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

描述(申请人提供)：全球医院感染治疗面临的最新挑战之一是对所有β-内酰胺类抗生素耐药的葡萄球菌的出现和全球传播(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关联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，对β-内酰胺类抗生素的耐药性都是由于获得了编码β-内酰胺类不敏感靶标酶青霉素结合蛋白(PBP)2a的基因(MecA)。这种酶使细菌能够交联细胞壁并生长，而细胞中通常的交联酶被β-内酰胺类抗生素结合并失活。一些研究表明，MRSA感染的发病率和死亡率比MSSA(甲氧西林敏感金黄色葡萄球菌)感染的发病率和死亡率高得多，这主要是因为最初的抗菌治疗不足。因此，准确检测金黄色葡萄球菌对甲氧西林的耐药性不仅具有重要的临床意义，而且对医院感染控制具有重要意义。？-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。耐甲氧西林金黄色葡萄球菌的主要特征是对β-内酰胺类耐药的异质性表达。我们检查了一些临床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，亚特兰大，佐治亚州)提交给我们的实验室，因为这些分离株对β-内酰胺类药物的暴露会导致高水平耐药(HoR)。事实上，我们已经在代表性菌株SA13011中确定，在暴露于亚抑制浓度的β-内酰胺类抗生素后，发生了从异型((HER)到同型耐药(HoR)表型的选择。这种选择除了增加MecA的表达外，还包括触发β-内酰胺介导的SOS反应和增加突变率。因此，这一建议的中心假设是，在暴露于β-内酰胺类药物后，SA13011通过β-内酰胺类药物诱导的SOS反应从异型(HER)选择为同型耐药表型(HoR)，从而导致农业基因控制的突变率增加，从而帮助维持细胞壁的完整性。目的：明确β-内酰胺类抗生素诱导的SOS反应在临床耐甲氧西林菌株SA13011对苯唑西林高度耐药中的作用。探讨苯唑西林介导的HER-HoR选择SA#3中β-内酰胺诱导SOS反应和细胞壁完整性的机制。

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.