The role of central metabolism in the successful infection of macrophages and mice by Salmonella Typhimurium

沙门氏菌（Salmonella enterica serovar Typhimurium）。鼠伤寒沙门氏菌（Typhimurium）是动物和人类疾病的致病菌，它会引起人类肠胃炎，症状为胃痛和带血腹泻。S.鼠伤寒是造成全球每年多达2000万例胃肠炎的原因。在美国和英国，沙门氏菌比任何其他食源性病原体导致更多的人类死亡。感染的过程开始于摄入受污染的食物或水。S.鼠伤寒杆菌进入肠道，侵入肠壁的上皮细胞。然后细菌从上皮细胞中爆发，引起血性腹泻，并侵入负责对抗感染的免疫细胞（巨噬细胞）。虽然巨噬细胞的作用是杀死细菌，但S。鼠伤寒杆菌已经发展出躲避巨噬细胞用来杀死它的化学武器的能力。鼠伤寒杆菌通过在巨噬细胞内构建保护区来实现这一点，即含有沙门氏菌的巨噬细胞或SCV。沙门氏菌在体内的巨噬细胞中存活和生长，使细菌有机会感染其他器官，包括淋巴结，脾脏和肝脏。我们对SCV内部的环境了解不多，特别感兴趣的是沙门氏菌可以使用哪些化合物作为燃料，为细菌提供生存和生长所需的能量。沙门氏菌可以使用各种不同的化学物质作为燃料，但同样地，我们需要不同的汽车发动机来使用汽油或柴油，沙门氏菌需要制造不同的细胞机器（酶和运输蛋白质）来有效地使用不同的化学物质。运输蛋白将燃料化学物质带入沙门氏菌细胞，不同的酶组一起作用形成加速燃料化学物质分解的途径。这意味着，如果我们知道细菌正在制造哪些运输蛋白质和酶，我们就可以获得细菌使用哪些燃料化学物质生长的线索。细胞中产生的转运蛋白和酶由RNA分子的存在决定，RNA分子充当信使信号并告诉细胞产生哪些特定的转运蛋白和酶。通过使用一种称为转录组学的特殊技术来观察细胞中存在哪些RNA分子，我们可以知道哪些转运蛋白和酶可能会产生。我们已经有了沙门氏菌感染期间的转录组学数据，这表明巨噬细胞内沙门氏菌的潜在燃料来源包括糖和脂肪。这项提案旨在确定糖和脂肪是否真的被沙门氏菌在感染过程中用作燃料。我们将通过阻断参与燃料分解途径的特定酶和转运蛋白的制造来实现这一点，并观察这是否会降低沙门氏菌在SCV内生存的能力。我们将查明在感染过程中使用的是相同的燃料还是不同类型的燃料。巨噬细胞还产生一种叫做干扰素的化学物质，它可以刺激生活在巨噬细胞内的其他细菌的脂肪分解途径。当这些途径被阻止参与途径的特定酶产生时，细菌的存活率就会降低。我们的目标是找出干扰素是否刺激沙门氏菌类似的分解途径，以及阻断这些途径是否也会减少感染。确定沙门氏菌在巨噬细胞内生存的分解途径和化学物质可能会提出预防沙门氏菌感染的方法。

The bacterium Salmonella enterica serovar Typhimurium (S. Typhimurium) is responsible for disease in animals and man. It causes gastroenteritis in humans characterised by stomach ache and bloody diarrhoea. S. Typhimurium is responsible for up to 20 million cases of gastroenteritis each year worldwide. In the USA and UK, Salmonella causes more human deaths than any other food-borne pathogen. The process of infection starts when contaminated food or water is ingested. S. Typhimurium bacteria travel to the intestine where they invade the cells which line the gut wall (epithelial cells). The bacteria then break out of the epithelial cells, causing bloody diarrhoea, and invade immune cells which are responsible for fighting infection (macrophages). Although the macrophages are designed to kill bacteria, S. Typhimurium has developed the ability to evade the chemical weapons deployed by the macrophage to kill it. S. Typhimurium does this by constructing a protective region within the macrophage, the Salmonella Containing Vacuole or SCV. The Salmonella survive and grow inside the macrophages which carried around the body, giving the bacteria the opportunity to infect other organs including the lymph nodes, spleen and liver. We don't know very much about the environment inside the SCV and are particularly interested in which chemical compounds are available for Salmonella to use as fuel, providing the bacteria with the energy it needs to survive and grow. Salmonella can use a variety of different chemicals as fuel, but in the same way we need different car engines to use petrol or diesel, Salmonella needs to make different cellular machines (enzymes and transport proteins) to use the different chemicals efficiently. The transport proteins bring fuel chemicals into the Salmonella cells and different sets of enzymes act together to form pathways which speed up breakdown of the fuel chemicals. This means if we know which transport proteins and enzymes the bacteria are making we can get clues about which fuel chemicals the bacteria are using to grow. The transport proteins and enzymes made in the cell are determined by the presence of RNA molecules which act as messenger signals and tell the cell which particular transport proteins and enzymes to make. By using a special technique called transcriptomics to look at which RNA molecules are present in the cell, we can tell which transport proteins and enzymes are likely to be produced. We already have transcriptomics data from Salmonella during infection which suggests that the potential fuel sources for Salmonella inside macrophages include sugars and fats. This proposal aims to determine whether sugars and fats are actually used as fuel by the Salmonella during infection. We will do this by blocking the manufacture of specific enzymes and transport proteins involved in the fuel breakdown pathways and seeing whether this reduces the ability of Salmonella to survive inside the SCV. We will find out whether the same fuel or different types of fuel are used during infection. Macrophages also make a chemical called interferon that stimulates the breakdown pathways of fat in other species of bacteria that live inside macrophages. When these pathways are blocked by stopping specific enzymes involved in the pathway from being produced, the survival of bacteria reduces. We aim to find out whether interferon stimulates similar breakdown pathways in Salmonella, and whether blocking these pathways also reduces infection. Identification of the breakdown pathways and the chemicals used by Salmonella to survive inside the macrophage is likely to suggest ways of preventing Salmonella infections.