Chlamydia trachomatis, commonly known as chlamydia, is one of four bacterial species in the genus Chlamydia. Chlamydia is a genus of pathogenic bacteria that are obligate intracellular parasites. C. trachomatis is a Gram-negative bacterium. It is ovoid in shape and nonmotile. The bacteria are nonspore-forming, but the elementary bodies act like spores when released into the host.