A laminar flow cabinet protects both the operator and the culture work from contamination during handling of mycobacterial cultures. The critical property of the HEPA filters used in such cabinets is:
- A They remove particles larger than 0.22 micrometer by size exclusion alone
- B They retain 99.97% of particles 0.3 micrometer in diameter or larger ✓
- C They trap all microorganisms but permit free passage of airborne viruses
- D They sterilize air by ultraviolet irradiation generated across the filter matrix
Correct answer: B. They retain 99.97% of particles 0.3 micrometer in diameter or larger
Explanation
HEPA filters are defined by their ability to retain at least 99.97% of particles of 0.3 micrometer diameter, the most penetrating particle size. Filtration occurs by interception, impaction and diffusion, not simple sieving, so smaller particles including virus-carrying droplet nuclei are also effectively removed. Class I and II biological safety cabinets rely on HEPA-filtered exhaust and supply air for protection of operator and sample respectively.
Reference: Mackie and McCartney Practical Medical Microbiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.