Assessment of microbial contamination MCQs With Answer

Assessment of microbial contamination MCQs With Answer is an essential study resource for B.Pharm students preparing for exams and practicals in pharmaceutical microbiology. This concise, keyword-rich introduction covers microbial contamination assessment, bioburden testing, sterility testing, environmental monitoring, endotoxin limits, aseptic processing, and validation principles used in QA/QC and GMP. These MCQs focus on methods like plate counts, membrane filtration, MPN, ATP bioluminescence, air and surface sampling, and regulatory expectations from pharmacopeias and ISO standards. Each question is designed to deepen understanding of contamination control, risk assessment, and laboratory techniques critical to pharmaceutical manufacturing. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the best definition of microbial contamination in pharmaceuticals?

Presence of any chemical impurities in a drug product
Presence of unwanted microorganisms in a drug product or process environment
Intentional addition of probiotics to formulations
Physical damage to packaging materials

Correct Answer: Presence of unwanted microorganisms in a drug product or process environment

Q2. What is the purpose of a bioburden test?

To measure endotoxin levels in a sterile product
To determine the number of viable microorganisms present before sterilization
To check chemical potency of an antibiotic
To detect viral contaminants only

Correct Answer: To determine the number of viable microorganisms present before sterilization

Q3. Which methods are commonly accepted for pharmacopeial sterility testing?

Gram staining and microscopy
Membrane filtration and direct inoculation (direct transfer) into culture media
ATP bioluminescence only
Polymerase chain reaction (PCR) only

Correct Answer: Membrane filtration and direct inoculation (direct transfer) into culture media

Q4. What is the commonly required sterility assurance level (SAL) for terminally sterilized parenterals?

10^0
10^-3
10^-6
10^-9

Correct Answer: 10^-6

Q5. Which assay is most widely used for bacterial endotoxin testing?

Western blot
Limulus Amebocyte Lysate (LAL) assay
Gram staining
ELISA for proteins

Correct Answer: Limulus Amebocyte Lysate (LAL) assay

Q6. Which air sampling technique actively draws a known volume of air to quantify airborne microorganisms?

Settle plate (passive) method
Contact plate method
Volumetric (active) air sampling
Surface swabbing

Correct Answer: Volumetric (active) air sampling

Q7. What is the primary advantage of membrane filtration for sterility testing of bulk liquids?

It removes endotoxins completely
It concentrates microorganisms from large volumes onto a membrane for incubation
It measures viral particles accurately
It sterilizes the product during testing

Correct Answer: It concentrates microorganisms from large volumes onto a membrane for incubation

Q8. Which method is suitable for rapid, non-culture detection of viable microorganisms by measuring cellular ATP?

MPN (Most Probable Number)
ATP bioluminescence
Gram staining
Endotoxin LAL test

Correct Answer: ATP bioluminescence

Q9. What does CFU stand for in microbial contamination assessment?

Colony Forming Unit
Cell Formation Unit
Contaminant Fungal Unit
Certified Fungal Understanding

Correct Answer: Colony Forming Unit

Q10. Which of the following is a quantitative method to estimate low levels of bacteria in water using statistical probability?

Direct microscopy
Most Probable Number (MPN)
Settle plate
Gram staining

Correct Answer: Most Probable Number (MPN)

Q11. Which environmental monitoring sample is best for assessing viable organisms on personnel gloves?

Air volumetric sampling
Contact plate (RODAC) method
Settle plate exposed to air
Surface conductivity test

Correct Answer: Contact plate (RODAC) method

Q12. Which medium is commonly used for total aerobic bacterial counts in pharmaceutical QC?

Sabouraud dextrose agar
Nutrient agar or tryptic soy agar
MacConkey agar
Thiosulfate-citrate-bile salts-sucrose (TCBS) agar

Correct Answer: Nutrient agar or tryptic soy agar

Q13. For fungal counts in environmental monitoring, which incubation temperature is typically used?

37°C
20–25°C
50°C
4°C

Correct Answer: 20–25°C

Q14. What is the role of a negative control in sterility testing?

To show the media supports growth
To demonstrate absence of contamination from the test procedure
To add known bacteria to the test
To neutralize disinfectant residues

Correct Answer: To demonstrate absence of contamination from the test procedure

Q15. Which organism is commonly used as a biological indicator for steam (moist heat) sterilization validation?

Bacillus stearothermophilus (Geobacillus stearothermophilus)
Bacillus subtilis var. niger
Staphylococcus aureus
Escherichia coli

Correct Answer: Bacillus stearothermophilus (Geobacillus stearothermophilus)

Q16. Which parameter indicates thermal resistance of microorganisms and is defined as the time required at a given temperature to reduce population by 90%?

Z-value
D-value
F0 value
SAL

Correct Answer: D-value

Q17. What does the Z-value represent in sterilization kinetics?

