Identification Of A Pathogen Associated With Swollen Abdomen Of Cultured Turbot And Antigenicity Of Its Outer Membrane Proteins

Turbot(Scophthalmus maximus) was introduced to China since 1992. With the development of the culture industry, there were more and more diseases and Vibriosis was one of the most serious. In this study, a bacterium was isolated from a turbot with swollen abdomen, and proved to be a pathogen by artificial injection experiments. The strain was identified to be Vibrio alginolyticus by physiological and biochemical characterization and molecular methods. A rabbit was immunized, and immunofluorescence antibody technology(IFAT) was used to detecte the speciality of the antiserum. Sarkosyl method was used to prepare the major outer membrane proteins(MOMPs) of the strain and some main aquatic Vibrio and bacteria of other genus. The MOMPs were analyzed by using SDS-PAGE and Western-blot.A disease causing mortality among turbot juveniles reared in Rongcheng, Shandong province, China broke out at the water temperature of 16-17℃in June, 2002. Gross signs of diseased turbot included swollen abdomen, loss of appetite, skin ulceration and extruding eyeballs. A predominant bacterium named strain SR1 was isolated from the ascites of a moribund fish with swollen abdomen, and was proved to be a pathogenic bacterium by muscle injection experiments. The LD50 of injected strain SR1 was calculated to be 1.4×106 CFU/fish, and it indicated that SR1 had stronge virulence.By routine characterizations and API ID32E systematic identification, strain SR1 was indentified as Vibrio alginolyticus. In order to identify strain SR1 in molecular level, 16S rRNA and 60 kDa heat shock protein (HSP60) genes particial sequences were determined. The length of 16S rRNA gene was 1 431 bp, and the accession number in Genbank was DQ269211. Phylogenetic tree of Vibrio based on 16S rRNA gene indicated that strain SR1 showed the highest level of similarity to V.