Pathogenic strategies of the swine pathogen Streptococcus suis

猪链球菌（血清型2）是造成世界范围内养猪业重大经济损失的猪病原体。这种病原体引起的主要感染包括关节炎、败血症、脑膜炎和心内膜炎。我实验室的研究项目主要集中在猪链球菌致病策略的鉴定和表征。更具体地说，未来五年的研究计划依赖于两个特定的假设：1)猪链球菌的细胞表面蛋白酶SspA在感染过程中起着几个关键作用；2)猪链球菌分泌的膜囊泡具有广泛的病理功能，是一种新的毒力机制。下面列出的与每个假设相关的研究是我在过去NSERC研究资助期间所做工作的合理延续。

Streptococcus suis (serotype 2) is a swine pathogen responsible for important economic losses in the swine industry worldwide. Major infections caused by this pathogen include arthritis, septicemia, meningitis and endocarditis. The research program of my laboratory focusses on the identification and characterization of pathogenic strategies developed by S. suis. More specifically, the research proposed for the next five years relies on two specific hypotheses: 1) The cell surface protease SspA of S. suis plays several key roles in the infectious process; and 2) Membrane vesicles secreted by S. suis possess a wide array of pathological functions and represent a new virulence mechanism. The studies related to each hypothesis are outlined below are a logical continuation of the work performed during my past NSERC research funding. In the first part of my research program, I propose to investigate the mechanisms by which the SspA protease may contribute to S. suis infections. We will first determine the parameters and growth conditions (biofilm growth, co-culture with host cells, presence of serum or sub-minimal inhibitory concentrations of antibiotics, etc) upregulating the expression of sspA gene. Then, using an SspA-deficient mutant as well as the purified recombinant protease, we will investigate the effects of S. suis SspA on i) inactivation of the innate immune components (antimicrobial peptide, epithelial cell barrier integrity), and ii) amplification of the inflammatory response through shedding of active TNF-alpha and generation of bradykinin from high-molecular-weight kininogens. In the second part of my research program, I propose to characterize membrane vesicles produced by S. suis and to identify their pathological functions. We will first study the modulation of S. suis vesicle production by various environmental conditions. Then, we will investigate the role of vesicles in toxin delivery by characterizing their composition using a proteomic approach. Given that preliminary data revealed that vesicles possess a high DNase activity, we will evaluate their ability to allow S. suis to escape from neutrophil extracellular traps. Lastly, the inflammatory potential of S. suis membrane vesicles will be tested by investigating their ability to i) activate the nuclear factor-kB signaling pathway, and ii) induce the secretion of inflammatory mediators by a co-culture model of microvascular endothelial cells and macrophages. Significance: The proposed studies have two complementary objectives: (i) to increase our basic knowledge of the pathogenic strategies used by S. suis to counteract the host defense system and amplify the destructive inflammatory response, and (ii) to use this knowledge to identify new vaccine molecule candidates and to design drugs targeting bacterial virulence factors in view to more efficiently control S. suis infections.