Sterility testing of liquids MCQs With Answer

Introduction:

Mastering Sterility testing of liquids MCQs With Answer is essential for B. Pharm students preparing for exams and practical work in sterile manufacturing. This concise SEO-friendly guide focuses on key concepts such as membrane filtration, direct inoculation, USP <71> requirements, media selection, incubation conditions, validation, and assessment of bacteriostasis/fungistasis during sterility testing. It emphasizes regulatory expectations, sampling, interpretation of results, and common pitfalls in aseptic processing to build exam-ready knowledge and practical confidence. Clear MCQs with answers will help reinforce learning and prepare you for academic and regulatory challenges. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary objective of sterility testing of pharmaceutical liquids?

• To determine the potency of the drug
• To detect viable microorganisms in the product
• To measure chemical impurities
• To assess physical stability

Correct Answer: To detect viable microorganisms in the product

Q2. Which USP chapter specifically outlines sterility testing procedures?

• USP <51>
• USP <61>
• USP <71>
• USP <85>

Correct Answer: USP <71>

Q3. Which sterility test method is most suitable for heat-sensitive liquid pharmaceuticals?

• Direct inoculation in growth media
• Membrane filtration
• Autoclave sterility test
• Dry heat sterilization test

Correct Answer: Membrane filtration

Q4. In membrane filtration sterility testing, what is the usual pore size of the filter used?

• 5.0 µm
• 0.45 µm
• 0.1 µm
• 10 µm

Correct Answer: 0.45 µm

Q5. Why is a bacteriostasis and fungistasis test performed during sterility testing?

• To check product color stability
• To ensure the product does not inhibit microbial growth in the test
• To measure pH changes
• To assess container integrity

Correct Answer: To ensure the product does not inhibit microbial growth in the test

Q6. What incubation conditions are typically used for sterility testing with Fluid Thioglycollate Medium (FTM)?

• 30–35°C for 14 days
• 20–25°C for 7 days
• 36–38°C for 3 days
• 4°C for 14 days

Correct Answer: 30–35°C for 14 days

Q7. Which medium is commonly used for detection of aerobic microorganisms during sterility testing?

• Fluid Thioglycollate Medium (FTM)
• Synthetic Urine Medium
• Soybean-Casein Digest Medium (SCDM or TSB)
• MacConkey Agar

Correct Answer: Soybean-Casein Digest Medium (SCDM or TSB)

Q8. For a sterility test sample, what is the minimum total volume recommended for membrane filtration when product volume allows?

• 10 mL
• 100 mL
• 1 mL
• 500 mL

Correct Answer: 100 mL

Q9. Direct inoculation sterility testing is most appropriate for which type of product?

• Large-volume parenterals where filtration is impractical
• Highly viscous solutions that cannot be filtered
• Products with known preservatives that may inhibit growth
• Both a and b

Correct Answer: Both a and b

Q10. What is the significance of using two different media (FTM and SCDM) in sterility testing?

• To reduce testing time
• To detect both anaerobic and aerobic/facultative microorganisms
• To provide redundancy for regulatory inspections only
• To test chemical stability

Correct Answer: To detect both anaerobic and aerobic/facultative microorganisms

Q11. When performing membrane filtration, why is a rinse with sterile diluent required after filtration?

• To dilute the product to a safe pH
• To remove residual product that may inhibit microbial recovery
• To sterilize the filter
• To dry the membrane

Correct Answer: To remove residual product that may inhibit microbial recovery

Q12. Which of the following is a critical quality attribute assessed during sterility testing validation?

• Color of the product
• Disintegration time
• Limit of detection for viable organisms
• Viscosity at 50°C

Correct Answer: Limit of detection for viable organisms

Q13. What is the typical incubation time for sterility test cultures according to common pharmacopeias?

• 3 days
• 7 days
• 14 days
• 28 days

Correct Answer: 14 days

Q14. Which environmental control is most important during sampling for sterility testing?

• Ambient humidity only
• Airborne particulate and viable monitoring in the clean area
• Room color scheme
• Worker comfort temperature

Correct Answer: Airborne particulate and viable monitoring in the clean area

Q15. In sterility testing, what does the term “incubation at 20–25°C” primarily detect?

• Obligate anaerobes
• Psychrophilic organisms only
• Fungi and some bacteria (environmental organisms)
• Viral contaminants

Correct Answer: Fungi and some bacteria (environmental organisms)

Q16. What is a false negative result in sterility testing most commonly caused by?

• High microbial load
• Product-induced inhibition of microbial growth
• Using two types of media
• Over-incubation

Correct Answer: Product-induced inhibition of microbial growth

Q17. Which control is used to ensure filter integrity after membrane filtration?

• Bubble point or pressure hold test
• Visual color check
• pH measurement of filtrate
• Weighing the filter

Correct Answer: Bubble point or pressure hold test

Q18. When validating a sterility test, which organism is commonly used as a biological indicator for bacteriostatic challenge?

