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

描述（由申请人提供）：全球医院获得性感染治疗的最新挑战之一是对所有？-内酰胺类抗生素（称为耐甲氧西林金黄色葡萄球菌; MRSA）。最近，MRSA也在医院外建立，出现在没有医疗保健协会或可识别的感染风险因素的社区人群中。在任何情况下，抵抗？内酰胺类抗生素是由于获得了一个编码？-内酰胺不敏感靶酶，青霉素结合蛋白（PBP）2a。这种酶使细菌具有交联细胞壁和生长的能力，而细胞通常的交联酶被？内酰胺类抗生素几项研究表明，MRSA感染的发病率和死亡率远高于MSSA（甲氧西林敏感金黄色葡萄球菌）感染，主要是因为初始抗菌治疗不足。因此，准确检测耐甲氧西林链球菌。金黄色葡萄球菌不仅在临床上重要，而且对于医院感染控制程序是必需的。?-内酰胺类抗生素由于其杀菌活性而成为治疗（MSSA）的首选药物。MRSA菌株的主要特征是它们的？内酰胺抗性。我们已经检查了一些临床MRSA菌株，这些菌株由于其极端的异质性而被误解为MSSA。由于这些分离株暴露于？-，因此将这些分离株从疾病控制和预防中心（CDC，Atlanta，GA）转诊至我们的实验室，认为具有临床相关性。内酰胺类药物可导致高水平耐药（HoR）。事实上，我们已经在代表性菌株SA 13011中确定，在暴露于亚抑制浓度的？-？后，发生了从异型（HeR）到同型抗性（HoR）表型的选择。内酰胺类抗生素除了增加MecA的表达外，这种选择还涉及触发？内酰胺介导的SOS反应和增加的突变率。因此，该建议的中心假设是，在暴露于？SA 13011通过β-内酰胺类抗生素从异型（HeR）至同型耐药表型（HoR）中选择，内酰胺诱导的SOS反应，导致agr基因控制的突变率增加，有助于维持细胞壁的完整性等。SA#1.定义？-内酰胺诱导的SOS反应对临床耐甲氧西林分离株SA 13011产生高水平苯唑西林耐药性的影响。SA# 2。找出其中的机制？-在苯唑西林介导的HeR-HoR选择SA #3期间内酰胺诱导的SOS应答诱导和细胞壁完整性。研究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.