Legionella pneumophila - developmental cycle and the transmission of legionnaires' disease

Legionnaires' disease is a severe pneumonia caused by the intracellular bacterial pathogen Legionella pneumophila. Legionella thrives in the freshwater environment where it infects protozoa. Transmission of Legionella is always one way - from the environment to humans, and despite nearly 30 years of research, a satisfactory explanation for why Legionella is not spread from person-to-person has not been offered. A potential breakthrough in resolving this enigma is my recent discovery that highly infectious bacteria are produced when Legionella grows in protozoa, but not when Legionella grows in macrophages, which are the cells targeted by Legionella within the human host. I propose to study these highly infectious forms of Legionella to understand how they are produced, how do they interact with protozoa in the environment, and how are they transmitted to the human lung to cause disease. Completion of these studies will provide new knowledge about the role that the highly infectious forms play in the pathogenesis and transmission of Legionella, and lead to better measures to control the spread of Legionnaires' disease. In addition, we expect that our studies with Legionella will help us to better understand the spreading mechanisms of human diseases caused by other intracellular bacterial pathogens, some of which have been identified as bioterrorism agents.