Shigella

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Organism
- Four species
- Shigella dysenteriae=most disease, no flagella
Epidemiology
- Strictly human disease
- Common infectious diarrhea
- Fecal-oral
- Low infecting dose (<200)
- S. dysentariae type 1 causes most severe disease
Pathogenesis
- Acid resistant
- Invasion of colonic mucosa
- Adheres to M cells, translocates to phagocytic cells
- Cause apoptosis in macrophages/M cells
- Apoptosis leads to viral release -> incasin protein Ag -> unique actions
- Create actin tail by contoling polymerization of actin fibriles
- Cell to cell spread
- Focal ulcers in mucosa -> inflammatory diarrhea
- Stx -> increases morbidity
Manifestations
- Acute inflammatory colitis and bloody diarrhea
- Triad: cramps, painful straining, frequent, small volume bloody mucoid discharge
- Diagnosis: Selective media
- Tx: usually self-limiting, high resistance to ampicillin