3.08 Bacillus Species

Microbiology review for the USMLE Step 1 exam

• Bacillus species are aerobic, sporulating, gram + rod-shaped bacteria found in nature such as soil, water, and air
• Two main species to discuss: Bacillus cereus and Bacillus anthracis
• Bacillus cereus is associated with foodborne infections and specifically with reheated rice, as spores can survive cooking and continue to grow in refrigerated rice, leading to enteritis symptoms
• Bacillus anthracis causes anthrax, most commonly contracted through contact with infected animals, particularly grazing animals such as sheep, goats, and cattle.
• There are three forms of anthrax: cutaneous anthrax, inhalation anthrax, and gastrointestinal anthrax
• Cutaneous anthrax is the most common form and results from inoculation of spores through a cut or opening in the skin
• Inhalation anthrax occurs when spores are inhaled and leads to systemic illness, mediastinal widening, septic shock, and death
• Gastrointestinal anthrax results from ingesting spores in contaminated food and leads to severe abdominal symptoms.