Mechanism of Salmonella-dependent disruption of propionate-mediated colonization resistance

项目总结 感染非伤寒沙门氏菌是全世界腹泻疾病的重要原因，导致 每年约有1.5亿人患病，6万人死亡。在胃肠道，S.TM遇到了 寄生共生细菌(肠道微生物区系)。肠道微生物区系保护宿主免受入侵 病原体(耐定殖性)和限制病原体扩张。丙酸，一种短链脂肪酸 由肠道微生物群的成员产生，预计通过以下方式介导对S.TM的定殖抗性 下调侵袭，抑制生长。作为一种成功的病原菌，S.TM可能具有 减轻丙酸的毒性作用。PrpBCDE操纵子的发现，它使S.TM能够代谢 丙酸转化为丙酮酸，初步了解了S.TM克服丙酸抑制的能力。 然而，目前还不清楚S.TM在什么条件下使用prpBCDE操纵子来消除细胞内 丙酸。在感染期间，宿主的炎症反应提供电子受体，使S.TM能够 将各种营养物质代谢成碳源，以支持病原体的生长。我的数据显示丙酸盐 作为S.TM的碳源，特别是在无氧呼吸期间，当炎症产生时 电子受体存在。在初步实验中，我确定炎症衍生的电子 受体还可以改变S.TM侵袭机制中丙酸依赖的表达变化。因此， 炎症衍生的电子受体可能为S.TM提供了消除抑制效应的机会 在感染期间，丙酸和燃料的生长。事实上，我的初步研究表明，丙酸代谢 在小鼠体内作为S.TM的野生型菌株比PrPC突变菌株具有生长优势 沙门氏菌肠胃炎模型的建立。因此，这一提议的中心假设是S.TM代谢 丙酸在发炎的肠道中调节其入侵并支持其腔内生长，最终允许 病原菌克服丙酸依赖的定植抗性。为了验证这一假设，我将使用 肠道微生物区系和S.TM突变株的共生成员与细菌的创新组合- 自由和传统的小鼠模型，以探索在感染过程中S.TM如何与丙酸抗衡。 目标1中提出的实验将确定丙酸是否作为碳源来推动S.TM在 体外和体内。在目标2中，我将确定丙酸是否需要肠道炎症和无氧呼吸 新陈代谢在感染期间对S.TM有利。目标3将调查丙酸新陈代谢不仅 通过在呼吸过程中提供碳源，但通过向S.TM发出信号以减少入侵来促进生长。如果 如果成功，这项研究将挑战短链脂肪酸抑制沙门氏菌生长的教条 直觉。本项目将描述S.TM如何通过代谢丙酸来减轻丙酸的有害影响 代谢产物转化为可利用的碳源，以促进生长。预期的发现将提供更深层次的理解 一种被这种细菌病原体用来逃避肠道微生物区系并建立感染的新机制。

PROJECT SUMMARY Infection with non-typhoidal Salmonella is a significant cause of diarrheal disease worldwide, causing approximately 150 million illnesses and 60,000 deaths each year. In the gastrointestinal tract, S. Tm encounters the resident commensal bacteria (gut microbiota). The gut microbiota protects the host against invading pathogens (colonization resistance) and limits pathogen expansion. Propionate, a short-chain fatty acid produced by members of the gut microbiota, is predicted to mediate colonization resistance against S. Tm by down-regulating invasion and inhibiting growth. As a successful pathogen, S. Tm may possess mechanisms to mitigate the toxic effects of propionate. Discovery of the prpBCDE operon, which enables S. Tm to metabolize propionate into pyruvate, provided initial insight into the ability of S. Tm to overcome propionate inhibition. However, it remains unknown under what conditions S. Tm uses the prpBCDE operon to eliminate intracellular propionate. During infection, the host's inflammatory response provides electron acceptors that allow S. Tm to metabolize diverse nutrients into carbon sources to support pathogen growth. My data suggests that propionate serves as a carbon source for S. Tm, specifically during anaerobic respiration when inflammation-derived electron acceptors are present. In preliminary experiments, I determined that inflammation-derived electron acceptors also alter propionate-dependent changes in expression of S. Tm invasion machinery. Thus, inflammation-derived electron acceptors may provide S. Tm with the opportunity to eliminate the inhibitory effects of propionate and fuel growth during infection. Indeed, my pilot studies demonstrate that propionate metabolism benefits S. Tm in vivo as a wildtype strain of S. Tm had a growth advantage over a prpC mutant strain in mouse models of S. Tm gastroenteritis. Therefore, the central hypothesis of this proposal is that S. Tm metabolizes propionate in the inflamed gut to regulate its invasion and support its luminal growth, ultimately allowing this pathogen to overcome propionate-dependent colonization resistance. To test this hypothesis, I will use an innovative combination of commensal members of the gut microbiota and S. Tm mutant strains along with germ- free and conventional mouse models to explore how S. Tm contends with propionate during infection. Experiments proposed in Aim 1 will determine if propionate serves as a carbon source to fuel S. Tm growth in vitro and in vivo. In Aim 2, I will identify if gut inflammation and anaerobic respiration are required for propionate metabolism to be beneficial to S. Tm during infection. Aim 3 will investigate if propionate metabolism not only fuels growth by providing a carbon source during respiration but by signaling to S. Tm to decrease invasion. If successful, this research will challenge the dogma that short-chain fatty acids inhibit Salmonella growth in the gut. This project will describe how S. Tm mitigates the detrimental effects of propionate by metabolizing this metabolite into a usable carbon source to fuel growth. Expected findings will provide a deeper understanding of a novel mechanism used by this bacterial pathogen to evade the intestinal microbiota and establish infection.