Mechanical methods of sterilization MCQs With Answer — This concise guide covers essential mechanical sterilization concepts B. Pharm students must master, including sterile filtration, HEPA air filtration, depth vs. membrane filters, sterilizing-grade filters (0.22 μm), filter integrity testing (bubble point, forward flow, diffusion), aseptic processing, and filter materials like PVDF, PES and PTFE. Learn practical applications for heat-sensitive pharmaceuticals, sterile gas vents, tangential flow filtration, and validation strategies. The SEO-focused content is tailored to exam preparation and practical laboratory use, emphasizing keywords such as mechanical methods of sterilization, MCQs, sterile filtration, filter integrity and aseptic processing. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary mechanical method for sterilizing heat-sensitive pharmaceutical liquids?
- Autoclaving
- Chemical sterilization
- Sterile membrane filtration
- Dry heat sterilization
Correct Answer: Sterile membrane filtration
Q2. Which pore size is commonly used for sterilizing-grade membrane filters to remove bacteria?
- 0.45 μm
- 0.22 μm
- 1.2 μm
- 5 μm
Correct Answer: 0.22 μm
Q3. Which filter type is characterized by a tortuous path and particle trapping throughout a thick matrix?
- Membrane filter
- Depth filter
- HEPA filter
- Hydrophobic vent filter
Correct Answer: Depth filter
Q4. What does a bubble point test primarily assess for a membrane filter?
- Chemical compatibility
- Filter color change
- Pore integrity and maximum pore size
- Flow rate under vacuum
Correct Answer: Pore integrity and maximum pore size
Q5. Which material is commonly used for hydrophobic gas sterilizing filters?
- Polyethylene (PE)
- Polytetrafluoroethylene (PTFE)
- Cellulose acetate
- Glass fiber
Correct Answer: Polytetrafluoroethylene (PTFE)
Q6. Which test measures filter integrity by passing a wetting liquid and detecting gas flow at a defined pressure?
- Forward flow test
- Diffusion test
- Bubble point test
- Viscosity test
Correct Answer: Bubble point test
Q7. What is the role of a prefilter before a sterilizing-grade membrane filter?
- Increase sterility by itself
- Reduce particulate load and extend membrane life
- Change chemical composition of solution
- Sterilize gas streams
Correct Answer: Reduce particulate load and extend membrane life
Q8. Tangential flow filtration (TFF) is mainly used to:
- Sterilize air in cleanrooms
- Separate and concentrate biological macromolecules while reducing fouling
- Replace autoclaving for glassware
- Perform bubble point tests
Correct Answer: Separate and concentrate biological macromolecules while reducing fouling
Q9. Which of the following is a limitation of membrane filtration for sterilization?
- Effective against all viruses by standard 0.22 μm filters
- Potential for filter fouling and product adsorption
- Always faster than autoclaving
- Does not require validation
Correct Answer: Potential for filter fouling and product adsorption
Q10. HEPA filters are typically rated to remove what minimum particle size with high efficiency?
- 10 μm
- 0.3 μm
- 5 μm
- 1 mm
Correct Answer: 0.3 μm
Q11. Which membrane material is noted for low protein binding and wide chemical compatibility?
- Nylon
- PVDF (polyvinylidene fluoride)
- Cellulose nitrate
- Glass fiber
Correct Answer: PVDF (polyvinylidene fluoride)
Q12. The term “sterilizing-grade filter” means:
- A filter that removes visible particles only
- A filter validated to retain microorganisms under defined conditions
- A filter made only of PTFE
- A filter that does not require integrity testing
Correct Answer: A filter validated to retain microorganisms under defined conditions
Q13. Which integrity test measures gas diffusion through a wetted filter at low differential pressure?
- Bubble point test
- Forward flow test
- Diffusion (or forward diffusion) test
- Backpressure test
Correct Answer: Diffusion (or forward diffusion) test
Q14. For sterilizing liquids containing cells or large bioparticles, which method is preferred?
- 0.22 μm dead-end filtration
- Tangential flow filtration with appropriate pore size
- HEPA filtration
- Dry heat
Correct Answer: Tangential flow filtration with appropriate pore size
Q15. What does “nominal” filter rating indicate?
- Absolute retention of all particles above the size
- Approximate efficiency for a given particle size
- Guaranteed sterile performance
- Filter made of natural materials
Correct Answer: Approximate efficiency for a given particle size
Q16. Which method is commonly used to sterilize air entering sterile product containers during filling?
- HEPA filtration in laminar flow hoods
- 0.45 μm membrane liquid filters
- Autoclaving of air
- Sonic irradiation
Correct Answer: HEPA filtration in laminar flow hoods
Q17. Which parameter is most critical when filtering viscous pharmaceutical solutions?
