Wang Rui, Li Li-Ping, Huang Ting, Lei Ai-Ying, Huang Yan, Luo Fu-Guang, Wang Dong-Ying, Huang Wei-Yi, Chen Ming, Huang Jun
Institute of Animal Science and Technology, Guangxi University, Nanning 530005, China; Guangxi Key Laboratory for Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Institute of Fisheries, Nanning 530021, China.
Guangxi Key Laboratory for Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Institute of Fisheries, Nanning 530021, China.
Vet Microbiol. 2017 Aug;207:164-169. doi: 10.1016/j.vetmic.2017.06.007. Epub 2017 Jun 13.
Streptococcus agalactiae or Group B Streptococcus (GBS) is the major pathogen causing pneumonia and meningitis in human, mastitis in dairy cows, and streptococcal disease in tilapia. Previous studies have shown that fish GBS strains are correlated with human GBS strains in evolution and might have cross-host infection ability. Although the invasive disease caused by ST1 GBS in non-pregnant adults and cows is increasing worldwide, infection of fish by ST1 GBS has not been reported. The aim of this study was to determine whether ST1 GBS was virulent in fish and to investigate the genomic characteristics of ST1 GBS strains with different pathogenicity in tilapia. The human-derived serotype V ST1 GBS strains NNA048 and NNA038 were used to intraperitoneally challenge Nile tilapia (Oreochromis niloticus) with doses of 1.0×10CFU/fish, 1.0×10CFU/fish, and 1.0×10CFU/fish, respectively. The cumulative mortality rates of NNA048 infection at three different doses were 100.00%, 83.33%, and 40.00%. In contrast, there were no any sick or dead fish in NNA038 infection group. Histopathological results indicated that challenge of tilapia with NNA048 caused different degree of degeneration and necrosis in brain, liver, spleen, head kidney, and gut, and a large number of blue-stained Streptococcus granules were observed in the tissues. In contrast, there were no any lesions in the tissues of tilapia that were challenged with NNA038. Genome comparison showed that the major genome differences between NNA048 and NNA038 were attributed to the different phage sequences, and there was a 49.8kb length, intact phage sequence encoding 68 proteins in NNA048 genome. SNV and Indels analysis between NNA038 and NNA048 genomes indicated that there were a total of 96 SNVs, 5 deletions and 1 insert. Taken together, serotype V ST1 GBS was comprised of virulent and nonvirulent strains to tilapia, and gene rearrangement might be the main reason of causing different levels of virulence between strains.
无乳链球菌或B群链球菌（GBS）是导致人类肺炎和脑膜炎、奶牛乳腺炎以及罗非鱼链球菌病的主要病原体。先前的研究表明，鱼类GBS菌株在进化上与人类GBS菌株相关，并且可能具有跨宿主感染能力。尽管由ST1 GBS在非妊娠成年人和奶牛中引起的侵袭性疾病在全球范围内呈上升趋势，但尚未有ST1 GBS感染鱼类的报道。本研究的目的是确定ST1 GBS对鱼类是否具有致病性，并研究罗非鱼中具有不同致病性的ST1 GBS菌株的基因组特征。使用源自人类的血清型V ST1 GBS菌株NNA048和NNA038分别以1.0×10CFU/鱼、1.0×10CFU/鱼和1.0×10CFU/鱼的剂量对尼罗罗非鱼（Oreochromis niloticus）进行腹腔注射攻击。在三种不同剂量下，NNA048感染的累积死亡率分别为100.00%、83.33%和40.00%。相比之下，NNA038感染组没有任何患病或死亡的鱼。组织病理学结果表明，用NNA048攻击罗非鱼会导致脑、肝、脾、头肾和肠道出现不同程度的变性和坏死，并且在组织中观察到大量蓝色染色的链球菌颗粒。相比之下，用NNA038攻击的罗非鱼组织中没有任何病变。基因组比较表明，NNA048和NNA038之间的主要基因组差异归因于不同的噬菌体序列，并且在NNA048基因组中有一个长度为49.8kb、编码68种蛋白质的完整噬菌体序列。NNA038和NNA048基因组之间的单核苷酸变异（SNV）和插入缺失（Indels）分析表明，共有96个SNV、5个缺失和1个插入。综上所述，血清型V ST1 GBS对罗非鱼由毒力菌株和无毒力菌株组成，基因重排可能是导致菌株间毒力水平不同的主要原因。
