In species of Bacillus and Clostridium, the endospore allows such bacteria to sustain themselves when nutrients are unavailable. Bacterial cells normally grow and mature, reproducing to form actively metabolizing, vegetative cells. However, when nutrients are low and the population begins to decline, Bacilli and Clostridia enter a stationary phase and begin sporulation (spore formation). Endospores are particularly problematic because they are extremely resistant. For instance, endospores can remain viable in boiling water for up to 2 hours. Their resistance to heat makes them particularly difficult to eliminate from contaminated medical materials and food products.
