Molecular Epidemiology of Community-Associated MRSA

描述(申请人提供)：金黄色葡萄球菌是一种多功能病原体，它已经成功地适应和进化，产生了各种毒力因子，使其能够在人类身上定居并随后导致各种疾病。耐甲氧西林金黄色葡萄球菌(MRSA)曾经是现代医院的主要祸害，现在已经在没有任何已知危险因素的社区环境中找到了一席之地。我们的长期研究目标是了解影响社区相关MRSA(CA-MRSA)流行病学变化的遗传因素。我们对这一应用的特定假设是，1998年超强毒力的CA-MRSA原型株MW2(1998年在美国北达科他州导致一名16个月大的美国印第安人女孩发生致命败血症)是从一个特定的威斯康星州CA-MRSA主要克隆群-2(MCG-2)进化而来的，该克隆群于1992年在威斯康星州的一个美洲原住民社区(NAC)首次分离。我们进一步假设，MCG-2菌株已经进化到从NACS中的甲氧西林敏感金黄色葡萄球菌(MSSA)菌株获得特定的遗传特征，从而使它们变得更适应、更成功和更毒力的病原体。其具体目的是：1)确定早期(1992年)属于MCG-2的CA-MRSA菌株是否是成功的CA-MRSA菌株MW2的前体。具体地说，我们将确定来自威斯康星州的两株美国本土CA-MRSA菌株，WI-34和WI-99是否为MW2的前体菌株。我们将使用Affymetrix Inc.定制的MW2基因芯片，将WI-34和WI-99的基因组与CA-MRSA、MW2毒株的基因组进行比较。此外，我们还将通过几种基因分型方法对WI-34和WI-99进行彻底的基因分型。2)确定当代CA-MRSA菌株是否属于克隆群，MCG-2是由在威斯康星州5个NAC中循环的MSSA菌株进化而来的。我们将对以下菌株进行分型：i)75株来自MCG-2的MRSA(回顾收集)，ii)75株NAC-MSSA(回顾收集)，iii)75株来自非NAC的MSSA(回顾收集)，iv)75株最近收集的NAC-CA-MRSA(2002-04)，以及v)20株过渡型MRSA(追溯收集)，它们通过脉冲场凝胶电泳(PFGE)、多位点测序类型(MLST)、葡萄球菌盒染色体mec(SCCmec)、SpA和CoA分型，具有CA-MRSA的部分但非全部特征。3)通过从其他MRSA/MSSA获得更多的毒力因子来确定当代CA-MRSA是否已经进化或继续进化，成为一种广泛成功的病原体。我们将确定在AIM 2中列出的所有320株菌株中是否存在40种不同的毒力因子基因，并确定当代CA-MRSA中毒力因子基因的进化。

DESCRIPTION (provided by applicant): Staphylococcus aureus is a versatile pathogen that has successfully adapted and evolved to produce a variety of virulence factors that allow it to colonize and subsequently cause a variety of diseases in humans. Methicillin-resistant S. aureus (MRSA), once a scourge of modern hospitals primarily, has found a niche in community settings in people without any known risk factors. Our long-term research goal is to understand the genetic factors that are influencing the changing epidemiology of community-associated MRSA (CA- MRSA). Our specific hypothesis for this application is that the 1998 hypervirulent 'prototype' CA-MRSA strain, MW2 (caused fatal septicemia in a 16-month old American Indian girl in 1998 in North Dakota, USA), evolved from a specific Wisconsin CA-MRSA major clonal group-2 (MCG-2), which was first isolated in 1992 in a Native American community (NAC) in Wisconsin. We further hypothesize that the MCG-2 strains have evolved to acquire specific genetic traits from methicillin-sensitive S. aureus (MSSA) strain in NACs that allowed them to become more adaptable, successful, and virulent pathogens. The specific aims are to: 1) Determine if the early (1992) CA-MRSA strains belonging to the MCG-2 are the progenitors of the successful CA-MRSA strain, MW2. Specifically, we will determine if the two Native American CA- MRSA strains, WI-34 and WI-99, from Wisconsin were the progenitor strains of MW2. We will compare the genomes of WI-34 and WI-99, with that of the 'prototype' CA-MRSA, MW2 strain using a custom-made MW2 GeneChip¿ from Affymetrix Inc. Additionally, we will thoroughly genotype WI-34 and WI-99 by several genotypic methods. 2) Determine whether or not contemporary CA-MRSA strains belonging to clonal group, MCG-2 evolved from MSSA strains circulating in five NACs in Wisconsin. We will genotype: i) 75 MRSA from MCG-2 (retrospective collection), ii) 75 NAC-MSSA strains (retrospective collection), iii) 75 MSSA strains from a non-NAC (retrospective collection), iv) 75 most recently collected NAC-CA-MRSA (years 2002-04) and v) 20 transitional MRSA strains (retrospective collection) that have some but not all features of CA- MRSA by pulsed-field gel electrophoresis (PFGE), multilocus sequence type (MLST), staphylococcal cassette chromosome mec (SCCmec), spa and coa typing. 3) Determine whether or not the contemporary CA-MRSA have evolved or continue to evolve by acquiring additional virulence factors from other MRSA/MSSA to become a widely successful pathogen. We will determine the presence or absences of 40 different virulence factor genes in all 320 isolates listed in aim 2 and determine evolution of virulence factor genes in contemporary CA-MRSA.