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

项目摘要 非伤寒沙门氏菌感染是全球4种最常见的腹泻病原因之一。在 美国，沙门氏菌肠道血清型鼠伤寒沙门氏菌（S. TM）感染导致135万人患病 每年。感染胃肠道，S。Tm与肠道内的常驻细菌（肠道 微生物群）。肠道微生物群通过限制肠道病原体扩张（定植）而有益于宿主 抗性），部分地通过产生抑制性代谢物如短链脂肪酸（SCFA）（例如， 丙酸盐）和养分螯合（例如，氨基酸）。因此，成功的细菌病原体必须具备 在肠道竞争性生态系统中生存的机制。S. Tm使用III型分泌系统（T3SS-1）。 I）侵入肠上皮细胞（EIC）并诱导肠道炎症。因此，S. Tm破坏了 宿主-微生物群生态系统，并通过使用炎症- 衍生的电子受体，如富马酸盐和硝酸盐，用于无氧呼吸。然而，机制 驱动沙门氏菌诱导的肠道微生物生态系统破坏以及这种破坏如何影响 宿主生理学和促进病原体扩张仍然是未知的。在本申请中，我们将阐明 S. Tm诱导的肠道炎症使病原体能够（i）压倒SCFA- 介导的定殖抗性和（ii）获得微生物来源的天冬氨酸用于厌氧富马酸 呼吸我们从体外研究和小鼠模型中获得的可靠的初步数据表明， 病原体可能利用丙酸代谢通过调节T3SS-I表达来微调毒力。我们 研究进一步揭示了S. TM诱导的炎症导致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燃料S。体外和体内富马酸Tm呼吸 vivo.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允许 S. Tm通过以下方式克服由微生物群建立的定殖抗性机制：（i）下调 通过类杆菌衍生的丙酸盐的催化作用侵入EIC，和（ii）通过 嗜盐拟杆菌属（Bacteroides），S. Tm用于胜过细菌性肠杆菌科。为了验证这一 假设，我们将定义丙酸催化剂对S. Tm在炎症肠道中的发病机制（目的 1）。目标2将确定肠道炎症促进天冬氨酸利用率增加的机制 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克服定殖抗性 肠杆菌科是一种在保护宿主免受沙门氏菌感染中起关键作用的细菌分类群。感染。 如果成功，这项研究将建立关键的概念性进展，了解肠道病原体如何 在肠胃炎期间利用肠道微生物群进行扩张。预期结果将提供更深入的 了解这种细菌病原体逃避肠道微生物群的新机制， 建立感染。

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.