Nutritional immunity and microbial competition during Clostridioides difficile infection

总结 艰难梭菌（Clostridioides difficile）（以前称为艰难梭菌（Clostridium difficile））是一种革兰氏阳性的孢子形成病原体， 导致医院内和医院相关的肠道感染。对C.菌感染 (CDI)然而，通常在抗生素治疗和随后的肠道微生物群破坏之后， 在健康的年轻人中感染的增加表明还有其他因素导致CDI。到 定殖于胃肠道，C.艰难梭菌必须与宿主和肠道微生物群的成员竞争 关键的营养物质。获得营养金属可以深刻影响CDI的结果，因为金属是必需的 所有蛋白质的大约30%的辅因子。这一事实被宿主金属结合蛋白所利用， 螯合营养金属以在称为营养免疫的过程中限制微生物生长。CDI的标志 是分泌强效毒素，对胃肠道上皮造成严重损害，并引发 促炎细胞因子和趋化因子的产生。这些事件启动免疫介导的 炎症因子向感染部位的募集。一种最丰富的炎症蛋白， 在CDI位点积聚的是钙卫蛋白。钙卫蛋白是中性粒细胞中最丰富的蛋白质，是一种免疫调节剂。 营养免疫的组成部分，通过营养金属螯合直接抑制微生物生长。 钙卫蛋白也是一种有效的免疫调节蛋白，并且是一种常见的临床炎症生物标志物，其 丰度与CDI严重程度相关。目前尚不清楚钙卫蛋白的大量浸润如何影响金属 胃肠道中的可用性和C.艰难梭菌和肠道成员 微生物群此外，C.艰难梭菌适应钙卫蛋白依赖性金属限制， CDI期间的免疫力仍不清楚。我们提出了一个模型，使营养金属作出关键贡献 CDI的结果。毒素驱动的炎症驱动免疫细胞进入肠道， 大量CP的积累。CP螯合有效的营养金属，并发挥强大的促进作用， 炎症活动。这种巨大的炎症反应和营养的重新分配改变了C。艰难梭基因 表达并影响C.艰难梭菌和微生物群的成员。最后我们 假设C.艰难梭菌编码多种基因产物，这些基因产物与CP和微生物群竞争， 营养金属和这种竞争对CDI的结果有着深远的影响。本文中描述的实验 建议将测试这一模型，并确定营养免疫的贡献，发病机制的C。difficile， 确定金属结合和免疫细胞募集在钙卫蛋白保护特性中的作用，以及 识别C.在炎症期间与微生物组竞争营养金属所需的艰难基因。 总的来说，这项提案的结果将为开发有效的治疗或预防方法提供信息。 治疗CDI的策略。

SUMMARY Clostridioides difficile (formerly named Clostridium difficile) is a Gram-positive, spore-forming pathogen, and the leading cause of nosocomial and antibiotic-associated intestinal infections. Susceptibility to C. difficile infection (CDI) often follows antibiotic treatment and subsequent disruption of the resident intestinal microbiota, however the rise of infections in healthy young adults suggests that there are additional factors that contribute to CDI. To colonize the gastrointestinal tract, C. difficile must compete with both the host and members of the gut microbiota for critical nutrients. Access to nutrient metals can profoundly impact the outcome of CDI as metals are required cofactors for approximately 30% of all proteins. This fact is exploited by host metal binding proteins which sequester nutrient metals to restrict microbial growth in a process termed nutritional immunity. A hallmark of CDI is the secretion of potent toxins that cause severe damage to the gastrointestinal epithelium and trigger the production of pro-inflammatory cytokines and chemokines. These events initiate the immune-mediated recruitment of inflammatory factors to the site of infection. One of the most abundant inflammatory proteins that accumulates at the site of CDI is calprotectin. Calprotectin is the most abundant protein in neutrophils and is a component of nutritional immunity that directly inhibits microbial growth through nutrient metal sequestration. Calprotectin is also a potent immunomodulatory protein, and a common clinical inflammatory biomarker whose abundance correlates with CDI severity. It is unknown how the massive infiltration of calprotectin affects metal availability in the gastrointestinal tract and shapes competition between C. difficile and members of the gut microbiota. In addition, how C. difficile adapts to calprotectin-dependent metal limitation and resists nutritional immunity during CDI remains unclear. We propose a model whereby nutrient metals make a critical contribution to the outcome of CDI. Toxin driven inflammation drives the recruitment of immune cells into the gut which leads to the accumulation of large amounts of CP. CP chelates available nutrient metals and exerts potent pro- inflammatory activities. This massive inflammatory response and redistribution of nutrients alters C. difficile gene expression and affects the interaction between C. difficile and members of the microbiota. Finally, we hypothesize that C. difficile encodes multiple gene products that compete with both CP and the microbiota for nutrient metals and this competition has a profound effect on the outcome of CDI. Experiments described in this proposal will test this model and define the contribution of nutritional immunity to the pathogenesis of C. difficile, determine the role of metal binding and immune cell recruitment in the protective properties of calprotectin, and identify C. difficile genes required to compete with the microbiome for nutrient metals during inflammation. Collectively, the findings from this proposal will inform the development of effective therapeutic or prevention strategies for the treatment of CDI.