Identification of conditionally essential genes for Streptococcus suis infection in pigs. suis_tnseq

Streptococcus suis is a Gram positive bacterium and zoonotic pathogen that causes meningitis and sepsis in pigs and humans. The aim of this study was to identify genes required for S. suis infection. We created Tn-seq libraries in a virulent S. suis strain 10, which was used to inoculate pigs in an intrathecal experimental infection. Comparative analysis of the relative abundance of mutants recovered from different sites of infection (blood, cerebrospinal fluid and meninges of the brain) identified 361 conditionally essential genes, i.e. required for infection, which is about 18% of the genome. The conditionally essential genes were primarily involved in metabolic and transport processes, regulation, ribosomal structure and biogenesis, transcription, and cell wall membrane and envelope biogenesis, stress defenses and immune evasion. Directed mutants were created in a set of 10 genes of different genetic ontologies and their role was determined in ex vivo models. Mutants showed different levels of sensitivity to survival in whole blood, serum, cerebrospinal fluid, thermic shock and stress conditions, as compared to the wild type. Additionally, the role of three selected mutants was validated in co-infection experiments in which pigs were infected with both wild type and isogenic mutant strains. The genetic determinants of infection identified in this work contribute to novel insights in S. suis pathogenesis and could serve as targets for novel vaccines or antimicrobial drugs.猪链球菌（Streptococcus suis）是一种革兰氏阳性（Gram-positive）人畜共患病原菌，可引发猪与人类的脑膜炎及败血症。本研究旨在鉴定猪链球菌感染过程中必需的基因。我们在强毒猪链球菌菌株10中构建了转座子测序（Transposon sequencing, Tn-seq）文库，随后利用该菌株开展鞘内注射猪实验感染。对从不同感染部位（血液、脑脊液及脑膜）回收的突变体相对丰度进行比较分析后，共鉴定出361个条件必需基因（即感染必需基因），约占其基因组的18%。上述条件必需基因主要参与代谢与转运过程、基因调控、核糖体结构与生物发生、转录过程、细胞壁膜及包膜生物发生、应激防御以及免疫逃逸等生物学过程。我们针对10个隶属于不同基因本体类别的基因构建了定向突变体，并通过离体模型测定了其功能。相较于野生型菌株，各突变体在全血、血清、脑脊液、热击胁迫及其他应激条件下的存活能力呈现不同程度的敏感性差异。此外，我们通过共感染实验验证了3个筛选得到的突变体的功能：实验猪同时接种野生型菌株与同基因（isogenic）突变株。本研究鉴定得到的感染相关遗传决定因子，为猪链球菌的致病机制研究提供了全新见解，同时可作为新型疫苗或抗菌药物的研发靶点。