Studies on the pathogenesis of the infection caused by Streptococcus suis

猪链球菌是养猪业最重要的经济病原体之一，主要引起猝死和脑膜炎。血清型2和9是世界上最常见的分离和毒性类型。S.猪流感是由多种因素引起的，对感染的发病机制的认识仍然不完全。色葡萄迄今为止，已发表的猪毒力因子研究主要是用同源的欧亚血清型2菌株进行的，这些菌株属于（通过多位点序列分型研究）序列型（ST）1。大多数北美（NA）血清型2菌株在基因型/表型上与欧亚菌株非常不同，为ST 25（毒性型）或ST 28（毒性较低型）。此外，关于血清型9毒力因子的知识很少。最后，临床S.猪流感病例通常发生在伴随病毒感染的猪群中，如猪流感病毒（SwIV）和生殖与呼吸综合征病毒（PRRSV）。然而，这些病原体之间的协同作用的机制尚未研究。在接下来的5年里，我的研究计划的短期目标分为两个相连的轴：**1。为进一步研究沙门氏菌的毒力因子。首先，我们将描述一个假定的毒力因子（抗原I/II），它已经在S.猪血清型2和9，通过获得缺乏该蛋白的突变体。将评价其在口腔感染持续性和毒力中的作用。随后将对强毒力和低毒力参考血清型2和9 NA菌株的DNA进行完全测序。此后，将100多个现场菌株的DNA与相应参考菌株的DNA进行比较。将鉴定存在于强毒力菌株中的保守基因（但在低毒力菌株中不存在），并通过使用体外和体内试验测试其作用来获得/表征缺乏这些因子的突变体。2.为了研究病毒混合感染时细菌与宿主的相互作用：首先，我们将完成我们以前对S.猪感染SwIV的猪上皮细胞。为了评价病毒感染如何影响抗S.猪的免疫细胞如猪树突状细胞和肺泡巨噬细胞将被SwIV或PRRSV感染，然后与S.分析细胞反应，包括毒性和细胞死亡，免疫细胞消除S. suis和产生免疫应答介质（细胞因子）。还将评价毒力因子（目标1）对病毒合并感染的可能作用。** NSERC过去的研究帮助我们发现了关于S的新见解。猪感染。未来5年的研究将巩固我们对加拿大菌株的了解，使我们能够在这一领域保持国际领先地位。**

Streptococcus suis is one of the most economically important pathogens for the porcine industry, mainly causing sudden death and meningitis. Serotypes 2 and 9 are the most frequently isolated and virulent types worldwide. Virulence in S. suis is multifactorial and knowledge on the pathogenesis of the infection remains incomplete. The S. suis virulence factor studies published so far have been mainly performed with homogenous Eurasian serotype 2 strains that belong (as studied by multilocus sequence typing) to sequence type (ST)1. Most North American (NA) serotype 2 strains are genotypically/phenotypically very different from Eurasian strains, being either ST25 (virulent type) or ST28 (less virulent type). Also, little knowledge is available regarding serotype 9 virulence factors. Finally, clinical S. suis cases often occur in herds affected with concomitant viral infections such as the Porcine Swine Influenza Virus (SwIV) and the Reproductive and Respiratory Syndrome Virus (PRRSV). However, mechanisms underlying the synergy between these pathogens have not been studied. For the next 5 years, the short-term objectives of my research program are divided in two connected axes: ******1. To further characterize virulence factors of S. suis: Firstly, we will characterize one putative virulence factor (antigen I/II), already identified in NA strains of S. suis serotypes 2 and 9, by obtaining mutants lacking this protein. Its role in persistence of the infection in the oral cavity and virulence will be evaluated. This objective will be followed by completely sequencing the DNA of virulent and low-virulent reference serotype 2 and 9 NA strains. Thereafter, the DNA of more than 100 field strains will be compared to that of the respective reference strains. Conserved genes present in virulent (but absent in low-virulent) strains will be identified and mutants lacking these factors will be obtained/characterized by testing their role using in vitro and in vivo tests. ******2. To dissect bacterial-host interactions in the presence of viral co-infections: Firstly, we will complete our previous studies on the interactions of S. suis with SwIV-infected swine epithelial cells. In order to evaluate how viral infections affect the response against S. suis, immune cells such as porcine dendritic cells and pulmonary alveolar macrophages will be infected with either SwIV or PRRSV, and then co-infected with NA strains of S. suis to analyze cell responses including toxicity and cell death, capacity of immune cells to eliminate S. suis, and production of immune response mediators (cytokines). The possible role of virulence factors (objective 1) on viral co-infections will be also evaluated. ******Past NSERC research helped us discover new insights on the S. suis infection. The research proposed for the next 5 years will consolidate the knowledge of our Canadian strains, allowing us to keep the international leadership on this subject. **