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Top sterility test interview questions with clear answers. Learn methods, media, incubation period, regulations, and troubleshooting in pharmaceuticals.
Sterility Test: Top 20+ Interview Questions and Answers
Sterility Test: Top 20+ Interview Questions and Answers 2
Sterility testing is a critical quality control requirement in the pharmaceutical, biotechnology, and medical device industries. Below are commonly asked sterility test interview questions with clear, professional answers.
1. What is a sterility test?
A sterility test is a microbiological examination performed to verify that pharmaceutical products, medical devices, or biologics are free from viable microorganisms, including bacteria and fungi.
Sterility testing is mandatory for products intended for parenteral administration, ophthalmic use, implants, and sterile surgical devices.
These tests are performed under aseptic conditions and incubated for 14 days to detect microbial growth.
2. Why is sterility testing important in pharmaceutical manufacturing?
Sterility testing ensures:
Patient safety
Regulatory compliance
Product quality and efficacy
Prevention of infections and adverse reactions
Contaminated sterile products can cause severe infections, sepsis, or death, making sterility testing a critical GMP requirement.
3. What are the methods used in sterility testing?
a) Direct Inoculation Method
Product is directly inoculated into:
Tryptic Soy Broth (TSB) – aerobic organisms
Fluid Thioglycollate Medium (FTM) – anaerobic organisms
Incubated for 14 days
b) Membrane Filtration Method
Product is filtered through a 0.45 µm or 0.22 µm membrane
Filter is incubated in culture media
Preferred for large-volume or antimicrobial products
4. What culture media are used in sterility testing?
Medium
Purpose
Tryptic Soy Broth (TSB)
Detects aerobic bacteria and fungi
Fluid Thioglycollate Medium (FTM)
Detects anaerobic bacteria
These media support broad-spectrum microbial growth.
5. Why is the incubation period 14 days?
The 14-day incubation period allows detection of:
Slow-growing bacteria
Fungi
Low-level contamination
This duration complies with USP <71>, EP, and IP standards.
6. At what temperatures are sterility tests incubated?
FTM: 30–35°C (Anaerobic bacteria)
TSB: 20–25°C (Aerobic bacteria and fungi)
7. What is the difference between sterility testing and microbial limit testing?
Sterility Test
Microbial Limit Test
Detects absence of microorganisms
Measures acceptable microbial count
Required for sterile products
Used for non-sterile products
Qualitative test
Quantitative test
8. How do you differentiate contamination from a true positive sterility result?
Review aseptic technique
Check environmental monitoring data
Examine media sterility controls
Perform root cause analysis
A confirmed positive result indicates product contamination, not laboratory error.
9. What steps do you take if sterility test contamination occurs?
Quarantine the batch
Investigate the testing procedure
Review environmental monitoring
Perform root cause analysis
Implement CAPA
Retest or reject the batch
10. How do you maintain aseptic conditions during sterility testing?
Laminar airflow workstation
Sterile instruments and media
Proper gowning and PPE
Surface and equipment disinfection
Controlled cleanroom environment
11. What are biological indicators in sterility testing?
Biological indicators are standardized microorganisms (e.g., Bacillus spores) used to:
Validate sterilization processes
Confirm effectiveness of autoclaving, dry heat, or irradiation
12. What regulatory guidelines govern sterility testing?
USP <71>
European Pharmacopoeia (EP)
Indian Pharmacopoeia (IP)
WHO GMP
FDA & EMA Guidelines
13. What is a media growth promotion test (GPT)?
GPT confirms that culture media:
Supports microbial growth
Is suitable for sterility testing
Is tested using a low-level inoculum
14. What organisms are used for growth promotion testing?
Staphylococcus aureus
Pseudomonas aeruginosa
Candida albicans
Clostridium sporogenes
Aspergillus brasiliensis
15. What is a false positive sterility test result?
A false positive occurs when:
The product appears contaminated
Actual contamination is due to a testing error
Causes include poor aseptic technique or environmental contamination
16. What is environmental monitoring in sterility testing?
Environmental monitoring ensures:
Cleanroom compliance
Control of airborne and surface microorganisms
Includes air sampling, settle plates, contact plates
17. Can sterility testing guarantee product sterility?
No. Sterility testing:
It is a probabilistic test
Confirms absence of detectable microorganisms
Must be supported by validated sterilisation processes
18. How are sterility test results documented?
Sample details and batch number
Test method and media
Incubation conditions
Observations and final results
Deviations and CAPA (if any)
Compliance with GDP
19. What action is taken when a sterility test is negative?
Review documentation
Confirm compliance with SOPs
Approve batch for release
Notify QA/QC departments
20. What is the role of QA in sterility testing?
Quality Assurance ensures:
SOP compliance
Data integrity
Investigation of failures
Regulatory readiness
Conclusion
Sterility testing is a critical quality control tool that ensures the safety of pharmaceuticals and medical devices. Understanding its principles, methods, regulations, and troubleshooting steps is essential for QC Microbiologists, QA professionals, and pharmaceutical interview candidates.
