A bacterial spore is a spore or spore-like structure produced by bacteria. These include endospores, Akinetes, and spores produced by Actinobacteria and Azotobacter. Spore formation in bacteria is not the principal method of reproduction but simply a method of surviving unfavourable conditions. They have a number of features:

1. They can tolerate extreme dryness.
2. Some cannot be killed even at subzero temperatures.
3. Some can spread poisonous chemicals, such as the Cry toxin synthesised by Bacillus thuringiensis

Bacterial spores are extremely resistant. Spores of tetanus and anthrax, for example, can survive in the soil for many years. The origin of these spores was discovered in the 19th century, when a biologist noticed, under the microscope, a small, round, bright body inside bacterial cells. This survived even when the bacteria were boiled for five minutes. This killed the bacteria, but not the spores. They]germinated when conditions were right. Because spores are so resistant, they are highly transmissible. This makes them a very problematic aspect of spore-forming pathogens such as Clostridium difficile.