Microbial Ecology and Molecular Pathogenesis of Clostridium difficile

据估计，艰难梭菌每年在美国导致100万至300万例腹泻和结肠炎，仅医院感染一项的年成本就高达11亿美元。大多数病例与广谱抗生素的使用有关。人们一直认为，抗生素的使用会引起正常胃肠道微生物区系的变化。这些变化允许艰难梭菌过度生长，艰难梭菌要么在使用抗生素之前在胃肠道中以少量存在，要么在使用抗生素期间从环境中获得。此外，艰难梭菌孢子而不是营养细菌很可能是类似于其他致病梭状芽胞杆菌的直接传染病。孢子很耐寒，不容易通过自然方式从体内清除，而且对抗生素具有抗药性。 我们推测正常的胃肠道微生物区系干扰艰难梭菌在肠道的定植。 还可以调节有机体对毒素的表达。此外，我们假设，孢子形态本身不仅对艰难梭菌最初进入宿主有很大贡献，而且对反复复发和脱落/传播也有很大贡献。为了解决这些假设，本项目提出了三个具体目标。在第一个目标中，我们将比较无症状定植者和初次或复发艰难梭菌感染不同严重程度的患者的粪便微生物区系。我们将确定特定的社区结构是否与疾病易感性和临床结果/严重程度相关。第二个目标是在艰难梭菌感染的小鼠模型中扩展这些观察结果，以确定对艰难梭菌产生定植抗性的微生物学因素。在第三个目标中，将确定萌发和产孢量对临床疾病和传播的贡献。我们将确定艰难梭菌临床分离株的产孢量/萌发特性，并在小鼠艰难梭菌模型中测试自然发生的变异株和已定义的突变株。这些目的将对艰难梭菌感染中微生物生态学和分子细菌致病机制的作用提供重要的见解。

The toxin producing bacterium Clostridium difficile causes an estimated 1,000,000 to 3,000,000 cases of diarrhea and colitis in the United States each year at an annual cost of $1.1 Billion dollars for nosocomial infections alone. Most cases are associated with the administration of broad-spectrum antibiotics. It has been assumed that the administration of antibiotics causes changes in the normal gastrointestinal microbiota. These changes allow overgrowth of C. difficile, which has either been present in low numbers in the gastrointestinal tract before the administration of antibiotics, or is acquired from the environment during antibiotic administration. Furthermore, it is likely that C. difficile spores and not the vegetative bacilli are the direct contagion analogous to other pathogenic Clostridia sp. Spores are hardy, not easily cleared from the body by natural means and are resistant to antibiotics. We theorize that the normal gastrointestinal microbiota interferes with gut colonization by C. difficile and may also regulate expression of toxin by the organism. Additionally, we hypothesize that the spore morphotype itself contributes heavily to not only the initial introduction of C. difficile to the host, but also to recurrent relapse and shedding/transmission. To address these hypotheses, three specific aims are proposed for this project. In the first aim, we will compare the fecal microbiota in asymptomatically colonized individuals and patients with initial or recurrent C. difficile infection of varied severity. We will determine if specific community structures correlate with susceptibility to disease and with clinical outcomes/severity. The second aim will extend these observations in a murine model of C. difficile infection to define the microbiologic factors that contribute to colonization resistance against C. difficile. In the third aim the contribution of germination and sporulation to clinical disease and transmission will be determined. We will characterize clinical C. difficile isolates for sporulation/germination attributes and test naturally occurring variants and defined mutants in the murine C. difficile model. These aims will provide important insight in the roles of microbial ecology and molecular bacterial pathogenesis in C. difficile infection.