- Filter color
- Transmembrane pressure and flux to control fouling
- Ambient humidity only
- Filter manufacturer’s brand name
Correct Answer: Transmembrane pressure and flux to control fouling
Q18. A hydrophilic membrane is preferred for:
- Filtering aqueous solutions with good wettability
- Filtering nonpolar organic solvents only
- Air filtration in cleanrooms
- Gas sterilization vents
Correct Answer: Filtering aqueous solutions with good wettability
Q19. What is the main advantage of capsule filters over cartridge filters?
- They are always cheaper
- Smaller footprint and easier single-use implementation
- They never require integrity testing
- They have larger pore sizes
Correct Answer: Smaller footprint and easier single-use implementation
Q20. Which of the following is an indicator of filter fouling during a filtration run?
- Increased flow rate at constant pressure
- Decreased transmembrane pressure
- Progressive decline in flow rate at constant pressure
- Immediate color change of filtrate
Correct Answer: Progressive decline in flow rate at constant pressure
Q21. For sterile filtration of vaccines containing proteins, which membrane property is desirable?
- High protein binding
- Low protein adsorption
- Pore size >10 μm
- Hydrophobic surface for aqueous solutions
Correct Answer: Low protein adsorption
Q22. What is the typical validation organism for demonstrating retention by a sterilizing-grade filter during bacterial challenge tests?
- Escherichia coli
- Brevundimonas diminuta (formerly Pseudomonas diminuta)
- Saccharomyces cerevisiae
- Staphylococcus aureus
Correct Answer: Brevundimonas diminuta (formerly Pseudomonas diminuta)
Q23. Which filtration mode reduces cake formation by allowing tangential flow across the membrane?
- Dead-end filtration
- Tangential flow filtration
- Depth filtration only
- Gravity filtration
Correct Answer: Tangential flow filtration
Q24. Which gas filter property is essential to prevent liquid passage while allowing air flow?
- Hydrophobicity
- High thermal conductivity
- Electrical conductivity
- UV transmittance
Correct Answer: Hydrophobicity
Q25. What is a key reason to choose membrane filtration over chemical sterilization for parenteral solutions?
- Membrane filtration always kills viruses
- Chemical residues from chemical sterilants can be problematic; membrane filtration avoids residues
- Membrane filters are reusable indefinitely without validation
- Chemical sterilization is faster for all products
Correct Answer: Chemical residues from chemical sterilants can be problematic; membrane filtration avoids residues
Q26. Which of the following best describes an absolute filter rating?
- Filter will remove most particles smaller than the rating
- Filter has a defined retention efficiency (e.g., 99.9%) for a stated particle size
- Filter color standard
- Nominal designation only
Correct Answer: Filter has a defined retention efficiency (e.g., 99.9%) for a stated particle size
Q27. What is the purpose of a vent filter on a pharmaceutical container?
- To warm incoming gases
- To allow sterile venting of gases while preventing microbial ingress
- To increase pressure inside the container
- To remove dissolved gases from liquids
Correct Answer: To allow sterile venting of gases while preventing microbial ingress
Q28. Which of the following is NOT typically a mechanical sterilization method?
- Membrane filtration
- HEPA air filtration
- Autoclaving (steam under pressure)
- Depth filtration
Correct Answer: Autoclaving (steam under pressure)
Q29. What is a key quality parameter monitored during sterile filtration validation runs?
- Filter brand logo visibility
- Log reduction value of challenge organisms and integrity test results
- Ambient music in lab
- Color of the filter housing
Correct Answer: Log reduction value of challenge organisms and integrity test results
Q30. In a pull-through integrity test, what is typically measured?
- Retention of proteins by the filter
- Flow rate under applied pressure after wetting and drying
- Bubble point after wetting the membrane
- Electrical resistance of the filter
Correct Answer: Bubble point after wetting the membrane
Q31. Which filter fouling mechanism involves particles forming a cake layer on the membrane surface?
- Adsorptive fouling
- Pore constriction only
- Cake formation (surface fouling)
- Thermal denaturation
Correct Answer: Cake formation (surface fouling)
Q32. What is the recommended filter pore size for prefiltration to remove larger particulates before sterilizing-grade filtration?
- 0.1 μm
- 0.22 μm
- 0.45 μm
- 0.01 μm
Correct Answer: 0.45 μm
Q33. Which of the following is true about HEPA filters in cleanrooms?
- They are typically washable and reused indefinitely without replacement
- They provide high-efficiency removal of airborne particles and must be integrity tested periodically
- They are used to sterilize liquids
- They allow all bacteria to pass through
Correct Answer: They provide high-efficiency removal of airborne particles and must be integrity tested periodically
Q34. Which integrity test is most suitable for in-line testing of filters after use without removing wetting liquid?
