Question

Heat labile liquids are sterilized by which method?

• A. Hot air oven
• B. Autoclaving
• C. Membrane filter
• D. Moist heat

Hint:

If heat would wreck the liquid, you must physically strain out the microbes instead.

Answer 1

The Correct Option is C

Step 1: Concept. Heat-labile means the substance is damaged or destroyed by heat. So any heat-based sterilization method is unsuitable, and a non-thermal method must be chosen.

Step 2: Why membrane filter. Filtration physically removes microbes from a fluid without heating it. Membrane filters (pore size about 0.22 micrometres) are used to sterilize heat-sensitive liquids such as serum, antibiotic solutions, ophthalmic preparations, oils, and liquid culture media. Hence option (c) is correct.

Step 3: Why the others are wrong. The hot air oven uses dry heat at about 160 degrees C and would denature the liquid. Autoclaving and moist heat both use steam under pressure at about 121 degrees C, again destroying a heat-labile substance.

Step 4: Note. Standard membrane filters remove bacteria and fungi but not viruses, so they sterilize only with respect to those larger organisms.