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. In an article published last week in Cell Host & Microbe, Yousef Abu Kwaik, PhD, professor, and Chris Price, PhD, senior research scientist, both of the Department of Microbiology and Immunology, and other researchers at UofL explain that L. pneumophila uses the same mechanism or virulence determinant in both amoeba and the accidental human host, but with different results. A virulence determinant is a gene or protein that plays a key role in disease development.