Dissemination of intracellular and extracellular Listeria from the gut

兼性胞内致病菌单核细胞增生性李斯特菌的食源性传播 导致严重程度不等的人类疾病，从轻度胃肠炎到危及生命的败血症或 脑膜脑炎。决定疾病严重程度的宿主和细菌因素没有得到很好的定义， 我们对李斯特菌病肠道阶段的了解尤其有限。要解决这个问题 知识缺口，我们开发了一种食源性金黄色葡萄球菌感染的小鼠模型，它密切模拟了 人类疾病。在初步研究中，我们发现肠道中的大多数LM是细胞外的， 而且该LM不能在肠道中存在的许多单核吞噬细胞亚群中复制 固有层。这是一个意想不到的结果，因为细胞内的生长和在细胞之间的传播 在没有遇到胞外环境的情况下，通常被认为是 Lm.这一提议的总体假设是食源性LM可以使用三种不同的途径之一来 从肠道固有层扩散到肠系膜淋巴结(MLN)：1)LM“搭便车” 附着于迁移性炎性单核细胞，但不能有效入侵；2)LM入侵 传统的树突状细胞(CDC)是一种“特洛伊木马”，可在细胞内传递非复制性 细菌到淋巴被膜；以及3)细胞外LM通过淋巴管自由流动到被膜下 上颌窦。我们认为，这三条途径在体内感染过程中可能是多余的， 但可能受LM侵袭肠道上皮的途径的影响。在目标1中，细胞的作用- 联合细菌与自由流动的胞外细菌在促进传播到MLN方面的比较 回肠或结肠将被确定。在目标2中，我们将确定 Lm影响细菌在MLN中生存和复制的能力，并进一步促进全身 散开。这些探索性研究将通过定义LM使用的机制来推动该领域的发展 清除MLN是避免口腔获得性病原体系统性传播的关键瓶颈。

Foodborne transmission of the facultative intracellular bacterial pathogen Listeria monocytogenes (Lm) results in human disease that ranges in severity from mild gastroenteritis to life-threatening septicemia or meningoencephalitis. The host and bacterial factors that determine disease severity are not well defined, and our understanding of the intestinal phase of listeriosis, in particular, is severely limited. To address this knowledge gap, we developed a mouse model of foodborne Lm infection that closely mimics all phases of the human disease. In preliminary studies, we found that the majority of Lm in the gut were extracellular, and that Lm was not able to replicate in many of the mononuclear phagocyte subsets present in the intestinal lamina propria. This was an unexpected result, because intracellular growth and spread from cell-to-cell without encountering the extracellular milieu are generally regarded as the primary virulence strategies for Lm. The overall hypothesis of this proposal is that foodborne Lm can use one of three distinct pathways to disseminate from the intestinal lamina propria to the mesenteric lymph nodes (MLN): 1) Lm “hitch a ride” attached to migratory inflammatory Ly6Chi monocytes which they cannot efficiently invade; 2) Lm invade conventional dendritic cells (cDC) which serve as a “Trojan horse” to deliver non-replicating, but intracellular bacteria to the MLN; and 3) extracellular Lm traffic free-flowing through lymphatic vessels to the subcapsular sinus of the MLN. We propose that these three pathways are likely to be redundant during in vivo infection, but may be influenced by the route used by Lm to invade the intestinal epithelium. In Aim 1, the role of cell- associated vs. free-flowing extracellular bacteria in promoting dissemination to the MLN that drain either the ileum or the colon will be determined. In Aim 2, we will determine how the dissemination pathway used by Lm affects the ability of the bacteria to survive and replicate in the MLN and to promote further systemic spread. These exploratory studies will advance the field by defining the mechanisms used by Lm to avoid clearance in the MLN a critical bottleneck to avoid systemic spread of orally acquired pathogens.