Staphylococcal methicillin resistance locus

描述（由申请人提供）：葡萄球菌是医院获得性感染的主要原因，尤其是医院内菌血症。两种最有效和最广泛使用的抗葡萄球菌治疗剂是糖肽类和β -内酰胺类，它们都靶向细胞壁的生物合成。然而，随着耐药性的发展，这些药物的治疗效果越来越差，首先是对β -内酰胺的耐药性，最近是对糖肽的耐药性。对β -内酰胺类耐药的最重要机制是获得新的靶标，即未被抗生素灭活的细胞壁转肽酶或青霉素结合蛋白（PBP2a）。这种类型被称为甲氧西林或氧西林耐药性（or），介导这种耐药性的基因mecA被编码在一个名为SCCmec的致病性岛中。以下建议寻求继续研究，探索介导OR和葡萄球菌对破坏其细胞壁的药物产生抗性所需的基因组适应的基因的起源，传播和调控。第一个特定目标将是研究SCCmec在金黄色葡萄球菌（SA）菌株之间以及从不同葡萄球菌物种表皮葡萄球菌（SE）到SA的转移。有证据表明，一种新的SCCmec类型，即IV型，最近已转移到社区中流行的SA分离株中，并且存在于大多数SE分离株中。将研究该元素的切除、转移（通过质粒和噬菌体）和重新插入。

DESCRIPTION (provided by applicant): Staphylococci are the leading cause of hospital-acquired infections, especially nosocomial bacteremia. The two most effective and widely used anti-staphylococcal therapeutic agents are glycopeptides and beta-lactams, both of which target cell wall biosynthesis. However, therapy with these agents is becoming less effective as resistance has developed, first to beta-lactams and, more recently, to glycopeptides. The most important mechanism of resistance to beta-lactams is the acquisition of a new target, a cell wall transpeptidase or penicillin binding protein (PBP2a) that is not inactivated by the antibiotic. This type is called methicillin or oxacillin resistance (OR) and the gene that mediates this resistance, mecA, is encoded within a pathogenicity island called SCCmec. The following proposal seeks to continue studies that explore the origin, dissemination and regulation of genes that mediate OR and genomic adaptations required for staphylococci to become resistant to agents that damage their cell walls. The First Specific Aim will be to investigate the transfer of SCCmec between strains of Staphylococcus aureus (SA) and from a different staphylococcal species, S. epidermidis (SE), to SA. There is evidence that a new SCCmec type, Type IV, has recently moved into SA isolates prevalent in the community and it is present in the majority of SE isolates. The excision, transfer (by plasmid and phage) and reinsertion of this element will be investigated. The Second Specific Aim will be to continue studies on the induction of mecA transcription through the sensor/transducer, MecR1, resulting in the release of the transcriptional repressor, Mecl, from its DNA binding site. The basis of signal transduction and role of proteolytic cleavage of inducer and repressor will be assessed by constructing chimeric molecules, determining the crystal structure of repressors and identifying additional chromosomal genes required for induction. The Third Specific Aim will be to confirm and expand observations made by microarray transcriptional profiling that purine biosynthesis is altered in strains that develop high level resistance to vancomycin and oxacillin, but in opposite directions (increased and decreased respectively). These two phenotypes appear to be mutually exclusive. The purine biosynthetic operons will be genetically manipulated and correlated with development of VR and OR. In addition, microarray and proteomic studies will be pursued on other agents that perturb the cell wall.