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Bacillus anthracis

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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