Abstract

One of the most serious fish pathogens infecting both cultured and wild fish species was found to be Edwardsiella tarda which contains important virulence factors that enhance bacterial survival and pathogenesis in hosts. The present study aims to isolate, identify and characterize E. tarda in freshwater fishes in Kafr El-Sheikh governorate, Egypt using selective differential cultural medium (Rimler Shotts agar), morphological and biochemical tests (oxidase, catalase, methyl red, voges proskauer, indole, citrate utilization, gelatine hydrolysis, H2S production, oxidation-fermentation, nitrate reduction and sugar utilization tests). Pathogenesis of E. tarda was checked by experimental infection to Oreochromis niloticus fish together with screening of the highly virulent three virulence genes (esrB, mukF and gadB). The obtained results revealed the presence of the three virulence genes in the selected strain of E. tarda which gave severe lesions in the experimentally infected Oreochromis niloticus. E. tarda strain having more than one virulence gene results in more severe lesions than strains having one or even no virulence genes.

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