Question

What is the typical pore size of a membrane filter used to sterilize heat-sensitive liquids?

• A. 1.0 µm
• B. 0.45 µm
• C. 0.22 µm
• D. 5.0 µm

Hint:

Membrane sterilization → 0.22 µm filter → Removes bacteria effectively.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Filtration is a mechanical method to remove microbes from liquids or gases that cannot withstand the high heat of an autoclave (e.g., vaccines, antibiotics).
Step 2: Detailed Explanation:
Microorganisms vary in size, but most common bacteria fall in the range of 0.5 to 2.0 $\mu$m in diameter.
To ensure that all vegetative bacterial cells are removed, a membrane filter with a pore size smaller than the smallest bacteria must be used.
The industry standard for bacterial sterilization is a pore size of 0.22 $\mu$m.
While 0.45 $\mu$m filters are sometimes used for general clarification, they may allow smaller bacteria like Pseudomonas or Mycoplasma to pass through.
Viruses are much smaller and usually pass through a 0.22 $\mu$m filter.
Step 3: Final Answer:
The typical pore size for sterilizing heat-sensitive liquids is 0.22 $\mu$m.