关键词: 草鱼, 腐败希瓦氏菌, 16S rDNA, 生理生化, 药敏试验

Abstract: A bacterial strain was isolated from the grass carp（Ctenopharyngodon idellus）, and named C0703. The morphological observation, physiological and biochemical characteristics, sequencing of 16S rDNA and phylogenetic tree analysis were carried out in this study. Results showed that the C0703 strain was a rod-shaped, gram-negative bacillus; The isolated strain was positive for oxidase, esculin and nitrate reduction, and negative reaction for lysine decarboxylase and glucose etc. Furthermore, the 16S rDNA sequences were amplified by PCR method, to get fragment size of sequencing 1 409 bp. It had a 98.23% similarity with 16S rDNA sequence of Shewanella putrefaciens ATCC 8071（NR 119141.1）, and clustered into one group with Shewanella putrefaciens（NR 119141.1）, thus the C0703 strain was identified as Shewanella putrefaciens. Animal experiment showed that the isolated strain has pathogenic to grass carp and causeddeath with a 100% rate, which were consistent with the natural symptoms of diseased fishes. The antibiotic susceptibility testing showed that it was sensitive to amoxicillin, meropenem and nalidixic acid etc, but resistant to ampicillin, cefazolin and vancomycin etc. This study firstly reported the isolation and identification of Shewanella putrefaciens from grass carp, which will provide a scientific reference for prevention and treatment in fishes.

Key words: grass carp, Shewanella putrefaciens, 16S rDNA, physiological and biochemical, antibiotic sensitivity test