15.1.1.1: Bacillus anthracis

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Organism

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.

Habitat

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

Source

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

Epidemiology

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: http://textbookofbacteriology.net/Anthrax.html