Shigella Study Notes

Shigella Overview

  • Characteristics:
    • Non-motile bacteria, unlike Salmonella.
    • Attachment structures called fimbriae.

Key Differences from Salmonella

  • Motility: Shigella is always non-motile.
  • Both cause gastroenteritis but are distinct organisms.

Aspects for Study

  1. Natural Life:
    • Exclusively infects humans, unlike Salmonella which infects animals and humans.
    • Human-specific, occasionally infects gorillas.
    • Shigella and E. Coli share high genetic similarity (over 97%).
  2. Clinical Presentation:
    • Causes bacillary dysentery; differs from amoebic dysentery (hence the term is used to denote its bacterial nature).
    • Symptoms include:
      • Blood and mucus in stool.
      • Severe nausea, vomiting, headaches, and fever.
    • Contents can lead to dehydration due to lack of intake (not through diarrhea).
    • Dysenteryi species known for high mortality rates, especially in infants in developing countries (up to 50%).
  3. Laboratory Identification:
    • Part of the Enterobacteriaceae family.
    • Non-lactose fermenter: MacConkey agar maintains the original color (no pink).
    • Confusion with E. Coli due to genetic similarity.
    • Use of biochemical tests (e.g., MIL tube for motility) and additional confirmatory tests (e.g., agglutination with antiserum).
  4. Virulence Factors:
    • Very low infectious dose (1 to 10 cells can cause infection).
    • Type III secretion system:
      • Acts like a syringe to inject proteins into host cells (enterocytes), leading to cell death and rearrangement of cell architecture to aid bacterial movement.
  5. Treatment:
    • Ciprofloxacin as a recommended treatment.
    • Rising concern over multi-drug resistance making treatment more difficult.

Key Points on Treatment and Public Health

  • Risk of multi-drug resistant strains spreading among populations, complicating treatment.
  • Importance of tracking outbreaks through laboratory confirmation as a notifiable disease.