• Saccharomyces cerevisiae
• Pseudomonas aeruginosa
• Bacillus subtilis
• Staphylococcus aureus

Correct Answer: Pseudomonas aeruginosa

Q19. Which problem in sterility testing can be identified by performing media growth promotion tests?

• Non-sterile filtration apparatus
• Invalid incubation temperatures
• Inadequate media support for target microorganisms
• Incorrect labeling of samples

Correct Answer: Inadequate media support for target microorganisms

Q20. What is the recommended action if turbidity appears in a sterility test culture during the holding period?

• Discard the sample immediately
• Record as a positive result and investigate cause
• Assume contamination of lab equipment only
• Repeat incubation at lower temperature

Correct Answer: Record as a positive result and investigate cause

Q21. Which of the following is not a valid reason for rejecting a sterility test result?

• Apparent contamination in the media control
• Failure of growth promotion test
• Proper incubation temperatures were maintained
• Evidence of aseptic breach during sampling

Correct Answer: Proper incubation temperatures were maintained

Q22. What is the role of neutralizers in sterility testing of preserved products?

• To enhance preservative activity
• To inactivate preservatives so microorganisms can grow in the test
• To sterilize the product
• To change the pH to growth-favorable range

Correct Answer: To inactivate preservatives so microorganisms can grow in the test

Q23. Which organism is typically used to validate detection of anaerobic bacteria in sterility testing?

• Clostridium sporogenes
• Escherichia coli
• Bacillus megaterium
• Micrococcus luteus

Correct Answer: Clostridium sporogenes

Q24. What is the purpose of using replicate testing or multiple sample units for sterility testing?

• To reduce the number of tests required
• To increase statistical confidence in detecting contamination
• To shorten incubation period
• To allow different incubation temperatures

Correct Answer: To increase statistical confidence in detecting contamination

Q25. Which of the following best describes a growth promotion test?

• Testing whether media can support growth of specified microorganisms
• Testing filter integrity
• Counting colony-forming units of environmental samples
• Measuring residual preservatives

Correct Answer: Testing whether media can support growth of specified microorganisms

Q26. What is an acceptable interpretation if one unit out of 20 tested shows growth in sterility testing of a sterile product?

• Product batch is automatically approved
• Batch must be investigated and considered contaminated until proven otherwise
• Ignore the result as sporadic
• Increase incubation time

Correct Answer: Batch must be investigated and considered contaminated until proven otherwise

Q27. Which documentation is crucial to demonstrate compliance for sterility testing?

• Standard operating procedures (SOPs), batch records, and test reports
• Only verbal operator confirmation
• Packaging artwork files
• Purchase invoices

Correct Answer: Standard operating procedures (SOPs), batch records, and test reports

Q28. In the context of sterility testing, what is “aseptic technique” primarily intended to prevent?

• Loss of active pharmaceutical ingredient
• Introduction of extrinsic microbial contaminants during handling
• Changes in product viscosity
• Evaporation of solvents

Correct Answer: Introduction of extrinsic microbial contaminants during handling

Q29. Which parameter is not directly assessed by sterility testing?

• Presence of viable microorganisms
• Endotoxin levels
• Filter integrity post-filtration
• Effectiveness of neutralizers

Correct Answer: Endotoxin levels

Q30. How should sterility test samples be stored before testing if immediate analysis is not possible?

• At any convenient temperature
• Under conditions that prevent microbial growth or loss of viability, as per protocols
• Exposed to sunlight
• At high temperature to accelerate testing

Correct Answer: Under conditions that prevent microbial growth or loss of viability, as per protocols

Q31. Which of the following is a limitation of direct inoculation sterility testing?

• It is always more sensitive than membrane filtration
• Product preservatives may inhibit recovery of microorganisms
• It requires specialized filters
• It cannot detect aerobic organisms

Correct Answer: Product preservatives may inhibit recovery of microorganisms

Q32. For sterility testing of large-volume parenterals, why is membrane filtration preferred when feasible?

• It reduces sample handling and increases microbial recovery
• It is faster than any other method
• No media are required
• It eliminates need for incubators

Correct Answer: It reduces sample handling and increases microbial recovery

Q33. What should be done if growth is observed in media control tubes used alongside sterility tests?

• Ignore and report sterility test as valid
• Invalidate the corresponding sterility test results and investigate contamination sources
• Proceed to release the batch
• Repeat only the media control

Correct Answer: Invalidate the corresponding sterility test results and investigate contamination sources

Q34. Which sterility testing step ensures that microorganisms trapped on the membrane are accessible to culture media?

• Pre-wetting the filter with alcohol
• Placing the membrane on appropriate agar or transferring to liquid media after filtration
• Heating the membrane
• Drying the membrane before incubation

Correct Answer: Placing the membrane on appropriate agar or transferring to liquid media after filtration

Q35. What is the main regulatory concern if a sterility test uses inadequate sample size?

