Understanding the role of inflammation, fibrinogen and neutrophils in persistence of E. faecalis during CAUTI

描述(由申请人提供)：导管相关性尿路感染(CAUTIs)是最常见的医院感染之一，如果不进行治疗，可能会导致严重的并发症，包括菌血症和死亡。粪肠球菌是CAUTI的主要病原体之一，由于其能够在医院环境下传播，在导管和其他留置医疗器械上黏附和形成生物膜，以及对多种抗生素的固有和获得性耐药性，其治疗变得越来越困难。对CAUTI发病机制的分子细节缺乏了解，限制了预防和治疗这种感染的新疗法的发展。在CAUTI的小鼠模型中，我们复制了人类临床CAUTI的许多方面，我们发现导尿引起膀胱炎、水肿、炎性细胞因子的产生和中性粒细胞的募集，而矛盾的是，它提供了一个能使粪肠球菌茁壮成长的膀胱环境。我发现，宿主纤维蛋白原(Fg)在导管诱导的炎症时释放，对于粪肠球菌与导管的粘连以及促进膀胱内导管的生长和生物膜的形成至关重要。这些发现表明，控制宿主炎症环境以限制导尿时炎症和/或纤维蛋白原释放到膀胱腔内可能是一种有效的策略，可以大大降低CAUTI的发生率。此外，尽管Fg似乎促进了CAUTI中粪肠球菌的感染，但在其他系统中，已经证明Fg是一种由IL-1、IL-6和肿瘤坏死因子α诱导的促炎分子，它与多种人类炎症性疾病有关。这就提出了另外一个问题，即粪肠球菌如何能够利用发炎的膀胱环境，并抵抗宿主防御机制来定植导尿管膀胱。此外，中性粒细胞是CAUTI期间最丰富的免疫细胞，尽管有它们的存在，粪肠球菌仍能够在膀胱中存活。目前尚不清楚为什么中性粒细胞无法完全清除感染。一些报道表明，FG能与中性粒细胞结合，抑制凋亡途径，这对细菌的吞噬和清除以及炎症的消退都是重要的。因此，我推测，在CAUTI期间，粪肠球菌利用导尿引起的炎症反应释放纤维蛋白原，以维持和规避中性粒细胞的杀菌功能，限制炎症将减少粪肠球菌感染。我的第一个目标是研究炎性细胞因子在膀胱中FG的释放和积聚中的作用以及它们在粪肠球菌持久性中的作用。我的第二个目标是研究FG在调节中性粒细胞活性中的作用，以及这种相互作用在CAUTI期间粪肠球菌免疫逃避中的作用。为了了解CAUTI的病理生理，需要阐明粪肠球菌与宿主的相互作用机制，以便发现有效预防宿主炎症和治疗粪肠球菌感染的可能策略。这些结果将对需要急诊或长时间导尿的患者具有重要意义。

DESCRIPTION (provided by applicant): Catheter-associated urinary tract infections (CAUTIs) are one of the most common nosocomial infections and if untreated can lead to serious complications including bacteremia and death. Enterococcus faecalis is one of the leading causative agents of CAUTI and its treatment has become increasingly difficult due to its ability to disseminate in hospital settings, adhere and form biofilms on catheters and other indwelling medical devices, and its inherent and acquired resistance to multiple antibiotics. The poor understanding of the molecular details of CAUTI pathogenesis has limited the development of new therapies to prevent and treat this infection. In a mouse model of CAUTI, which replicates many aspects of human clinical CAUTI, we have shown that urinary catheterization elicits bladder inflammation, edema, production of inflammatory cytokines, and neutrophil recruitment, while paradoxically, providing a bladder environment in which E. faecalis can thrive. I have found that host fibrinogen (Fg), which is released upon catheter-induced inflammation, is critical for E. faecalis adherence to catheters and for promoting growth and biofilm formation on catheters within the bladder. These findings suggest that manipulating the host inflammatory environment to limit inflammation and/or Fg release into the bladder lumen upon catheterization may be an effective strategy to greatly reduce the incidence of CAUTI. Further, while Fg seems to promote E. faecalis infection in CAUTI, in other systems it has been shown that Fg is a proinflammatory molecule that is induced by IL-1, IL-6, and TNFα it is linked to multiple human inflammatory diseases. This raises additional questions of how E. faecalis is able to exploit the inflamed bladder environment and withstand host defense mechanisms to colonize the catheterized bladder. Furthermore, neutrophils are the most abundant immune cells during CAUTI and despite their presence E. faecalis is able to persist in the bladder. It is unclear why neutrophils are unable to completely clear the infection. Several reports have shown that Fg binds to neutrophils suppressing the apoptosis pathway, which is important for bacterial phagocytosis and clearance, and for resolution of the inflammation. Therefore I hypothesize that during CAUTI E. faecalis exploits the release of fibrinogen due to the inflammatory response to catheterization for persistence and for circumvention of neutrophil bactericidal function and that limiting inflammation will decrease E. faecalis CAUTI. My first Aim will investigate the contribution of inflammatory cytokines to the release and accumulation of Fg in the bladder and their role in E. faecalis persistence. My second Aim will examine the role of Fg in modulating neutrophil activity and the contribution of this interaction to E. faecalis immune evasion during CAUTI. Elucidation of E. faecalis-host interaction mechanisms is needed to understand CAUTI pathophysiology in order to uncover possible strategies to efficiently prevent host inflammation and treat E. faecalis infection. These results will be of significant importance for patients that require acute or prolonged catheterization.