Chlamydia trachomatis: Properties, Disease, Lab Diagnosis

Chlamydia trachomatis, an obligate intracellular bacteria, causes significant infection and disease worldwide. It is the most common sexually transmitted bacterial pathogen and a major cause of pelvic inflammatory disease (PID) in the USA.

General Properties

Life Cycle of Chlamydia-trachomatis
Life Cycle of Chlamydia trachomatis
  1. A small group of non-motile coccoid bacteria with Gram-negative cell wall.
  2. Chlamydiae have a rigid cell wall but do not have a typical peptidoglycan layer. Structurally, the chlamydial elementary body resembles Gram-negative bacteria but lacks muramic acid.
  3. Obligate intracellular bacteria (they were once regarded as viruses)
  4. Occurs in two forms:
    1. Elementary body (EB): Non-replicating, infectious particle (transmitted from infected person/site to noninfected person/site). #Infective form
    2. Reticulate body (RB): Intracellular growth or replicative form.
  5. Single genus: Chlamydia 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, CHand to eye from fomites, fliesEndemic trachoma
L1, L2, L3SexualLymphogranuloma venereum
D-KSexual, 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 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 lymph nodes)

 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 Chlamydia are diagnosed based on their clinical manifestations. Laboratory diagnosis of C. trachomatis can be achieved by cytology, culture, direct antigen or nucleic acid detection, and serologic testing.


Scrapings from the eyes or urogenital tract, materials aspirated from epididymis, fallopian tubes, sera, tissue biopsy.

In general, the Gram stain is not useful as the organisms are too small to visualize within the cytoplasm.


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 a microscope. Staining of C. trachomatis elementary bodies by fluorescent monoclonal antibodies.


Serologic testing has limited value for diagnosing urogenital infections in adults because most adults with chlamydial infection have had 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 diagnosing neonatal infections.

In situ DNA hybridization with cloned C. trachomatis DNA probes in tissue biopsy specimens.


It is a 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 time and temperature.  Cell lines used to isolate C. trachomatis in cell culture are McCoy (cycloheximide treated), Hela, and Monkey kidney cells.


  1. Mishori, R., McClaskey, E. L., & WinklerPrins, V. J. (2012). Chlamydia trachomatis infections: screening, diagnosis, and management. American family physician, 86(12), 1127–1132.
  2. Paavonen, J., & Eggert-Kruse, W. (1999). Chlamydia trachomatis: impact on human reproduction. Human reproduction update, 5(5), 433–447.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

2 thoughts on “Chlamydia trachomatis: Properties, Disease, Lab Diagnosis

  1. Hello Tankeshwor sir,
    Your blogs really help a lot of Nepalese and Indian students studying MBBS. I really appreciate your efforts.

    1. Thank you, Shivam for your inspiring comment. Please share how can I make it more useful.

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