GENETIC REQUIREMENTS OF HELICOBACTER PYLORI INFECTION

描述（由申请人提供）：幽门螺杆菌慢性感染全球50%人口的胃。10%到30%的感染者会出现严重的疾病，包括消化性溃疡和胃癌。幽门螺杆菌相关疾病不能仅仅归因于特定细菌毒素的表达。相反，我们的总体工作假设是幽门螺杆菌疾病是建立和维持感染所需的细菌因素与由此产生的宿主防御之间相互作用的副产品。这种相互作用是动态的，细菌和宿主在几十年的感染中都会发生变化。为了研究这一复杂的过程，我们利用小鼠感染模型并研究人类临床人群中分离株的遗传变异。在之前的资助期内，我们对幽门螺杆菌定殖基因的体内筛选显示，29%的测试基因存在定殖缺陷，60%的定殖基因显示菌株特异性表型16。这项对超过一半基因组的分析证实了先前涉及的途径，但也发现了意想不到的和研究较少的基因类别，包括参与DNA摄取和修饰的基因以及大量假设的蛋白质（81）。在我们的更新中，我们专注于完成对胃定植的基因的全球分析，并探索参与DNA转化和重组DNA修复的自然能力的基因促进感染的机制。幽门螺杆菌的自然能力允许超级感染菌株之间的重组，在感染期间产生新的基因型，并在菌株群体中产生新的等位基因传播。我们将探讨在单个菌株感染过程中DNA交换和基于重组的修复可能发挥的作用，包括1)修复感染过程中遇到的DNA损伤2)适应性遗传变异的产生3)影响促进（或限制）定植的基因表达的遗传开关事件的催化。我们对致病基因的全面研究将确定持续感染的介质，对临床人群遗传变异的研究将显示这些介质在与感染相关并导致严重疾病（溃疡、癌症）的慢性炎症期间如何适应。我们对幽门螺杆菌促进遗传交换和多样化的机制的研究也应该增加对抗菌药物耐药性传播的理解，这是幽门螺杆菌治疗中日益严重的临床问题。这符合NIAID了解和治疗传染病的使命。公共卫生相关性：幽门螺杆菌感染世界上50%的人的胃，在那里它可以引起轻度炎症、溃疡疾病甚至胃癌，这部分取决于感染菌株的遗传多样性。在这个项目中，我们询问哪些基因是持久定植所必需的，并测试通过基因交换和与其他细菌重组来使基因组多样化的能力是否实际上是成功定植所必需的。我们的工作将确定开发抗菌素疗法的靶点，并通过研究遗传交换，为抗菌素耐药性在细菌群体中传播的机制带来新的知识。

DESCRIPTION (provided by applicant): Helicobacter pylori chronically infect the human stomach of 50% of the population worldwide. Ten to 30% of those infected will present with severe disease including peptic ulcers and gastric cancers15. H. pylori associated diseases cannot be attributed solely to expression of particular bacterial toxins. Instead, our overall working hypothesis is that H. pylori disease is a by-product of the interaction between bacterial factors necessary for establishing and maintaining infection and the resultant host defenses. This interaction is dynamic with both the bacteria and host changing over decades of infection. To study this complex process, we utilize a mouse model of infection and study genetic variation among isolates from human clinical populations. Our in vivo screen for H. pylori colonization genes in the previous funding period showed 29% of genes tested had a colonization defect and 60% of our colonization genes showed strain specific phenotypes16. This analysis, of over half of the genome, confirmed pathways previously implicated, but also identified unexpected and less well studied classes of genes, including genes involved in DNA uptake and modification plus a large number of hypothetical proteins (81). In our renewal we focus on completing our global analysis of genes contributing to stomach colonization and explore the mechanisms by which genes involved in natural competence for DNA transformation and recombination-based DNA repair promote infection. H. pylori's natural competence allows recombination between super-infecting strains to generate new genotypes during infection and spread of new alleles generated within a strain population. We will explore the roles DNA exchange and recombination-based repair may play during infection of a single strain including 1.) repair of DNA damage encountered during infection 2.) generation of adaptive genetic variation and 3). catalysis of genetic switching events affecting the expression of genes promoting (or limiting) colonization. Our efforts to fully map the genes contributing to virulence will identify the mediators of persistent infection and studies of genetic variation in the clinical population will show how these mediators adapt during chronic inflammation that is associated with infection and leads to severe disease (ulcer, cancer). Our study of the mechanisms by which H. pylori promotes genetic exchange and diversification should also increase understanding of the spread of antimicrobial resistance, an increasing clinical problem in the treatment of H. pylori. This fits the mission of NIAID to understand and treat infectious diseases. PUBLIC HEALTH RELEVANCE: Helicobacter pylori infect the human stomach of 50% of the world's population where it can cause mild inflammation, ulcer disease and even gastric cancer, depending in part on the genetic diversity of the infecting strain. In this project we ask which genes are necessary for persistent colonization and test whether the ability to diversify the genome through genetic exchange and recombination with other bacteria is in fact required for successful colonization. Our work will identify targets for developing antimicrobial therapies and, through the study of genetic exchange, bring new knowledge on the mechanisms by which antimicrobial resistance is spread through bacterial populations.