Sterility testing of solids MCQs With Answer provides B.Pharm students a focused, exam-ready overview of sterility testing principles for solid dosage forms. This introduction covers key concepts like pharmacopeial standards (USP & EP), membrane filtration and direct inoculation methods, sample extraction for solids, growth promotion and validation, incubation conditions, neutralization of preservatives, and common sterilization techniques. Carefully designed to boost understanding of pharmaceutical quality control, aseptic processing, bioburden vs sterility, and troubleshooting, these MCQs help reinforce practical and theoretical knowledge. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary objective of sterility testing for solid dosage forms?
- To determine chemical stability of the active ingredient
- To detect the presence of viable microorganisms in the product
- To measure dissolution rate of the solid
- To quantify endotoxin levels
Correct Answer: To detect the presence of viable microorganisms in the product
Q2. Which official pharmacopeial chapter primarily describes sterility test methods in the United States?
- USP <71>
- USP <61>
- EP 5.1
- BP 3.2
Correct Answer: USP <71>
Q3. What are the two main sterility test methods recommended for pharmaceutical products?
- Membrane filtration and direct inoculation
- Plate count and Most Probable Number
- PCR and ELISA
- Gram stain and acid-fast stain
Correct Answer: Membrane filtration and direct inoculation
Q4. Which two media are commonly used in sterility testing to cover a broad range of microorganisms?
- Buffered peptone water and MacConkey broth
- Fluid thioglycollate medium and tryptic soy broth (or soybean-casein digest)
- Nutrient agar and Sabouraud dextrose agar
- McFarland broth and Mueller-Hinton broth
Correct Answer: Fluid thioglycollate medium and tryptic soy broth (or soybean-casein digest)
Q5. What is the standard incubation period for a sterility test according to pharmacopeial guidance?
- 48 hours
- 7 days
- 14 days
- 30 days
Correct Answer: 14 days
Q6. At which temperatures are sterility test media typically incubated to detect a wide range of organisms?
- 4°C and 37°C
- 30–35°C for fluid thioglycollate and 20–25°C for soybean-casein digest
- 50–55°C for heat-resistant spores
- 15–20°C for psychrophiles only
Correct Answer: 30–35°C for fluid thioglycollate and 20–25°C for soybean-casein digest
Q7. What is the purpose of a growth promotion (suitability) test in sterility testing?
- To sterilize the media before use
- To confirm that the media will support growth of target organisms and detect inhibition
- To measure the turbidity caused by non-microbial particles
- To determine endotoxin levels in media
Correct Answer: To confirm that the media will support growth of target organisms and detect inhibition
Q8. Why is membrane filtration often chosen for products that contain antimicrobial preservatives?
- Because filtration sterilizes the product
- Because it separates microorganisms from inhibitors before incubation
- Because it removes endotoxins
- Because it concentrates viruses
Correct Answer: Because it separates microorganisms from inhibitors before incubation
Q9. For solid dosage forms, what is a common pre-treatment step before performing sterility testing?
- Direct plating of whole tablet without manipulation
- Grinding or dissolving and extracting into a sterile diluent
- Heating to 121°C for 15 minutes
- Lyophilizing to dryness
Correct Answer: Grinding or dissolving and extracting into a sterile diluent
Q10. What does a false-negative result in a sterility test indicate?
- The test correctly identified that no microbes are present
- Microorganisms were present but the test failed to detect them
- The media was contaminated during incubation
- A non-viable organism produced visible growth
Correct Answer: Microorganisms were present but the test failed to detect them
Q11. What is the role of a positive control in sterility testing?
- To ensure containers are sterile
- To demonstrate that the test system can detect microbial growth using known organisms
- To neutralize preservatives in samples
- To measure filtration efficiency
Correct Answer: To demonstrate that the test system can detect microbial growth using known organisms
Q12. What does a negative control (sterility control) confirm during sterility testing?
