Shigella

Shigella

Updated: 02/03/2024

© Jun Wang, MD, PhD

 

General features

  • G-negative rods, non-motile, noncapsulated, facultatively anaerobic
  • Highly virulent
  • Leading cause of diarrheal death, with most common in south Asia and sub-Saharan Africa
  • 4 groups: S. dysenteriae, S. flexneri, S. boydii, S. sonnei

Key clinical features

  • Fecal-oral Transmission
  • Severity depends on age of patient and the strain
    • S. dysenteriae type 1 with toxin most severe
  • Fever (generally >101.0°F)
  • Lower abdominal cramps; tenesmus; multiple scanty, bloody, mucoid stools
  • Diarrhea: first watery, then bloody with WBCs

Pathogenesis:

  • Invasive but rarely causes septicemia
  • Invade submucosa through M-cells (Microfold cells over lymphoid aggregates)
  • Proliferate in macrophage
  • Invade the basolateral side of colonic epithelial cells
  • Polymerize actin “jet trails” to spread laterally
  • Endotoxin triggers inflammation
  • Exotoxin
    • Produced by S. dysenteriae, type 1
    • Similar to EHEC toxin, causing hemolytic uremic syndrome (HUS)
    • Three activities:
      • Neurotoxic
      • Cytotoxic
      • Enterotoxic

Diagnosis

  • Culture on selective media, may grow on MacConkey agar
  • G-, Non-lactose, H2S negative
  • Serology (anti-O antibody) and molecular testing

Management

  • Mild cases: fluid and electrolyte replacement
  • Severe cases: antibiotics

 

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