Characterization and Phylogenetic Analysis of the Bitrichous Pathogenic Aeromonas hydrophila Isolated from Diseased Siberian sturgeon (Acipenser baerii)

Diseases have been the bottle-neck to sustainable development of sturgeon cultivation. Bacterial septicemia that caused mass mortalities of sturgeons is still prevalent in Shanxi and Yunnan provinces in China. The epidemiology and pathogenicity of the disease were investigated. Four predominant isolates of bacteria were isolated from Siberian sturgeons (Acipenser baerii) suffering from bacterial septicemia in outdoor culture ponds. Induced infection experiments with these isolates of bacteria showed that only one isolate was pathogenic and showed the same signs as in naturally infected sturgeon. Re-isolates from diseased sturgeon had the same morphological characteristics. Physiological and biochemical tests and sequence similarity analysis of the 16S rDNA genes of this isolate indentify it as Aeromonas hydrophila. An antibiotic sensitivity test showed that the isolate was sensitive to netilmicin, cefur oxime, cephradine, gentamicin, neomycin, streptomycin, and cefobid, and moderately sensitive to nalidixic acid, kanamycin, cephalothin V.