广东五地区养殖罗非鱼无乳链球菌的分离、鉴定与特性分析

Isolation,identification and characterization of Streptococcus agalactiae isolated from tilapia fish farms in five districts of Guangdong

目的了解广东省罗非鱼主要养殖区内感染罗非鱼的无乳链球菌感染状况。方法从广东省内5个罗非鱼主要养殖区内收集罗非鱼样本,分离可疑病原菌,生理生化鉴定分离菌株种类;特异性PCR鉴定;多重PCR鉴定分离菌株的血清型。结果从广东5个罗非鱼主要养殖区发生病害的养殖场采集成鱼206条,共分离到单菌落172个,分离阳性率介于75.29%~89.47%。经生化鉴定无乳链球菌145株、戊糖片球菌18株、血链球菌7株、粪肠球菌2株。特异PCR鉴定显示171株为无乳链球菌,1株生理生化鉴定为戊糖片球菌菌株（GDSA078）,特异性PCR扩增结果阴性。血清型多重PCR鉴定显示170株为Ia血清型,两株扩增结果阴性（GDSA078,GDSA017）。结论广东省主要罗非鱼养殖区内感染链球菌为无乳链球菌,血清型高度一致,均为Ia型。

Objective To investigate the epidemiological characters of Streptococcus agalactiae isolated from tilapia in fish farms of Guangdong province. Methods Tilapia samples were collected from six tilapia farms in Guangdong province.The suspect pathogens were isolated and purified by culture. Each isolate was identified by morphology, physiological and biochemical tests, and duplex PCR. The serotypes of identified isolates were determined by multiplex PCR. Results One hundred and seventy-two strains were isolated from two hundred and six tilapia samples which were collected from six tilapia farms in Guangdong province. The positive rates of different districts varied from 75.29% to 89.47%. One hundred and forty-five isolates were identified as Streptococcus agalactiae through physiological and biochemical tests, whereas 27 isolates were identified as Pediococcus pentosaceus（18）, Streptococcus sanguis（7）, and Enterococcus faecalis（2）.The further duplex PCR results showed that 171 isolates were confirmed to be Streptococcus agalactiae. Only one isolate（GDSA078） which previously identified as Pediococcus pentosaceus through physiological and biochemical tests showed native amplification of target genes by duplex PCR. The serotyping tests showed that 170 isolates were determined as serotype Ia, whereas two isolates（GDAS078 and GDSA017） showed negative amplification for all serotypes. Conclusion Here we confirmed that Streptococcus agalactiae was the predominant agent of tilapia infection in Guangdong province.The highly consistent serotype was serotype Ia.