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

B-内酰胺介导的 SOS 反应和临床 MRSA 耐药性的表达

• 批准号: 8141805
• 负责人: ADRIANA E ROSATO
• 金额: $ 29.45万
• 依托单位: METHODIST HOSPITAL RESEARCH INSTITUTE
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-04-01 至 2015-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8141805
• 关键词: lactam; mediated; SOS; response; expression

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. PUBLIC HEALTH RELEVANCE: Clinical Methicillin-Resistant S.aureus (MRSA) isolates expressing low levels of resistance and being misinterpreted as oxacillin-susceptible are a growing concern. These strains spread unnoticed in the hospital environment in both patients and staff. Oxacillin susceptible low level mecA mediated resistance MRSA strains are very heterogeneous (HeR) in expression and clinically relevant since exposure of such isolates to ?-lactams can result in high-level resistance. The central hypothesis of this proposal is that upon exposure to ?-lactams, MRSA (SA13011) is selected from a heterotypic (HeR) to a 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.

描述（由申请人提供）：全球范围内医院获得性感染治疗面临的最新挑战之一是对所有 β-内酰胺抗生素耐药的葡萄球菌（称为耐甲氧西林金黄色葡萄球菌；MRSA）的出现和全球传播。最近，MRSA 也在医院外蔓延，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。无论哪种情况，对β-内酰胺抗生素的耐药性都是由于获得了编码β-内酰胺不敏感靶酶、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，而细胞通常的交联酶则被β-内酰胺抗生素结合并失活。多项研究表明，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，这主要是因为初始抗菌治疗不充分。因此，准确检测金黄色葡萄球菌中的甲氧西林耐药性不仅具有临床意义，而且对于医院感染控制计划也至关重要。 β-内酰胺抗生素因其杀菌活性而成为治疗（MSSA）的首选药物。 MRSA菌株的主要特征是其对β-内酰胺耐药性的异质表达。我们检查了许多临床 MRSA 菌株，这些菌株因其极端异质性而被误解为 MSSA。这些分离株被从疾病控制和预防中心（CDC，亚特兰大，佐治亚州）移交给我们的实验室，因为这些分离株具有临床相关性，因为这些分离株暴露于β-内酰胺可导致高水平耐药性（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-内酰胺抗生素后，发生了从异型（HeR）到同型抗性（HoR）表型的选择。这种选择除了增加MecA，触发β-内酰胺介导的SOS反应并增加突变率因此，该提议的中心假设是在暴露于β-内酰胺时， SA13011 通过 β-内酰胺诱导的 SOS 反应从异型 (HeR) 中选择为同型抗性表型 (HoR)，从而导致 agr 基因控制的突变率增加，从而有助于维持细胞壁完整性等。 1. 明确β-内酰胺诱导的 SOS 反应对临床耐甲氧西林菌株 SA13011 产生高水平苯唑西林耐药的作用。 2. 确定苯唑西林介导的 HeR-HoR 选择 SA #3 过程中涉及 β-内酰胺诱导的 SOS 反应诱导和细胞壁完整性的机制。研究agr在β-内酰胺诱导的SOS反应和突变率中的调节作用。 公共卫生相关性：临床耐甲氧西林金黄色葡萄球菌 (MRSA) 分离株表现出低水平的耐药性并被误解为对苯唑西林敏感，这一问题日益引起人们的关注。这些菌株在医院环境中的患者和工作人员中不知不觉地传播。苯唑西林敏感的低水平 mecA 介导的耐药性 MRSA 菌株的表达非常异质 (HeR)，并且具有临床相关性，因为此类分离株暴露于 β-内酰胺可导致高水平耐药性。该提议的中心假设是，当暴露于β-内酰胺时，MRSA（SA13011）通过β-内酰胺诱导的SOS反应从异型（HeR）选择为同型耐药表型（HoR），从而导致agr-基因控制的突变率增加，有助于维持细胞壁的完整性等。