Morphologically,
they are coiled Gram-negative bacilli (2 to 11 μm long; 0.2
to 0.5 μm in diameter) and are motile due to the presence
of flagella (8 to 30). These anaerobic intestinal spirochetes
colonize the large intestine of humans and many animal
species, and several species may cause diarrhea and other
gastrointestinal diseases in these hosts [