This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'Sterilization of culture media containing serum is by- \nSelect and explain. \nA. Autoclaving, B. Micropore filter, C. Gamma radiation, D. Centrifugation', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Sterilization of culture media\n\nThe constituents of culture media must be carefully sterilized.\nTwo methods are commonly used to sterilize culture media -\n\n1) Autoclaving\n- Constituents like water, salts and supplements like peptone, tryptose etc., which are heat stable, are autoclaved.\n- Generally autoclaving is carried out at 121°C and at a pressure of 15 psi.\n\nThe time required for sterilization depends upon the volume of medium in the vessel-\n\n\nFor small volumes of liquids (100 ml or less), the time required for autoclaving is 15-20min.\nFor large quantities (2-4 liter) 30-40 min is required.\n\n2) Membrane filtration\n- Constituents like serum, trypsin, growth factors, proteins, amino acids, vitamins, hormones, carbohydrates and plant extracts are thermolabile and may decompose during autoclaving.\n- These must be sterilized by filtration.\n\nThe 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.\n\n\nThese 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.-\n\n- 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.\nSome media containing serum or egg fluid can be sterilized by heating to 80-85°C for 2-4 hours.', 'role': 'assistant'}]