Legionella: An environmental intracellular pathogen with diverse hosts
Howard Shuman, University of Chicago, USA

Some bacterial pathogens cause disease by growing inside macrophages, the immune cells that are usually capable of destroying infectious agents. One example is Legionella pneumophila. This bacterial species is a common cause of community and hospital acquired pneumonia. Legionella species are ubiquitous in soil and water. It is likely that in nature they grow and survive within amoebae. Legionella's ability to both cause disease and survive in environmental hosts require the same specialized protein secretion system that delivers numerous proteins called "effectors" to both human macrophages and amoebae. Efforts to understand what the "effectors" do at the molecular level after they are delivered to the host cells are complicated by the fact that many appear to have redundant functions. Current approaches to clarify what the effectors do to the host cells include whole genome studies of many different Legionella species with different effector genes as well as using chemicals that alter the physiology of macrophages so that they become resistant to infection.

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