Isolation，identification and drug sensitivity of Streptococcus iniae from hybrid sturgeons (Huso dauricus female×Acipenser schrencki male)

Abstract:

Abstract:［Objective］Sturgeons were the important economic species in Beijing．In July 2012，continuous mortality of cultured hybrid sturgeons was occurred on a farm in Huairou．［Methods］We isolated three pathogens from liver，kidney and spleen of the dying sturgeons with clinical symptoms，marked HRS12718L， HRS12718K and HRS12718S respectively．Then we analyzed theirs morphological，physiological and biochemical characteristics，and drug sensitivity．We also cloned and partially sequenced the 16S rDNA of strain HRS12718K． Moreover，we identified the pathogenic characteristic of strain HRS12718K by artificial infection．［Results］The morphological，physiological and biochemical characteristics of three strains were consistent with that of Streptococcus iniae isolated from other fishes in China，and 16S rDNA sequence of the strain HRS12718K was more than 99.1% homology with that of Streptococcus iniae．The LD50 of the pathogen to hybrid sturgeon was 4.42×105 CFU/mL，and challenged sturgeons presented the similar signs as the natural infected sturgeons． In addition，the bacterium was sensitive to norfloxacin，enrofloxacin，neomycin sulfate，doxycyline hyclate and tetracycline hydrochloride，and was highly sensitive to enrofloxacin． ［Conclusion］Streptococcus iniae was the pathogen to cultured hybrid sturgeons in Beijing area，and enrofloxacin can be used against the disease．