BACILLUS ANTHRACIS

Morphology

• Bacillus anthracis is a Gram-positive, endospore-forming, rod-shaped bacterium.
• It measures 4-6 μm in length and 1-2 μm in width.
• It has a central, terminal, or sub-terminal spore.
• The spore is typically 1-2 μm in length and 0.5-1 μm in width.

Pathogenicity

• Bacillus anthracis is a zoonotic pathogen, meaning it can infect both humans and animals.
• It causes anthrax, a disease characterized by cutaneous, pulmonary, or gastrointestinal symptoms.
• The pathogenesis of Bacillus anthracis involves several steps:
  1. → Ingestion or inhalation of spores by the host.
  2. → Germination of the spore in the host's environment.
  3. → Release of toxins, including lethal factor (LF), edema factor (EF), and protective antigen (PA).
  4. → Binding of PA to cell surface receptors.
  5. → Internalization of the toxin complex into the host cell.
  6. → Activation of the toxin complex, leading to cell death.

Life Cycle

1. → Bacillus anthracis grows as a vegetative cell in the host's environment.
2. → The vegetative cell undergoes a process called sporulation, resulting in the formation of a spore.
3. → The spore is resistant to environmental stressors and can remain dormant for long periods.
4. → When conditions are favorable, the spore germinates, and the cycle begins again.

Memory Trick

"PA is a key, EF is a pump, LF is a knife, and spores are the bombs."

Clinical Features

• Cutaneous anthrax:
  • → A painless, ulcerative lesion at the site of infection.
  • → Swelling and edema around the lesion.
• Pulmonary anthrax:
  • → Symptoms include fever, cough, chest pain, and difficulty breathing.
  • → Can lead to respiratory failure and death.
• Gastrointestinal anthrax:
  • → Symptoms include fever, abdominal pain, and bloody diarrhea.
  • → Can lead to intestinal obstruction and death.

Complications

• Septicemia: the spread of the infection to the bloodstream.
• Meningitis: inflammation of the membranes surrounding the brain and spinal cord.
• Respiratory failure: failure of the lungs to exchange oxygen and carbon dioxide.

Laboratory Diagnosis

• Culture: Bacillus anthracis can be grown on agar plates.
• Smear: a Gram stain can be used to identify the bacteria.
• Serology: tests can be used to detect antibodies against the bacteria.
• PCR: polymerase chain reaction can be used to detect DNA from the bacteria.
• ELISA: enzyme-linked immunosorbent assay can be used to detect antibodies against the bacteria.

Management

• Supportive care: treatment of symptoms and supportive care.
• Antibiotics: antibiotics can be used to treat anthrax.
• Vaccination: a vaccine is available to prevent anthrax.
• Decontamination: contaminated materials and equipment should be decontaminated to prevent the spread of the disease.