Chlamydia trachomatis is a gram-negative bacterium that causes chlamydia. It is an obligate intracellular pathogen, meaning it can only replicate within host cells. The bacterium has a unique life cycle involving two distinct forms: the elementary body (EB) and the reticulate body (RB). The elementary body is the infectious, metabolically inactive form that can survive outside host cells and is responsible for transmission. Once inside a host cell, the EB transforms into the reticulate body, which is non-infectious but metabolically active and capable of replication through binary fission.

Chlamydia trachomatis infects various mucous membranes, including those in the genital tract, rectum, throat, and eyes. It causes several clinical conditions such as genital infections (urethritis, cervicitis, and pelvic inflammatory disease), ocular infections (trachoma, which can lead to blindness if untreated), and respiratory infections (pneumonia in newborns). Early detection and treatment with antibiotics like azithromycin or doxycycline are essential to prevent complications and the spread of the infection.