<unk> , an obligate intracellular human pathogen, is one of four bacterial species in the genus<unk> .<unk>  is a Gram-negative bacterium, therefore its cell wall components retain the counter-stain safranin and appear pink under a light microscope. It is ovoid in shape.<unk>  includes three human biovars, based on variations in the major outer membrane protein (MOMP):
serovars Ab, B, Ba, or C — cause trachoma: infection of the eyes, which can lead to blindness
serovars D-K — cause urethritis, pelvic inflammatory disease, ectopic pregnancy, neonatal pneumonia, and neonatal conjunctivitis
serovars L1, L2 and L3 — lymphogranuloma venereum (LGV)
The L2 serovar can be further differentiated into L2, L2', L2a, and L2b based on significant amino acid differences
Many, but not all,<unk>  strains have an extrachromosomal plasmid.<unk>  can exchange DNA between its different strains, thus the evolution of new strains is common.
Chlamydia trachomatis
Chlamydophila trachomatis
Neisseria gonorrhoeae
Trichomonas vaginalis
Haemophilus ducreyi
Treponema pallidum
Klebsiella rhinoscleromatis
Ureaplasma urealyticum