Studies on the pathogenesis of the infection caused by Streptococcus suis

猪链球菌感染发病机制的研究

• 批准号: RGPIN-2015-04435
• 负责人: Gottschalk, Marcelo
• 金额: $ 4.15万
• 依托单位: Université de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=690726
• 关键词: Studies; pathogenesis; infection; caused; Streptococcus

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. **

猪链球菌是养猪业最重要的经济致病菌之一，主要引起猝死和脑膜炎。血清型2和9型是世界范围内最常见的分离和毒力类型。猪链球菌的毒力是多因素的，对这种感染的发病机制的了解还不完全。到目前为止发表的猪链球菌毒力因子研究主要是针对欧亚地区同源的2型毒株进行的，这些毒株属于序列类型(ST)1。大多数北美(NA)2型毒株的基因/表型与欧亚毒株非常不同，要么是ST25(毒力型)，要么是ST28(毒力较弱的型)。此外，关于血清9型毒力因子的知识也很少。最后，猪链球菌临床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，这些病原体之间协同作用的潜在机制尚未被研究。在接下来的5年里，我的研究计划的短期目标被分成两个相互关联的轴：*1.为了进一步表征猪链球菌的毒力因子：首先，我们将通过获得缺乏该蛋白的突变株来鉴定一个假定的毒力因子(抗原I/II)，该因子已在猪链球菌2型和9型NA株中被鉴定。将评估其在口腔内持续感染和毒力方面的作用。在这一目标之后，将对强毒和低毒参考血清2型和9型NA毒株的DNA进行完全测序。之后，100多个野生菌株的DNA将与各自的参考菌株的DNA进行比较。将鉴定存在于强毒株(但在低毒株中不存在)的保守基因，并将通过体外和体内试验测试它们的作用，获得/表征缺乏这些因子的突变株。*2.剖析病毒混合感染情况下的细菌-宿主相互作用：首先，我们将完成我们之前关于猪链球菌与感染了SwIV的猪上皮细胞相互作用的研究。为了评价病毒感染对猪链球菌免疫应答的影响，将猪树突状细胞和肺泡巨噬细胞等免疫细胞分别感染SwIV和PRRSV，然后与猪链球菌NA株共感染，分析包括毒性和细胞死亡在内的细胞反应，免疫细胞清除猪链球菌的能力，以及免疫反应介质(细胞因子)的产生。还将评估毒力因子(目标1)在病毒联合感染中的可能作用。过去的NSERC研究帮助我们发现了对猪链球菌感染的新见解。建议在未来5年进行的研究将巩固我们对加拿大菌株的了解，使我们能够在这一问题上保持国际领先地位。**