Invasion of the enteric nervous system by neurotropic Listeria monocytogenes

单核细胞增生李斯特菌（Lm）是革兰氏阳性，兼性细胞内细菌，导致两种类型的脑 人类感染：弥漫性（脑膜炎/脑膜脑炎）和局灶性脑干（菱形脑炎）。 脑膜炎发生在免疫妥协的背景下，可能是由于免疫系统无法限制 Lm在组织如脾或肝中的指数生长。这导致高滴度菌血症， 血脑屏障（BBB）的侵袭或与髓源性细胞相关的Lm的“隐形转运”， 穿过BBB。相比之下，菱形脑炎是一种迟发性感染，发生在年轻人， 健康的免疫能力强的人，这表明感染是依赖于细菌编码的 神经毒力因子这一建议的核心假设是， 菱形脑炎期间的嗜神经性在肠中而不是在脑中介导关键的早期事件。 支持这一假设的是我们的初步数据，显示当注射亲神经性Lm时， 静脉注射（绕过感染的肠道阶段），它们不会传播到大脑。此外，其他 表明菱形脑炎分离株在牛中的存活和复制能力没有增加， 器官型脑切片相对于其他Lm菌株的离体。直到最近，菱形脑炎才得以研究， 由于缺乏Lm脑干感染的小动物模型，仅在牛或羊中进行。然而，我们最近 结果表明，一些临床分离的Lm（UKVDL 9和SD 4000）可以优先定殖于脑干， 小鼠在感染过程后期，血液中没有达到高滴度。两种嗜神经性菌株， 据报道，属于谱系III，最小和最少的特点组的Lm分离株。这项提案的目的是 目的是确定在肠道阶段促进Lm UKVDL 9和SD 4000向神经营养性的因素。 我们预测嗜神经性Lm在肠道感染的三个不同方面具有优势; 这三个具体目标构成了该建议的三个具体目标。在目标1中，我们确定用于穿过肠道的路线 粘膜或炎症反应诱导的促进嗜神经性Lm菌株在神经束中的定位， 肠粘膜下层或肠内淋巴管周围的迷走神经隐窝末梢内。在 目的2，我们鉴定了新的Lm表面蛋白，其介导肠神经胶质细胞的侵袭增强， 围绕在肠道神经周围的一种在目标3中，我们检验了在人中发现的截短actA等位基因的假设， 亲神经性Lm促进改变类型的细胞内运动，其允许细菌沿着沿着细胞壁迁移。 整个轴突一直延伸到脑干这项工作将通过提供 这是在这种危及生命的食源性感染中对嗜神经性的第一个真实的见解，也可能奠定 为致病机理或微生物组相关研究的新领域奠定基础，以了解细菌如何相互作用 肠神经系统的细胞。

Listeria monocytogenes (Lm) are Gram-positive, facultative intracellular bacteria that cause two types of brain infections in humans: diffuse (meningitis/meningoencephalitis) and focal brainstem (rhombencephalitis). Meningitis occurs in the setting of immune compromise, likely due to the failure of the immune system to limit exponential growth of Lm in tissues such as spleen or liver. This leads to high titer bacteremia and either direct invasion of the blood-brain-barrier (BBB) or “stealth transport” of Lm associated with myeloid-derived cells that cross the BBB. In contrast, rhombencephalitis is an infection of a delayed nature that occurs in young, otherwise healthy immune competent people, which suggests that the infection is dependent on bacterially encoded neurovirulence factors. The central hypothesis of this proposal is that the virulence factors which define neurotropism during rhombencephalitis mediate critical early events in the intestines, rather than in the brain. Support for this hypothesis comes from our preliminary data showing that when the neurotropic Lm are injected intravenously (bypassing the gut phase of the infection), they do not disseminate to the brain. In addition, others showed that rhombencephalitis isolates did not have an increased ability to survive and replicate in bovine organotypic brain slices ex vivo relative to other Lm strains. Until recently, rhombencephalitis could be studied only in cows or sheep due to the lack of a small animal model of Lm brainstem infections. However, we recently showed that some clinical isolates of Lm (UKVDL9 and SD4000) could preferentially colonize the brainstems of mice late in the course of infection, without reaching high titer in the blood. Both of the neurotropic strains we reported belong to lineage III, the smallest and least characterized group of Lm isolates. The goal of this proposal is to define the factors that promote neurotropism by Lm UKVDL9 and SD4000 during the gut phase of listeriosis. We predict that neurotropic Lm could have an advantage in three different aspects of the intestinal infection; these form the three Specific Aims of the proposal. In Aim 1, we determine if the route used to cross the gut mucosa or inflammatory response induced promotes localization of neurotropic Lm strains in neural bundles in the intestinal submucosa or within the vagal crypt endings surrounding lymphoid cryptopatches in the gut. In Aim 2, we identify the novel Lm surface protein that mediates enhanced invasion of enteric glial cells, the cell type that surrounds nerves in the gut. In Aim 3, we test the hypothesis that a truncated actA allele found in neurotropic Lm promotes an altered type of intracellular movement that allows the bacteria to migrate along the entire length of an axon all the way to the brainstem. This work will move the listeriosis field forward by providing the first real insights into neurotropism during this life-threatening foodborne infection and could also lay the groundwork for new areas of pathogenesis or microbiome-related research to understand how bacteria interact with cells of the enteric nervous system.