Preserving pure cultures is essential for maintaining bacterial viability and genetic stability over extended periods.
Common preservation methods include:
1) Refrigeration
Temperature: 4°C
Duration: Short-term storage (weeks to months).
Procedure: Cultures are stored on agar slants or in broth media in a refrigerator.
Advantages: Simple and easy for short-term use.
2) Freezing
Temperature: -20°C to -80°C
Duration: Long-term storage (years).
Procedure: Cultures are mixed with a cryoprotectant (e.g., glycerol) to prevent ice crystal formation and stored in a deep freezer.
Advantages: Effective for long-term preservation with high viability.
3) Lyophilization (Freeze-Drying) (Preservation Methods)
Procedure: Cultures are frozen and then subjected to a vacuum to remove water by sublimation, leaving a dry powder.
Storage: The powder is sealed in ampoules or vials and stored at room temperature or in a refrigerator.
Advantages: Very long-term storage (decades), maintains viability and genetic stability.
4) Cryopreservation in Liquid Nitrogen
Temperature: -196°C
Duration: Very long-term storage (decades).
Procedure: Cultures are suspended in a cryoprotectant and stored in liquid nitrogen.
Advantages: Maintains high viability and genetic stability over very long periods.
5) Use of Culture Media Additives
Procedure: Addition of substances like glycerol, dimethyl sulfoxide (DMSO), or skim milk as protectants during freezing.
Goal: Enhance survival rates during storage and thawing.
Advantages: Increases the effectiveness of freezing methods.