ECF Sigma Factors and the Cell Envelope Stress Response of Clostridium difficile

描述（由申请人提供）：艰难梭菌是医院获得性感染性腹泻的最常见原因，仅在美国每年造成的损失就超过11亿美元。尽管艰难梭菌具有临床影响，但尚不清楚艰难梭菌如何定殖并逃避宿主的免疫防御。一些证据表明，先天免疫系统的抗菌肽在控制艰难梭菌感染中起重要作用。然而，艰难梭菌如何对抗菌肽引起的应激作出反应尚不清楚。缺乏了解的一个主要原因是无法从基因上操纵这种严格的厌氧菌。我们已经成功构建了艰难梭菌稳定的靶向突变。我们的长期目标是更好地了解艰难梭菌在感染过程中如何抵抗先天免疫防御。胞质外功能因子（ECF）是一类重要的信号转导系统，它对细胞包膜应力作出反应。虽然ECF因子参与了革兰氏阴性病原体对先天免疫防御的抵抗，但在革兰氏阳性病原体引起的感染中，ECF因子的作用尚未确定。本应用程序的目的是确定ECF sigma因子在艰难梭菌细胞包膜应激反应中的作用，并确定这些ECF sigma因子如何促进艰难梭菌的毒力特性。初步证据表明，艰难梭菌基因组编码三个ECF sigma因子，这些因子在响应细胞包膜应激时被诱导。ECF sigma因子在艰难梭菌耐药细胞包膜应激和发病机制中的作用将在以下几个具体目标中确定：1)确定PrsW如何控制艰难梭菌ECF因子CsfT和CsfU的表达；2)确定艰难梭菌ECF因子在细胞包膜应激抵抗和发病机制中的作用；3)确定艰难梭菌ECF因子的调控规律。拟议的研究与NIH的使命相关，因为它有望推进我们对这种日益重要的临床革兰氏阳性病原体如何抵抗细胞包膜应激和宿主先天免疫防御的认识。更好地了解细胞包膜应激反应可能为艰难梭菌感染的治疗提供新的靶点。

DESCRIPTION (provided by applicant): Clostridium difficile is the most common cause of hospital-acquired infectious diarrhea, at a cost of greater than 1.1 billion dollars per year in the United States alone. Despite the clinical impact of C. difficile it remains unclear how C. difficile colonizes the host and evades the host immune defenses. Several lines of evidence suggest antimicrobial peptides of the innate immune system play an important role in controlling C. difficile infections. However how C. difficile responds to the stress caused by antimicrobial peptides is poorly understood. One major reason for this lack of understanding is the inability to genetically manipulate this strict anaerobe. We have successfully constructed stable targeted mutations in C. difficile. Our long-term goal is to better understand how C. difficile resists the innate immune defenses during an infection. Extra-Cytoplasmic Function (ECF) factors represent an important class of signal transduction systems which respond to cell envelope stresses. Although ECF factors are involved in resistance to innate immune defenses in Gram- negative pathogens, the role of ECF factors during infections caused by Gram-positive pathogens has not been established. The objective of this application is to define the role of ECF sigma factors in the cell envelope stress response of C. difficile and determine to how these ECF sigma factors contribute to the virulence properties of C. difficile. Preliminary evidence suggests the C. difficile genome encodes three ECF sigma factors which are induced in response to cell envelope stress. The role of ECF sigma factors in resistance cell envelope stress and pathogenesis C. difficile will be determined in the following specific aims: 1) Determine how PrsW controls expression of the C. difficile ECF factors CsfT and CsfU, 2) Define the role of these C. difficile ECF factors in resistance to cell envelope stress and pathogenesis, and 3) Identify the regulons of these C. difficile ECF factors. The proposed research is relevant to the mission of the NIH because it is expected to advance our knowledge of how this increasingly clinically important Gram-positive pathogen resists cell envelope stress and host innate immune defenses. A better understanding of the cell envelope stress response may provide new targets for treatment of C. difficile infections. PUBLIC HEALTH RELEVANCE: The proposed studies will broaden the understanding of a significant human pathogen which has not been well investigated. C. difficile infections are of great public health concern as the incidence and severity of C. difficile-associated disease continues to rise. The research proposed here has relevance to public health, because it focuses on understanding how C. difficile resists damage to its cellular envelope which is an important target of both antibiotics and the innate immune defenses.