Acinetobacter virulence and host immunopathogenesis

描述(申请人提供)：鲍曼不动杆菌是美国和全世界对抗生素抗药性最强的生物之一。高达70%的鲍曼不动杆菌临床分离株现在具有广泛的耐药性(XDR；即对除粘菌素或替格环素以外的所有抗生素都具有耐药性)，反映出自2000年以来增加了15倍。此外，由于缺乏治疗鲍曼不动杆菌的新药，鲍曼不动杆菌(对所有可用的抗生素都具有抗药性)引起的感染已经出现，而且还将继续增加。开发新的鲍曼不动杆菌感染预防和治疗策略需要了解宿主-微生物之间的相互作用。然而，使鲍曼不动杆菌引起严重感染的微生物和宿主因素仍然没有明确的定义。新的数据证实了鲍曼不动杆菌临床分离株毒力的多样性(见初步数据)。然而，组织细菌负荷在感染了更多或更少毒力(即致命性与非致命性)菌株的小鼠之间没有差异，从组织病理学来看，任何小鼠都没有发现组织微脓肿或细菌入侵。相反，在血管内发现了生物体，并且存在毛细管炎，这与脂多糖(LPS)介导的全身脓毒症的诱导一致。与其他革兰氏阴性杆菌一样，TLR4之前被认为是抵御鲍曼不动杆菌宿主所必需的，因为在鲍曼不动杆菌感染的非致死性模型中，TLR4缺陷小鼠清除细菌负担的速度比野生型小鼠慢。挑战主流科学观点的是初步数据表明TLR4是反保护的，因为 系统感染强毒鲍曼不动杆菌导致TLR4突变小鼠无死亡，而野生型对照小鼠的死亡率为100%。最后，毒力较强的菌株的内毒素在体外比毒力较弱的菌株更能诱导TLR4的激活。因此，推测内毒素的TLR4激活能力是区分鲍曼不动杆菌毒力高低的一个关键因素。它还假设，比较基因组学，重点是内毒素合成途径，将识别毒力较高的菌株与较低毒力的菌株的基因图谱的变化。基于这些结果，本研究的具体目的是：1)阐明感染过程中细菌内毒素活性、毒力和体内炎症严重程度之间的关系；2)确定与鲍曼不动杆菌临床分离株毒力增强或降低相关的分子遗传特征。鲍曼不动杆菌已经成为院内感染最耐药、最常见的原因之一。到目前为止，对致病机理的研究还很少，微生物毒力因素和宿主因素对毒力的影响尚不清楚。目前的应用是基于一项新的观察结果，即TLR4在体内对鲍曼不动杆菌感染具有抗保护性，并将定义关键的内毒素-毒力关系 跨毒力不同的菌株。目前的提议将为未来的R01奠定基础，重点是剖析体内不同感染部位毒力的分子机制。

DESCRIPTION (provided by applicant): Acinetobacter baumannii is one of the most highly antibiotic-resistant organisms in the United States (US) and throughout the world. Up to 70% of A. baumannii clinical isolates are now extensively drug resistant (XDR; i.e. resistant to all antibiotics except colistin or tigecycline), reflecting a >15-fold increase since 2000. Furthermore infections caused by pandrug-resistant (PDR) A. baumannii (resistant to all available antibiotics) are already being seen, and will continue to increase given the lack of new drugs in the pipeline to treat A. baumannii. Development of new prevention and treatment strategies for A. baumannii infections requires an understanding of host-microbe interactions. Yet microbial and host factors that enable A. baumannii to cause severe infection remain poorly defined. New data confirm diversity of virulence in clinical isolates of A. baumannii (see Preliminary Data). Yet tissue bacterial burden did not differ between mice infected with the more or less virulent (i.e. lethal vs. non-lethal) strains, and by histopathology no tissue micro-abscesses or bacterial invasion was found in any mice. Rather, organisms were found intravascularly and capillaritis was present, consistent with lipopolysaccharide (LPS)-mediated induction of systemic sepsis. TLR4 was previously believed to be required for host defense against A. baumannii, as for other Gram negative bacilli, because TLR4-deficient mice more slowly cleared bacterial burden compared to wild type mice in non-lethal models of A. baumannii infection. Challenging the prevailing scientific opinion are Preliminary Data indicating that TLR4 is anti-protective, because systemic infection with virulent A. baumannii resulted in no mortality of TLR4-mutant mice vs. 100% mortality of wild-type control mice. Finally, LPS from the more virulent strain more potently induced TLR4 activation in vitro than from the less virulent strain. Hence, it is hypothesized that TLR4-activation potency of LPS is a key factor that distinguishes more and less virulent strains of A. baumannii. It is also hypothesized that comparative genomics, focusing on LPS synthetic pathways, will identify altered genetic profiles in higher vs. lower virulence strains. Based on these results, the Specific Aims are: 1) To elucidate relationships between LPS activity, virulence, and severity of inflammation in vivo during infection; and 2) To define molecular genetic signatures linked to increasing or decreasing virulence in clinical isolates of A. baumannii. Acinetobacter baumannii has emerged as one of the most antibiotic-resistant, common causes of nosocomial infections. To date, very little pathogenesis research has been conducted, and microbial virulence factors and host factors contributing to virulence remain unknown. The current application is based on the novel observation that TLR4 is anti-protective against A. baumannii infection in vivo, and will define key LPS- virulence relationships across strains with diverse virulence. The current proposal will lay the groundwork for a future R01 focused on dissecting the molecular mechanisms of virulence in vivo at different sites of infection.