Vegetative cells may form a spore when the conditions for survival are not optimal for the cell, such as high heat or lack of water and food.
Spores of Bacillus and Clostridium species are metabolically dormant and extremely resistant to acute environmental stresses such as heat, desiccation, UV and γ-radiation, mechanical disruption, enzymatic digestion and toxic chemicals.
Spores also can survive for extremely long periods in milder environmental conditions. As soon as spores get into human or animal organisms, as well as into canned foods, they germinate and become a source of serious infectious diseases.
Heat does not destroy spores. Once the conditions are conducive to growth again, the spore will again become a vegetative cell. A typical case of food borne illness occurs when a piece of meat is cooked, but the spore survives.
The outermost layer is the exosporium. While probably not present in spores of all species, in some spores the exosporium is by far the largest spore layer and is a loosely fitting, balloon-like structure containing carbohydrate and protein but mostly water.
Based on studies with B. cereus, the exosporium is composed principally of protein (43–52% of dry weight), but also contains lipids (15–18% of dry weight) and carbohydrates (20–22% of dry weight), as well as a minor (around 4%) component described as ash, which contained both calcium and magnesium as well as some undetermined components.
Bacterial spores
