Chlamydia trachomatis

Microbiology - The Silent Intruder

• Obligate intracellular bacterium, Gram-indeterminate.
• Two-phase lifecycle:
  • Elementary Body (EB): Enfectious, Enters cell.
  • Reticulate Body (RB): Replicates, Resides in cell.
• Clinical: Urethritis, PID, neonatal conjunctivitis, trachoma (serovars A-C), LGV (serovars L1-L3).

⭐ Often asymptomatic. High rate of coinfection with Neisseria gonorrhoeae.

Pathogenesis - Two-Faced Invader

• Obligate intracellular bacterium with a unique biphasic developmental cycle, allowing it to evade host defenses.
• Inhibits phagolysosomal fusion, creating a protected "inclusion body" within the host cell cytoplasm.

⭐ Host immune response is the primary driver of pathology. Chronic inflammation (Type IV hypersensitivity) in response to chlamydial antigens, especially Heat Shock Proteins (HSPs), leads to scarring, fibrosis, and long-term complications like infertility and blindness.

📌 Mnemonic: Elementary body Enters. Reticulate body Replicates.

Clinical Syndromes - A Tale of Serovars

• Serovars A, B, C:

  • Trachoma: The leading cause of preventable infectious blindness worldwide.
  • Chronic keratoconjunctivitis → follicular inflammation → conjunctival scarring (Arlt's line) → trichiasis & corneal opacification.
  • 📌 ABC for Africa, Blindness, Chronic infection.

• Serovars D-K:

  • Urogenital Infections: Most common bacterial STI.
    • Men: Urethritis, epididymitis. Often asymptomatic.
    • Women: Cervicitis, Pelvic Inflammatory Disease (PID), often asymptomatic leading to infertility or ectopic pregnancy.
    • Perihepatitis (Fitz-Hugh-Curtis syndrome): "Violin-string" adhesions.
  • Neonatal: Acquired via birth canal.
    • Inclusion Conjunctivitis: Occurs 5-14 days post-delivery.
    • Pneumonia: Afebrile, with a staccato cough.

• Serovars L1, L2, L3:

  • Lymphogranuloma Venereum (LGV):
    • Painless, transient genital ulcer followed by painful, swollen inguinal/femoral lymph nodes (buboes).
    • "Groove sign" is pathognomonic.

⭐ Reactive Arthritis (Reiter's Syndrome): An autoimmune sequela of serovars D-K, not a direct joint infection. Classic triad: "Can't see, can't pee, can't climb a tree" (Conjunctivitis/uveitis, Urethritis, Arthritis).

Diagnosis & Treatment - Detect and Defeat

• Diagnosis

  • NAAT (Nucleic Acid Amplification Test) is the gold standard; use urine or swab.
  • Giemsa stain reveals intracytoplasmic inclusion bodies (reticulate bodies).
  • Culture is specific but rarely used due to slow growth on McCoy cells.

• Treatment

  • Azithromycin (1g single dose) or Doxycycline (100mg BID for 7 days).
  • Crucial to treat all sexual partners to prevent reinfection.
  • Neonatal conjunctivitis/pneumonia: Oral Erythromycin.

⭐ Reactive Arthritis (Reiter Syndrome): A key sequela. 📌 Mnemonic: "Can't see, can't pee, can't climb a tree" (conjunctivitis, urethritis, arthritis).

High‑Yield Points - ⚡ Biggest Takeaways

• Obligate intracellular bacteria that lacks a classic peptidoglycan cell wall.
• Two-phase lifecycle: infectious Elementary Body (Enters) and replicative Reticulate Body (Replicates).
• Most common bacterial STI in the United States; frequently asymptomatic.
• Serotypes A, B, C: cause Trachoma, the leading cause of preventable blindness.
• Serotypes D-K: cause urethritis, cervicitis, PID, and reactive arthritis.
• Serotypes L1-L3: cause Lymphogranuloma Venereum (LGV) with tender inguinal/femoral lymphadenopathy.
• Treat with azithromycin or doxycycline.