Membrane filtration (0.22 µm pore size) is used to sterilize heat-labile solutions. However, it CANNOT sterilize solutions contaminated with:
- A Mycoplasma species (diameter 0.2–0.3 µm), which can pass through 0.22 µm filters ✓
- B Pseudomonas aeruginosa (diameter ~0.5–1 µm)
- C Staphylococcus aureus cocci (diameter ~0.8–1 µm)
- D Clostridium spores (diameter ~1–1.5 µm)
Correct answer: A. Mycoplasma species (diameter 0.2–0.3 µm), which can pass through 0.22 µm filters
Explanation
A 0.22 µm (220 nm) membrane filter retains all bacteria with a diameter greater than the pore size, including Pseudomonas (~0.5–1 µm), Staphylococcus (~0.8–1 µm), and even most Chlamydia EBs. However, Mycoplasma species (the smallest self-replicating organisms, 0.1–0.3 µm diameter, pleomorphic, without cell walls) can pass through 0.22 µm filters, leading to contamination of tissue culture media and biological products. Mycoplasma-safe filtration requires 0.1 µm filters.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.