[Isolation and identification of a pathogenic Plesiomonas shigelloides from diseased grass carp]. 
The aim of this study is to identify strain JX-09 and confirmed that the strain is the pathogen of diseased grass carp (Ctenopharyngodon idellus).  A pathogenic strain JX-09 was isolated from the diseased grass carp.  The strain was identified based on physiological and biochemical characteristics, and the sequence analysis of 16S rRNA.  Virulence of strain JX-09 to healthy grass carp was also tested.  Furthermore, drug sensitivity was detected Strain JX-09 was identified as Plesiomonas shigelloides by with Kirby-Bauer's agar diffusion method.  biochemical analysis and molecular biology.  The P. shigelloides strain was re-isolated from the artificial infected grass carp, and the LD50 was about 6.4 x 10(4) cfu/g. Drug sensitive tests showed that strain JX-09 was susceptible to aztreonam, cefazolin, cephalothin and ceftriaxone, and resistant to kanamycin, medicamycin, vancomycin and piperacillin.  Strain JX-09 was the pathogen of grass carp with muscle erosive disease.  To the best of our knowledge, this is the first report that P. shigelloides as the pathogenic strain of grass carp.