Maintenance of stock cultures MCQs With Answer

Maintenance of stock cultures MCQs With Answer

Introduction: Maintaining microbial and cell stock cultures is a critical skill for M.Pharm students working in bioprocessing, pharmaceutical development, and quality control. This set of MCQs covers preservation techniques (cryopreservation, lyophilization, agar slants, mineral oil overlays), cell banking concepts (master and working cell banks), cryoprotectants, storage conditions, contamination control, viability and genetic stability testing, and regulatory documentation. Questions focus on practical and theoretical aspects relevant to pharmaceutical laboratories, emphasizing best practices, equipment, and decision-making to ensure long-term viability, purity, and reproducibility of cultures used in research and manufacturing.

Q1. What is the primary reason for using glycerol or DMSO in cryopreservation of bacterial and mammalian cells?

• To provide nutrients during storage
• To act as cryoprotectants that prevent intracellular ice formation
• To reduce contamination by bacteria
• To increase metabolic activity at low temperatures

Correct Answer: To act as cryoprotectants that prevent intracellular ice formation

Q2. Which storage temperature is most appropriate for long-term preservation of bacterial stock cultures in a typical laboratory without liquid nitrogen?

• 4°C in a refrigerator
• -20°C in a regular freezer
• -80°C in an ultra-low temperature freezer
• Room temperature in a dry cabinet

Correct Answer: -80°C in an ultra-low temperature freezer

Q3. Which of the following is considered a critical advantage of lyophilization (freeze-drying) for bacterial and fungal stock cultures?

• It eliminates the need for any cryoprotectant
• It allows stable storage at ambient temperatures for many strains
• It guarantees zero genetic drift over centuries
• It is always faster and cheaper than cryopreservation

Correct Answer: It allows stable storage at ambient temperatures for many strains

Q4. In a two-tier cell banking system used in biopharmaceuticals, what is the role of the master cell bank (MCB)?

• To supply cells directly for all production batches without testing
• To serve as the primary, well-characterized source from which working cell banks are derived
• To be used for routine QC assays only
• To provide transient production increases during scale-up

Correct Answer: To serve as the primary, well-characterized source from which working cell banks are derived

Q5. Which practice helps minimize genetic drift and phenotypic variation in long-term maintained microbial stocks?

• Continuous serial subculturing at high frequency
• Maintaining large single master cultures for years
• Using aliquoted, low-passage working stocks derived from a characterized master bank
• Storing a single stock at room temperature

Correct Answer: Using aliquoted, low-passage working stocks derived from a characterized master bank

Q6. Which of these is an important step before placing a culture into long-term storage to ensure future recoverability?

• Performing only a Gram stain
• Recording inoculation time but not growth phase
• Assessing viability, purity and identity through QC tests
• Adding antibiotics to the storage vial to prevent future contamination

Correct Answer: Assessing viability, purity and identity through QC tests

Q7. What is the main hazard associated with using liquid nitrogen storage for biological cultures?

• High risk of spontaneous thawing due to reagent instability
• Potential for cross-contamination due to sample leakage if cryovials are compromised
• All cultures will die because -196°C is too cold
• Liquid nitrogen causes immediate denaturation of nucleic acids

Correct Answer: Potential for cross-contamination due to sample leakage if cryovials are compromised

Q8. Why are controlled-rate freezers recommended for cryopreservation of mammalian cells?

• They allow for rapid warming rates only
• They control cooling rate to minimize intracellular ice formation and osmotic shock
• They replace the need for cryoprotectants
• They sterilize cells during freezing

Correct Answer: They control cooling rate to minimize intracellular ice formation and osmotic shock

Q9. Which of the following is NOT a recommended practice to prevent contamination of stock cultures?

• Using sterile cryovials and aseptic technique
• Labeling vials with strain ID, date, and passage number
• Adding broad-spectrum antibiotics to all storage media as routine
• Maintaining documented SOPs and segregation of stocks

Correct Answer: Adding broad-spectrum antibiotics to all storage media as routine

Q10. What is the effect of repeated freeze-thaw cycles on microbial and mammalian stocks?

