[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Spirochetes](https://durgical.com/en/microbiology/groups/spirochetes/) › Treponema pallidum

[Microbiology](https://durgical.com/en/microbiology/) · [Spirochetes](https://durgical.com/en/microbiology/groups/spirochetes/)

# Treponema pallidum

- Bacterium
- Does not Gram-stain
- Exam priority: high

The syphilis spirochete: it spreads through sex and from mother to baby in pregnancy; penicillin cures it.

Updated 2026-11-01

Also called: syphilis spirochete

## Key points

- Painless chancre (syphilis) versus painful ulcer (chancroid, herpes)
- Non-treponemal = screens and tracks treatment; treponemal = confirms and stays positive
- Penicillin in pregnancy, always (desensitise if allergic)
- Jarisch-Herxheimer in the first hours of treatment
- False-positive VDRL: lupus, antiphospholipid syndrome, pregnancy, other infections

## At a glance

**Gram**
Does not Gram-stain

**Shape**
Thin, tightly coiled spirochete

**Oxygen**
Microaerophilic

**Family**
Spirochaetaceae

**Stain**
Not seen on Gram: dark-field, direct immunofluorescence or silver stain

**Size**
Very thin (about 0.15 µm wide)

## Morphology

- Fine spiral with endoflagella and corkscrew motility
- Outer membrane with very few exposed proteins: evades the immune system
- Not cultured on routine media

## Transmission

- Sexual contact (vaginal, anal or oral) with an active lesion
- Transplacental at any stage of pregnancy: congenital syphilis
- Rarely by transfusion; not by objects such as toilet seats

**Reservoir:** Humans only

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Crosses mucosa and microabraded skin and spreads through the blood very early
- Obliterative endarteritis: the basis of vascular lesions and aortitis
- Few surface proteins: evades antibodies and persists in latency for years

## Diseases it causes

- Primary, secondary, latent and tertiary syphilis; neurosyphilis; gestational and congenital syphilis [Syphilis →](https://durgical.com/en/conditions/syphilis/)

## Clinical picture

- Primary: painless, indurated chancre with regional lymphadenopathy
- Secondary: rash on palms and soles, condylomata lata, patchy alopecia
- Tertiary: gummas, aortitis, tabes dorsalis, Argyll Robertson pupil
- Congenital: stillbirth, rhinitis, hepatosplenomegaly; late: Hutchinson teeth, saddle nose, deafness

## Diagnosis

- Non-treponemal tests (VDRL, RPR): screening and treatment follow-up by titre
- Treponemal tests (FTA-ABS, TP-PA, rapid tests): confirm and stay positive for life
- Both types are needed; some labs use the reverse algorithm (treponemal first)
- Dark-field of chancre fluid; CSF VDRL for neurosyphilis

## Treatment

Parenteral penicillin is the treatment of choice (benzathine penicillin; aqueous crystalline penicillin for neurosyphilis). In pregnancy it is the only treatment effective for the fetus: allergic patients are desensitised. Alternatives outside pregnancy: doxycycline or ceftriaxone. There is no penicillin resistance; there is azithromycin resistance.

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

In Pharmacology:

- [Benzylpenicillin (penicillin G)](https://durgical.com/en/pharmacology/benzylpenicillin/)
- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)

## Prevention

- Screening at prenatal visits and immediate treatment of the pregnant woman and her partner
- Condoms; screening of higher-risk groups
- Notification and treatment of sexual contacts

## In Colombia

Gestational and congenital syphilis are mandatory notifiable events in SIVIGILA (INS) and targets of PAHO's initiative to eliminate mother-to-child transmission. Colombia uses rapid treponemal tests in prenatal care so treatment can start at the same visit.

## Memory aid

Syphilis is «the great imitator» that arrives painlessly: a painless chancre, spots on palms and soles, and decades later it strikes the aorta and spinal cord. Penicillin has never failed against it.

## Test yourself

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

## Which serological test type tracks the response to syphilis treatment?

A non-treponemal test (VDRL or RPR), because its titres fall with cure.

## A pregnant woman with syphilis is allergic to penicillin. What is done?

She is desensitised and treated with penicillin, the only drug proven to protect the fetus.

## Where does the secondary syphilis rash typically appear?

On the trunk and, characteristically, on the palms and soles.

## Which late signs suggest congenital syphilis?

Hutchinson teeth, saddle nose, sabre shins, interstitial keratitis and deafness.

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

## Related

- [Leptospira interrogans](https://durgical.com/en/microbiology/leptospira-interrogans/)
- [Borrelia burgdorferi](https://durgical.com/en/microbiology/borrelia-burgdorferi/)

## Related conditions

- [Syphilis](https://durgical.com/en/conditions/syphilis/)

## 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: Spirochetes](https://durgical.com/en/microbiology/groups/spirochetes/)

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

Sources: [Syphilis](https://www.who.int/news-room/fact-sheets/detail/syphilis) (World Health Organization (WHO), 2025); [Syphilis and Congenital Syphilis - PAHO/WHO | Pan American Health Organization](https://www.paho.org/en/topics/syphilis) (Pan American Health Organization (PAHO), 2025); [Syphilis - STI Treatment Guidelines](https://www.cdc.gov/std/treatment-guidelines/syphilis.htm) (Centers for Disease Control and Prevention (CDC), 2021); [About Syphilis | Syphilis | CDC](https://www.cdc.gov/syphilis/about/index.html) (Centers for Disease Control and Prevention (CDC), 2025).

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Representative model, for educational purposes only.

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