THE CONGRUENCE OF VIRULENCE GENES AND PATHOGENICITY OF Edwardsiella
Tarda STRAINS OF Oreochromis Niloticus AND Clarias
Gariepinus ORIGIN ON Oreochromis Niloticus
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 Depat., Central Laboratory for Aquaculture Research, A.R.C. Ministry of Agriculture, Egypt.
Edwardsiella tarda infection is considered a dangerous septicaemic disease with high economic losses. The present work was planned to investigate the LD50 and pathogenicity of E. tarda strains isolated from two different fish species (O. niloticus and C. gariepinus) in correlation with the number of virulence genes in each strain. The results revealed that the most virulent strain was strain 1 (group 1) causing 50% mortality within 12h at concentration of 1.8 X 105 CFU. The clinical signs of experimentally infected O. niloticus with E.tarda of the four fish groups were recorded. The signs were clearly prominent in the fish group one infected with E.tarda strain containing the four virulence genes. However, the signs were also present in the other three groups containing three, two and one virulence genes respectively, with variant mild degrees, while as the control group showed no clinical changes. Some hematological and serum biochemical parameters were studied on the blood and sera of experimentally infected fish, which revealed a decrease in Hb, RBCs, PCV, total proteins, albumin and globulins and an increase in TLC, Lysozym concentration. Histopathological studies on the tissues of fish were also recorded.
Edwardsiella tarda virulence genes.