ABSTRACT: Streptococcus iniae is a Gram-positive, opportunistically zoonotic bacterium infective to a wide variety of farmed and wild fish species worldwide. Outbreaks in wild fish can have detrimental environmental and cultural impacts, and mortality events in aquaculture can result in significant economic losses. As an emerging or re-emerging pathogen of global significance, understanding the coalescing factors contributing to piscine streptococcosis is crucial for developing strategies to control infections. Intraspecific antigenic and genetic variability of S. iniae has made development of autogenous vaccines a challenge, particularly where the diversity of locally endemic S. iniae strains is unknown. This study genetically and phenotypically characterized 11 S. iniae isolates from diseased wild and farmed fish from North America, Central America, and the Caribbean. A multilocus sequence analysis (MLSA) scheme was developed to phylogenetically compare these isolates to 84 other strains of Streptococcus spp. relevant to aquaculture. MLSA generated phylogenies comparable to established genotyping methods, and isolates formed distinct clades related to phenotype and host species. The endothelial Oreochromis mossambicus bulbus arteriosus cell line and whole blood from rainbow trout Oncorhynchus mykiss, Nile tilapia Oreochromis niloticus, and white sturgeon Acipenser transmontanus were used to investigate the persistence and virulence of the 11 isolates using in vitro assays. In vivo challenges using an O. niloticus model were used to evaluate virulence by the intragastric route of infection. Isolates showed significant differences (p < 0.05) in virulence and persistence, with some correlation to genogroup, establishing a basis for further work uncovering genetic factors leading to increased pathogenicity.

中文翻译：

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多种链球菌分离株的多基因座序列分析表明表型异质性的潜在遗传基础。

摘要：链球菌是革兰氏阳性，机会性人畜共患病菌，可感染全世界多种养殖和野生鱼类。野生鱼类的爆发会对环境和文化造成不利影响，而水产养殖中的死亡事件可能导致重大的经济损失。作为具有全球意义的新兴或新出现的病原体，了解导致鱼链球菌病的合并因素对于制定控制感染的策略至关重要。猪链球菌的种内抗原和遗传变异性已使自体疫苗的开发面临挑战，特别是在本地地方性链球菌的多样性方面菌株未知。这项研究从北美，中美洲和加勒比海地区的患病野生鱼和养殖鱼中分离出11种海豚链球菌，从遗传和表型上对它们进行了鉴定。开发了多基因座序列分析（MLSA）方案，以系统地比较这些分离物与其他84种链球菌菌株。与水产养殖有关。MLSA产生的系统发育与已建立的基因分型方法相当，并且分离物形成了与表型和宿主物种相关的独特进化枝。虹鳟Oncorhynchus mykiss，尼罗罗非鱼Oreochromis niloticus和白色st鱼的内皮Oreochromis mossambicus bulbus arteriosus细胞系和全血Acipenser transmontanus用于使用体外测定法调查11种分离株的持久性和毒力。使用尼罗罗非鱼（O. niloticus）模型进行的体内攻击用于通过胃内感染途径评估毒力。分离株在毒力和持久性方面显示出显着差异（p <0.05），与基因组有一定的相关性，为进一步开展工作揭示了导致致病性增加的遗传因素奠定了基础。