[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/) › Chlamydia trachomatis

[Microbiology](https://durgical.com/en/microbiology/) · [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

# Chlamydia trachomatis

- Bacterium
- Gram-negative
- Exam priority: high

The most common sexually transmitted bacterium: often silent but can cause infertility; it also causes trachoma in the eyes.

Updated 2026-11-01

Also called: chlamydia

## Key points

- Elementary body = enters (infectious); reticulate body = replicates
- Silent in women: a leading preventable cause of tubal infertility
- NAAT is the test of choice
- Urethritis + arthritis + conjunctivitis = reactive arthritis
- Afebrile pneumonia with staccato cough and eosinophilia in infants

## At a glance

**Gram**
Gram-negative

**Shape**
Small coccobacillus

**Oxygen**
Obligate intracellular (depends on host-cell ATP)

**Family**
Chlamydiaceae

**Stain**
Barely seen on Gram; Giemsa or iodine show cytoplasmic inclusions

## Morphology

- Two forms: elementary body (infectious, extracellular) and reticulate body (divides inside the cell)
- Gram-negative-type envelope with almost no peptidoglycan
- Glycogen-rich inclusions that stain with iodine

## Transmission

- Vaginal, anal or oral sex without a condom
- Mother to baby during vaginal birth
- Trachoma: contact with eye and nose secretions, hands, cloths and flies

**Reservoir:** Humans only

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- The small, tough elementary body binds an epithelial cell and enters by endocytosis
- Inside a vacuole (inclusion) it blocks fusion with the lysosome
- It turns into a larger, metabolically active reticulate body
- The reticulate body divides by binary fission using host-cell ATP
- Reticulate bodies condense back into elementary bodies
- The cell bursts or extrudes the inclusion and elementary bodies infect new cells

## Virulence factors

- Intracellular life: escapes antibodies and beta-lactams
- Repeated chronic inflammation scars fallopian tubes and eyelids
- Serovars A–C: trachoma; D–K: genital and neonatal; L1–L3: lymphogranuloma venereum

## Diseases it causes

- Cervicitis, urethritis, proctitis and epididymitis [Chlamydia infection →](https://durgical.com/en/conditions/chlamydia-infection/)
- Pelvic inflammatory disease: infertility, ectopic pregnancy, chronic pelvic pain [Pelvic inflammatory disease →](https://durgical.com/en/conditions/pelvic-inflammatory-disease/)
- Inclusion conjunctivitis in adults and newborns [Conjunctivitis →](https://durgical.com/en/conditions/conjunctivitis/)
- Trachoma: chronic keratoconjunctivitis and preventable blindness [Trachoma →](https://durgical.com/en/conditions/trachoma/)
- Lymphogranuloma venereum; infant pneumonia; reactive arthritis

## Clinical picture

- Most genital infections cause no symptoms, especially in women
- Discharge, post-coital bleeding, dysuria; in men, scant urethral discharge
- Perihepatitis (Fitz-Hugh–Curtis) in PID
- Infant: conjunctivitis and afebrile pneumonia with staccato cough

## Diagnosis

- Nucleic acid amplification tests (NAAT) on urine or vaginal, endocervical, rectal or throat swabs
- Gram stain shows neutrophils without bacteria (non-gonococcal urethritis)
- Does not grow on agar: culture needs living cells
- Lymphogranuloma venereum: a specific molecular test

## Treatment

Doxycycline first; azithromycin in pregnancy and for neonatal conjunctivitis. Sexual partners are treated, and if gonorrhoea is suspected, ceftriaxone is added.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)

## Prevention

- Condoms and screening of sexually active young women
- Partner treatment and retesting because reinfection is common
- Prenatal screening to prevent newborn infection
- Trachoma: SAFE strategy (surgery, antibiotics, facial cleanliness, environmental improvement)

## In Colombia

One of the most frequent sexually transmitted infections in young Colombians. Trachoma foci have been documented in Indigenous communities of the Amazon and Orinoquía (Vaupés, Guainía).

## Memory aid

Chlamydia is «a tenant with no kitchen»: it makes no energy of its own, lives on the cell's ATP, arrives as a seed (elementary body) and grows as a plant (reticulate body).

## Test yourself

Think of the answer, then tap the question to see it.

## Which Chlamydia form is infectious and which replicates?

The elementary body is the infectious extracellular form; the reticulate body divides inside the cell.

## Which test is preferred for genital C. trachomatis infection?

Nucleic acid amplification tests (NAAT) on urine or a swab.

## Which serovars cause lymphogranuloma venereum?

Serovars L1, L2 and L3, which invade lymph nodes.

## Why is penicillin not useful against Chlamydia?

Because it lives inside cells and has almost no peptidoglycan in its envelope.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/chlamydia-trachomatis/)

## Related

- [Chlamydia pneumoniae / Chlamydia psittaci](https://durgical.com/en/microbiology/chlamydia-pneumoniae-chlamydia-psittaci/)
- [Mycoplasma genitalium / Ureaplasma](https://durgical.com/en/microbiology/mycoplasma-genitalium-ureaplasma/)

## Related conditions

- [Chlamydia infection](https://durgical.com/en/conditions/chlamydia-infection/)
- [Pelvic inflammatory disease](https://durgical.com/en/conditions/pelvic-inflammatory-disease/)
- [Conjunctivitis](https://durgical.com/en/conditions/conjunctivitis/)
- [Trachoma](https://durgical.com/en/conditions/trachoma/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Chlamydia](https://www.who.int/news-room/fact-sheets/detail/chlamydia) (World Health Organization (WHO), 2025); [About Chlamydia | Chlamydia | CDC](https://www.cdc.gov/chlamydia/about/index.html) (Centers for Disease Control and Prevention (CDC), 2025); [Trachoma](https://www.who.int/news-room/fact-sheets/detail/trachoma) (World Health Organization (WHO), 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/chlamydia-trachomatis/