Towards an understanding of the molecular basis for Legionella pneumophila pathogenesis

Legionella pneumophila is an aerobic, motile, gram-negative bacterium and a facultative intracellular parasite. L. pneumophila inhabits aquatic environments where its host cells are presumably unicellular organisms, a large variety of which the bacterium multiplies within in vitro. L. pneumophila is transmitted to humans by the airborne and probably the waterborne route. In humans, it causes Legionnaires– disease, a severe and often fatal form of pneumonia. It also causes Pontiac Fever, a febrile, non-pneumonic, non-fatal, flulike illness, and a variety of extrapulmonary infections. One of over 40 species in the family Le-gionellaceae, L. pneumophila causes over 90% of human infections. The host cells for L. pneumophila in humans are mononuclear phagocytes, chiefly alveolar macrophages and monocytes, in which L. pneumophila multiplies in vitro (1, 2).