A 25-year-old sexually active man presents with urethral discharge. Gram stain of discharge shows only polymorphs but no gram-negative diplococci. NAAT (nucleic acid amplification test) is positive for Chlamydia trachomatis. Regarding the biology of C. trachomatis, which statement is CORRECT?

• A Chlamydia is gram-negative and can be cultured on MacConkey agar with supplemented glucose
• B Elementary bodies (EBs) are the metabolically active intracellular form responsible for replication; reticulate bodies (RBs) are the infectious form
• C C. trachomatis lacks a cell wall and is therefore resistant to beta-lactam antibiotics and doxycycline
• D C. trachomatis serovars D–K cause genital tract infection; it is an obligate intracellular organism that cannot be grown on routine culture media; NAAT on urine/urethral swab is the gold standard ✓

Explanation

Chlamydia trachomatis serovars D–K are the commonest cause of non-gonococcal urethritis (NGU) and ascending genital tract infections (PID, epididymo-orchitis). As obligate intracellular bacteria, Chlamydia cannot be grown on standard bacteriological media — they require cell culture (e.g., McCoy cells). NAAT (PCR/TMA/SDA) on urine, urethral swabs, or cervical swabs is the gold standard for diagnosis with >95% sensitivity. Elementary bodies (EBs) are the small, metabolically dormant infectious extracellular form; reticulate bodies (RBs) are the larger, metabolically active intracellular replicative form — not the other way round. Chlamydia has a cell wall (reduced peptidoglycan) and is sensitive to doxycycline; Mycoplasma lacks a cell wall.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.