an oval or rounded formation that occurs within bacilliform cells (sporiferous bacteria). Within each bacterial spore is a compact mass of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein. Bacterial spores are resistant to the effects of poisonous substances and other unfavorable external factors; the resistance results from the lower water content (15–20 percent) in spores than in vegetative cells, the presence of four to five dense, poorly permeable membranes, and the transition of the enzymes to an inactive state. The resistance of spores to high temperatures—some spores can survive boiling for 30 minutes or longer—is caused by the presence of a large quantity of the calcium salt of dipicolinic acid in the membranes.

Upon encountering a fresh nutrient medium, the spores germinate in a polar or equatorial manner, giving rise to new bacterialcells.