Chlamydia trachomatis: properties, disease and laboratory diagnosis

Chlamydia trachomatis, an obligate intracellular bacteria, causes significant infection and disease worldwide. It is a most common sexually transmitted bacterial pathogen and major cause of Pelvic Inflammatory disease in USA.

General properties:

Life Cycle of Chlamydia-trachomatis
Life Cycle of Chlamydia trachomatis
  1. Small group of non-motile cocciod bacteria with gram negative like cell wall
  2. Obligate intracellular bacteria (they were once regarded as viruses)
  3. Occurs in two forms:
    1. Elementary body (EB): Non replicating, infectious particle (that can be transmitted from infected person/site to noninfected person/site). #Infective form
    2. Reticulate body (RB): Intracellular growth or replicative form.
    3. Single genus: Chalmydia which contains species C. trachomatis, C. psittaci and C. pneumonia (TWAR Strains)

Diseases caused by C. trachomatis

Subtypes Route(s) of Transmission Clinical Syndrome
A, B, Ba, C Hand to eye from fomites, flies Endemic trachoma
L1, L2, L3 Sexual Lymphogranuloma venereum
D-K Sexual, hand to eye by autoinoculation of genital secretions; eye to eye from infected secretions; neonatal. Urethritis, cervicitis, pelvic inflammatory disease, epididymitis, infant pneumonia and conjunctivitis

 Eyes infection:

  • Trachoma :(An infection of the conjunctival epithelial cells which may lead to blindness)
  • Inclusion conjunctivitis: (An eye disease that is milder than trachoma, which consists of purulent conjunctivitis that heals spontaneously without scaring).

 Sexually transmitted Genital and rectal infections:

  • Major cause of Pelvic Inflammatory disease (PID)
  • Proctitis
  • Nongonococcal urethritis
  • Salpingitis
  • Cervicitis
  • Lymphogranuloma venerum (LGV) usually occurs in men (Inguinal lymphnodes)

 Disease caused by C. psittaci and C. pneumoniae

  • Upper respiratory tract infections
  • Bronchitis
  • Pneumonia

Route of transmission:

a. Direct contact

  • Primarily spread from human to human by sexual transmission: Genital infections
  • From mother to infant during birth: Neonatal pneumonia or inclusion conjunctivitis

b. Respiratory route: C. psittaci and C. pneumoniae

Laboratory diagnosis of C. trachomatis infection:

Most diseases caused by the Chlamydiae are diagnosed on the basis of their clinical manifestations. Laboratory diagnosis of C. trachomatis can be achieved by cytology, culture, direct detection of antigen or nucleic acid, and serologic testing.
Specimen: Scrapings from the eyes or urogenital tract, materials aspirated from epididymis, fallopian tubes, sera, tissue biopsy

  1. Cytologic examination of cell scrapings from the conjunctiva of newborns or persons with ocular trachoma by Giemsa staining. Inclusion bodies in scraped tissues can also be identified by iodine staining of glycogen present in the cytoplasmic vacuoles of infected cells and viewing under microscope. Staining of C. trachomatis elementary bodies by Fluorescent monoclonal antibodies.
  2. Serodiagnosis: Serologic testing has limited value for diagnosis of urogenital infections in adults because most adults with chlamydial infection have had a previous exposure to C. trachomatis and are therefore seropositive.  But negative serology can reliably exclude chlamydial infections.  Complement fixation test can be used and antibody titer of 1: 64 is indicative of lymphogranuloma venerum (LGV). Detection of C. trachomatis specific IgM is useful in the diagnosis of neonatal infections.
  3. In situ DNA hybridization with cloned C trachomatis DNA probes in tissue biopsy specimens.
  4. Cultivation/Culture: It is highly specific test but has lower sensitivity than amplification tests.  Unfortunately, It is highly expensive, technically complex and has stringent transport requirements in terms of both time and temperature.  Cell lines that have been used to isolate C. trachomatis  in cell culture  are McCoy (cycloheximide treated), Hela, Monkey kidney cells

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