Key Features
- Organisms: Certain Gram-positive bacteria (Bacillus and Clostridium species).
- When formed: In response to nutrient depletion.
- Spore properties:
- Metabolically inactive
- Extremely resistant to heat, chemicals, and desiccation
- Core contains dipicolinic acid → responsible for heat resistance
Sterilization
- An autoclave (121 °C, 15 minutes, 15 psi) is required to destroy spores reliably.
- Other sporicidal agents: hydrogen peroxide, iodine-based compounds.
- Mnemonic: “Autoclave to kill ABC” → Anthracis, Bacillus cereus, Clostridium.
Examples of Spore-Forming Bacteria
| Genus / Species | Disease Association |
|---|---|
| Bacillus anthracis | Anthrax |
| Bacillus cereus | Food poisoning |
| Clostridium botulinum | Botulism |
| Clostridioides difficile | Pseudomembranous colitis |
| Clostridium perfringens | Gas gangrene, food poisoning |
| Clostridium tetani | Tetanus |
Learning Objective (USMLE Step 1): Recognize that spore formation is a survival strategy of certain Gram-positive bacteria (Bacillus and Clostridium) and understand that spores are highly resistant to standard disinfection, requiring autoclaving or sporicidal agents for sterilization.
