Role of host & bacterial factors in persistence of Salmonella in the bovine lymphatic system

沙门氏菌是一种导致人类严重腹泻的细菌。由于沙门氏菌能够在养殖动物体内持续存在，感染通常是通过食物链和环境从养殖动物身上获得的。全世界每年约发生9400万例人间病例和15.5万例死亡。牛是这种感染的重要来源，部分原因是沙门氏菌可以通过被称为淋巴系统的血管和结节状腺体的分支网络离开牛肠道。淋巴系统通常有助于抵抗感染，然而某些类型的沙门氏菌适应在淋巴结中生存并逃避免疫系统。在现代牛肉生产的规模上，切除这样的淋巴结是不可能的，因为它们很小，分布广泛，难以接近。因此，它们经常被掺入碎牛肉中供人类食用。由于碎牛肉引起的大规模疫情已经发生，其中包括对一线药物具有耐药性的菌株，因此需要制定预防或减少牛中沙门氏菌感染的战略。加强动物健康也需要这样的战略，因为沙门氏菌是导致牛腹泻、血液中毒和流产的重要原因。史蒂文斯实验室一直走在研究沙门氏菌如何在牛的肠道中定居，以及在某些情况下如何通过淋巴系统在体内迁移的前沿。我们已经开发了一种新的手术模型，我们将管子插入血液和淋巴系统，在细菌从肠道迁移时捕获它们。这表明，通过淋巴系统从淋巴结逃逸可以部分解释为什么一些菌株在全身扩散，而另一些菌株则局限于肠道或被清除。在我们的知识中，一个关键的空白是沙门氏菌是如何进入淋巴系统的。关于沙门氏菌在牛肠道中的宿主细胞类型，以及这些细胞是否会迁移到淋巴系统，我们几乎一无所知。这种相互作用对沙门氏菌的影响和保护性免疫反应的发展尚不清楚。这种知识上的差距限制了我们设计控制感染策略的能力。霍普金斯大学和霍普大学的实验室开展了世界领先的研究，以了解传染性病原体与反刍动物免疫系统细胞之间相互作用的性质和后果，这反过来又有助于改进结核病、约翰氏病、病毒和寄生虫感染的疫苗。我们的提案汇集了辉瑞动物保健公司和具有互补专业知识的研究人员的大量现金投资：了解沙门氏菌是如何进入牛的淋巴系统的。这将包括将导管插入淋巴管，引流到小牛和老牛肠道不同部位的淋巴结。我们将检查哪些细胞类型与沙门氏菌相互作用，它们如何反应以及细菌发生了什么。然后我们会问，这些事件是否可以解释为什么某些类型的沙门氏菌被牛清除，而其他类型的沙门氏菌在体内传播。这些信息将有助于我们针对相关细胞类型开发疫苗，并促进有益的反应。确定不同的与牛有关的沙门氏菌菌株通过淋巴系统传播的能力是否相同。这将告诉我们，疫苗或药物是必须针对广泛的沙门氏菌菌株，还是专注于高风险类型。确定在淋巴系统中生存所需的沙门氏菌基因。我们最近使用了一种新方法来同时调查数百种沙门氏菌突变体的能力，每种突变体都缺乏不同的特征，在牛肠壁上定植。我们能够回顾性地将这种方法应用于同一动物的淋巴结，以确定影响淋巴系统持久性的因素。这些因子可能适合纳入疫苗或作为药物靶点。

Salmonella is a bacterium that causes severe diarrhoea in humans. Infections are often acquired via the food chain and environment from farmed animals owing to the ability of Salmonella to persist in their bodies. Around 94 million human cases and 155 thousand deaths occur worldwide each year. Cattle are a significant source of such infections, partly because Salmonella can leave the bovine gut via a branching network of vessels and nodular glands termed the lymphatic system. The lymphatic system normally helps to fight infection, however some types of Salmonella are adapted to survive in lymph nodes and evade the immune system. Removal of such lymph nodes is not possible on the scale of modern beef production as they are small, widely dispersed and hard to access. As a consequence, they are often incorporated into ground beef for human consumption. Large outbreaks due to ground beef have occurred, including by strains resistant to frontline medicines, and a need exists to devise strategies to prevent or reduce Salmonella infection in cattle. Such strategies are also required to enhance animal health as Salmonella are a significant cause of diarrhoea, blood-poisoning and abortion in cattle. The Stevens laboratory has been at the forefront of research to understand how Salmonella colonises the intestines of cattle and, in some cases, migrates around the body via the lymphatic system. We have developed a novel surgical model in which we insert tubes into the blood and lymphatic systems to capture bacteria as they migrate from the gut. This has shown that escape from lymph nodes via the lymphatic system can partly explain why some strains spread around the body, whereas others are confined to the gut or cleared. A key gap in our knowledge is how Salmonella enters the lymphatic system in the first place. Almost nothing is known about the host cell types with which Salmonella associates in the bovine gut or whether these migrate to the lymphatic system. The consequences of such interactions for Salmonella and the development of protective immune responses are unknown. Such gaps in knowledge are constraining our ability to design strategies to control infection. The Hopkins and Hope laboratories conduct world-leading research to understand the nature and consequences of interactions between infectious agents and cells of the ruminant immune system, which in turn is helping to improve vaccines for tuberculosis, Johne's disease, viruses and parasitic infections. Our proposal brings together substantial cash investment from Pfizer Animal Health and researchers with complementary expertise to:1. Understand how Salmonella enters the lymphatic system of cattle. This will involve inserting tubes into lymph vessels draining to lymph nodes at various sites in the gut of young calves and older steers. We will examine which cell types interact with Salmonella, how they respond and what happens to the bacteria. We will then ask whether such events can explain why some types of Salmonella are cleared by cattle whereas others spread around the body. The information will help us to target vaccines to relevant cell types and boost beneficial responses.2. Determine if different cattle-associated strains of Salmonella are equally able to spread through the lymphatic system. This will tell us whether vaccines or drugs must target a wide range of Salmonella strains, or focus on high-risk types.3. Identify Salmonella genes required for survival in the lymphatic system. We recently used a novel method to simultaneously survey the ability of hundreds of Salmonella mutants, each lacking a different character, to colonise the bovine gut wall. We are able to retrospectively apply this method to lymph nodes from the same animals to identify factors that influence persistence in the lymphatic system. Such factors may be suitable for inclusion into vaccines or as targets for drugs.