Isolation and identification of the hemorrhagic septicemia pathogen of Amur Sturgeon, Acipenser schrenckii Brandt

A strain of causative pathogen was isolated from the spleen tissue of freshly died amur sturgeon(Acipenser schrenckii Brandt)suffered from hemorrhagic septicemia.Experimental infection model was established based on the Koch rule.In initial infection test and regressive infection test,the typical diseased symptoms as naturally occurred were experimentally reproduced by intraperitoneal injection with isolated bacterium suspension.The result of infection test showed the LD50 was 1.17×107 cfu/mL,calculated by the Reed-Muench method.Considering the results of the Gram's staining,VITEK bacterial automatic identification system,sequencing of 16S rRNA gene and phylogenetic analysis,the isolated pathogen was identified as Aeromonas hydrophila.The susceptibility test to antibiotics revealed the isolated pathogen was resistant to ampicillin,sulbactam,cefazolin,piperacillin and sensitive to ciprofloxacin,gentamicin,etc.