- Bubble point test only
- Diffusion or forward flow test
- Chemical assay
- Visual inspection
Correct Answer: Diffusion or forward flow test
Q35. Why are sterilizing-grade filters validated using Brevundimonas diminuta?
- Because it is a very large bacterium easy to trap
- Because of its small size and high motility, making it a stringent challenge organism for 0.22 μm filters
- Because it is a virus
- Because it changes filter color during passage
Correct Answer: Because of its small size and high motility, making it a stringent challenge organism for 0.22 μm filters
Q36. Which component of a sterile filtration system helps minimize airborne contamination during sterile fill?
- Hydrophobic vent filters on containers
- Laminar flow hoods with HEPA-filtered air
- Depth filters downstream of the product
- Room temperature control only
Correct Answer: Laminar flow hoods with HEPA-filtered air
Q37. What is a common cause for failing a filter integrity test after filtration?
- Proper filter selection
- Physical damage to the membrane or improper installation
- Excessively low product viscosity
- Perfect operating conditions
Correct Answer: Physical damage to the membrane or improper installation
Q38. Which term describes the percentage of particles of a specific size removed by a filter?
- Permeability
- Retention efficiency
- Membrane thickness
- Viscosity index
Correct Answer: Retention efficiency
Q39. For gas filtration of sterilizing-grade air filters, which membrane pore size is typically used to prevent microbial ingress?
- 5 μm
- 0.22 μm or 0.2 μm hydrophobic membranes
- 10 μm
- 1 mm
Correct Answer: 0.22 μm or 0.2 μm hydrophobic membranes
Q40. Which cleaning method is typically mechanical but not a sterilization technique and is used prior to sterilization?
- Ultrasonic cleaning to remove debris
- Steam sterilization
- Gamma irradiation
- Chemical sporicidal treatment
Correct Answer: Ultrasonic cleaning to remove debris
Q41. What is the main risk when filtering biologics through a membrane with high adsorption properties?
- Increased sterility assurance
- Loss of product due to adsorption to the membrane
- Improved viral clearance
- Lower transmembrane pressure
Correct Answer: Loss of product due to adsorption to the membrane
Q42. Which filter integrity parameter is most influenced by the presence of air pockets or incomplete wetting?
- Bubble point which may be higher than expected
- Color of the filtrate
- Protein binding
- Ambient noise
Correct Answer: Bubble point which may be higher than expected
Q43. Viral removal by filtration typically requires:
- Standard 0.22 μm membrane only
- Specialized nanofiltration with much smaller pore sizes or affinity methods
- Only HEPA filters
- No validation is needed
Correct Answer: Specialized nanofiltration with much smaller pore sizes or affinity methods
Q44. Which factor does NOT significantly affect sterile filtration performance?
- Solution viscosity
- Particle load in the feed
- Filter pore size and chemistry
- Brand of laboratory coat worn
Correct Answer: Brand of laboratory coat worn
Q45. What is the acceptable practice after completing sterile filtration of a parenteral batch?
- Discard all integrity test records
- Perform and document post-use filter integrity testing before product release
- Assume sterility without testing
- Reuse the same filter for another batch without validation
Correct Answer: Perform and document post-use filter integrity testing before product release
Q46. Which membrane type is often avoided for alcohol-based solutions due to solvent incompatibility?
- PES (polyethersulfone)
- Cellulose acetate which may be sensitive to some solvents
- PTFE for hydrophobic gas filters
- Glass fiber for depth filtration
Correct Answer: Cellulose acetate which may be sensitive to some solvents
Q47. In sterile filtration, what does validation with a “bacterial challenge test” demonstrate?
- That the filter increases microbial growth
- That the filter can retain a specified organism under defined conditions
- Only the flow rate capability
- That the filter will stop viruses without additional methods
Correct Answer: That the filter can retain a specified organism under defined conditions
Q48. Which operational change will help reduce membrane fouling during a filtration run?
- Increasing transmembrane pressure indefinitely
- Implementing crossflow/tangential flow to sweep the membrane surface
- Using only dead-end filtration for all feeds
- Ignoring prefiltration
Correct Answer: Implementing crossflow/tangential flow to sweep the membrane surface
Q49. What is the primary purpose of HEPA filters in HVAC systems for pharmaceutical manufacturing areas?
- Temperature control
- Removal of airborne particulates to maintain cleanroom classifications
- Sterilization of liquids
- Increase humidity to prevent static
Correct Answer: Removal of airborne particulates to maintain cleanroom classifications
Q50. Which statement best describes “sterile filtration” in aseptic processing?
- Filtration that removes all chemicals from a solution
- Filtration using validated sterilizing-grade membranes combined with process controls and integrity testing to ensure product sterility
- Any filtration performed in a non-validated environment
- Use of a mesh screen to remove large debris only
Correct Answer: Filtration using validated sterilizing-grade membranes combined with process controls and integrity testing to ensure product sterility
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