Isolation and identification of the hemorrhagic septicemia pathogen from Amur sturgeon, Acipenser schrenckii

A strain of bacteria was isolated from the spleen tissue of moribund Amur Sturgeon (Acipenser schrenckii) which suffered from a hemorrhagic septicemia disease. An experimental infection model was established fulfilling the Koch's postulate. In the initial artificial infection test and the regressive infection test the typical disease symptoms were experimentally reproduced by intraperitoneal injection with isolated bacterium suspension. These symptoms were identical with those observed in naturally infected fish. The result of the infection test showed the lethal dose that killed 50% of the exposed individuals (LD50) was 1.17 x 10(7) cfu ml(-1). Considering the results of the Gram's staining, VITEK Bacterial Automatic Identification System, sequencing of 16S rDNA gene and phylogenetic analysis, the isolated pathogen was identified as Aeromonas hydrophila. The test on the susceptibility to antibiotics revealed that the isolated pathogen was sensitive to sensitive to Amikacin, Ciprofloxacin, Gentamicin, etc., and were resistant to Ampicilin, Sulbactam, Cefazolin, etc.