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.
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 | Colon and small bowel | Neutrophils in superficial mucosa, crypt abscesses, crypts preserved | Guillain–Barré, reactive arthritis |
| Shigella | Left colon, sometimes ileum | Haemorrhagic ulcerated mucosa, pseudomembranes, aphthous ulcers | Reactive arthritis, HUS |
| Non-typhoidal Salmonella | 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.
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.
Connections
Microorganisms4
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 (Centers for Disease Control and Prevention, 2024); About Campylobacter infection (Centers for Disease Control and Prevention, 2024).
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Representative model, for educational purposes only.