- That the product contains antimicrobial agents
- That the testing environment and media are not contaminated
- That the incubators are at the correct temperature
- That the membrane filter pore size is correct
Correct Answer: That the testing environment and media are not contaminated
Q13. Which of the following factors is a common cause of false-positive sterility test results?
- Use of sterile diluent
- Contamination introduced during sample handling
- Adding neutralizers to the sample
- Using validated media
Correct Answer: Contamination introduced during sample handling
Q14. Sterility testing detects which type of contaminants in a product?
- Only chemical impurities
- Viable microorganisms such as bacteria and fungi
- Only endotoxins
- All viruses and prions
Correct Answer: Viable microorganisms such as bacteria and fungi
Q15. How does bioburden differ from sterility?
- Bioburden measures non-viable particles, sterility measures viable organisms
- Bioburden is the total viable microbial count before sterilization; sterility is absence of viable organisms after sterilization
- They are identical terms
- Sterility is quantitative while bioburden is qualitative
Correct Answer: Bioburden is the total viable microbial count before sterilization; sterility is absence of viable organisms after sterilization
Q16. What does the Sterility Assurance Level (SAL) 10^-6 represent?
- A six-log reduction in impurities
- A probability of one non-sterile unit in one million sterilized units
- The incubation temperature in °C
- The pore size of sterilizing filters
Correct Answer: A probability of one non-sterile unit in one million sterilized units
Q17. Which sterilization methods are commonly used for solid dosage forms or solid medical devices?
- Gamma irradiation, dry heat, and ethylene oxide
- Chlorination and ozonation
- Microfiltration and ultrafiltration
- Lyophilization and sonication
Correct Answer: Gamma irradiation, dry heat, and ethylene oxide
Q18. What is the purpose of a bubble point or integrity test for sterilizing filters?
- To measure media sterility
- To verify the physical integrity and performance of the filter before use
- To quantify endotoxin adsorption
- To determine the filter’s chemical compatibility
Correct Answer: To verify the physical integrity and performance of the filter before use
Q19. What pore size is generally considered sterilizing-grade for membrane filters used during aseptic processing?
- 5.0 µm
- 0.45 µm
- 0.22 µm
- 1.2 µm
Correct Answer: 0.22 µm
Q20. Why are neutralizers added to sterility test sample preparations for certain products?
- To change the color of the medium for visual inspection
- To inactivate antimicrobial preservatives that could inhibit microbial growth during testing
- To increase incubation temperature stability
- To add nutrients for faster growth
Correct Answer: To inactivate antimicrobial preservatives that could inhibit microbial growth during testing
Q21. What is the acceptance criterion for a pharmacopeial sterility test?
- No growth observed in any test vessel during the incubation period
- Less than 100 CFU per mL
- At least one vessel must show growth
- Absence of Pseudomonas aeruginosa only
Correct Answer: No growth observed in any test vessel during the incubation period
Q22. Which organisms are commonly used in growth promotion tests for sterility media?
- Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Candida albicans
- Mycobacterium tuberculosis and Hepatitis virus
- Only environmental Bacillus isolates
- Clostridium botulinum and poliovirus
Correct Answer: Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Candida albicans
Q23. Fluid thioglycollate medium (FTM) is particularly useful for detecting which type of organisms?
- Obligate aerobic bacteria only
- Anaerobic and microaerophilic bacteria
- Viruses and prions
- Only fungi
Correct Answer: Anaerobic and microaerophilic bacteria
Q24. What is the main advantage of using membrane filtration for sterility testing of solids after extraction?
- It sterilizes the sample
- It concentrates any microorganisms onto a filter for better detection
- It removes endotoxins
- It shortens incubation time to 24 hours
Correct Answer: It concentrates any microorganisms onto a filter for better detection
Q25. What is the function of validated neutralizing agents in sterility test sample preparations?