• Improves recovery and genetic stability
• Has no effect if cryoprotectant was used
• Causes decreased viability and increases risk of cell damage
• Automatically sterilizes the sample

Correct Answer: Causes decreased viability and increases risk of cell damage

Q11. For maintenance of bacterial spore stocks, which method is most suitable for long-term stability?

• Storing vegetative cells at 4°C
• Lyophilization of purified spore preparations
• Keeping spores in nutrient broth at room temperature
• Continuous subculturing on agar plates

Correct Answer: Lyophilization of purified spore preparations

Q12. Which parameter is essential to record in the inventory and documentation of stock cultures for regulatory compliance?

• Only the organism’s common name
• Passage number, storage location, date of freezing, and QC results
• Personal notes about experimental results unrelated to the stock
• Only the researcher’s preferred growth medium

Correct Answer: Passage number, storage location, date of freezing, and QC results

Q13. What is the primary purpose of performing viability assays on thawed stock culture vials?

• To check whether the vial label is legible
• To estimate the percentage of live cells and suitability for downstream use
• To measure the nutrient content of the cryoprotectant
• To determine the genetic sequence of the organism

Correct Answer: To estimate the percentage of live cells and suitability for downstream use

Q14. Which cryoprotectant concentration is commonly used for bacterial stocks stored at -80°C?

• 0.01% glycerol
• 10-25% glycerol
• 100% DMSO
• 50% ethanol

Correct Answer: 10-25% glycerol

Q15. When preparing a working cell bank from a master cell bank, which practice helps ensure traceability and contamination control?

• Preparing all vials on an open bench to speed up the process
• Using multiple thaw-refreeze cycles on the same vial
• Aliquoting sterile small-volume vials under aseptic conditions and labeling uniquely
• Pooling multiple vials into one large stock

Correct Answer: Aliquoting sterile small-volume vials under aseptic conditions and labeling uniquely

Q16. Which method is most appropriate for preserving filamentous fungi cultures that are prone to morphological changes with subculturing?

• Continuous subculturing on agar plates weekly
• Storage in mineral oil overlay on agar slants or cryopreservation with glycerol
• Keeping at room temperature in broth
• Repeatedly exposing cultures to UV light to maintain phenotype

Correct Answer: Storage in mineral oil overlay on agar slants or cryopreservation with glycerol

Q17. What is a primary advantage of maintaining multiple replicate aliquots (biobanking) of the same stock culture?

• Increases risk of cross-contamination
• Allows distribution of identical low-passage stocks while limiting freeze-thaw cycles
• Reduces the need for documentation
• Ensures all aliquots are used simultaneously

Correct Answer: Allows distribution of identical low-passage stocks while limiting freeze-thaw cycles

Q18. Which of the following tests is essential to confirm the identity of a bacterial strain before long-term storage intended for pharmaceutical use?

• Colony color only
• Molecular identification such as 16S rRNA sequencing or specific PCR
• Only Gram staining
• Observing growth speed on a single medium without controls

Correct Answer: Molecular identification such as 16S rRNA sequencing or specific PCR

Q19. In the event of a freezer failure, which preparedness measure best reduces loss of critical stock cultures?

• Storing all samples in one central freezer for easy access
• Having an off-site duplicate backup storage and emergency transfer SOPs
• Relying on ambient temperature storage as a backup
• Thawing and refreezing samples immediately to equalize temperatures

Correct Answer: Having an off-site duplicate backup storage and emergency transfer SOPs

Q20. Which factor most contributes to maintaining genetic stability of production cell lines used in biopharmaceutical manufacturing?

• High passage number and continuous culture without characterization
• Strict control of passage number, well-characterized master/working banks, and limited expansion cycles
• Frequent exposure to mutagens to increase diversity
• Using antibiotics in all culture media to prevent contamination

Correct Answer: Strict control of passage number, well-characterized master/working banks, and limited expansion cycles

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