Coloured transmission electron micrograph of the Gram-negative, rod-shaped bacterium Pseudomonas aeruginosa. This species, commonly present in the human intestine, can cause serious wound, skin and urinary tract infections. It can also multiply in the warm, moist conditions prevailing inside baby incubators or ventilating machines and so be inhaled in large numbers. Such infections of the respiatory tract are usually harmless, but sometimes cause a necrotizing pneumonia, which may be fatal. Outbreaks of P. aeruginosa skin infections sometime occur among users of swimming pools with inadequate chlorination. Magnification: x8500 at 6x7 cm size, x4250 at 35mm size.