Microbiologists at UofL have found that Legionella pneumophila uses a “tool” that allows it to thrive in an amoeba host and in human lung cells, but with very different results. In the amoeba, considered the bacterium’s natural host, it results in coexistence, making the amoeba host a suitable, safe home for the bacteria’s proliferation. In the human, however, it leads to a deadly form of pneumonia and a paradoxical inflammatory response in the lungs.