USMLE

Bacillus anthracis

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Bacteria - Gram Positive
  1. Staph aureus: Overview
  2. Staph aureus: Presentation
  3. Methicillin-Resistant Staph aureus (MRSA)
  4. Staph saprophyticus
  5. Strep pneumoniae: Overview
  6. Strep pneumoniae: Presentation
  7. Strep viridans
  8. Strep pyogenes: Overview
  9. Strep pyogenes: Presentation
  10. Strep agalactiae
  11. Strep bovis
  12. Enterococcus
  13. Bacillus anthracis
  14. Bacillus cereus
  15. Clostridium tetani
  16. Clostridium perfringens
  17. Clostridium botulinum
  18. Clostridium difficile
  19. Corynebacterium diphtheriae
  20. Listeria monocytogenes
  21. Nocardia
  22. Actinomyces

Bacillus anthracis 

  • Characteristics
    • Gram + rod
    • Spore-forming
      • Survives in soil
    • Colonies form a long-chain that is described as being “serpentine”/“medusa head” on appearance. show a halo of projections
  • Virulence Factors
    • Produces anthrax toxin consisting of 3 parts:
      • protective antigen 
        • binds to cell surface and mediates entry of edema and lethal factor into the cytosol of cells
      • lethal factor
        • Protease that impairs many cell signalling pathways by cleaving  mitogen-activated protein kinase kinases (MAPKK)
        • Impairs many cell functions, causing death/necrosis (lethal to cells)
          • Responsible for necrosis in ulcers and tissue damage in anthrax infections
      • edema factor 
        • ↑ cAMP levels
          • Acts as calmodulin-dependent adenylate cyclase
        • Causes accumulation of fluid (edema) in tissues and suppresses innate immune function
    • Polypeptide capsule made of D-glutamate
      • Produces an antiphagocytic capsule that is required for pathogenicity. The capsule is unique in that it contains D-glutamate instead of polysaccharide.
  • Exposure
    • animals hair/hides/wool
      • Goat hair is the most commonly implicated (e.g. woolsorter’s disease)
      • Common in areas where animal vaccination rates are low; e.g. developing countries
    • bioweapon
  • Presentation: Anthrax
    • Cutaneous anthrax
      • spores introduced into subcutaneous tissue; most common form
      • papule → painless necrotic ulcer covered with black eschar
        • Formed by release of toxins LF and EF leading to edema and necrosis
        • uncommonly progresses to bacteremia and death
    • Pulmonary anthrax
      • Inhalation of spores; relatively rare (~5% of cases)
      • Also known as woolsorter's disease
      • flu-like symptoms (myalgia, fever, malaise) → rapidly progress to hemorrhagic mediastinitis (widened mediastinum on X-ray), pulmonary hemorrhage (bloody pleural effusions), septic shock, and death
    • Gastrointestinal anthrax
      • Ingestion of spores; extremely rare
  • Treatment 
    • Ciprofloxacin or doxycycline for all patients
    • Protein synthesis inhibitor
      • For systemic anthrax in combination with quinolone or doxycycline
      • Reduces toxin production
    • Antitoxin for all patients
      • Monoclonal antibodies (raxibacumab)
      • Anthrax immunoglobulin