The interactions between Clostridium difficile, intestinal microbiota and the host response in hospitalised patients

艰难梭菌是一种引起慢性腹泻和有时危及生命的疾病的细菌（称为C。艰难梭菌感染或CDI），主要发生在老年人和住院患者中。C.艰难梭菌现在是最重要的医院获得性感染，去年英国有超过34，000例病例，估计每年的费用为5亿英镑。在过去的十年中，CDI的报告发病率急剧上升，并与侵袭性菌株的出现有关。考虑到C. CDI很难进化成高毒性，再加上人口老龄化和住院率的增加，CDI的问题可能会继续下去。这是一个目前的NHS当务之急，以减少CDI的负担。CDI在感染中是独特的，因为在几乎所有情况下，疾病都是在服用抗生素后发生的，这些抗生素破坏了肠道中存在的“正常”细菌（称为微生物群）。它提供了C。使其难以有机会过度生长，产生毒素并导致疾病。很明显，微生物群的平衡在疾病中起着关键作用。关于CDI最令人困惑的问题之一是临床症状的多样性。例如，C.艰难梭菌定殖可导致从无症状携带到死亡的一系列临床结果。C.艰难梭菌显然在决定临床结果中起作用，但这种作用的性质尚未确定。高达30%的成功治疗症状性CDI的患者死于疾病复发，但目前尚不清楚为什么只有一些患者复发。除了病原体之外，宿主免疫应答和/或宿主微生物群也可能是临床结果的重要决定因素，但在很大程度上仍未探索。我们的中心假设是C.艰难梭菌遗传学、常驻肠道微生物群的组成和宿主对细菌的免疫应答塑造了临床结果。我们将通过监测一组独特的有和没有CDI的患者来研究病原体、宿主和微生物群之间的三方相互作用。C.艰难梭菌血清和粪便样本将进行前所未有的详细研究，为后续研究提供一个平台，以了解C。difficile引起疾病。我们已经建立了一个高质量的前瞻性收集的生物档案，包括细菌，血液和血清样本，从300例CDI和完整的临床病史。这些样本与详细的临床数据和疾病严重程度评分指数沿着，以及来自暴露于抗生素但未发生CDI的住院患者的150份对照样本相关。我们将使用现有的队列来验证方法，然后招募另一个队列，其中包括150例确诊的CDI病例、100例腹泻对照和100例健康志愿者（例如患者的配偶），以证实我们的发现。这一独特的资源将用于监测宿主反应（包括免疫系统对感染的反应），确定感染C. difficile并通过测序和培养来识别肠道微生物群。这些研究还将使我们能够区分再次感染（由另一种菌株引起的感染）和复发（由同一菌株引起的再次感染）。对疾病严重程度、宿主反应、感染病原体和肠道菌群组成的统计分析将有助于对C.很难确定它是如何以及为什么引起疾病的。这将通过选择C来实现。艰难梭菌基因和构建确定的突变体，并在申请人实验室建立的一系列测定中与亲本菌株一起研究这些突变体。艰难梭菌、宿主反应和肠道微生物群的研究将加强我们对微生物的理解，并开发新的策略来减轻CDI的负担。

Clostridium difficile is a bacterium that causes chronic diarrhoea and sometimes life-threatening disease (referred to as C. difficile infection or CDI) mainly in elderly and hospitalized patients. C. difficile is now the most significant hospital acquired infection with over 34,000 UK cases last year and an estimated cost to be £500 million per annum. The reported incidence of CDI has risen dramatically over the last decade and is related to the emergence of aggressive strains. Given the ability of C. difficile to evolve to be highly virulent coupled with the ageing population and increasing rates of hospitalization, the problem of CDI is likely to continue. It is a current NHS imperative to reduce the burden of CDI. CDI is unique among infections in that in almost all cases, disease follows the administration of antibiotics that disrupt the "normal" bacteria (called microbiota) present in the gut. It provides C. difficile the opportunity to overgrow, produce toxins and cause disease. It has become apparent that the balance of the microbiota plays a key role in disease. One of the most perplexing questions concerning CDI is the diversity of clinical symptoms. For example, C. difficile colonization can result in a spectrum of clinical outcomes ranging from asymptomatic carriage to death. The relative virulence of C. difficile organism clearly plays a role in determining clinical outcome, but the nature of this role has not been identified. Up to 30% of patients treated successfully for symptomatic CDI succumb to recurrent disease, but it is unclear why only some patients relapse. In addition to the pathogen, the host immune response and/or host microbiota are also likely important determinants of clinical outcome, but remain largely unexplored. Our central hypothesis is that variations in C. difficile genetics, the composition of the resident intestinal microbiota and the host immune response to the bacterium shape the clinical outcome. We will investigate the three-way interaction between pathogen, host and microbiota by monitoring a unique group of patients with and without CDI. C. difficile serum and faecal samples will be studied in unprecedented detail to provide a platform for follow up studies to understand how C. difficile causes disease. We have established a high quality prospectively collected bioarchive comprising bacterial, blood and serum samples from 300 patients with CDI and full clinical history. These samples are linked to detailed clinical data and a disease severity-scoring index along with 150 control samples from hospitalised patients who have been exposed to antibiotics but did not develop CDI. We will use the existing cohort to validate methodologies and then also recruit another cohort of 150 confirmed CDI cases, 100 diarrhoea controls and 100 healthy volunteers (e.g. patient's spouses) to confirm our findings. This unique resource will be used to monitor the host response (including how the immune system responds to the infection), determine the complete genome sequence of infecting C. difficile and identify the intestinal microbiota by sequencing and culturing. The studies will also allow us to distinguish between re-infection (infection caused by another strain) and relapse (re-infection caused by the same strain). Robust statistical analysis comparing disease severity, host response, infecting pathogen and the composition of intestinal microbiota will facilitate subsequent studies on C. difficile to determine how and why it causes disease. This will be achieved by selecting C. difficile genes and constructing defined mutants and studying these alongside the parent strain in a range of assays established in the applicants' laboratories.A comprehensive understanding of C. difficile, the host response and the intestinal microbiota will strengthen our understanding of the microorganism and to develop novel strategies to reduce the burden of CDI.