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

描述（由申请方提供）：鲍曼不动杆菌是呼吸机相关性肺炎患者中最常分离到的细菌之一，可引起多种感染，尤其是重症监护室中的高度易感个体。A.鲍曼不动杆菌导致我们有效治疗感染的能力显著下降。因此，针对替代预防措施和治疗的研究有了相当大的扩展。了解A.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，并可能鉴定出可作为开发新的抗菌剂或疫苗的目标的细菌因子。钙卫蛋白（CP）是一种存在于炎症部位的宿主蛋白，在那里它显示促炎活性。CP还通过螯合必需金属锌（Zn）和锰（Mn）表现出抗微生物活性。CP介导的锌螯合抑制A. baumannii生长过程中，A.在鲍曼不动杆菌肺炎中，CP的丧失增强了细菌增殖和传播。众所周知，细菌 通过表达专门的获取系统、改变代谢过程和改变金属蛋白质组来感知和响应营养饥饿。缺乏这些能力的细菌通常无法建立成功的感染。因此，A.鲍曼不动杆菌必须采取策略在宿主体内获得锌。在实验中，以确定所需的细菌因子A。鲍曼不动杆菌对CP介导的锌饥饿的适应，我们发现了一个A.鲍曼不动杆菌Zn采集系统，我们将其命名为ZnuABC。这个系统是在一个锌响应调节器，我们命名为Zur的控制下。对编码Zur和ZnuABC的基因上游的基因组区域的进一步计算机分析发现了称为Zur盒的保守序列，Zur与其结合以抑制下游基因表达。在A.鲍曼不动杆菌基因组鉴定了可能受Zur和Zn调控的其他基因。我们假设，感染后，CP产生一个锌饥饿的环境，和A。鲍曼不动杆菌通过上调锌获得系统和其它对发病机理至关重要的锌应答基因来应答。这一建议在以下三个综合具体目标系列中解决了我们的假设。目的1：确定CP介导的锌饥饿对A.鲍氏肺炎。目标2：定义A。鲍曼不动杆菌对锌限制条件的反应。目的3：阐明两个锌调控基因在拟南芥中的功能。鲍曼不动杆菌锌稳态。这些研究将提高我们对细菌性肺炎期间宿主营养免疫的理解，并确定A。鲍曼不动杆菌破坏了宿主的这种防御机制而致病。此外，这些机制的表征将为在面对目前治疗A的疗效迅速下降的情况下开发改进的治疗方法奠定基础。鲍曼不动杆菌感染

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.