• Reduced statistical confidence to detect contamination
• Increased cost of testing
• Slower detection of chemical degradation
• Overestimation of potency

Correct Answer: Reduced statistical confidence to detect contamination

Q36. Which practice helps prevent contamination during aseptic sampling for sterility testing?

• Perform sampling in uncontrolled area
• Use validated aseptic technique and appropriate cleanroom classification
• Open containers for extended periods
• Use non-sterile tools to speed up the process

Correct Answer: Use validated aseptic technique and appropriate cleanroom classification

Q37. During sterility testing validation, what does a “spike recovery” experiment evaluate?

• Ability to remove endotoxins
• Ability to recover a known number of microorganisms from the product matrix
• Filter tensile strength
• pH stability of the product

Correct Answer: Ability to recover a known number of microorganisms from the product matrix

Q38. Which factor must be demonstrated for preserved products before conducting sterility testing?

• That preservatives do not interfere with microbial detection (neutralization validated)
• That preservatives increase microbial growth
• That preservatives reduce active ingredient potency
• That preservatives evaporate during incubation

Correct Answer: That preservatives do not interfere with microbial detection (neutralization validated)

Q39. What is the recommended action if sterility test results are positive for environmental organisms consistent with a cleanroom breach?

• Release the batch after retesting unrelated samples
• Quarantine the batch, perform root cause investigation, and take corrective actions
• Ignore and continue production
• Change labels and distribute product

Correct Answer: Quarantine the batch, perform root cause investigation, and take corrective actions

Q40. Which record should show details of incubation temperature, duration, and observations during sterility testing?

• Purchasing ledger
• Sterility test logbook or electronic test record
• Payroll sheet
• Marketing brochure

Correct Answer: Sterility test logbook or electronic test record

Q41. How does the presence of particulate matter in a liquid sample affect membrane filtration sterility testing?

• It can clog the filter and reduce recovery of microorganisms
• It sterilizes the membrane
• It always enhances microbial growth
• It has no effect

Correct Answer: It can clog the filter and reduce recovery of microorganisms

Q42. What is an advantage of using pre-sterilized disposable filtration units for sterility testing?

• They require extensive cleaning between uses
• They reduce risk of cross-contamination and save validation time
• They are always less reliable than reusable units
• They increase the likelihood of false positives

Correct Answer: They reduce risk of cross-contamination and save validation time

Q43. Which type of contamination is least likely to be detected by routine sterility testing?

• Low-level chronic contamination below detection limit
• High-level bacterial contamination
• Fungal contamination visible after incubation
• Gross contamination visible on container

Correct Answer: Low-level chronic contamination below detection limit

Q44. Which procedural control is important when transferring membranes to growth media after filtration?

• Use non-sterile instruments to speed transfer
• Ensure aseptic transfer and minimal contact to prevent external contamination
• Expose membrane to open air for 10 minutes
• Use heated tweezers without validation

Correct Answer: Ensure aseptic transfer and minimal contact to prevent external contamination

Q45. When reporting sterility test results, which statement is correct for a negative result?

• “No growth observed after the specified incubation period”
• “Test not performed”
• “Growth observed in all media”
• “Product is sterile in all circumstances forever”

Correct Answer: “No growth observed after the specified incubation period”

Q46. What role does personnel training play in sterility testing outcomes?

• Minimal role; only equipment matters
• Critical role; improper technique can introduce contamination and invalidate results
• Only important for documentation
• No role if using automated systems

Correct Answer: Critical role; improper technique can introduce contamination and invalidate results

Q47. Which is a typical follow-up action when sterility test failure is confirmed?

• Immediate product distribution
• Batch recall or quarantine and full investigation including root cause and corrective actions
• Ignore the failure if only one unit failed among many
• Reduce incubation time for future tests

Correct Answer: Batch recall or quarantine and full investigation including root cause and corrective actions

Q48. Which of the following best describes “sample aseptic transfer”?

• Transfer of samples without any sterility precautions
• Controlled, validated movement of test samples under aseptic conditions to prevent contamination
• Shipping samples at room temperature
• Labeling samples after analysis

Correct Answer: Controlled, validated movement of test samples under aseptic conditions to prevent contamination

Q49. What is an important consideration when selecting sterility test media for a highly colored liquid?

• Color will always sterilize the media
• Colored products may mask turbidity; use subculture and visual checks or membrane filtration to ensure detection
• Color has no effect on interpretation
• Only use direct inoculation

Correct Answer: Colored products may mask turbidity; use subculture and visual checks or membrane filtration to ensure detection

Q50. Which quality system element is essential to ensure continuous reliability of sterility testing results?

• Random undocumented practices
• Robust QA oversight, routine equipment calibration, validated methods, and trending of results
• Only annual inspections
• Ignoring deviations unless serious

Correct Answer: Robust QA oversight, routine equipment calibration, validated methods, and trending of results

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com