The University of Queensland, School of Biological Sciences and Centre for Marine Science, St. Lucia Campus, Brisbane, Queensland, Australia.
Biosecurity Queensland (North Region), Department of Agriculture and Fisheries, Townsville, Queensland, Australia.
Appl Environ Microbiol. 2018 Aug 1;84(16). doi: 10.1128/AEM.00859-18. Print 2018 Aug 15.
(group B [GBS]) causes disease in a wide range of animals. The serotype Ib lineage is highly adapted to aquatic hosts, exhibiting substantial genome reduction compared with terrestrial conspecifics. Here, we sequence genomes from 40 GBS isolates, including 25 isolates from wild fish and captive stingrays in Australia, six local veterinary or human clinical isolates, and nine isolates from farmed tilapia in Honduras, and compared them with 42 genomes from public databases. Phylogenetic analysis based on nonrecombinant core-genome single nucleotide polymorphisms (SNPs) indicated that aquatic serotype Ib isolates from Queensland were distantly related to local veterinary and human clinical isolates. In contrast, Australian aquatic isolates are most closely related to a tilapia isolate from Israel, differing by only 63 core-genome SNPs. A consensus minimum spanning tree based on core-genome SNPs indicates the dissemination of sequence type 261 (ST-261) from an ancestral tilapia strain, which is congruent with several introductions of tilapia into Australia from Israel during the 1970s and 1980s. Pangenome analysis identified 1,440 genes as core, with the majority being dispensable or strain specific, with non-protein-coding intergenic regions (IGRs) divided among core and strain-specific genes. Aquatic serotype Ib strains have lost many virulence factors during adaptation, but six adhesins were well conserved across the aquatic isolates and might be critical for virulence in fish and for targets in vaccine development. The close relationship among recent ST-261 isolates from Ghana, the United States, and China with the Israeli tilapia isolate from 1988 implicates the global trade in tilapia seed for aquaculture in the widespread dissemination of serotype Ib fish-adapted GBS. (GBS) is a significant pathogen of humans and animals. Some lineages have become adapted to particular hosts, and serotype Ib is highly specialized to fish. Here, we show that this lineage is likely to have been distributed widely by the global trade in tilapia for aquaculture, with probable introduction into Australia in the 1970s and subsequent dissemination in wild fish populations. We report here the variability in the polysaccharide capsule among this lineage but identify a cohort of common surface proteins that may be a focus of future vaccine development to reduce the biosecurity risk in international fish trade.
（GBS）可引起多种动物患病。血清型 Ib 谱系高度适应水生宿主，与陆生同系物相比，其基因组有实质性的减少。在这里，我们对来自澳大利亚野生鱼类和圈养黄貂鱼的 40 个 GBS 分离株，包括 25 个分离株、6 个当地兽医或人类临床分离株以及来自洪都拉斯养殖罗非鱼的 9 个分离株进行了测序，并将其与来自公共数据库的 42 个基因组进行了比较。基于非重组核心基因组单核苷酸多态性（SNP）的系统发育分析表明，昆士兰州的水生血清型 Ib 分离株与当地兽医和人类临床分离株关系较远。相比之下，澳大利亚的水生分离株与来自以色列的罗非鱼分离株最为密切相关，仅相差 63 个核心基因组 SNPs。基于核心基因组 SNPs 的共识最小生成树表明，261 型（ST-261）序列从一个祖先罗非鱼菌株中传播，这与 20 世纪 70 年代和 80 年代以色列向澳大利亚多次引入罗非鱼是一致的。泛基因组分析确定了 1440 个基因为核心基因，其中大多数是可有可无的或菌株特异性的，非蛋白编码基因间区（IGR）分为核心和菌株特异性基因。水生血清型 Ib 菌株在适应过程中丢失了许多毒力因子，但 6 种黏附素在水生分离株中得到了很好的保守，这可能对鱼类的毒力和疫苗开发的靶点至关重要。加纳、美国和中国的最近 ST-261 分离株与 1988 年来自以色列的罗非鱼分离株密切相关，这表明用于水产养殖的罗非鱼种子的全球贸易导致了血清型 Ib 鱼类适应性 GBS 的广泛传播。（GBS）是人类和动物的重要病原体。一些谱系已经适应了特定的宿主，而血清型 Ib 则高度特化于鱼类。在这里，我们表明，通过全球范围内的罗非鱼养殖贸易，这种谱系可能已经广泛传播，可能在 20 世纪 70 年代引入澳大利亚，并随后在野生鱼类种群中传播。我们报告了该谱系中多糖荚膜的变异性，但鉴定出了一组共同的表面蛋白，这可能是未来疫苗开发的重点，以降低国际鱼类贸易中的生物安全风险。
