Wang Rui, Li Liping, Huang Yin, Huang Ting, Tang Jiayou, Xie Ting, Lei Aiying, Luo Fuguang, Li Jian, Huang Yan, Shi Yunliang, Wang Dongying, Chen Ming, Mi Qiang, Huang Weiyi
Guangxi Key Laboratory for Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Institute of Fisheries, Nanning, China.
Institute of Animal Science and Technology, Guangxi University, Nanning, China.
Front Microbiol. 2017 Oct 6;8:1933. doi: 10.3389/fmicb.2017.01933. eCollection 2017.
, or Group B (GBS), is a major pathogen causing neonatal sepsis and meningitis, bovine mastitis, and fish meningoencephalitis. CC23, including its namesake ST23, is not only the predominant GBS strain derived from human and cattle, but also can infect a variety of homeothermic and poikilothermic species. However, it has never been characterized in fish. This study aimed to determine the pathogenicity of ST23 GBS to fish and explore the mechanisms causing the difference in the pathogenicity of ST23 GBS based on the genome analysis. Infection of tilapia with 10 human-derived ST23 GBS isolates caused tissue damage and the distribution of pathogens within tissues. The mortality rate of infection was ranged from 76 to 100%, and it was shown that the mortality rate caused by only three human isolates had statistically significant difference compared with fish-derived ST7 strain ( < 0.05), whereas the mortality caused by other seven human isolates did not show significant difference compared with fish-derived ST7 strain. The genome comparison and prophage analysis showed that the major genome difference between virulent and non-virulent ST23 GBS was attributed to the different prophage sequences. The prophage in the P1 region contained about 43% GC and encoded 28-39 proteins, which can mediate the acquisition of YafQ/DinJ structure for GBS by phage recombination. YafQ/DinJ belongs to one of the bacterial toxin-antitoxin (TA) systems and allows cells to cope with stress. The ST23 GBS strains carrying this prophage were not pathogenic to tilapia, but the strains without the prophage or carrying the pophage that had gene mutation or deletion, especially the deletion of YafQ/DinJ structure, were highly pathogenic to tilapia. In conclusion, human ST23 GBS is highly pathogenic to fish, which may be related to the phage recombination.
B组链球菌（GBS）是引起新生儿败血症和脑膜炎、牛乳腺炎以及鱼类脑膜脑炎的主要病原体。CC23，包括其同名的ST23，不仅是源自人类和牛的主要GBS菌株，还能感染多种恒温动物和变温动物。然而，它从未在鱼类中得到过特征描述。本研究旨在确定ST23 GBS对鱼类的致病性，并基于基因组分析探索导致ST23 GBS致病性差异的机制。用10株源自人类的ST23 GBS分离株感染罗非鱼，导致组织损伤和病原体在组织内的分布。感染死亡率在76%至100%之间，结果表明，仅由三株人类分离株引起的死亡率与源自鱼类的ST7菌株相比具有统计学显著差异（P<0.05），而其他七株人类分离株引起的死亡率与源自鱼类的ST7菌株相比未显示出显著差异。基因组比较和前噬菌体分析表明，有毒和无毒ST23 GBS之间的主要基因组差异归因于不同的前噬菌体序列。P1区域的前噬菌体含有约43%的GC，编码28至39种蛋白质，可通过噬菌体重组介导GBS获得YafQ/DinJ结构。YafQ/DinJ属于细菌毒素-抗毒素（TA）系统之一，可使细胞应对压力。携带这种前噬菌体的ST23 GBS菌株对罗非鱼无致病性，但没有前噬菌体或携带发生基因突变或缺失的前噬菌体，尤其是缺失YafQ/DinJ结构的菌株，对罗非鱼具有高度致病性。总之，人类ST23 GBS对鱼类具有高度致病性，这可能与噬菌体重组有关。
