Early agr Activation is a Key Pathogenic Signature in Persistent MRSA Bacteremia

描述(申请人提供)：金黄色葡萄球菌是社区获得性和医院感染的主要原因。此外，它是皮肤和皮肤结构感染以及心内膜炎的最常见原因，也是导致菌血症的第二大常见原因。尽管使用了新一代抗生素，但与金黄色葡萄球菌感染相关的发病率和死亡率仍然高得令人无法接受。持续性耐甲氧西林金黄色葡萄球菌菌血症(PB)是金黄色葡萄球菌感染的一个重要亚型，与特别严重的预后相关。因此，PB对医学界提出了重大的治疗挑战。了解PB的相关分子机制对于优化治疗危及生命的金黄色葡萄球菌感染至关重要。我们的初步数据表明，与解决MRSA菌血症(RB)相比，PB的临床结果与关键致病特征的差异显著相关。这些初步数据为研究我们的中心假设提供了坚实的基础：早期AGR激活是持续性MRSA菌血症的重要致病标志。为了验证我们的假设，我们将实现以下综合的特定目标：1)在特征良好的PB和RB菌株的扩大集合中定义agr RNAIII的体外转录、功能和基因座序列谱；以及2)使用实验IE模型定义体内的agr转录和功能，并在该模型中评估这些agr谱对天然MRSA毒力和抗菌效果结果的影响。该项目将采用Northern杂交分析、基因测序、核酸序列扩增(NASBA)和定量RT-PCR等技术。这些研究将极大地促进我们对MRSA感染发病机制的理解。我们的长期目标是识别独特的PB信号，用于开发快速诊断手段和针对MRSA感染的新型抗菌策略，例如PB。

DESCRIPTION (provided by applicant): Staphylococcus aureus is a predominant cause of community-acquired and nosocomial infections. In addition, it is the most common cause of skin and skin structure infections, and endocarditis, and is the second most common cause of bacteremia. Despite the use of new generation antibiotics, morbidity and mortality associated with S. aureus infections remain unacceptably high. Persistent MRSA bacteremia (PB) represents an important subset of S. aureus infections, and correlates with particularly severe outcomes. Therefore, PB presents a significant therapeutic challenge to the medical community. Understanding the relevant molecular mechanisms of PB is essential to optimize therapy against life-threatening S. aureus infections. Our preliminary data indicate that PB clinical outcomes significantly correlated with differences in key pathogenic characteristics as compared with resolving MRSA bacteremia (RB). These preliminary data provide a solid foundation to investigate our central hypotheses: early agr activation is an important pathogenic signature in persistent MRSA bacteremia. To test our hypotheses, we will achieve the following integrated Specfic Aims: 1) Define agr RNAIII transcription, functionality and locus sequence profiles in vitro in an expanded collection of well- characterized PB vs. RB strains; and 2) Define agr transcription and functionality in vivo using the experiment IE model, and evaluate the impact of these agr profiles on innate MRSA virulence and antimicrobial efficacy outcomes in the model. Northern blot analyses, gene sequence, nucleic acid sequence-based amplification (NASBA) and quantitative RT-PCR will be employed in this project. These studies will significantly advance our understanding the pathogenesis of MRSA infections. Our long-term goal is to identify unique PB signatures for development of rapid diagnostic means and novel antimicrobial strategies against MRSA infections, such as PB.