[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Enterobacterales](https://durgical.com/en/microbiology/groups/enterobacterales/) › Salmonella Typhi

[Microbiology](https://durgical.com/en/microbiology/) · [Enterobacterales](https://durgical.com/en/microbiology/groups/enterobacterales/)

# Salmonella Typhi

- Bacterium
- Gram-negative
- Contact
- Exam priority: high

A Salmonella that infects only humans and causes typhoid fever: a long high fever from contaminated water or food.

Updated 2026-11-01

Also called: Salmonella enterica serovar Typhi, Salmonella Paratyphi, typhoid bacillus

## Key points

- Humans only: the source is always a sick person or a carrier.
- Stepwise fever, relative bradycardia and rose spots: typhoid fever.
- Blood culture in week one; bone marrow culture is the most sensitive.
- Chronic gallbladder carrier, especially with gallstones (the "Typhoid Mary" story).
- Perforation of the terminal ileum (Peyer patches) around week three.

## At a glance

**Gram**
Gram-negative

**Shape**
Rod

**Oxygen**
Facultative anaerobe

**Family**
Enterobacteriaceae

**Stain**
Gram: red rods

## Morphology

- Motile Gram-negative rod (flagella, H antigen)
- Non-lactose fermenter; makes H2S (black-centered colonies on XLD)
- Capsule carrying the Vi antigen

## Transmission

- Fecal-oral: water or food contaminated with feces or sewage
- Carrier food handlers who do not wash their hands
- Contact (on top of standard) for diapered or incontinent patients

**Reservoir:** Humans only: patients and chronic carriers (gallbladder)

### Isolation precautions

What the care team adds to standard precautions.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

## Virulence factors

- Vi capsule: resists complement and phagocytosis
- Invades Peyer patches through M cells (type III secretion system)
- Survives inside macrophages and travels to liver, spleen and bone marrow
- Colonizes the gallbladder, especially with stones, creating chronic carriers
- LPS: fever and systemic toxicity

## Diseases it causes

- Typhoid and paratyphoid fever (enteric fever) [Typhoid (enteric) fever →](https://durgical.com/en/conditions/typhoid-fever/)

## Clinical picture

- Fever that climbs step by step over days, headache, malaise and abdominal pain
- Pulse slower than the fever predicts (relative bradycardia)
- Rose spots on the abdomen, hepatosplenomegaly, constipation or diarrhea
- Complications around week three: intestinal bleeding and perforation

## Diagnosis

- Blood culture: the key test in week one
- Bone marrow culture: the most sensitive, even after antibiotics
- Stool and urine cultures turn positive later; useful to find carriers
- The Widal test is inaccurate and does not confirm the diagnosis

## Treatment

Antibiotics chosen by local resistance: third-generation cephalosporins (ceftriaxone), azithromycin, or fluoroquinolones where they still work; carbapenems for extensively drug-resistant strains. Resistance is common in South Asia, with extensively drug-resistant strains reported in Pakistan.

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

In Pharmacology:

- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)
- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)
- [Ciprofloxacin](https://durgical.com/en/pharmacology/ciprofloxacin/)
- [Meropenem](https://durgical.com/en/pharmacology/meropenem/)

## Prevention

- Safe water and sanitation
- Food-handler hygiene and carrier control
- Vaccines: conjugate (TCV), injectable Vi polysaccharide, and live oral
- For travelers: well-cooked food, no ice or water of doubtful origin

**Vaccine:** Single-dose typhoid conjugate vaccine (TCV) from 6 months, Vi polysaccharide vaccine and a live oral vaccine. In Colombia it is not in the routine PAI schedule; it is used for travelers and risk groups.

## In Colombia

Typhoid and paratyphoid fever is a notifiable event in SIVIGILA (INS), with cases tied to untreated water and foodborne outbreaks.

## Memory aid

"Typhoid takes the stairs": the fever climbs one step a day, the pulse lags behind, and rose spots appear on the landing.

## Test yourself

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

## What is the only reservoir of Salmonella Typhi?

Humans, including chronic carriers with the bacterium in the gallbladder.

## Which test is most useful in the first week of typhoid fever?

Blood culture; bone marrow culture is the most sensitive.

## Which classic cardiovascular sign goes with typhoid fever?

Relative bradycardia: a pulse slower than expected for the temperature.

## Which serious complication appears around the third week?

Intestinal bleeding or perforation in the ileum, where the Peyer patches are.

## Which capsular antigen is the basis of the injectable vaccines?

The Vi antigen.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/microbiology/salmonella-typhi/)

## Related

- [Non-typhoidal Salmonella](https://durgical.com/en/microbiology/non-typhoidal-salmonella/)
- [Shigella](https://durgical.com/en/microbiology/shigella/)

## Related conditions

- [Typhoid (enteric) fever](https://durgical.com/en/conditions/typhoid-fever/)

## 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.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

[← Back to the group: Enterobacterales](https://durgical.com/en/microbiology/groups/enterobacterales/)

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

Sources: [Typhoid](https://www.who.int/news-room/fact-sheets/detail/typhoid) (WHO, 2023); [About Typhoid Fever and Paratyphoid Fever](https://www.cdc.gov/typhoid-fever/about/index.html) (CDC, 2024); [Fichas y Protocolos](https://www.ins.gov.co/buscador-eventos/Paginas/Fichas-y-Protocolos.aspx) (Instituto Nacional de Salud (INS), Colombia, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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