- To accelerate microbial growth
- To inactivate residual disinfectants or preservatives without harming microbes
- To sterilize the sample before testing
- To change the pH beyond microbial growth limits
Correct Answer: To inactivate residual disinfectants or preservatives without harming microbes
Q26. Why are sterility tests incubated at two different temperature ranges?
- To save incubator space
- To detect organisms with different temperature growth optima (mesophiles and fungi)
- To intentionally inhibit bacterial growth
- To test refrigerated stability
Correct Answer: To detect organisms with different temperature growth optima (mesophiles and fungi)
Q27. In sterilization validation, what does the D-value represent?
- The time required to reduce the microbial population by 90% at a specific temperature
- The dosage of gamma irradiation in Grays
- The diameter of microbial colonies
- The diffusion coefficient of sterilant gas
Correct Answer: The time required to reduce the microbial population by 90% at a specific temperature
Q28. What is the Z-value in thermal sterilization terminology?
- The pH at which a microorganism grows fastest
- The temperature change required to change the D-value by one log (tenfold)
- The number of survivors after sterilization
- The depth of product penetration by heat
Correct Answer: The temperature change required to change the D-value by one log (tenfold)
Q29. Which of the following tests is not part of a sterility test but is a separate microbiological quality control test?
- Direct inoculation sterility test
- Total aerobic microbial count (TAMC) / microbial limit test
- Membrane filtration sterility test
- Growth promotion test
Correct Answer: Total aerobic microbial count (TAMC) / microbial limit test
Q30. Which solid dosage forms are most likely to require sterility assurance?
- Oral immediate-release tablets for systemic use only
- Ophthalmic powders, surgical implants, and sterile granules for reconstitution
- Chewable vitamins
- Enteric-coated tablets for stomach protection
Correct Answer: Ophthalmic powders, surgical implants, and sterile granules for reconstitution
Q31. When producing a sterile solid product by terminal sterilization, what pre-sterilization test is most relevant?
- Stability testing under light
- Bioburden testing to quantify viable microorganisms before sterilization
- Viscosity measurement
- Dissolution profiling
Correct Answer: Bioburden testing to quantify viable microorganisms before sterilization
Q32. How can residual antimicrobial preservatives in a solid sample affect the sterility test?
- They have no effect on sterility testing
- They can inhibit microbial growth and produce false-negative results unless neutralized
- They always enhance microbial growth
- They convert bacteria to spores
Correct Answer: They can inhibit microbial growth and produce false-negative results unless neutralized
Q33. Which step is critical to ensure representative sterility testing of a batch of solid product?
- Testing only the largest tablets in the batch
- Proper sampling from different containers or batches following a sampling plan
- Always testing after 30 days of storage
- Only testing the first and last units produced
Correct Answer: Proper sampling from different containers or batches following a sampling plan
Q34. Which of the following observations during incubation indicates microbial growth in sterility test vessels?
- Clarity of medium remains unchanged
- Turbidity, pellet formation, or surface films in the medium
- Colorless filter with no change
- No odor change
Correct Answer: Turbidity, pellet formation, or surface films in the medium
Q35. Why are spore-forming environmental organisms like Bacillus spp. important in sterility assurance?
- They are non-viable and harmless
- They can survive harsh conditions and indicate inadequate sterilization or environmental control
- They only grow at cold temperatures
- They are used as indicators for viral contamination
Correct Answer: They can survive harsh conditions and indicate inadequate sterilization or environmental control
Q36. In membrane filtration sterility testing, why is the filter rinsed after sample passage?
- To remove detached microorganisms from the filter
- To remove residual product and neutralize antimicrobials that may remain on the filter
- To sterilize the filter for reuse
- To add nutrients to the filter
Correct Answer: To remove residual product and neutralize antimicrobials that may remain on the filter
Q37. Are sterility tests suitable for detecting viruses in pharmaceutical products?
- Yes, sterility tests reliably detect viruses
- No, sterility tests are designed for bacteria and fungi; viral detection requires specific virology methods
- Only if incubated for 60 days
- Only if additional antibiotics are added
Correct Answer: No, sterility tests are designed for bacteria and fungi; viral detection requires specific virology methods
Q38. Which quality assurance practice complements sterility testing to ensure product safety?
