During the death phase of a microbial growth curve, which of the following occurs?

• A. Growth continues while the population decreases.
• B. Metabolic activity remains high and cell numbers stabilize.
• C. Growth stops and the number of viable cells decreases; cells become more susceptible to physical, chemical and antibiotic agents.
• D. The population becomes dormant with no changes in viability.

Answer: (C)

In the death phase, the environment has become hostile for the cells due to depleted nutrients and the buildup of toxic waste products. This leads to more cells dying than are produced, so growth stops and the number of viable cells declines. The surviving cells are stressed, often with reduced energy reserves and damaged membranes, which makes them more vulnerable to external stresses. As a result, they are more susceptible to physical factors (like heat or desiccation), chemical factors (such as changes in pH or oxidizing agents), and antibiotics that target cellular processes. Some cells may still be metabolically active for a time, but overall viability continues to decrease.