杂交鲟海豚链球菌分离鉴定及药物敏感性

Isolation,Identification and Susceptibilities of Hybrid Sturgeon Streptococcus iniae

【目的】确定导致云南省景东县鲟鱼养殖场杂交鲟[西伯利亚鲟(Acipenser baerii)(♀)×施氏鲟(Acipenser schrenckii)(♂)]大量发病死亡的病原。【方法】从病鱼的内脏中分离获得病原菌,通过细菌的分离纯化、形态及分子生物学鉴定分离菌;以人工感染试验及药物敏感性测试验证分离菌株的感染性并筛选出敏感药物。【结果】分离菌为革兰氏阳性菌,16S rRNA系统发育分析将该菌株鉴定为海豚链球菌(Streptococcus iniae)。人工感染杂交鲟能复制出类似症状,并能从感染鱼体内再次分离到该菌株,证实其病原性,且杂交鲟2周的半数致死剂量(LD50)为4.11×10^2 CFU/g。药敏结果显示:其对抗菌药物氟苯尼考和多西环素敏感,但对磺胺间甲氧嘧啶和磺胺甲噁唑/甲氧苄啶等多种药物耐药。【结论】海豚链球菌为引起景东县鲟鱼养殖场杂交鲟大量死亡的致病菌,为杂交鲟海豚链球菌病的控制和预防提供了理论依据,并揭示其在杂交鲟养殖过程中的潜在危险。

[Purpose]To determine the pathogen that caused the massive death of hybrid sturgeon[Acipenser baerii(♀)×Acipenser schrenckii(♂)]in the sturgeon farm in Jingdong,Yunnan Province.[Method]The 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.[Result]A 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 4.11×10^2 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.[Conclusion]S.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.