- Environmental monitoring of cleanrooms and aseptic areas
- Only chemical purity testing
- Measuring tablet hardness
- Visual inspection of printed labels
Correct Answer: Environmental monitoring of cleanrooms and aseptic areas
Q39. What does turbidity in a sterility test vessel most likely indicate?
- Sterile product
- Microbial growth
- Presence of inorganic salts only
- Expired media that cannot support growth
Correct Answer: Microbial growth
Q40. Which of the following best describes why sterility testing is qualitative rather than quantitative?
- It measures exact colony counts
- It is designed to demonstrate absence or presence of viable microorganisms, not to quantify their number
- It detects chemical impurities
- It provides the exact species identity of contaminants
Correct Answer: It is designed to demonstrate absence or presence of viable microorganisms, not to quantify their number
Q41. If sterility test vessels show growth, what is the typical immediate regulatory interpretation?
- Batch is non-sterile and potentially subject to rejection or investigation
- Batch is automatically approved
- Results are ignored for solid products
- Batch is re-tested without investigation
Correct Answer: Batch is non-sterile and potentially subject to rejection or investigation
Q42. How can antibiotics or other antimicrobial residues in a sample be managed during sterility testing?
- By heating the sample to 100°C for 1 minute
- By using validated neutralizers and appropriate sample preparation to eliminate inhibitory effects
- By diluting the medium only
- By adding more antibiotics to counteract residues
Correct Answer: By using validated neutralizers and appropriate sample preparation to eliminate inhibitory effects
Q43. What sample preparation step may be necessary for coated tablets before sterility testing?
- Coating the tablet again
- Grinding or removing the coating and extracting into sterile diluent
- Soaking in oil for one week
- Autoclaving the intact tablet
Correct Answer: Grinding or removing the coating and extracting into sterile diluent
Q44. Is the sterility test quantitative or qualitative, and why does this matter for solid dosage forms?
- Quantitative; because it gives exact CFU counts for solids
- Qualitative; because it determines presence or absence of viable organisms, which is critical for sterility assurance of solids intended to be sterile
- Quantitative; because it measures endotoxin levels
- Qualitative; because solids cannot be tested at all
Correct Answer: Qualitative; because it determines presence or absence of viable organisms, which is critical for sterility assurance of solids intended to be sterile
Q45. Which European Pharmacopeia chapter corresponds to sterility testing?
- EP 2.6.1
- EP 5.1
- EP 1.2.3
- EP 7.0
Correct Answer: EP 2.6.1
Q46. What is the primary reason for employing aseptic technique during sterility testing?
- To accelerate colony formation
- To prevent introduction of contaminants and ensure test integrity
- To increase incubation temperature
- To enhance chemical stability of the sample
Correct Answer: To prevent introduction of contaminants and ensure test integrity
Q47. Under which circumstances is direct inoculation preferred over membrane filtration for sterility testing?
- When the product is filterable and contains no antimicrobial activity
- When the sample volume is small and the product does not interfere with the test
- When the sample contains high levels of particulate matter
- When viral detection is required
Correct Answer: When the sample volume is small and the product does not interfere with the test
Q48. For detecting fungal contaminants in sterility testing, which incubation temperature range is most appropriate?
- 30–35°C
- 20–25°C
- 0–5°C
- 45–50°C
Correct Answer: 20–25°C
Q49. How many different media types are standardly used together in pharmacopeial sterility testing to increase detection breadth?
- One
- Two
- Three
- Four
Correct Answer: Two
Q50. Which organisms are typically included to demonstrate growth promotion for tryptic soy broth/soybean-casein digest medium?
- Only environmental mold isolates
- Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Candida albicans
- Mycoplasma species and viruses
- Only Clostridium species
Correct Answer: Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Candida albicans
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