Mechanisms of Salmonella-mediated disruption of colonization resistance in the inflamed gut

项目总结 感染非伤寒沙门氏菌是全球腹泻疾病最常见的4个原因之一。在……里面 美国肠道沙门氏菌血清鼠伤寒沙门氏菌感染导致135万人患病 每年一次。为了感染胃肠道，S.TM与常驻的共生细菌(肠道)进行斗争 微生物区系)。肠道微生物区系通过限制肠道病原体的扩张(定植)而使宿主受益 抗药性)，部分通过产生抑制代谢物，例如短链脂肪酸(SCFA)(例如， 丙酸)和养分封存(如氨基酸)。因此，成功的细菌病原体必须具备 在竞争激烈的肠道生态系统中生存的机制。S.TM使用III型分泌系统(T3SS- 1)侵袭肠上皮细胞(EICs)，引起肠道炎症。因此，S.TM扰乱了 宿主-微生物区系生态系统和克服微生物区系介导的定植抗性通过利用炎症- 衍生的电子受体，如富马酸和硝酸盐，用于厌氧呼吸。然而，这些机制 驱动沙门氏菌引起的肠道微生物生态系统的破坏，以及这种破坏如何影响 寄主生理学和促进病原体扩张在很大程度上仍不清楚。在本申请中，我们将阐明 金黄色葡萄球菌引起肠道炎症的机制是：(1)抑制SCFA-- 介导的定植抗性和(Ii)获得厌氧富马酸的微生物群衍生天冬氨酸 呼吸。我们从体外研究和小鼠模型中获得的强有力的初步数据表明， 病原菌可能利用丙酸代谢，通过调节T3SS-I的表达来微调毒力。我们的 研究进一步表明，S.TM诱导的炎症导致小鼠体内类杆菌衍生的天冬氨酸增加。 肠腔和天冬氨酸转化为富马酸在体外和体内促进了S.TM富马酸呼吸。 活着。我们的初步数据支持我们的中心假设，即病原体诱导的肠道炎症 通过(I)下调来克服微生物群建立的定殖抗性机制 类杆菌丙酸分解代谢侵袭EICS和(Ii)促进天冬氨酸的释放 共生类杆菌，S.TM用它来竞争共生肠杆菌科。为了测试这一点 假设，我们将定义丙酸分解代谢在肠炎的S.TM发病机制中的影响(目的 1)。目标2将确定肠道炎症促进天冬氨酸利用度增加的机制 在发炎的肠子里。在目标3中，我们将确定天冬氨酸如何使S.TM克服定植抗性 肠杆菌科细菌，一种在保护宿主免受S.TM感染方面发挥关键作用的细菌分类群。 如果成功，这项研究将在理解肠道病原体如何 在胃肠炎期间利用肠道微生物群进行扩张。预期的发现将提供更深层次的 了解这种细菌用来逃避肠道微生物区系和 确定感染。

PROJECT SUMMARY Infection with non-typhoidal Salmonella is 1 of 4 most prevalent global causes of diarrheal disease. In the United States, Salmonella enterica serovar Typhimurium (S. Tm) infection results in 1.35 million illnesses annually. To infect the gastrointestinal tract, S. Tm contends with the resident commensal bacteria (gut microbiota). The gut microbiota benefits the host by limiting enteric pathogen expansion (colonization resistance), partially via the production of inhibitory metabolites such as short-chain fatty acids (SCFA) (e.g., propionate) and nutrient sequestration (e.g., amino acids). Thus, successful bacterial pathogens must possess mechanisms to survive in the competitive ecosystem of the gut. S. Tm uses a Type III secretion system (T3SS- I) to invade intestinal epithelial cells (EICs) and induce intestinal inflammation. As a result, S. Tm disrupts the host-microbiota ecosystem and overcomes microbiota-mediated colonization resistance by using inflammation- derived electron acceptors such as fumarate and nitrate for anaerobic respiration. However, the mechanisms that drive Salmonella-induced disruption of the microbial ecosystem in the gut and how this disruption affects host physiology and promotes pathogen expansion remain largely unknown. In this application, we will elucidate the mechanisms by which S. Tm-induced intestinal inflammation enables the pathogen to (i) overpower SCFA- mediated colonization resistance and (ii) gain access to microbiota-derived aspartate for anaerobic fumarate respiration. Our robust preliminary data obtained from in vitro studies and murine models demonstrate that the pathogen may use propionate metabolism to fine-tune virulence through modulation of T3SS-I expression. Our studies further reveal that S. Tm-induced inflammation causes an increase in Bacteroides-derived aspartate in the intestinal lumen and that aspartate conversion into fumarate fuels S. Tm fumarate respiration in vitro and in vivo. Our preliminary data support our central hypothesis that pathogen-induced intestinal inflammation allows S. Tm to overcome mechanisms of colonization resistance established by the microbiota by (i) downregulating invasion of EICs via catabolism of Bacteroides-derived propionate and (ii) promoting the release of aspartate by commensal Bacteroides, which S. Tm uses to outcompete commensal Enterobacteriaceae. To test this hypothesis, we will define the impact of propionate catabolism on S. Tm pathogenesis in the inflamed gut (Aim 1). Aim 2 will identify the mechanism by which intestinal inflammation promotes increased aspartate availability in the inflamed gut. In Aim 3, we will determine how aspartate enables S. Tm to overcome colonization resistance by Enterobacteriaceae, a bacterium taxon that plays a critical role in protecting the host against S. Tm infection. If successful, this research will establish critical conceptual advances in understanding how enteric pathogens exploit the gut microbiota for expansion during gastroenteritis. Expected findings will provide a deeper understanding of a novel mechanism used by this bacterial pathogen to evade the intestinal microbiota and establish infection.