A spore is a reproductive cell produced by certain fungi, plants (moss, ferns), and some bacteria.
Certain bacteria make spores as a way to defend themselves. Bacterial spores have thick walls and can resist high temperatures, humidity, and other poor conditions.
The bacteria Clostridia form spores. These spores create the living bacteria that cause gas gangrene and antibiotic-associated colitis.
Chemical disinfectants can kill bacteria, but do not destroy their spores.
A process called sterilization destroys spores and bacteria. It is done at high temperatures and under high pressures. In health-care settings, sterilization is usually done using a device called an autoclave.