False-colour scanning electron micrograph (SEM) of a cluster of Pseudomonas aeruginosa bacteria. They are Gram-negative and rod-shaped. This species of Pseudomonas is common in the human intestine, but 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 respiratory tract are usually harmless, but sometimes result in a necrotizing and dangerous pneumonia. P. aeruginosa can cause skin infections among users of swimming pools. Magnification: x1,150 at 6x7cm size.