closely related to the virulence divergence and niche adaptation of the pathogen resulting in reliable vaccines and useful treatments. Fifty-three bacterial isolates formerly identified as E.tarda on the basis of their biochemical properties, isolated from two different naturally diseased fish species (Clarias gariepinus and Oreochromis niloticus)
at Kafr El-sheikh governorate fish farms, preserved in TSA semisolid media were succumbed PCR identification using specific primers. Four virulence genes and its distribution in E. tarda positive isolates were detected as well as DNA sequencing analysis to the positive virulence genes compared to the gene bank database of the National Center for Biotechnology Information (NCBI). Out of fifty-three bacterial isolates; confirmed with PCR, only fifty isolates were identified as E. tarda; forty-six strains from C. gariepinus and four strains from O. niloticus, and all the examined positive isolates carried one or more of the tested virulence genes. E. tarda strains were divided into four groups with eight genotypes (genetic profiles), depending on the frequency of the virulence genes in the positive E. tarda strains. Gene sequencing revealed very high similarity (98-100%) between the detected virulence genes and the published sequences of E. tarda virulence genes in the gene bank database of (NCBI).

Key words: Edwardsiellosis E. tarda virulence genes. gene bank NCBI gene sequencing