Chlamydia trachomatis taken from a urethral scrape. Untreated, chlamydia can cause severe, costly reproductive and other health problems including both short- and long-term consequences, i.e. pelvic inflammatory disease (PID), infertility, and potentially fatal tubal pregnancy. Chlamydia is a genus of pathogenic bacteria that are obligate intracellular parasites. Chlamydia trachomatis is a gram-negative bacterium. It is ovoid in shape and non-motile. The bacteria are non-spore-forming, but the elementary bodies act like spores when released into the host. Disorders caused by Chlamydia trachomatis include chlamydia, trachoma, lymphogranuloma venereum, nongonococcal urethritis, cervicitis, salpingitis, pelvic inflammatory disease, and pneumonia. Chlamydial infections.