Which of the following can be used to preserve bacterial cultures?

• A. Freezing at -80 ^\circ C
• B. Storing at room temperature in nutrient broth
• C. Incubation at 37 ^\circ C
• D. Exposure to ultraviolet light

Answer: (A)

Verified step by step guidance

1. Understand the goal: preserving bacterial cultures means maintaining their viability and preventing changes in their characteristics over time.
2. Evaluate each option based on how it affects bacterial survival and growth: storing at room temperature in nutrient broth and incubation at 37 ^\circ C both promote bacterial growth but do not effectively preserve cultures long-term.
3. Consider the effect of ultraviolet light exposure, which damages bacterial DNA and is used to kill or reduce bacteria, so it is not suitable for preservation.
4. Recognize that freezing at -80 ^\circ C slows down all metabolic processes and prevents bacterial growth, effectively preserving the cultures for extended periods.
5. Conclude that freezing at -80 ^\circ C is the best method among the options for preserving bacterial cultures.