Proteus vulgaris bacterium, coloured transmission electron micrograph (TEM). The yellow threads are flagella, hair-like structures that the bacterium beats for motility. This bacterium forms a natural part of the intestinal flora in animals and humans, and is also found in water. In people whose immune systems are suppressed, for instance those with AIDS or those taking immunosuppressant drugs, it can be pathogenic, infecting the urinary tract or causing pneumonia or septicaemia. Negatively stained. Magnification: x60,500 when printed 10cm wide.