<s>[INST] context: Sterilization of culture media

The constituents of culture media must be carefully sterilized.
Two methods are commonly used to sterilize culture media -

1) Autoclaving
- Constituents like water, salts and supplements like peptone, tryptose etc., which are heat stable, are autoclaved.
- Generally autoclaving is carried out at 121°C and at a pressure of 15 psi.

The time required for sterilization depends upon the volume of medium in the vessel-


For small volumes of liquids (100 ml or less), the time required for autoclaving is 15-20min.
For large quantities (2-4 liter) 30-40 min is required.

2) Membrane filtration
- Constituents like serum, trypsin, growth factors, proteins, amino acids, vitamins, hormones, carbohydrates and plant extracts are thermolabile and may decompose during autoclaving.
- These must be sterilized by filtration.

The porosity of the filter membrane should be no longer than 0.2 microns (U m). - Empty glassware that is to hold media must be sterilized in an autoclave before filter sterilization.


These two (autoclaving and membrane filtration) are the most commonly used methods for sterilization of culture media. But when these are not available other methods can be used; e.g.-

- For media containing sugar or gelatin, an exposure of 100°C for 20 minutes on three successive days may be used. This is known as Tyndallization.
Some media containing serum or egg fluid can be sterilized by heating to 80-85°C for 2-4 hours. [/INST] question: Sterilization of culture media containing serum is by- | options: A: Autoclaving B: Micropore filter C: Gamma radiation D: Centrifugation | answer: B </s>