[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/) › Shigella

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

# Shigella

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

A bacterium that invades the colon and causes dysentery: bloody diarrhea, fever and straining. A tiny dose is enough to get sick.

Updated 2026-11-01

Also called: Shigella sonnei, Shigella flexneri, Shigella dysenteriae, dysentery bacillus

## Key points

- Infectious dose of only 10 to 100 bacteria: spreads easily between people.
- Non-motile, non-lactose fermenter, no H2S (unlike Salmonella).
- Invades the colonic mucosa and moves cell to cell on actin tails.
- S. dysenteriae type 1: Shiga toxin and hemolytic uremic syndrome.
- Febrile seizures in a child with dysentery: think Shigella.

## At a glance

**Gram**
Gram-negative

**Shape**
Rod

**Oxygen**
Facultative anaerobe

**Family**
Enterobacteriaceae

**Stain**
Gram: red rods

## Morphology

- Non-motile Gram-negative rod (no flagella)
- Non-lactose fermenter, no H2S: red colonies without black centers on XLD
- Four species: S. sonnei, S. flexneri, S. boydii and S. dysenteriae

## Transmission

- Fecal-oral from person to person, through hands, objects, water or food
- Oral-anal sexual contact
- Outbreaks in day care, among travelers and where sanitation is poor
- Contact (on top of standard) for diapered children or incontinent patients

**Reservoir:** Humans only (and other primates)

### 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

- Very low infectious dose: survives stomach acid
- Enters through M cells, invades colonic epithelium and spreads cell to cell using actin
- Causes ulcers and microabscesses in the colonic mucosa
- Shiga toxin in S. dysenteriae type 1: endothelial damage, hemolytic uremic syndrome

## Diseases it causes

- Shigellosis (bacillary dysentery) [Bacterial infectious diarrhoea and dysentery →](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/)
- Hemolytic uremic syndrome, mainly with S. dysenteriae type 1 [Hemolytic uremic syndrome (HUS) →](https://durgical.com/en/conditions/hemolytic-uremic-syndrome/)

## Clinical picture

- Diarrhea that starts watery and turns to mucus and blood, fever, cramps and tenesmus
- Febrile seizures in young children
- Reactive arthritis days or weeks later, more in HLA-B27 carriers

## Diagnosis

- Stool culture on MacConkey, XLD or Hektoen
- Many white and red cells in stool
- Stool PCR panels

## Treatment

Rehydration in every case. Antibiotics shorten illness and shedding: azithromycin, fluoroquinolones or ceftriaxone by susceptibility. Resistance to ampicillin and trimethoprim-sulfamethoxazole is common, and extensively drug-resistant strains exist. Antimotility drugs are avoided.

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

In Pharmacology:

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

## Prevention

- Handwashing with soap and water, especially when changing diapers
- Safe water and sanitation
- Keeping sick food handlers off work
- No licensed vaccine

## In Colombia

It is an important cause of bloody diarrhea in children; acute diarrheal disease is an INS surveillance event.

## Memory aid

"Shigella cannot walk but it can jump": no flagella, yet it leaps from one colon cell to the next on its actin tail.

## Test yourself

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

## Why does Shigella spread so easily between people?

Its infectious dose is tiny, about 10 to 100 bacteria.

## Which lab traits separate Shigella from Salmonella?

Shigella is non-motile, makes no H2S and has no animal reservoir; Salmonella is motile and makes H2S.

## Which species makes Shiga toxin and is linked to hemolytic uremic syndrome?

Shigella dysenteriae type 1.

## Which joint complication can follow shigellosis?

Reactive arthritis, mainly in people with HLA-B27.

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

## Related

- [Escherichia coli](https://durgical.com/en/microbiology/escherichia-coli/)
- [Campylobacter jejuni](https://durgical.com/en/microbiology/campylobacter-jejuni/)
- [Non-typhoidal Salmonella](https://durgical.com/en/microbiology/non-typhoidal-salmonella/)

## Related conditions

- [Bacterial infectious diarrhoea and dysentery](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/)
- [Hemolytic uremic syndrome (HUS)](https://durgical.com/en/conditions/hemolytic-uremic-syndrome/)

## 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: [Shigellosis](https://www.msdmanuals.com/professional/infectious-diseases/gram-negative-bacilli/shigellosis) (MSD Manual Professional Edition, 2026); [About Shigella Infection](https://www.cdc.gov/shigella/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).

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Representative model, for educational purposes only.

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