Liquid sterilization techniques MCQs With Answer

Introduction: This collection of multiple-choice questions focuses on liquid sterilization techniques relevant to M.Pharm students studying Bioprocess Engineering and Technology. The quiz covers thermal methods (autoclaving, batch and continuous heat sterilization), membrane and depth filtration, chemical and radiation approaches, and essential validation concepts such as filter integrity testing and biological indicators. Questions are designed to deepen understanding of when to apply each technique, material compatibility, critical parameters (pore size, temperature, time, pressure), and routine quality controls used in pharmaceutical manufacturing. Each question includes a clear answer to aid learning and exam preparation, with emphasis on practical considerations and regulatory expectations for sterile liquid processing.

Q1. What is the most commonly accepted pore size for a sterilizing-grade membrane filter used for terminal filtration of aqueous pharmaceutical solutions?

• 0.45 micrometer
• 0.22 micrometer
• 0.1 micrometer
• 1.2 micrometer

Correct Answer: 0.22 micrometer

Q2. Which microorganism is typically used to challenge sterilizing-grade filters during bacterial retention validation?

• Escherichia coli
• Brevundimonas diminuta
• Staphylococcus aureus
• Pseudomonas aeruginosa

Correct Answer: Brevundimonas diminuta

Q3. Which integrity test determines the pressure at which a wetted membrane filter suddenly allows a large increase in gas flow (indicating pore displacement of liquid)?

• Diffusive flow test
• Forward flow test
• Bubble point test
• Microbial challenge test

Correct Answer: Bubble point test

Q4. Which membrane material is generally preferred for low protein-binding and pharmaceutical parenteral filtration?

• Cellulose acetate
• Polytetrafluoroethylene (PTFE)
• Polyethersulfone (PES)
• Nylon 6,6

Correct Answer: Polyethersulfone (PES)

Q5. For saturated steam sterilization of sealed aqueous pharmaceutical containers, what is the typical validated parameter at 121°C?

• 121°C for 3 minutes at atmospheric pressure
• 121°C for at least 15 minutes with adequate come-up time
• 121°C for 60 minutes with intermittent cooling
• 121°C for 1 minute under vacuum

Correct Answer: 121°C for at least 15 minutes with adequate come-up time

Q6. Which sterilization approach is most suitable for heat-sensitive biological products like many vaccines and certain antibiotics?

• Dry heat sterilization
• Steam autoclaving at 134°C
• Sterilizing-grade membrane filtration
• Boiling for 30 minutes

Correct Answer: Sterilizing-grade membrane filtration

Q7. What is the primary purpose of using depth filters upstream of a final sterile cartridge filter?

• To achieve final sterility without further filtration
• To remove dissolved salts
• To reduce turbidity and bioburden, protecting the final membrane
• To sterilize by heat retention

Correct Answer: To reduce turbidity and bioburden, protecting the final membrane

Q8. Which biological indicator organism is most commonly used to validate moist heat (steam) sterilization cycles?

• Bacillus subtilis
• Geobacillus stearothermophilus
• Clostridium botulinum
• Brevundimonas diminuta

Correct Answer: Geobacillus stearothermophilus

Q9. In bubble point testing, which property of the wetting liquid most directly affects the measured bubble point pressure for a given pore size?

• Viscosity of the liquid
• Surface tension of the liquid
• Dielectric constant of the liquid
• Color of the liquid

Correct Answer: Surface tension of the liquid

Q10. Which continuous thermal process is commonly used for large-volume liquid sterilization with short exposure times and is often applied in food but conceptually similar in pharma for certain products?

• Batch autoclaving
• High Temperature Short Time (HTST) treatment
• Dry heat tunnel
• Cold sterilization

Correct Answer: High Temperature Short Time (HTST) treatment

Q11. Which of the following is a major disadvantage of gamma irradiation for sterilizing liquid pharmaceutical products?

• It cannot penetrate plastic containers
• It often causes radiolysis and degradation of some drug molecules
• It is always slower than steam sterilization
• It leaves toxic residues in the liquid

Correct Answer: It often causes radiolysis and degradation of some drug molecules

Q12. What is the regulatory expectation for bacterial log reduction during sterilizing filtration validation using a suitable challenge organism?

• At least 1 log reduction
• At least 3 log reduction
• At least 7 log reduction or greater (commonly ≥7 log10)
• No specific log reduction is required

Correct Answer: At least 7 log reduction or greater (commonly ≥7 log10)

Q13. Which chemical is commonly used for in-place sterilization (SIP) of equipment and piping for aqueous pharmaceutical processes?

• Peracetic acid
• Sodium bicarbonate
• Methylene chloride
• Hydrofluoric acid

Correct Answer: Peracetic acid

Q14. Which filter type is most suitable for removal of particulate matter down to a micron range but not intended to provide sterility?

• Sterilizing 0.22 µm membrane filter
• Depth filter
• Ultrafiltration membrane with 10 kDa cutoff
• Nanofiltration membrane for salts

Correct Answer: Depth filter

Q15. During aseptic filtration, which practice is essential to minimize product contamination risk?

• Heating the filtrate to boiling after filtration
• Using pre-sterilized, validated filter housings and maintaining aseptic connections
• Using the largest possible pore size to maximize flow
• Adding antibiotics to the filtrate to kill residual microbes

Correct Answer: Using pre-sterilized, validated filter housings and maintaining aseptic connections

Q16. What does a forward flow integrity test primarily measure for a membrane filter?

• The chemical compatibility of the membrane
• The diffusive gas flow through wetted pores at low pressure
• The thermal resistance of the filter to steam
• The tensile strength of the cartridge housing

Correct Answer: The diffusive gas flow through wetted pores at low pressure

Q17. For sterilizing a heat-labile protein solution where membrane adsorption is a concern, which strategy can reduce protein loss during filtration?

• Use a hydrophobic PTFE membrane without pre-wetting
• Pre-condition the filter with a protein-containing buffer or add low concentration of compatible surfactant
• Increase flow rate to minimize residence time without changing membrane
• Use a pore size of 1.2 µm to reduce contact

Correct Answer: Pre-condition the filter with a protein-containing buffer or add low concentration of compatible surfactant

Q18. Which statement best describes sterilizing filtration for parenterals?

• It removes all viral particles and endotoxin by default
• It is effective for bacteria and particulates but may not remove all viruses or endotoxins unless specifically designed
• Any 0.45 µm filter qualifies as sterilizing-grade for parenterals
• Filtration always negates the need for aseptic manufacturing environments

Correct Answer: It is effective for bacteria and particulates but may not remove all viruses or endotoxins unless specifically designed

Q19. Which parameter is least relevant when selecting a membrane filter for organic solvent-based sterile solutions?

• Chemical compatibility of membrane with solvent
• Pore size appropriate for microbial retention
• Membrane color
• Adsorptive characteristics for active pharmaceutical ingredient

Correct Answer: Membrane color

Q20. What is a common validation indicator that a sterilization-in-place (SIP) steam cycle has achieved sterilizing conditions inside a process vessel?

• Presence of visible steam only
• Successful kill of biological indicators placed at hardest-to-sterilize locations
• Temperature probe reading at one convenient location only
• Short vent time after steam application

Correct Answer: Successful kill of biological indicators placed at hardest-to-sterilize locations

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