Question
Bacterial spore
Answer
A bacterial spore is a dormant, highly resistant, metabolically inactive form produced by certain Gram-positive bacteria (chiefly Bacillus and Clostridium species) when exposed to adverse environmental conditions — a survival mechanism, not a means of reproduction.
Structure (outside in): exosporium, spore coat (protein, resistant to chemicals/enzymes), cortex (peptidoglycan, important in heat resistance/dehydration), core wall, and the core (DNA, ribosomes, low water content).
Basis of resistance: high concentration of calcium dipicolinate in the core stabilizes DNA/proteins and confers resistance to heat, radiation, and desiccation; the thick, impermeable coat resists chemical disinfectants; low core water content reduces heat-mediated protein denaturation.
Clinical/practical significance: spores of Clostridium tetani, C. perfringens, C. botulinum, C. difficile, and Bacillus anthracis can survive in the environment for years and germinate under favourable conditions to cause disease; spores are the target organism used to validate sterilization procedures (autoclaving must kill even bacterial spores, unlike boiling or pasteurization).
Demonstration: not stained by ordinary stains; special spore stains (e.g., malachite green/Schaeffer-Fulton method) demonstrate spores as green structures within red/pink counterstained vegetative cells.