Time to achieve sterility at a given temperature
Temperature change required to change the D-value by one log
Initial microbial load
Sterility assurance level

Correct Answer: Temperature change required to change the D-value by one log

Q18. Which of the following is a common indicator organism for assessing water quality in pharmaceutical processes?

Pseudomonas aeruginosa
Streptococcus pneumoniae
Clostridium botulinum
Influenza virus

Correct Answer: Pseudomonas aeruginosa

Q19. Which cleaning validation parameter specifically measures removal of microbial contamination?

pH of rinse solution
Microbial bioburden before and after cleaning
Total organic carbon only
Visual inspection score

Correct Answer: Microbial bioburden before and after cleaning

Q20. What is the primary risk associated with fungal contamination in sterile manufacturing?

Only aesthetic defects
Allergenic or invasive infections and compromised product quality
Reduced drug potency by chemical reaction
Increased viscosity of solutions

Correct Answer: Allergenic or invasive infections and compromised product quality

Q21. Which test is used to detect mycoplasma contamination in cell cultures and some biologicals?

Gram staining
Culture on specialized media and PCR-based assays
LAL test
Endospore staining

Correct Answer: Culture on specialized media and PCR-based assays

Q22. Which of the following best describes a settle plate method?

An active air sampler that counts particles electronically
A passive method where plates are exposed to air to capture settling particles
A surface swab technique
A membrane filtration of air

Correct Answer: A passive method where plates are exposed to air to capture settling particles

Q23. In microbial limits testing, what is the purpose of inhibition testing?

To determine the presence of viruses
To check whether product components inhibit microbial growth, interfering with detection
To measure endotoxin content
To test for chemical impurities

Correct Answer: To check whether product components inhibit microbial growth, interfering with detection

Q24. Which disinfectant characteristic is most critical for routine pharmaceutical environmental control?

Color of the disinfectant
Broad-spectrum efficacy and validated contact time
Ability to act as a preservative in formulations
Smell

Correct Answer: Broad-spectrum efficacy and validated contact time

Q25. What is the main objective of environmental monitoring in sterile areas?

To ensure lights are functioning
To monitor trends in viable and non-viable contamination and ensure aseptic conditions
To assess chemical purity of air
To measure humidity only

Correct Answer: To monitor trends in viable and non-viable contamination and ensure aseptic conditions

Q26. Which organism is typically used as a biological indicator for dry heat sterilization?

Geobacillus stearothermophilus
Bacillus atrophaeus (formerly Bacillus subtilis var. niger)
Escherichia coli
Saccharomyces cerevisiae

Correct Answer: Bacillus atrophaeus (formerly Bacillus subtilis var. niger)

Q27. Which parameter is critical when validating filtration sterilization (sterile filtration) of a liquid?

Filter pore size (e.g., 0.22 µm) and integrity testing
pH of the filtrate only
Color of the filter
Atmospheric pressure in the lab

Correct Answer: Filter pore size (e.g., 0.22 µm) and integrity testing

Q28. What is the significance of incubation conditions in microbial enumeration tests?

They only affect fungal growth
Temperature and time determine which organisms will grow and be detected
They sterilize the plates
They are only needed for endotoxin tests

Correct Answer: Temperature and time determine which organisms will grow and be detected

Q29. Which selective medium is commonly used to isolate Gram-negative enteric pathogens?

Blood agar
MacConkey agar
SDA (Sabouraud Dextrose Agar)
YGC agar

Correct Answer: MacConkey agar

Q30. In a microbial limits test, which outcome would indicate the product passes specification?

Total viable count exceeds specified limit
No specified objectionable organisms and counts within allowed limits
Presence of Pseudomonas aeruginosa
Growth in sterility test controls

Correct Answer: No specified objectionable organisms and counts within allowed limits

Q31. Which factor most influences recovery of microorganisms from surface swabs?

Swab material and neutralizer, sampling technique, and contact pressure
Color of the swab
Time of day only
Humidity only

Correct Answer: Swab material and neutralizer, sampling technique, and contact pressure

Q32. What is an objectionable organism in pharmaceutical microbiology?

An organism with no clinical relevance
An organism whose presence may cause harm or affect product safety or efficacy
A beneficial probiotic
An organism used as a biological indicator

Correct Answer: An organism whose presence may cause harm or affect product safety or efficacy

Q33. Which regulation or guidance commonly defines microbial limits and sterility requirements for pharmaceuticals?

Pharmacopeias (USP, Ph. Eur., IP) and regulatory guidance (FDA, EMA)
Local school laboratory manual only
ISO 9001 exclusively
Food recipes

Correct Answer: Pharmacopeias (USP, Ph. Eur., IP) and regulatory guidance (FDA, EMA)

Q34. Why is neutralization of disinfectant residues important when sampling surfaces for microbiological testing?

