Elucidating the A. baumannii response to calprotectin-mediated zinc starvation

描述（由申请人提供）：鲍曼不动杆菌是呼吸机相关性肺炎患者中最常见的分离细菌之一，可引起多种感染，特别是重症监护病房的高度易感个体。鲍曼不动杆菌对抗生素耐药性的迅速发展导致我们有效治疗感染的能力显著下降。因此，针对其他预防措施和治疗方法的研究有了相当大的扩展。了解鲍曼不动杆菌的发病机制将提高我们成功进行治疗干预的能力，并可能确定可用于开发新的抗菌剂或疫苗的细菌因素。钙保护蛋白（CP）是一种存在于炎症部位的宿主蛋白，在那里它显示出促炎活性。CP还通过隔离必需金属锌（Zn）和锰（Mn）表现出抗菌活性。CP介导的锌螯合作用抑制鲍曼不动杆菌的生长，在鲍曼不动杆菌肺炎期间，CP的丧失增强了细菌的增殖和传播。众所周知，细菌

DESCRIPTION (provided by applicant): Acinetobacter baumannii is one of the most frequently isolated bacteria from patients with ventilator-associated pneumonia and causes a diverse number of infections, particularly in highly susceptible individuals in intensive care unit. The rapid development of antibiotic resistance by A. baumannii has led to a significant decrease in our ability to effectively treat infections. Consequently, there has been a considerable expansion in research directed towards alternative preventative measures and treatments. Understanding the mechanisms of A. baumannii pathogenesis will improve our capacity for successful therapeutic intervention and may identify bacterial factors that can be targeted for development of new antimicrobials or vaccines. Calprotectin (CP) is a host protein present at sites of inflammation where it displays pro-inflammatory activity. CP also exhibits antimicrobial activity through sequestration of the essential metals zinc (Zn) and manganese (Mn). CP- mediated Zn chelation inhibits A. baumannii growth, and during A. baumannii pneumonia, the loss of CP enhances bacterial proliferation and dissemination. It is well-established that bacteria sense and respond to nutrient starvation via expression of specialized acquisition systems, modification of metabolic processes, and alterations to the metalloproteome. Bacteria that lack these capabilities are generally unable to establish a successful infection. Therefore, A. baumannii must employ strategies to acquire Zn within the host. In experiments to identify bacterial factors required for A. baumannii adaptation to CP-mediated Zn starvation, we discovered an A. baumannii Zn acquisition system that we have named ZnuABC. This system is under the control of a Zn-responsive regulator, which we have named Zur. Further in silico analysis of the genomic region upstream of the genes encoding Zur and ZnuABC uncovered a conserved sequence called a zur box, to which Zur binds to repress downstream gene expression. A search for this consensus sequence within the A. baumannii genome identified additional genes that may be regulated by Zur and Zn. We hypothesize that following infection, CP generates a Zn-starved environment, and A. baumannii responds through the up- regulation of a Zn acquisition system and other Zn-responsive genes that are essential for pathogenesis. This proposal addresses our hypothesis in the following series of three integrated Specific Aims. Aim 1: Determine the role of CP-mediated Zn starvation to A. baumannii pneumonia. Aim 2: Define the A. baumannii response to Zn-limiting conditions. Aim 3: Elucidate the functions of two Zn-regulated genes in A. baumannii Zn homeostasis. Together these studies will improve our understanding of host nutritional immunity during bacterial pneumonia and define how A. baumannii subverts this host defense to cause disease. Furthermore, characterization of these mechanisms will lay the groundwork for the development of improved therapeutics in the face of the rapidly decreasing efficacy of the current treatments for A. baumannii infection.