them to survive in an extracellular form. When an EB encounters a susceptible host cell, it binds to the cell surface and is internalized. The second form, reticulate bodies (RBs) are 600 to 1500 nanometers across, and are found only within host cells. RBs have increased metabolic activity and are adapted for replication. Neither form is motile.

The evolution of C. trachomatis includes a reduced genome of approximately 1.04 megabases, encoding approximately 900 genes. In addition to the chromosome