Neutralizers accelerate microbial growth
To prevent residual disinfectant from killing microbes and giving false low counts
To change the swab color
Neutralizers are not required

Correct Answer: To prevent residual disinfectant from killing microbes and giving false low counts

Q35. Which rapid method can identify organisms by analyzing biochemical or mass spectral fingerprints?

Gram staining
MALDI-TOF mass spectrometry
Settle plate
MPN

Correct Answer: MALDI-TOF mass spectrometry

Q36. What is the principle of the membrane filtration technique for microbial enumeration?

Dilution until no growth is visible
Filtering a known volume through a membrane that retains microorganisms, then incubating the membrane on agar
Counting particles with a microscope without culture
Using PCR to quantify DNA

Correct Answer: Filtering a known volume through a membrane that retains microorganisms, then incubating the membrane on agar

Q37. Which practice reduces risk of contamination during aseptic operations?

Loose gowning and frequent face touching
Proper aseptic technique, validated procedures, and appropriate gowning
Working faster regardless of technique
Eating near the work area

Correct Answer: Proper aseptic technique, validated procedures, and appropriate gowning

Q38. What is the main limitation of culture-based environmental monitoring?

It detects viruses well
It may not detect viable but non-culturable organisms and is time-consuming
It provides instant results
It requires no incubation

Correct Answer: It may not detect viable but non-culturable organisms and is time-consuming

Q39. In sterility testing, why are both aerobic and anaerobic media used?

To increase incubation cost
To detect organisms that grow under different oxygen conditions
Because media color varies
To speed up results

Correct Answer: To detect organisms that grow under different oxygen conditions

Q40. Which action is recommended when an environmental monitoring alert or excursion occurs?

Ignore a single high count
Investigate root cause, review operations, and implement corrective actions
Immediately stop all production permanently
Replace monitoring equipment only

Correct Answer: Investigate root cause, review operations, and implement corrective actions

Q41. What does RODAC stand for in surface monitoring?

Reduction of Organisms by Direct Aseptic Contact
Replicate Organism Detection and Counting (contact) plate
Rapid Oligonucleotide Detection and Culturing
Randomized Operational Data and Culture

Correct Answer: Replicate Organism Detection and Counting (contact) plate

Q42. Which parameter is critical for interpreting viable air counts?

Volume of air sampled and sampler efficiency
Color of agar
Brand of incubator
Sampling technician’s age

Correct Answer: Volume of air sampled and sampler efficiency

Q43. Which microbiological test specifically measures pyrogenic substances from Gram-negative bacteria?

Sterility test
Endotoxin (LAL) test
Total viable count
Mycoplasma culture

Correct Answer: Endotoxin (LAL) test

Q44. What is the recommended action if a sterility test control shows growth?

Report product as sterile immediately
Invalidate the test run, investigate contamination source, and repeat testing
Ignore the control
Discard controls only

Correct Answer: Invalidate the test run, investigate contamination source, and repeat testing

Q45. Which term describes organisms that survive and grow in disinfectant solutions?

Disinfectant-susceptible organisms
Disinfectant-resistant organisms or biofilm formers
Endospore-free organisms
Gram-positive only

Correct Answer: Disinfectant-resistant organisms or biofilm formers

Q46. Which technique can be used to test filter integrity after sterile filtration?

Bubble point or diffusion test
Gram staining
Endotoxin assay
Settle plate exposure

Correct Answer: Bubble point or diffusion test

Q47. Which of the following best describes microbial trend analysis in environmental monitoring?

Single data point review only
Statistical evaluation of monitoring data over time to detect shifts or excursions
Visual inspection of equipment daily
Counting only fungal colonies annually

Correct Answer: Statistical evaluation of monitoring data over time to detect shifts or excursions

Q48. What is the effect of high organic load on disinfection efficacy?

Enhances disinfectant activity
Can neutralize disinfectants and reduce efficacy
Has no effect
Makes surfaces sterile instantly

Correct Answer: Can neutralize disinfectants and reduce efficacy

Q49. Which sampling frequency is most appropriate for critical Grade A/B aseptic operations?

Never sample
Frequent and routine monitoring with defined schedules and immediate sampling during operations
Once a year
Only after a contamination event

Correct Answer: Frequent and routine monitoring with defined schedules and immediate sampling during operations

Q50. Which statement best summarizes the goal of assessment of microbial contamination in pharmaceutical manufacturing?

To achieve the lowest possible production costs
To detect, control, and prevent microbial contamination to ensure product safety, efficacy, and regulatory compliance
To replace all manual testing with visual checks
To increase microbiological testing without corrective actions

Correct Answer: To detect, control, and prevent microbial contamination to ensure product safety, efficacy, and regulatory compliance

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

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