Isolation, Identification and Susceptibilities of Hybrid Sturgeon Streptococcus iniae

PurposeTo determine the pathogen that caused the massive death of hybrid sturgeon Acipenser baerii (♀)×Acipenser schrenckii (♂) in the sturgeon farm in Jingdong, Yunnan Province.

MethodThe pathogen was isolated from the internal organs of diseased hybrid sturgeons and was identified by morphological identification and molecular identification. Experimental infection assay and antimicrobial susceptibility test were conducted to determine the pathogenicity of isolate and to screen out the susceptible antimicrobial agents.

ResultA Gram-positive pathogenic bacterium was isolated and identified as Streptococcus iniae. Its pathogenicity was confirmed by experimental infection test and the half of lethal dose (LD₅₀) to hybrid sturgeon in two weeks was 4.11×10² CFU/g. The results of antimicrobial susceptibility test showed that the isolate was susceptible to florfenicol and doxycycline, but resistant to sulfamonomethoxine, sulfamethoxazole and other angents.

ConclusionS. iniae was isolated from the infected hybrid sturgeon and was highly lethal to hybrid sturgeon, indicating that it might be the main pathogen that caused the death of the hybrid sturgeon in sturgeon farm. This study provides a theoretical basis for disease control and prevention and reveals its potential risk in the process of hybrid sturgeon breeding.