Proteus vulgaris bacteria, scanning electron micrograph (SEM). The fine threadlike projections are flagella, which allow the bacterium to move. P. vulgaris 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 example those with AIDS or those taking immunosuppressant drugs, it can be pathogenic, infecting the urinary tract or causing pneumonia or septicaemia. Magnification: 13,500x when printed 10 centimetres high.