俄罗斯鲟源停乳链球菌停乳亚种分离、鉴定及药敏特性研究

Isolation, identification and drug sensitivity of Streptococcus dysgalactiae subsp. dysgalactiae from Acipenser gueldenstaedti

2016年6月~8月,湖北鲟养殖场的俄罗斯鲟发生一种以上下嘴唇充血肿胀为特征的病害。为确定其发病原因,本研究对自然发病鱼的病灶及内脏器官进行了病原菌的分离,并对分离株进行人工感染、毒力检测、生理生化特性测定及16S r RNA基因序列分析。结果从患病俄罗斯鲟体内分离到一株优势菌,人工感染试验出现与自然发病类似症状,确定其为俄罗斯鲟本次发病的病原菌,其对俄罗斯鲟幼鱼的半数致死剂量为3.64×10~4 cfu/g,该分离株生理生化特性与停乳链球菌停乳亚种一致;经16S rRNA基因序列比对及构建系统发育树结果显示,该分离株与停乳链球菌停乳亚种聚为一支,同源性在99%以上。该分离株鉴定为停乳链球菌停乳亚种(Streptococcus dysgalactiae subsp.dysgalactiae),命名为HD03。药敏试验结果表明,HD03株对环丙沙星、痢特灵及氟苯尼考等8种抗生素敏感,对苯唑西林、头孢唑林及阿莫西林等7种抗生素耐药。本研究首次证实停乳链球菌停乳亚种是俄罗斯鲟的病原菌,养殖时可以选用氟苯尼考进行防控。

During June and August of 2016, a serious disease characterized by lips swelling occurred in Acipenser gueldenstaedti in Hubei province. To elucidate the aetiology, the bacteria was isolated from the lesions and visceral organs. The artificial infection, physiological and biochemical analysis and 16S rRNA analysis of the isolate were conducted. The results showed that the isolate was Gram-positive, and was lethal to A.gueldenstaedti with similar clinical signs as naturally diseased fish and the LD50 was 3.64×10^4 cfu/g to the juveniles fish. Physiological and biochemical characteristics were consistent with S.dysg-alactiae subsp, dysgalactiae; The isolate and S.dysgalactiae subsp, dysgalactiae formed a tight cluster with 99% similarity by analysing the sequence and constructed phylogenetic tree based on the 16S rRNA gene, and named HD03. The result of drug sensitivity test showed that the HD03 was sensitive to ciprofloxacin, furazolidone, florfenicol and the other 8 antibiotics, and resistant to oxacillin, cefazolin, amoxicillin and the other antibiotics. Our results demonstrated that S.dysgalactiae subsp.dysgalactiae was the pathogen which caused high mortality in A.gueldenstaedti, and the disease could prevent by administering drugs such as florfenicol in the fishery breeding.