B-lactam mediated SOS response and expression of resistance in clinical MRSA

描述（由申请人提供）：当今世界范围内医院获得性感染治疗面临的最大挑战之一是耐药葡萄球菌的出现和全球传播。-内酰胺类抗生素（称为耐甲氧西林金黄色葡萄球菌；MRSA）。最近，耐甲氧西林金黄色葡萄球菌也已在医院外建立，出现在没有医疗保健协会或可识别的感染危险因素的社区人群中。在任何一种情况下，抵抗？-内酰胺类抗生素是由于获得了一种编码a ？-内酰胺不敏感靶酶，青霉素结合蛋白（PBP）2a这种酶为细菌提供了交联细胞壁和生长的能力，而细胞通常的交联酶被？内酰胺抗生素。一些研究表明，MRSA感染的发病率和死亡率明显高于MSSA（甲氧西林敏感金黄色葡萄球菌）感染，这主要是因为最初的抗菌治疗不充分。因此，准确检测金黄色葡萄球菌的甲氧西林耐药性不仅在临床上很重要，而且对医院感染控制计划至关重要。？内酰胺类抗生素是治疗（MSSA）的首选药物，因为它们具有杀菌活性。MRSA菌株的主要特点是异质表达？内酰胺阻力。我们已经检查了一些临床MRSA菌株，由于它们的极端异质性而被误解为MSSA。这些分离株从疾病控制和预防中心（CDC, Atlanta， GA）提交到我们的实验室，因为这些分离株暴露于？-内酰胺可导致高水平耐药性（HoR）。事实上，我们已经在一个有代表性的菌株SA13011中确定，在暴露于亚抑制浓度的？内酰胺抗生素。除了增加MecA的表达外，这种选择还涉及触发？-内酰胺介导的SOS反应和突变率增加。因此，本提案的中心假设是，在暴露于？-内酰胺，SA13011从异型（HeR）选择为同型抗性表型（HoR）。-内酰胺诱导的SOS反应，导致agr基因控制的突变率增加，这有助于维持细胞壁的完整性。SA # 1。定义的角色？-内酰胺诱导的SOS反应对临床耐甲氧西林分离株SA13011对oxacillin产生高水平耐药的影响SA # 2。以确定所涉及的机制？奥西林介导的HeR-HoR选择过程中-内酰胺诱导的SOS反应诱导和细胞壁完整性SA #3。探讨agr在？-内酰胺诱导的SOS反应和突变率。

DESCRIPTION (provided by applicant): One of the most contemporary challenges to the treatment of hospital-acquired infections worldwide is the appearance and global spread of staphylococci resistant to all ?-lactam antibiotics (known as methicillinresistant Staphylococcus aureus; MRSA). More recently, MRSA has also become established outside of the hospital, appearing in community populations without healthcare association or identifiable risk factors for infection. In either case, resistance to ?-lactam antibiotics is due to the acquisition of a gene (mecA) that encodes a ?-lactam insensitive target enzyme, penicillin-binding protein (PBP)2a. This enzyme affords the bacterium the ability to cross-link cell wall and grow while the cell's usual cross-linking enzymes are bound and inactivated by ?-lactam antibiotics. Several studies have shown that the morbidity and mortality in infections due to MRSA are considerably higher than in MSSA (methicillin susceptible Staphylococcus aureus) infections, mainly because of an inadequate initial antimicrobial therapy. As a consequence, accurate detection of methicillin resistance in S. aureus is not only clinically important but essential for hospital infection control programs. ?-lactam antibiotics are agents of choice to treat (MSSA) because of their bactericidal activity. The main characteristic of MRSA strains is their heterogeneous expression of ?-lactam resistance. We have examined a number of clinical MRSA strains that are misinterpreted as MSSA due to their extreme heterogeneity. These isolates were referred to our laboratory from the Centers for Diseases Control and Prevention (CDC, Atlanta, GA) as clinically relevant since exposure of such isolates to ?-lactams can result in high-level resistance (HoR). Indeed, we have determined in a representative strain SA13011, that selection from heterotypic ((HeR) to homotypic resistant (HoR) phenotype occurred after exposure to sub-inhibitory concentrations of ?-lactam antibiotics. This selection involved, in addition to increasing expression of MecA, the triggering of ?-lactam-mediated SOS response and increased mutation rate. Therefore, the central hypothesis of this proposal is that upon exposure to ?-lactams, SA13011 is selected from heterotypic (HeR) to homotypic resistant phenotype (HoR) by a ?-lactam-induced SOS response that leads to an agr-genetically controlled increased mutation rate that helps to maintain, among others, the cell wall integrity. SA# 1.To define the role of ?-lactam induced SOS response on the development of high level resistance to oxacillin in the clinical methicillin- resistant isolate SA13011. SA# 2. To identify the mechanisms involved in ?-lactam-induced SOS response induction and cell wall integrity during oxacillin-mediated HeR-HoR selection SA #3. To investigate the regulatory role of agr in ?-lactam-induced SOS- response and mutation rate.