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Biology LibreTexts Bacillus anthracis

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    Endospore stain of Bacillus anthracis. (Copyright; Kristen Catlin, Public Health Image Library. 2009.)


    • Bacillus anthracis is a large, Gram-positive endospore-forming rod, often found as streptobacilli
    • A catalase-positive facultative anaerobe which metabolizes using both aerobic respiration and fermentation
    • Able to use a wide variety of sugars and other biological material as carbon and energy sources
    • Encapsulated.  Unlike most bacterial capsules which are polysaccharide, the B. anthracis capsule is a polymer of the amino acid glutamate.


    •  Soil, particularly in locations with an active outbreak
    • Can be found in/on wool, fur, hair, and hides of livestock or other animals which have been exposed


    •  Historically of most concern as a lethal pathogen of livestock
    • Most natural infections of humans arise from exposure through contaminated animal products
    • Has been utilized as a biological weapon, notably in the months following the terrorist attacks of September 11, 2001


    • Naturally occurs infrequently and sporadically
    • Environmental endospores are introduced into compromised skin, inhaled, or ingested

    Clinical Disease

    • Cutaneous anthrax:
      • The least dangerous form of anthrax (~20% mortality rate without treatment)
      • Endospores enter through compromised skin and germinate, causing a localized infection
      • Produces a black necrotic lesion with a coal-like appearance; this is the source of its name (the same word route as the coal variety anthracite)
      • This form of anthrax is usually easily cured with antibiotic treatment
      • If the B. anthracis is able to enter the bloodstream from the infection site, however, it is highly likely to be fatal
    • Inhalational anthrax:
      • Occurs when endospores are inhaled and germinate in lungs, leading to infection
      • Sometimes called “woolsorter’s disease” due to its associated with exposure to animal products such as wool or hides
      • Early symptoms can resemble pneumonia or flu
      • Can lead to hemorrhaging in the lungs
      • Can be treated with antibiotics if diagnosed quickly, but much more likely to be fatal than cutaneous anthrax (~80% mortality rate)
    • Gastrointestinal anthrax:
      • Occurs when endospores are ingested
      • Very rare form of anthrax
      • Reported mortality rates vary from ~25-75%

     Primary Virulence Factors

    • Poly-D-glutamyl capsule
    • Anthrax toxin 
      • AB exotoxin
      • Two active (A) components: edema factor (EF) and lethal factor (LF)
      • Binding (B) component: protective antigen (PA)

    Additional information: Bacillus anthracis is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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