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)是导致住院患者感染的最常见和最致命的原因，在过去十年中，它已成为社区中越来越常见的感染原因，无论是否接触过医疗保健。耐甲氧西林金黄色葡萄球菌对β-内酰胺类(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-内酰胺类抗生素的靶标是维持细菌细胞壁完整性的酶(青霉素结合蛋白或PBPs)。甲氧西林耐药(MR)基因mecA编码一种新的PBP(PBP2a)，它可以维持细胞壁结构，但对β-内酰胺类药物抑制具有抵抗力。mecA携带在称为基因组岛的遗传元件上，该遗传元件以特定的序列(AttB)插入葡萄球菌染色体。除了mecA，这个被称为SCCmec的岛还携带称为CCR的基因，它催化SCCmec的插入和切除。SCCmec的插入和切除机制以及各种形式的流行病学都表明，该元件是可移动的，并在过去30年中多次在葡萄球菌菌株之间移动。然而，与甲氧西林敏感(MS)SA现有的广泛菌株类型相比，已经获得SCCmec的SA的遗传类型是有限的。这项建议试图了解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，它还将调查SCCmec如何丢失，将MRSA重新转换为MSSA。树的特异性目标是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)评估体内外自发的SCCmec切除的频率；以及3)将切除的SCCmec捕获到接合质粒上，将SCCmec和mecAc转移到合适的葡萄球菌受体，并确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证据表明，表皮葡萄球菌(SE)是一种毒力较低的葡萄球菌，也携带SCCmec，并可作为这种元素的遗传库，因此我们将在SA和SE中进行实验。这些研究的目的是确定SA和SE中可用作探针的序列，以剖析MRSA传播的流行病学。通过这种方式，我们可以追溯MRSA出现和快速传播的历史，防止SCCmec的未来传播，并支持减少抗生素将有利于SCCmec从宿主细菌中损失的论点，并降低MRSA表型的环境流行率。

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.