Treponema pallidum characteristics, morphology, habitat

Anthony Golden

The Treponema pallidum It is a bacterium that is the causative agent of syphilis. They are spirochetes, a term used to group bacteria with helical shapes, similar to a spring or corkscrew..

They are excessively thin microorganisms, to the point that their visualization in the microscope is impossible. Likewise, these bacteria are not culturable in vitro..

Syphilis is a sexually transmitted disease distributed throughout the world. However, there are other subspecies of this bacterium whose method of transmission is not sexual (it can be skin contact, for example).

They are equally pathogenic to man, causing diseases such as yaws. These pathogens predominate in African countries and areas with a warm climate.

Article index

  • 1 General characteristics
  • 2 Morphology
    • 2.1 Axial filaments
    • 2.2 Membrane
  • 3 Taxonomy
  • 4 Habitat and transmission
  • 5 Culture and identification
  • 6 Life cycle
  • 7 Symptoms and treatment
  • 8 References

General characteristics

-These spiral bacteria do not form spores.

-Their temperature tolerance range is limited and they are sensitive to high temperatures.

-They are anaerobic and use carbohydrates as a source of carbohydrates.

-They are chemoorganotrophic.

-Its metabolic capacity is quite low, an immediate consequence of the small size of its genome. This characteristic is common in parasitic organisms, since all essential nutrients can be taken from their host..

-It has a total of 113 genes that code for transport proteins used to take these macromolecules from the medium..

-They test negative for catalase and oxidase.


Spirochetes are characterized by an unusual morphology, compared to other bacteria. They have a spiral, cylindrical and flexible shape.

The size range is 5-20 µm in length and 0.1 to 0.4 µm in diameter. There is a gap of approximately 1-1.5 µm between the turns. They are so thin that it is not possible to visualize them using a traditional optical microscope.

Axial filaments

T. pallidum It is a bacterium that exhibits motility. One of the diagnostic characteristics of the group is the presence of axial filaments. The axial filaments, also known as endoflagella, help the bacteria to mobilize.

They are similar to a flagellum, and each filament attaches to one pole of the cell, allowing for rotary motion. Given the tiny size of the bacteria, the fluid represents a major impediment to movement.

These corkscrew-like bacteria are able to rotate and the speed of this movement is variable. Likewise, soft bending may occur..


Gram's stain is difficult to apply to these organisms because of their minute size. However, its membrane composition resembles gram negative bacteria; the membrane is thin and with a varied composition of lipids. A significant number of endoflagella are found in the membrane.

The membranes of pathogenic bacteria play an important role in immune responses and virulence.

For this bacterium, a supposed antigen has been reported that is exposed on the surface and weighs 47 Kd. Although this idea is debated, this element has been designated as the main antigen exposed on the outer membrane..


The gender Treponema It is composed of both harmful and non-pathogenic bacteria that inhabit humans and animals. Taxonomically, they belong to the Phylum Spirochaetes, order Spirochetales and family Spirochaetaceae.

Previously Treponema pallidum was known as Spirochaeta pallida. Furthermore, based on DNA hybridization studies, T. pallidum is genetically indistinguishable from Treponema pertenue, etiologic agent of yaws.

Habitat and transmission

The habitat of this microorganism is the human genital tract. As it is an obligate parasite, it cannot survive outside of its host..

Transmission occurs during sexual intercourse through direct contact with lesions, bodily secretions, blood, semen, and saliva..

Transmission is thought to occur through microscopic subcutaneous lesions resulting from sexual intercourse. The infection can also be transmitted through kissing, biting, and oral-genital sex..

Likewise, the bacteria can be transmitted from the mother to the fetus by placental transfer..

Culture and identification

It is not possible to grow this bacteria in vitro. This characteristic of the pathogen has made its study very difficult. Alternatively, it can be spread in rabbit testes.

They can be detected in the patient's serum using immunological techniques, serological tests or by viewing tissue samples from the lesions on a dark field microscope.

Due to the impossibility of cultivating the pathogen, the development of molecular techniques for its identification is crucial..

Biological cycle

In the 1950s, studies by DeLamater and colleagues helped elucidate and describe the complicated life cycle of this bacterium. The study grew the bacteria in rabbit testes.

According to these investigations, the pathogen could take two forms of vegetative reproduction: one by transversal division, being the most important under normal conditions, and a second form dominated by the production of gemmules..

The production of gems or "buds" is reminiscent of the saprophytic forms of spirochetes, which result in a cyst.

Preliminary works affirm that there could be a process involving cyst with multiple spirochetes, followed by the aggregation of two or more organisms. Within these cysts, numerous organisms develop that emerge as a kind of "tangled cords".

Finally, the emerging forms may undergo transverse division and gem formation..

Symptoms and Treatment

Syphilis is a complex infection that produces serious systemic diseases and can lead to the death of the patient when it is not treated.

The disease is characterized by periods of active symptoms and periods of latency. Different phases can be differentiated:

  • Primary syphilis occurs three to twelve weeks after sexual contact with the infected person. It is characterized by the formation of a lesion known as a chancre.
  • Secondary syphilis occurs within a week to six months of the initial contact. It is characterized by the formation of a maculopapular rash. After this period a latent phase may come.
  • Tertiary syphilis appears ten to twenty years after initial contact. Symptoms include cardiovascular, dermatological, skeletal, and neurological problems.

The infection is treated with antibiotics, penicillin being the most used. In case the patient is allergic, tetracycline is an effective alternative. Likewise, the use of erythromycin is suggested..


  1. DeLamater, E. D., Wiggall, R. H., & Haanes, M. (1950). Studies on the Life Cycle of Spirochetes: III. The Life Cycle of the Nichols Pathogenic Treponema Pallidum in the Rabbit Testis as Seen by Phase Contrast Microscopy. Journal of Experimental Medicine, 92(3), 239-246.
  2. Dworkin, M. (2006). The Prokaryotes: Vol. 7: proteobacteria: delta and epsilon subclasses. Deeply rooting bacteria. Springer Science & Business Media.
  3. Koneman, E. W., & Allen, S. (2008). Microbiological Diagnosis: Text And Atlas In Color. Panamerican Medical Ed..
  4. Peng, R. R., Wang, A. L., Li, J., Tucker, J. D., Yin, Y. P., & Chen, X. S. (2011). Molecular typing of Treponema pallidum: a systematic review and meta-analysis. PLoS neglected tropical diseases, 5(11), e1273.
  5. Samaranayake, L. (2011). Essential Microbiology for Dentistry E-Book. Elsevier Health Sciences.
  6. Sammarco, A. (2016). Women's health issues across the life cycle. Jones & Bartlett Publishers.
  7. Tortora, G. J., Funke, B. R., & Case, C. L. (2007). Introduction to microbiology. Panamerican Medical Ed..
  8. Wright, D. J., & Archard, L. C. (1992). Molecular and cell biology of sexually transmitted diseases. Springer Science & Business Media.
  9. Zobaníková, M., Mikolka, P., Čejková, D., Pospíšilová, P., Chen, L., Strouhal, M.,… & Šmajs, D. (2012). Complete genome sequence of Treponema pallidum strain DAL-1. Standards in genomic sciences, 7(1), 12.

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