Chlamydia / Chlamydophila

It has three medically important species. All are obligate intracellular microbes and characteristically produce intracytoplasmic inclusions, which can be used for diagnosis on smears. They are Gram-negative but stain poorly with the Gram stain, so Giemsa, Castaneda, or Macchiavello stains are used.

Two different forms are seen in the body:

• Elementary body: a metabolically inactive, infectious particle
• Reticulate body: a metabolically active, dividing form

The elementary body enters the host cell, becomes metabolically active, and then divides to form reticulate bodies.

C. trachomatis: It is the most common cause of STD in the USA. It causes urethritis, inclusion conjunctivitis, trachoma, lymphogranuloma venereum (LGV), and pneumonia.

• In males, it presents as urethritis, epididymitis, and proctitis.
• In females, it presents as urethritis, cervicitis, vaginitis, salpingitis, and infertility due to tubal scarring of the fallopian tube.
• Infants can acquire conjunctivitis during passage through the birth canal.

Trachoma is a preventable cause of blindness. It is a chronic keratoconjunctivitis with corneal scarring.

LGV is caused by C. trachomatis serovars L1 to L3. It presents as:

• Unilateral, tender inguinal or femoral lymphadenopathy (bubo), accompanied by a genital papule or ulcer
• Proctocolitis with blood and mucus discharge from the rectum, often confused clinically with IBD (inflammatory bowel disease)
• Draining sinuses and fistulae

Reiiter’s Syndrome is a “reactive” arthritis presenting with arthritis, urethritis, and conjunctivitis in patients who have genitourinary or gastrointestinal infections caused by Chlamydia, Salmonella, Shigella, or Campylobacter bacteria. It is not directly due to infection; it results from an immunological response triggered by the primary infection.

C. pneumoniae: It causes a community acquired atypical pneumonia. It typically presents as cough with laryngitis, bronchitis, runny nose, and other upper respiratory symptoms. It is usually mild, but complications like encephalitis and myocarditis can occur. It can cause severe exacerbation of asthma in susceptible individuals. It has also been strongly associated with the pathogenesis of atherosclerosis and plaque buildup in arteries.

C. psittaci: Infection is acquired from birds such as parrots, pigeons, and poultry. It presents as an influenza like illness, pneumonia, septicaemia, or meningoencephalitis.

Laboratory diagnosis of Chlamydia infections

Tissue scrapings or discharge can be sampled for diagnosis.

• Intracytoplasmic inclusions stain:
  • Blue with Castaneda
  • Red with Macchiavello
  • Purple or blue with Giemsa

Smears can also be stained with fluorescein isothiocyanate labelled antibodies (immunofluorescence) or detected by DNA probe hybridization. ELISA or PCR are other commonly employed techniques.

LGV and C. trachomatis can be detected using complement fixation test.

Cell culture or yolk sac culture can be done for isolation of organisms, but it is not needed for clinical diagnosis. In culture:

• C. trachomatis forms glycogen containing inclusions that stain brown with iodine.
• C. pneumoniae and C. psittaci inclusions lack glycogen, so they do not stain with iodine.