Legionella bacteria. Coloured transmission electron micrograph (TEM) of a section through Legionella pneumophila bacteria, the cause of Legionnaires' disease. Flagella (orange), which enable the bacteria to be motile, are seen. These are rod-shaped Gram-negative bacilli. They were 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 were found living in water tanks, shower heads and air-conditioning systems. The disease causes fatal pneumonic lung damage in the elderly and unfit. Magnification: x16,200 at 6x7cm size. x25,000 at 4x5"~PORTRAIT"