Which organism is the obligate intracellular bacterium associated with pelvic inflammatory disease and lymphogranuloma venereum?

• A. Neisseria gonorrhoeae
• B. Treponema pallidum
• C. Chlamydia trachomatis
• D. Mycoplasma hominis

Answer: (C)

Obligate intracellular bacteria must invade and replicate inside host cells to multiply. Chlamydia trachomatis fits this pattern, existing as infectious elementary bodies that enter cells and become replicating reticulate bodies within an inclusion. This intracellular lifestyle underpins its role as a sexually transmitted pathogen that can ascend and cause pelvic inflammatory disease, and it includes serovars (L1–L3) that cause lymphogranuloma venereum with regional lymphadenopathy. The other organisms are not obligate intracellular pathogens and are associated with different disease pictures: Neisseria gonorrhoeae can cause PID but is not strictly intracellular; Treponema pallidum causes syphilis; Mycoplasma hominis is wall-less and linked more with bacterial vaginosis or postpartum infections.