Key Laboratory of South China Sea Fishery Resources Exploitation & Utilization, Ministry of Agriculture and Rural Affairs, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, Guangdong Province, PR China.
College of Fisheries, Tianjin Agricultural University, Tianjin 300384, PR China.
FEMS Microbiol Lett. 2019 Jul 1;366(13). doi: 10.1093/femsle/fnz154.
Streptococcus agalactiae is an important pathogen of tilapia causing enormous economic losses worldwide. In this study, multilocus sequence typing indicated that 75 S. agalactiae isolates from tilapia in southern China belonged to sequence type-7, as well as belonging to serotype Ia, as confirmed by multiplex PCR assay. The putative-virulence gene profiles and genetic variation of these strains were determined by three sets of multiplex PCR and multi-virulence locus sequencing typing (MVLST), respectively. Analysis of putative-virulence gene profiles showed that each strain harbored 18 putative-virulence genes but lacked lmb and scpB. Three putative-virulence genes (srr-1, bibA and fbsA) were further selected for MVLST analysis. Our data showed that the strains had 14 MVLST types (1-14) and clustered in three groups (Groups I-Ⅲ). The period of time during 2013 and 2014 was an important turning point for the differentiation of the putative-virulence genes of S. agalactiae, as type 1 within Group Ⅱ became the predominant MVLST type. There were significant differences in MVLST types of S. agalactiae isolated from different tilapia farming regions. MVLST assay may improve the discriminatory power and is suitable for understanding the epidemiology of S. agalactiae serotype Ia and screening multivalent vaccine candidate strains.
无乳链球菌是一种重要的罗非鱼病原菌，在全球范围内造成了巨大的经济损失。在本研究中，多位点序列分型表明，来自中国南方罗非鱼的 75 株无乳链球菌分离株属于序列型 7，同时通过多重 PCR 检测也属于血清型 Ia。通过三套多重 PCR 和多位点序列分型（MVLST）分别确定了这些菌株的假定毒力基因谱和遗传变异。假定毒力基因谱分析表明，每株菌携带 18 个假定毒力基因，但缺乏 lmb 和 scpB。进一步选择了三个假定毒力基因（srr-1、bibA 和 fbsA）进行 MVLST 分析。我们的数据显示，这些菌株有 14 种 MVLST 类型（1-14），并聚类为三个组（I-III 组）。2013 年至 2014 年期间是无乳链球菌假定毒力基因分化的重要转折点，因为 II 组内的 1 型成为主要的 MVLST 类型。不同罗非鱼养殖区分离的无乳链球菌 MVLST 类型存在显著差异。MVLST 检测可能提高了鉴别力，适合于了解无乳链球菌血清型 Ia 的流行病学和筛选多价疫苗候选菌株。
