Treponema pallidum – An Overview


Class- Spirochaetes
Order- Spirochaetales
Family- Spirochaetaceae
Genus- Treponema
Species- Treponema pallidum

Treponema pallidum

Image Source: Russell Publishing Limited.

Morphology of Treponema pallidum

  • Treponemes are thin, delicate, helically coiled, corkscrew-shaped organisms.
  • They are microaerophilic and actively motile.
  • They are measures about 10 to 14 micrometers long and 0.1 to 0.2 micrometer wide.
  • They have 8-24 sharp and angular spirals, at regular intervals of about 1 micrometer.

Cultural Characteristics of Treponema pallidum

  • This organism has not been successfully cultured in vitro.
  • Preservation media: 18-21 days.
  • Dieterle stain: Can be used to visualize T. pallidum.

Biochemical Characteristics of Treponema pallidum

  • Treponema is composed of approximately 70% proteins, 20% lipids, and 5% carbohydrates.
  • This lipid content is relatively high.
  • The lipid composition of T. pallidum is complex, consisting of several phospholipids, including cardiolipin and poorly characterized glycolipid.

Antigenic Structure

Treponema induces at least 3 types of antibodies.

a) Reagin antibodies: react in standard or non-specific test for syphilis.
b) Group antigen: found in pathogenic and non-pathogenic treponemes.
c) Polysaccharide antigen: species-specific, demonstrated by specific T. pallidum tests.

Virulence Factors

  • Following attachment, a cell-bound toxin results in lysis of the cells.
  • Intact cell layers with tight junctions support bacterial attachment but hyaluronidase treatment of cells decreases attachment.


  • It is a fastidious organism that exhibits narrow optical ranges of pH 7.2 to 7.4 and temperature 30 to 37°C.
  • It is rapidly inactivated by mild heat (41-42°C in one hour), cold ( 0-4°C in 1-3 days), drying, and most disinfectants.


  • It caused Syphilis disease.
  • Humans are the only natural host for T. pallidum and infection occurs through sexual contact.
  • The organism penetrates the mucous membrane or enters minuscule breaks in the skin.
  • In the women, the initial lesion is usually on the labia, the walls of the vagina, or the cervix.
  • In men, it is on the shaft or glans of the penis.
  • A chancre (a small hard painless nodule at the site of entry of pathogen) also may occur on lips, tongue, tonsils, anus, or other skin areas.
  • Perivascular inflammation: This typically consists of a proliferation of adventitial cells; perivascular cuffing with lymphocytes, monocytes, and plasma cells; and swelling and proliferation of endothelial cells.

Clinical Manifestation of Treponema pallidum

1. Primary syphilis:-

Primary lesion or “Chancre” develops at the site of inoculation after 18-21 days.


• Progresses from macule to papule to ulcer.

• Typically painless, indurated, and has a clean base.

• Highly infectious

• Cartilage like consistency

• Heals spontaneously within 1 to 6 weeks.

• 25% present with multiple lesions.

• Chancre also can develop on the cervix, tongue, lips, or other parts of the body.

2. Secondary syphilis:-

• Secondary lesions occur 3 to 6 weeks after the primary chancre appears.

• may persist for weeks to months.

• primary and secondary stages may overlap.

• Mucocutaneous lesions are most common.

• SYMPTOMS: Fever, Swollen lymph glands, sore throat, patchy hair loss, weight loss, headache, muscle aches, fatigue.

3. Latent syphilis:-

  • The host suppresses infection – no lesions are clinically seen.
  • The only evidence is a positive serologic test.
  • May occur between:

a) primary & secondary stages
b) secondary relapses
c) after the secondary stage.

# Categories:

a) Early latent – <1 year duration

b) Late latent – > equal to 1 year duration.

A. Late syphilis

• Approximately 30% of untreated patients progress to the tertiary stage within 1 to 20 years.

• Rare because of the widespread availability and use of antibiotics.


I. Cardiovascular syphilis

II. Neurosyphilis

B. Congenital syphilis

• Occurs when T. pallidum is transmitted from a pregnant woman to her fetus.

• May leads to; stillbirth and neonatal death.

References and Sources

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