福建红罗非鱼源无乳链球菌的分离鉴定及其分子特征

Isolation, identification, and molecular characteristics of Streptococcus agalactiae from cultured red tilapia in Fujian Province

为探讨2017年福建省漳州市某养殖场红罗非鱼出现疾病的发病原因,并为该病的有效防治提供理论基础,以常规方法从患病红罗非鱼Oreochromis mossambicus×O.niloticus脑组织中分离优势菌株,采用形态观察和16S rRNA基因序列分析等方法对该优势菌进行鉴定,通过分子血清型、MLST和毒力基因等分型方法对分离株进行了分子特征分析,并采用K-B纸片扩散法检测分离株对26种抗生素的敏感性。结果表明:从病鱼脑组织中分离获得1株具致病力的不溶血(即γ溶血)无乳链球菌,该分离株是Ⅰa-ST7型,其毒力基因型为bac^+-bca^+-cfb^+-hylB^+-fbsA^+-fbsB^+-lmb^--scpB^--cpsE^+-sip^+,且对头孢类药物、强力霉素、氨苄青霉素等13种药物敏感,对氟罗沙星、青霉素G、多粘菌素B等4种药物中度敏感,而对新霉素、庆大霉素、卡那霉素等9种药物耐药。本研究结果可为福建红罗非鱼无乳链球菌病的疫病监测、疫苗研制和药物防治等研究提供基础数据。

A dominant bacterium was isolated from brain of eruptive diseased red tilapia Oreochromis mossambicus×O.niloticus collected from a farm in Zhangzhou, Fujian Province in 2017 using traditional method, and identified by morphological observation and 16 S rRNA gene sequence analysis. Genetic characteristics of the isolated strain were analyzed by molecular serotyping, multilocus sequence typing(MLST) and virulence-related gene sequencing, and the susceptibility of the isolated strain to 26 kinds of antimicrobial drugs was measured using Kirby-Bauer disc diffusion method to seek out the aetiological agent and to provide a theoretical foundation for effective treatment of the disease. It was found that the strain isolated from the diseased fish was a non-hemolysis(γ-hemolysis), type Ⅰa-ST7 Streptococcus agalactiae with pathogenicity, and virulence-related genotype of bac^+-bca^+-cfb^+-hylB^+-fbsA^+-fbsB^+-lmb^--scpB^--cpsE^+-sip^+. The strain was shown to be highly sensitive to 13 kinds of antibiotics including cephalosporin drugs, doxycycline, and ampicillin, intermediately sensitive to 4 antibiotics including fleroxacin, penicillin G, and polymyxin B, and resistant to 9 antibiotics including neomycin, gentamicin, and amikacin. The finding provides a theoretical basis for the epidemiology, vaccine development and disease treatment of Streptococcosis in red tilapia in Fujian Province.