Which of the following would be the most effective method in preserving bacterial cultures for long-term storage?

• A. Lyophilization (freeze-drying)
• B. Frequent subculturing on agar plates
• C. Storing at room temperature in nutrient broth
• D. Incubation at 37 ^\circ C

Answer: (A)

Verified step by step guidance

1. Understand the goal: The question asks for the most effective method to preserve bacterial cultures for long-term storage, which means maintaining viability and genetic stability over extended periods.
2. Evaluate each option based on how well it prevents bacterial degradation and contamination over time:
3. 1. Frequent subculturing on agar plates can lead to genetic drift and contamination, making it less ideal for long-term preservation.
4. 2. Storing at room temperature in nutrient broth promotes bacterial growth and metabolism, which can exhaust nutrients and cause cell death, so it is not suitable for long-term storage.
5. 3. Incubation at 37 ^\circ C is optimal for bacterial growth but not for preservation, as it encourages active metabolism and eventual depletion of resources.
6. 4. Lyophilization (freeze-drying) removes water under low temperature and pressure, effectively halting metabolic activity and preserving cells in a dormant state, which is ideal for long-term storage.