Aerobic Mesophilic Bacterial Spores
“Spores” or more precisely “bacterial endospores” are resistant dormant bodies produced by some microorganisms (Gram-positive bacteria) upon exposure to stressful environmental conditions. Aerobic microorganisms grow while exposed to oxygen, while mesophilic microorganisms grow on nutrient-rich media at temperatures comfortable for humans (roughly between 15 °C and 40 °C). Spores are capable of surviving extreme environmental conditions in a dormant state and proliferating when eintroduced into a hospitable environment. This particular type of spores is commonly used in planetary protection as reference microorganisms for the qualification of bioburden reduction processes. Numbering the spores per unit of surface is also used as a proxy when measuring the relative cleanliness of spacecraft components and systems.