anthracis

Bacillus anthracis is a Gram-positive, rod-shaped, spore-forming bacterium that causes anthrax in humans and animals. It is a member of the genus Bacillus and is considered a zoonotic pathogen found in soil, particularly in regions where grazing animals are exposed.

Virulence is largely due to two plasmids: pXO1, which encodes the tripartite toxin consisting of protective antigen, edema factor, and lethal factor, and pXO2, which encodes a poly-D-glutamic acid capsule that protects against phagocytosis. The combination of toxin production and capsule enables the organism to cause disease in susceptible hosts.

Transmission to humans typically occurs through contact with contaminated animal products or tissue or ingestion of contaminated meat. Inhalation of spores during handling dusty material can cause inhalational anthrax, the most severe form, while ingestion can lead to gastrointestinal disease. The disease is highly dependent on dose and route of exposure.

Clinical forms include cutaneous anthrax, which presents with a painless necrotic lesion and vesicular changes; inhalational anthrax, which begins with nonspecific symptoms and may progress to severe respiratory distress and shock if untreated; and gastrointestinal anthrax, which is less common but carries a high mortality.

Diagnosis relies on culture and Gram staining, with confirmation by PCR or serology. Treatment requires prompt antibiotics such as ciprofloxacin or doxycycline, often in combination with antitoxins for severe disease. Vaccines exist for persons at high risk, typically administered in multi-dose schedules.

Historically described in the late 19th century by Robert Koch, Bacillus anthracis has been a model organism for bacterial pathogenesis and remains a concern for biosecurity and public health. It persists in soil and continues to be monitored in veterinary and human health programs.