Studies on the Characteristics of Pathogenic Edwardsiella tarda Isolated from Diseased Scophthalmus maximus

A dominated strain CW-7 was isolated from the liver and ascites of juvenile turbot(Scophthalmus maximus) with ascites disease.Challenge test showed that the isolate CW-7 was highly pathogenic to juvenile turbot.The mortality of the fish was 100% injected with a dosage 1.4×10~3 cfu of CW-7 per fish.The same clinical signs as those of naturally infected turbot appeared in the injected ones.The strain was facultatively anaerobic,having both a respiratory and a fermentative type of metabolism.It is gram-negative, rod-shaped(0.4～0.8)×(0.6～2.0)μm,with peritrichous flagella,and without producing oxidase.The strain are similar in characteristics to Edwardsiella tarda.The sequence of 16SrDNA of the strain CW-7 was compared to the seguences in the GenBank database.It shared high similarity to that of Edwardsiella tarda.The strain CW-7 was identified to be Edwardsiella tarda.It was sensitive to 14 kinds of antibiotics such as gentamicin,kanamycin,and polymyxin B,but resistant to 14 other kinds of antibiotics.