Virulence Gene Discovery in Outbreak-Associated Pneumococci

描述(由申请人提供)：由肺炎链球菌引起的传染病的爆发在20世纪初的美国很常见。今天，在美国，肺炎球菌暴发发生在宿主人群中，具有可识别的危险因素。然而，人们严重担心，最近在美国引入的结合疫苗带来的肺炎球菌种群动态的变化，将扩大超强毒力、暴发相关菌株的生态位。导致肺炎球菌暴发的细菌毒力因子尚不清楚。在这项提案中，我们将使用分子流行病学的方法来发现在美国引起真正暴发并在其他国家出现超强毒力特征的12F型肺炎球菌的候选毒力基因。我们将使用多位点序列分型来表征12F菌株的克隆多样性，并将使用抑制消减杂交(AIM 1)来鉴定代表性菌株中的辅助基因。我们推测，辅助基因可能包括导致12F肺炎球菌超强毒力特征的毒力基因。我们将使用多重聚合酶链式反应筛选从鼻咽定植和侵袭性疾病中分离出来的不同集合的肺炎球菌，寻找已发现的辅助基因，以突出那些在侵袭性疾病中显著过度表达的基因(目标2)。这项提议建立了未来的实验研究，将解决在这里发现的候选毒力基因的功能。公共卫生相关性：自1989年以来，被囊型12F型肺炎球菌在美国至少引起了四次侵袭性疾病的暴发。此外，这种血清型在其他国家随着毒力潜力的增加而出现。揭示这些菌株的进化起源和任何与其毒力潜力相关的新基因将提供关于促进疫情爆发的细菌因素的基本知识，并最终可能揭示细菌致病的新机制、新的监测标记和疾病预防的新机会。

DESCRIPTION (provided by applicant): Outbreaks of infectious disease caused by the bacterium Streptococcus pneumoniae, the pneumococcus, were common in the United States early in the 20th century. Today, pneumococcal outbreaks in the U.S. occur in host populations with identifiable risk factors. However, there exist serious concerns that the changing dynamics of pneumococcal populations, brought about by the recent introduction of a conjugate vaccine in the U.S., will broaden the niche of hypervirulent, outbreak-associated strains. The bacterial virulence factors that predispose pneumococci to cause outbreaks are unknown. In this proposal, we will use a molecular epidemiological approach to discover candidate virulence genes in capsular serotype 12F pneumococci that have caused genuine outbreaks in the U.S. and have emerged with hypervirulent characteristics in other countries. We will characterize the clonal diversity of 12F strains using multilocus sequence typing, and we will identify accessory genes in representative strains using suppressive subtractive hybridization (Aim 1). We hypothesize that accessory genes may include virulence genes that contribute to the hypervirulent characteristics of 12F pneumococci. We will screen diverse collections of pneumococci, which were isolated from nasopharyngeal colonization and invasive disease in well-defined host populations, for the discovered accessory genes using multiplex PCR, in order to highlight those genes that are significantly over-represented from invasive disease (Aim 2). This proposal sets up future experimental studies that will address the function of candidate virulence genes that are discovered here. PUBLIC HEALTH RELEVANCE: Capsular serotype 12F pneumococci have caused at least four outbreaks of invasive disease in the United States since 1989. In addition, this serotype has emerged with increased virulence potential in other countries. Revealing the evolutionary origin of these strains and any novel genes linked to their virulence potential will provide basic knowledge about the bacterial factors that promote outbreaks, and may ultimately reveal new mechanisms of bacterial pathogenesis, new markers for surveillance, and new opportunities for disease prevention.