Proteus mirabilis bacteria, coloured scanning electron micrograph (SEM). These Gram-negative, rod-shaped bacteria are covered in flagella (thread-like projections), which are used for locomotion. P. mirabilis forms a natural part of the intestinal flora in animals and humans, and is also found in water. However, it can be pathogenic, infecting the urinary tract or causing pneumonia or septicaemia. Magnification: x24,000 when printed 15cm wide.