Mechanisms of MRSA intestinal colonization

摘要 我们的长期目标是找到控制耐甲氧西林金黄色葡萄球菌(MRSA)的方法。在这里我们 重点描述社区获得性(CA)-MRSA如何在胃肠道(GI)定植。一把钥匙，但是 被低估的是，观察到，GI的定植建立了一个传播的宿主，并且是最 婴儿和幼儿感染CA-MRSA的共同来源，他们感染的风险比 成年人。我们和其他人已经使用小鼠模型来识别支持GI定植的金黄色葡萄球菌的特征。然而， 与CA-MRSA相关的GI定植机制尚不清楚，部分原因是使用了 依赖抗生素耗尽肠道微生物区系来建立定植的动物模型。我们最近出版的 未发表的工作对一种婴儿小鼠模型进行了改造，以提供与CA-MRSA GI相关的易处理系统 在社区中的殖民，特别是在婴儿和儿童中。我们的初步数据，用这个获得的 模型表明，断奶与对CA-MRSA的定植抗性有关。我们还展示了毛孔- 形成白毒素可促进CA-MRSA在断奶小鼠体内定植，但对幼鼠无影响 或无菌成年小鼠。鉴于我们的发现，断奶与对CA的殖民抵抗有关- MRSA，一种被认为是由共生微生物区系赋予的性质，我们假设 毒素共生菌通过共生使CA-MRSA克服定植抗性 细菌。我们还证实了小鼠对CA-MRSA的定植抵抗力反常地增加 缺乏适应性免疫(B和T细胞)。鉴于先天免疫细胞在肠道微生物区系形成过程中 在这样的小鼠中，断奶和对病原体的抵抗力增强，我们第二次假设 先天免疫和微生物群共同抑制了CA-MRSA的定植。为了检验我们的假设，我们将1) 确定介导CA-MRSA肠道定植抵抗的共生物种，2)了解免疫 抑制CA-MRSA在非获得性免疫小鼠体内定植的机制，以及3)决定 影响细菌的特定CA-MRSA毒素及其与肠道共生菌的相互作用 竞争。这些研究的结果有望确定细菌分类群、先天免疫机制和 我们可能会操纵CA-MRSA基因座来干扰CA-MRSA的定植。这一结果将指导未来的努力 确定微生物区系和细胞类型特定的靶点，以合理设计调节 殖民主义。在一定程度上，这项工作确定了直接导致病原体的毒力因子 除了传播，我们的工作还将揭示可以被用作双重作用靶点的细菌机制 治疗学。

SUMMARY Our long-term objective is to find ways to control methicillin-resistant Staphylococcus aureus (MRSA). Here we focus on characterizing how community-acquired (CA)-MRSA colonizes the gastrointestinal (GI) tract. A key, but underappreciated, observation is that GI colonization establishes a reservoir for transmission and is the most common origin for CA-MRSA infection in infants and young children, who are at greater risk of infection than adults. We and others have used murine models to identify S. aureus traits that support GI colonization. However, the mechanisms governing GI colonization relevant to CA-MRSA are poorly understood, in part due to the use of animal models that rely on antibiotic depletion of gut microbiota to establish colonization. Our recent published and unpublished work adapted an infant mouse model to provide a tractable system relevant to CA-MRSA GI colonization in the community, especially among infants and children. Our preliminary data, obtained using this model, show that weaning is associated with colonization resistance to CA-MRSA. We also show that pore- forming leukotoxins (“toxins”) promote CA-MRSA colonization in weaned mice, but had no effect in infant mice or germ-free adult mice. Given our finding that weaning was associated with colonization resistance to CA- MRSA, a property thought to be conferred by commensal microbiota, we hypothesize that perturbation of commensal bacteria by toxins empowers CA-MRSA to overcome colonization resistance by commensal bacteria. We also established that colonization resistance against CA-MRSA is paradoxically increased in mice that lack adaptive immunity (B and T cells). Given that innate immune cells that shape the gut microbiota during weaning and confer resistance to pathogens are upregulated in such mice, we secondarily hypothesize that innate immunity and the microbiota combine to inhibit CA-MRSA colonization. To test our hypotheses, we will 1) identify commensal species that mediate CA-MRSA colonization resistance in the gut, 2) understand the immune mechanisms that inhibit the CA-MRSA colonization in mice without adaptive immunity, and 3) determine the specific CA-MRSA toxins and interactions between S. aureus and gut commensals that affect bacterial competition. The outcomes of these studies promise to identify bacterial taxa, innate immune mechanisms, and CA-MRSA loci we might manipulate to perturb CA-MRSA colonization. The results will guide future efforts to identify microbiota and cell-type-specific targets for rationally designed therapeutic strategies that modulate colonization. To the extent that the work identifies virulence factors that contribute directly to pathogen transmission, our work will also uncover bacterial mechanisms that could be exploited as targets for dual-action therapeutics.