Staphylococcal methicillin resistance locus

描述（由申请人提供）：耐甲氧西林金黄色葡萄球菌（MRSA）是住院患者感染的最常见和最致命的原因，在过去的十年中，已经在社区中出现，成为有和没有医疗保健暴露的个人感染的越来越常见的原因。MRSA对-内酰胺（青霉素及其衍生物）和许多其他抗生素（多重耐药）具有耐药性，严重限制了治疗严重感染的选择。β -内酰胺类抗生素靶向维持细菌细胞壁完整性的酶（青霉素结合蛋白或PBPs）。负责甲氧西林耐药（MR）的基因mecA编码一种新的PBP (PBP2a)，该PBP可以维持细胞壁结构，但对β -内酰胺抑制具有抗性。mecA由一种称为基因组岛的遗传元件携带，该基因元件以特定序列（attB）插入葡萄球菌染色体。除了容纳mecA外，这个名为SCCmec的岛还携带着一种名为ccr的基因，这种基因可以催化SCCmec的插入和切除。植入和切除的机制以及各种形式SCCmec的流行病学表明，该元件是可移动的，并且在过去30年中多次在葡萄球菌菌株中移动。然而，与可用的甲氧西林敏感（MS） SA的广泛菌株类型相比，获得SCCmec的SA的遗传类型有限。本研究旨在了解SCCmec是如何在葡萄球菌之间转移的，以及受体MSSA的特定遗传要求。此外，它将研究SCCmec如何丢失，将MRSA转换回MSSA。目的：1)阐明ccr介导的SCCmec插入和切除所需的分子机制和靶序列；2)评估体外和体内SCCmec自发切除的频率；3)在结合质粒上捕获切除的SCCmec，将SCCmec和meco转移到合适的葡萄球菌受体，并鉴定与获得和稳定维持相关的基因组变化。此外，由于有流行病学和基因组学证据表明，表皮葡萄球菌（SE），一种毒性较小的葡萄球菌物种，也携带SCCmec，并可以作为该元件的遗传库，我们将在SA和SE中进行实验。这些研究的目标是确定SA和SE中的序列，这些序列可以作为探针来剖析mr传播的流行病学。通过这种方式，我们可以追踪MRSA出现和快速传播的历史，防止SCCmec的未来传播，并支持减少抗生素有利于SCCmec从宿主细菌中丢失和降低MRSA表型环境流行的论点。

DESCRIPTION (provided by applicant): Methicillin-resitant Staphylococcus aureus (MRSA) are the most common and lethal causes of infections of hospitalized patients and, over the past decade, have appeared in the community as an increasingly common cause of infections of individuals who both have and do not have healthcare exposures. MRSA are resistant to beta-lactam (penicillin and derivatives) and many additional antibiotics (multiresistant), severely limiting options for treating serious infections. Beta-lactam antibiotics target the enzymes (penicillin binding proteins or PBPs) that maintain the integritiy of the bacterial cell wall. The gene responsible for methicillin resistance (MR), mecA, encodes a new PBP (PBP2a) that can maintain cell wall structure but is resistant to beta-lactam inhibition mecA is carried on a genetic element called a genomic island that inserts into the staphylococcal chromosome at a specific sequence (attB). In addition to housing mecA, this island, called SCCmec, carries genes called ccr that catalyze both insertion and excision of SCCmec. Both the mechanisms of insertion and excision and the epidemiology of various forms fo SCCmec suggest that the element is mobile and has moved among staphylococcal strains multiple times in the past thirty years. However, the genetic types of SA that have acquired SCCmec are limited compared to the wide range of strain types of methicillin susceptible (MS) SA that are available. This proposal seeks to understand how SCCmec is transferred among staphylococcie and the specific genetic requirements of recipient MSSA. In addition, it will investigate how SCCmec can be lost, converting MRSA back to MSSA. The tree Specific Aims are to 1) Elucidate the molecular mechanisms and target sequences required for ccr-mediated SCCmec insertion and excision; 2) Assess the frequency of spontaneous SCCmec excision in vitro and in vivo; and 3) Capture excised SCCmec on a conjugative plasmid, transfer SCCmec and mecAto suitable staphylococcal recipients and identify genomic changes associated with acquisition and stable maintenance. In addition, since there is epidemiologic and genomic evidence that S.epidermidis (SE), a less virulent staphylococcal species, also carries SCCmec and can serve as a genetic reservoir for this element, we will perform experiments in both SA and SE. The goal of these studies is to identify sequences in SA and SE that can be used as probes to dissect the epidemiology of the spread of MR. In this manner we can trace the history of the emergence and rapid spread of MRSA, prevent future dissemination of SCCmec and support arguments that reduce antibiotic will favor SCCmec loss from host bacteria and lower the environmental prevalence of the MRSA phenotype. PUBLIC HEALTH RELEVANCE: This project will provide molecular data that will allow researchers to trace the past and future spread of the gene responsible for methicillin resistance in Staphylococcus aureus (MRSA). In addition, it will investigate conditions that promote the loss of this gene that may suggest strategies for reducing the hospital prevalence of MRSA.