Polyamines in Staphylococcus aureus Physiology and Pathogenesis

描述(申请人提供)：由革兰氏阳性菌引起的疾病，金黄色葡萄球菌，是美国每年发病率和死亡率的重要来源。特别是，最近社区获得的耐甲氧西林金黄色葡萄球菌(CA-MRSA)的出现引起了公共卫生官员的极大关注。CA-MRSA的一个独特的克隆被称为USA-300，由于其超强毒力和在普通公众中传播的倾向，越来越被认为是最危险的新兴病原体之一。因此，更好地了解CA-MRSA相对于传统金黄色葡萄球菌分离株的潜在优势直接关系到全球公共卫生。 据报道，包括腐胺、亚精胺和精胺在内的多胺是由各种形式的生命合成的。这些多阳离子化合物在细胞生理上具有高度的多向性效应，它们的合成在哺乳动物中是必不可少的。在活跃生长的组织中观察到多胺的产生增加，包括炎症和愈合伤口的部位。多胺还调节细菌生理的许多方面，通常促进细菌生长。然而，13个测序的金黄色葡萄球菌基因组中没有一个编码典型的多胺生物合成途径，将金黄色葡萄球菌与几乎所有其他活着的生物区分开来。更重要的是，外源精胺和亚精胺在不影响其他生物生长的浓度下对金黄色葡萄球菌具有杀菌作用。唯一值得注意的例外是USA-300，它不受精胺或亚精胺的抑制。USA-300含有一个独特的名为ACME的遗传岛，这是其他金黄色葡萄球菌谱系中不存在的，包括其他CA-MRSA克隆。与WT USA-300固有的多胺抗性不同，？Acme突变体对外源精胺和亚精胺敏感。这个岛包含一个编码精胺/亚精胺乙酰转移酶(SSAT)的大肠杆菌SpeG的同源基因，我的实验室已经确定SSAT是ACME相关的多胺抗性所必需的，也是足够的。ACME在美国-300金黄色葡萄球菌超强毒力中的作用已经确定；然而，对ACME提供的CA-MRSA优势的机械理解尚未形成。我们认为，SpeG介导的多胺抗性可能为ACME赋予USA-300的优势提供了一种新的解释。因此，这一提议将检验我们的中心假设：1)宿主多胺的产生是金黄色葡萄球菌特有的一种新的先天免疫效应；2)金黄色葡萄球菌获得ACME代表着一种非常重要的进化适应，提供了多胺抗性并导致了USA-300疫情的出现。 与公共健康相关：多胺是由所有活着的有机体合成的化合物。它们具有多种功能，并且在快速生长的细胞中高度产生。有趣的是，人类细菌病原体金黄色葡萄球菌似乎是唯一已知的不能合成多胺的生物。这种细菌有几个完整的基因组序列，但没有一个包含典型的多胺生物合成途径。此外，人体内发现的多胺对金黄色葡萄球菌有很强的毒性。唯一的例外是一种新出现的被称为USA-300的金黄色葡萄球菌克隆，它会在没有明显危险因素的患者中导致高度侵袭性疾病。这种耐甲氧西林金黄色葡萄球菌(MRSA)菌株已成为美国和世界各地与传染病相关的发病率和死亡率的主要原因。我们已经在USA-300中发现了对寄主多胺具有抗性的基因。它是在美国存在的一个基因岛上编码的-300个分离株，但大多数其他金黄色葡萄球菌菌株没有编码。这项建议的目标是： 1.明确地表明，金黄色葡萄球菌不会制造多胺，将其与几乎所有其他形式的生命区分开来。 2.了解多胺对金黄色葡萄球菌的毒性作用。 3.证明寄主多胺的产生在疾病期间限制了金黄色葡萄球菌的增殖。 4.表明USA-300耐甲氧西林金黄色葡萄球菌的成功部分源于与该菌株相关的多胺耐药性。 有了这些信息，我们可以开始测试调节宿主多胺生产是否可以防止由MRSA引起的侵袭性疾病，MRSA是一种危险且代价高昂的人类病原体。

DESCRIPTION (provided by applicant): Disease caused by the gram-positive bacterium, Staphylococcus aureus, represents a significant source of morbidity and mortality annually in the US. Particularly, the recent emergence of community-acquired methicillin-resistant S. aureus (CA-MRSA) is a source of great concern for public health officials. A distinct clone of CA-MRSA known as USA-300 is increasingly appreciated as one of the most dangerous emerging pathogens due to its hypervirulence and its propensity to spread through the general public. A better understanding of the underlying advantages inherent to CA-MRSA over traditional S. aureus isolates therefore pertains directly to global public health. Polyamines including putrescine, spermidine and spermine are reportedly synthesized by all forms of life. These polycationic compounds exert highly pleitropic effects on cellular physiology and their synthesis is essential in mammals. Increased polyamine production is observed in actively growing tissue including sites of inflammation and healing wounds. Polyamines also modulate numerous aspects of bacterial physiology and generally promote bacterial growth. However, none of the 13 sequenced S. aureus genomes encode canonical polyamine biosynthetic pathways distinguishing S. aureus from nearly all other living organisms. More importantly, exogenous spermine and spermidine exert bactericidal effects on S. aureus at concentrations that do not affect the growth of other organisms. The only notable exception is USA-300, which is not inhibited by spermine or spermidine. USA-300 harbors a unique genetic island known as ACME that is not present in other S. aureus lineages, including other CA-MRSA clones. In contrast to the polyamine resistance inherent to WT USA-300, the ?ACME mutant is susceptible to exogenous spermine and spermidine. This island contains a homologue of E. coli speG encoding a spermine/spermidine acetyl transferase (SSAT), which my laboratory has established is necessary and sufficient for ACME-associated polyamine resistance. A role for ACME in the hypervirulence of USA-300 S. aureus has been established; yet a mechanistic understanding of the advantage afforded CA-MRSA by ACME has not been developed. We propose that speG-mediated polyamine resistance may provide a novel explanation for the advantage conferred to USA-300 by ACME. Thus, this proposal will test our Central Hypotheses: 1) Host polyamine production is a novel innate immune effector specific for S. aureus and 2) The acquisition of ACME by S. aureus represents a highly significant evolutionary adaptation providing polyamine resistance and contributing to the emergence of the USA-300 epidemic. PUBLIC HEALTH RELEVANCE: Polyamines are compounds made by all living organisms. They serve many functions and are highly produced in rapidly growing cells. Interestingly, the human bacterial pathogen Staphylococcus aureus appears to be the only known organism that is incapable of synthesizing polyamines. Several complete genomes sequences are available for this bacterium, yet none contain canonical polyamine biosynthetic pathways. Moreover, polyamines at levels found in the human body are highly toxic to S. aureus. The only exception is a newly emerging clone of S. aureus known as USA-300 that causes highly invasive disease in patients with no obvious risk factors. This methicillin-resistant S. aureus (MRSA) strain has become a leading cause of morbidity and mortality associated with infectious disease in the US and worldwide. We have identified the gene in USA-300 that confers resistance to host polyamines. It is encoded on a genetic island present in USA- 300 isolates, but absent from most other strains of S. aureus. The goal of this proposal is to: 1. Show definitively that S. aureus does not make polyamines distinguishing it from nearly all other forms of life. 2. Understand how polyamines exert toxicity towards S. aureus. 3. Demonstrate that host polyamine production limits the proliferation of S. aureus during disease. 4. Show that the success of USA-300 MRSA stems, in part, from the polyamine-resistance associated with this strain. With this information, we can begin to test whether modulating host polyamine production prevents invasive disease caused by MRSA, a dangerous and costly human pathogen.