Chlamydia trachomatis is a gram-negative bacterium that can replicate only within a host cell. Over the course of the C. trachomatis life cycle, the bacteria take on two distinct forms. Elementary bodies are 200 to 400 nanometers across, and are surrounded by a rigid cell wall that allows them to survive outside of a host cell. This form can initiate a new infection if it comes into contact with a susceptible host cell. Reticulate bodies are 600 to 1500 nanometers across, and are found only within host cells. Neither form is motile.
