Stock Culture – Definition, Meaning, Preparation Examples, and Importance: 

Definition of Stock Culture:

• Stock culture is a culture of a microorganism that is prepared by subculturing the pure culture into a fresh medium. 

• Stock culture means the preservation of microorganisms on a culture medium for future study.

What is stock culture:

• Stock culture is a culture of microorganisms that is used to maintain the viability of microorganisms and for future reference.
• The stock culture is prepared by subculturing the pure culture. 
• The stock cultures are transferred periodically onto or into a fresh medium (subculturing) to allow continuous growth and viability of microorganisms.
• Stock culture can preserve by various methods such as refrigeration, storage on agar slant, cryopreservation, and lyophilization (freeze-drying).
• The most common method for stock culture preservation is storage on agar slants and Freezing.

Stock culture Preparation on agar slant:

Requirements:

• Pure Culture
• Any agar medium (e.g. PDA, CDA or NAM)
• Culture tubes
• Test tube stand
• Autoclave
• Cotton plug
• Aluminum foil or paper

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Procedure:

• Agar slants are prepared to inoculate microbial culture. 
• To prepare the agar slant take a clean and empty number of culture tubes (4-5).
• The tubes are now cotton-plugged and sterilized in an autoclave at 121°C for 20 minutes.
• Now about 12 to 15 ml of liquified agar medium is poured into each of them. The amount of medium could be reduced or increased in proportion to the number of tubes for culture.
• Now the tubes get cooled and the medium in them is solidified resulting in a sloppy surface and agar slants are made.
• Finally, streak your pure culture colony on an agar slant if needed. You can also save them for later use.

Importance of Stock Culture: 

• Stock cultures of microorganisms are required for conducting future experiments.
• The microorganisms of stock culture can be grown, tested, characterized, and identified.
• Stock culture is necessary to maintain the viability and purity of the microorganism by keeping the pure culture free from contamination.

Frequently Asked Questions on Stock Culture: 

1. Why is stock culture important?

Answer: Stock cultures are extremely important resources, and should be maintained in a manner that ensures their long-term persistence. Stock cultures of microorganisms are required for conducting future experiments.

2. How do you maintain stock cultures?

Answer: There are several techniques by which we can maintain stock cultures such as regular freezing, deep freezing, freeze drying, storage at reduced temperature, storage on agar slant, etc. But freeze-drying and storage on agar slant is the preferred method for keeping reference strains and other isolates for long periods and is standard practice for large commercial use.

3. Why are agar slants better for stock cultures?

Answer:  Agar slants are better because they can be capped, preventing the agar and culture from drying out and maintaining the culture contamination free. Slants also take up less space for culture storage.

4. What is the stock culture definition?

Answer: A culture of a microorganism is maintained solely to keep it viable for subculture into fresh medium.