Importance of the intracellular energy metabolism of S. Typhimurium within epithelial cells and macrophages

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According to the latest European Food Standard Agency (EFSA) statistics (2008), Salmonella enterica serovar Typhimurium (S. Typhimurium) is the second most reported zoonotic infection in humans and the most frequent cause of food borne outbreaks in the EU. Worldwide Salmonella is responsible for up to 800,000 deaths from contaminated food and water. Following ingestion Salmonella bacteria travel to the intestine where they invade the cells lining the gut wall (epithelial cells), causing bloody diarrhoea. In the case of systemic infections (caused by S. Typhi and S. Paratyphi in humans), Salmonella invade the immune cells which are responsible for fighting infection (macrophages). Although the role of macrophages is to kill bacteria, Salmonella has adapted to evade the lethal chemical weapons deployed by macrophages. The Salmonella are able to survive and grow within the macrophages in a specialised compartment known as the 'Salmonella containing vacuole' (SCV), and thereby become systemically disseminated to other organs including the mesenteric lymph nodes, liver and spleen. We recently made the discovery that the major metabolic pathway required to catabolise sugars (glycolysis) is essential for the ability of Salmonella to grow and survive within macrophages, but not within epithelial cells. In order to grow and survive within host cells, Salmonella must also have a route for generating the energy required for these processes. Together with other evidence from our research, and published data, it seems likely that S. Typhimurium generates energy via different mechanisms in macrophages compared to epithelial cells. One of the aims of this proposal is to differentiate between these alternative energy generating pathways in macrophages and epithelial cells. Such information may facilitate therapeutic interventions. One of the major questions in infection biology is the extent to which the host cell contributes to the intracellular growth of Salmonella. We will use cutting edge techniques to determine the contribution of amino acids derived from host proteins and peptides to the intracellular growth of Salmonella in infected epithelial cells and macrophages. If Salmonella is dependent on the host for some of its requirements to enable intracellular growth, then this may also represent a way to facilitate therapeutic intervention.