Legionella bacteria. Colored Transmission Electron micrograph (TEM) of the bacteria Legionella pneumophila, cause of Legionnaires' disease. Here, numerous bacteria are seen sectioned at different angles: typically, as at center, they are rod shaped Gram-negative bacilli with a single motile flagellum. L.pneumophila was first identified as an agent of disease after a mysterious outbreak of pneumonia caused 29 deaths at an American Legion convention in 1976. The bacteria was found living in water-tanks, shower-heads and air-conditioning systems. The disease, also called legionellosis, causes fatal pneumonic lung damage in the elderly and unfit. Magnification: x20,000 at 5x7cm size. x26,000 at 6x9cm size.