Mechanisms of Microbial Competition During Salmonella Infection

项目总结 微生物区系是保护宿主免受微生物入侵的关键前线屏障，并使 常驻机会主义者被控制住了。肠道沙门氏菌、鼠伤寒沙门氏菌(STM)、 然而，它们擅长克服微生物群介导的定植抗性，导致生物失调和疾病。 在动态平衡下，微生物群产生的抗微生物短链脂肪酸(SCFA)保护宿主 通过胞质酸化来限制病原体的复制。在感染期间，STM使用其III型分泌物 系统(T3SS)触发炎症反应，耗尽产生SCFA的共生体。当前 范式认为，产生SCFA的物种的枯竭是STM大规模扩张的先决条件。 然而，使用抗生素天真的小鼠模型，我们观察到STM在3-4天前开花1000倍 当单链脂肪酸含量丰富和微生物区系的群落组成时，对显性炎症的开始 没有受到干扰。这意味着STM采用了一种迄今尚未描述的策略来恢复pH动态平衡和 在胃肠道定植期间，在单链脂肪酸存在的情况下生长。我们的初步发现表明，质子- 消耗代谢途径，包括氨基酸脱羧酶CADA和SpeF，可以缓解SCFA 体外生长抑制和体内完全毒力所必需的，但目前尚不清楚这些途径是否 特别是在宿主内存在单链脂肪酸的情况下调节生长，或者STM如何确保 在营养受限的胃肠道环境中为这些途径提供燃料。我假设在殖民统治期间 在胃肠道中，STM使用其T3SS来获得宿主衍生的氨基酸，这些氨基酸可以为质子消耗提供燃料 在共生产生的单链脂肪酸存在的情况下，反应和恢复pH动态平衡。 本应用的目的是阐明STM如何适应肠道环境并使用 这一理解使我开发了自己的独立研究计划，调查肠道病原体如何 克服固有的保护障碍，这样我们就可以发现新的治疗方法来支持 高危患者的定植抵抗。在AIM1中，我们将评估质子消耗的贡献 单链脂肪酸在体外恢复pH动态平衡和生长的代谢途径 这些途径在使用常规和诺生菌介导体内早期生态系统入侵中所起的作用 动物模型。在AIM2中，我们将使用细菌遗传学、小鼠感染模型和代谢组学来确定 STM如何利用其毒力因子设计一种新的胃肠道生态位来支持厌生菌 肠杆菌科在动态平衡条件下的扩张。微生物区系研究的这种机械方法 将在病原体介导的环境重塑和微生物生长变化之间提供因果联系 仅通过对细菌物种进行分类不能收集到的条件。圆满完成这项工作 将揭示通过识别和靶向新陈代谢途径来增强固有宿主防御的机会 肠道病原体用来克服定植抗性。

PROJECT SUMMARY The microbiota is a critical frontline barrier that protects the host from invading microorganisms and keeps resident opportunists in check. Frank pathogens such as Salmonella enterica serovar Typhimurium (STm), however, are adept at overcoming microbiota-mediated colonization resistance to cause dysbiosis and disease. Under homeostasis, antimicrobial short-chain fatty acids (SCFAs) produced by the microbiota protect the host by restricting pathogen replication through cytosol acidification. During infection, STm uses its type III secretion systems (T3SS) to trigger an inflammatory response that depletes SCFA-producing commensals. Current paradigm holds that the depletion of SCFA-producing species is a pre-requisite for luminal STm expansion. However, using an antibiotic-naïve mouse model we have observed that STm blooms 1000-fold 3-4 days prior to the onset of overt inflammation when SCFAs are abundant and the community composition of the microbiota is undisturbed. This implies that STm employs an as-of-yet undescribed strategy to restore pH homeostasis and grow in the presence of SCFAs during gastrointestinal colonization. Our preliminary findings suggest that proton- consuming metabolic pathways, including the amino acid decarboxylases CadA and SpeF, alleviate SCFA growth inhibition in vitro and are required for full virulence in vivo, yet it is unclear whether these pathways specifically mediate growth in the presence of SCFAs within the host, or how STm secures the metabolites that fuel these pathways in the nutrient-restricted gastrointestinal environment. I hypothesize that during colonization of the gastrointestinal tract, STm uses its T3SS to obtain host-derived amino acids that fuel proton-consuming reactions and restore pH homeostasis in the presence of commensal-produced SCFAs. The objective of this application is to elucidate how STm adapts to the intestinal environment and to use this understanding to develop my own independent research program that investigates how enteric pathogens overcome intrinsic protective barriers so that we may uncover new therapeutic approaches for bolstering colonization resistance in high-risk patients. In AIM1 we will assess the contribution of proton-consuming metabolic pathways in restoring pH homeostasis and growth in the presence of SCFAs in vitro, and investigate the role these pathways play in mediating early ecosystem invasion in vivo using conventional and gnotobiotic animal models. In AIM2 we will use bacterial genetics, murine infection models, and metabolomics to determine how STm uses its virulence factors to engineer a new gastrointestinal niche that supports dysbiotic Enterobacteriaceae expansion under homeostatic conditions. This mechanistic approach to microbiota research will provide causal links between pathogen-mediated environmental remodeling and changes in microbial growth conditions that cannot be gleaned from solely cataloging bacterial species. Successful completion of this work will reveal opportunities to enhance innate host defenses by identifying and targeting the metabolic pathways enteric pathogens use to overcome colonization resistance.