[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Gastrointestinal tract](https://durgical.com/en/general-pathology/areas/gi/) › Invasive bacterial enterocolitis

# Invasive bacterial enterocolitis

- Lesion

Some bacteria get inside the bowel lining, often through the immune sampling cells, inflaming it and causing fever and bloody stool.

Updated Nov 12, 2026

## Key points

- Campylobacter jejuni: commonest bacterial enteric pathogen in high-income countries; undercooked chicken; complications are reactive arthritis (HLA-B27), erythema nodosum and Guillain–Barré.
- Shigella: very low infective dose, humans only; enters M cells, kills macrophages, invades from the basolateral side; left colon; Shiga toxin in S. dysenteriae type 1.
- Shigella complications: reactive arthritis with urethritis and conjunctivitis, haemolytic uraemic syndrome, toxic megacolon; antidiarrhoeal drugs prolong it.
- Non-typhoidal Salmonella: eggs, poultry, meat; type III secretion system; antibiotics usually not given because they prolong carriage.
- Yersinia: pork, raw milk; ileum, appendix and right colon; mesenteric lymphadenitis mimics appendicitis; iron overload favours sepsis.

## What it is

These bacteria cause inflammatory diarrhoea or dysentery by adhering to, entering or passing through the epithelium. Many exploit M cells, the antigen-sampling cells over Peyer patches, which explains ileal involvement and aphthous ulcers that can mimic Crohn disease. Biopsies show acute self-limited colitis with neutrophils but preserved crypts; diagnosis relies on stool culture or molecular tests.

## Step by step

- Bacteria survive gastric acid (Shigella, Salmonella) or arrive in large numbers.
- They cross the epithelium through M cells over lymphoid follicles.
- Inside the lamina propria they infect or kill macrophages and invade enterocytes from below.
- Cytokines and chemoattractants (such as hepoxilin A3 for Salmonella) recruit neutrophils.
- Neutrophils and toxins damage the mucosa: ulcers, blood and pus in the stool.

## Four invasive bacteria compared

| Organism | Preferred site | Morphology | Extra-intestinal clue |
| --- | --- | --- | --- |
| [Campylobacter](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/) | Colon and small bowel | Neutrophils in superficial mucosa, crypt abscesses, crypts preserved | Guillain–Barré, reactive arthritis |
| [Shigella](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/) | Left colon, sometimes ileum | Haemorrhagic ulcerated mucosa, pseudomembranes, aphthous ulcers | Reactive arthritis, HUS |
| [Non-typhoidal Salmonella](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/) | Ileum and colon | Acute colitis, sometimes ulcers | Bacteraemia, osteomyelitis in sickle cell disease |
| Yersinia | Ileum, appendix, right colon | Peyer patch and node hyperplasia, aphthous ulcers, granulomas | Erythema nodosum, pseudo-appendicitis |

## Clinical notes

- Watery diarrhoea often precedes dysentery.
- Campylobacter and Salmonella infections raise the later risk of post-infectious irritable bowel syndrome and inflammatory bowel disease.

## Memory aid

Chicken gives Campy and paralysis; Shigella needs only a few; Yersinia fakes appendicitis.

## Test yourself

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

## Which cells do Shigella and Salmonella use to cross the intestinal epithelium?

M cells, the antigen-sampling cells overlying Peyer patches and lymphoid follicles.

## Which invasive bacterium can mimic acute appendicitis?

Yersinia enterocolitica, through terminal ileitis and mesenteric lymphadenitis.

## Why are antidiarrhoeal drugs avoided in shigellosis?

They prolong symptoms and delay clearance of the organism.

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## Connections

## Related 6

- [Infectious enterocolitis](https://durgical.com/en/general-pathology/infectious-enterocolitis/)
- [Toxin-mediated diarrhoea: cholera and E. coli](https://durgical.com/en/general-pathology/toxin-mediated-diarrhoea-cholera-and-e-coli/)
- [Typhoid fever: Peyer patch ulcers and typhoid nodules](https://durgical.com/en/general-pathology/typhoid-fever-peyer-patch-ulcers-and-typhoid-nodules/)
- [Crohn disease](https://durgical.com/en/general-pathology/crohn-disease/)
- [Acute appendicitis](https://durgical.com/en/general-pathology/acute-appendicitis/)
- [Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer](https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/)

## Related conditions 3

- [Bacterial infectious diarrhoea and dysentery](https://durgical.com/en/conditions/bacterial-infectious-diarrhoea-and-dysentery/)
- [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/)
- [Irritable bowel syndrome](https://durgical.com/en/conditions/irritable-bowel-syndrome/)

## Microorganisms 4

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

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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: [About Shigella Infection](https://www.cdc.gov/shigella/about/index.html) (Centers for Disease Control and Prevention, 2024); [About Campylobacter infection](https://www.cdc.gov/campylobacter/about/index.html) (Centers for Disease Control and Prevention, 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/invasive-bacterial-enterocolitis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/invasive-bacterial-enterocolitis/