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# Toxin-mediated diarrhoea: cholera and E. coli

- Mechanism

Cholera toxin switches intestinal cells into constant salt-and-water pumps; different E. coli strains cause diarrhoea in five distinct ways.

Updated Nov 12, 2026

## Key points

- Cholera toxin: ADP-ribosylates Gsα, raising cAMP; CFTR opens and secretes chloride, sodium absorption falls, water follows.
- Rice-water stools with a fishy smell; biopsies are nearly normal.
- Spread through faecally contaminated water, especially after disasters and war; Latin America had a large epidemic in the 1990s and Haiti after 2010.
- Severe untreated cholera kills about half of patients; timely rehydration saves almost all.
- ETEC is the main cause of travellers' diarrhoea: heat-labile toxin (cAMP, cholera-like) and heat-stable toxin (cGMP).
- EHEC O157:H7: undercooked beef; Shiga-like toxin; bloody diarrhoea, ischaemia-like colitis and haemolytic uraemic syndrome; antibiotics can raise HUS risk.

## What it is

Vibrio cholerae stays in the lumen and never invades, yet it can kill within hours through massive secretory diarrhoea. Its toxin, carried on a phage, has one A and five B subunits; the B subunits bind GM1 ganglioside and the toxin travels backwards to the endoplasmic reticulum, from where the A fragment reaches the cytosol and locks the stimulatory G protein in its active state. E. coli pathotypes use similar or different tricks, which explains their different clinical pictures.

## Step by step

- Cholera toxin B subunits bind GM1 ganglioside on enterocytes.
- The toxin travels by retrograde transport to the endoplasmic reticulum.
- The A fragment enters the cytosol and, with ADP-ribosylation factors, permanently activates Gsα.
- Adenylate cyclase raises cAMP, opening CFTR chloride channels.
- Chloride, bicarbonate and sodium accumulate in the lumen; water follows: litres of isotonic stool.

## The E. coli pathotypes

| Pathotype | How it causes disease | Disease | Who |
| --- | --- | --- | --- |
| ETEC (enterotoxigenic) | Heat-labile toxin (cAMP) and heat-stable toxin (cGMP); no invasion | Watery travellers' diarrhoea | Travellers, young children in poor settings |
| EPEC (enteropathogenic) | Attaching and effacing lesions that flatten microvilli | Watery diarrhoea, outbreaks | Children under two |
| EHEC (enterohaemorrhagic) | Shiga-like toxin | Bloody diarrhoea, haemolytic uraemic syndrome | All ages; children at highest HUS risk |
| EIEC (enteroinvasive) | Invades epithelium like Shigella; no toxin | Acute self-limited colitis | Young children in poor settings |
| EAEC (enteroaggregative) | Adherence fimbriae and dispersin; aggregates on cells | Non-bloody, sometimes prolonged diarrhoea | Children, travellers, immunodeficient |

## Clinical notes

- Oral rehydration solution uses sodium–glucose cotransport, which cholera toxin does not block.
- Vaccination during outbreaks and clean water are the main public-health controls.

## Memory aid

Cholera keeps the G protein stuck on Go; EHEC hits the kidney; ETEC travels.

## Test yourself

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

## How does cholera toxin cause diarrhoea?

It ADP-ribosylates Gsα, keeping adenylate cyclase active; high cAMP opens CFTR, chloride is secreted and water follows.

## Why are biopsies almost normal in cholera?

The organism stays in the lumen and acts through a toxin, without invading or destroying the mucosa.

## Which E. coli pathotype causes haemolytic uraemic syndrome?

Enterohaemorrhagic E. coli (such as O157:H7), through Shiga-like toxin.

## Which E. coli pathotype is the main cause of travellers' diarrhoea?

Enterotoxigenic E. coli (ETEC).

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## Elsewhere in DurgiPedia

- [Water and electrolyte absorption and how diarrhea happens](https://durgical.com/en/physiology/water-and-electrolyte-absorption-and-how-diarrhea-happens/)

## Connections

## Related 3

- [Infectious enterocolitis](https://durgical.com/en/general-pathology/infectious-enterocolitis/)
- [Invasive bacterial enterocolitis](https://durgical.com/en/general-pathology/invasive-bacterial-enterocolitis/)
- [Ischaemic bowel disease](https://durgical.com/en/general-pathology/ischaemic-bowel-disease/)

## Related conditions 4

- [Cholera](https://durgical.com/en/conditions/cholera/)
- [Bacterial infectious diarrhoea and dysentery](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/)
- [Dehydration in children (acute diarrhoeal disease)](https://durgical.com/en/conditions/dehydration-in-children/)
- [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/)

## Microorganisms 2

- [Vibrio cholerae](https://durgical.com/en/microbiology/vibrio-cholerae/)
- [Escherichia coli](https://durgical.com/en/microbiology/escherichia-coli/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Cholera](https://www.who.int/news-room/fact-sheets/detail/cholera) (World Health Organization, 2024); [About Escherichia coli Infection](https://www.cdc.gov/ecoli/about/index.html) (Centers for Disease Control and Prevention, 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/toxin-mediated-diarrhoea-cholera-and-e-coli/