Proteus bacteria. Coloured transmission electron micrograph (TEM) of a section through Proteus sp. bacteria. These Gram-negative bacteria occur in two forms. The two short bacilli (rod-shaped) bacteria (green & red) can attach to other cells and to substrates. The other larger form (red) is covered in whip-like flagella with which it moves around and colonises new areas by a process called swarming. Proteus bacteria are normally found in soil, but also occur in the human intestine. They can cause urinary tract infections, especially in people with weakened immune systems. Magnification unknown.