Subculture techniques MCQs With Answer

Introduction: This quiz collection on Subculture techniques is designed for M.Pharm students studying Modern Bio-Analytical Techniques (MPA 202T). It focuses on practical and theoretical aspects of microbial subculturing — aseptic transfers, isolation methods, preservation strategies, contamination control, and handling of aerobic and anaerobic organisms. Questions emphasize reasons behind procedural choices, effects of inoculum and growth phase, and best practices to maintain culture integrity and genetic stability. The set is aimed at reinforcing lab decision-making, preparing students for practical exams and research work, and deepening understanding of how subculture technique details influence experimental outcomes and reproducibility.

Q1. What is the primary purpose of routine subculturing in microbiology labs?

• To maintain viability and purity of cultures for continued study
• To deliberately increase contamination for robustness testing
• To induce spontaneous mutation for strain improvement
• To produce bulk biomass irrespective of purity

Correct Answer: To maintain viability and purity of cultures for continued study

Q2. Which best describes the principle of aseptic technique during subculture?

• Prevent contamination of the culture and the environment by excluding extraneous microbes
• Maximize oxygen exposure to encourage faster growth
• Use antibiotics in all transfers to ensure selective pressure
• Perform all transfers under bright light to sterilize instruments

Correct Answer: Prevent contamination of the culture and the environment by excluding extraneous microbes

Q3. What is the recommended method for sterilizing an inoculating loop between streaks?

• Flame the loop until it is red hot and allow it to cool briefly before use
• Wipe the loop with 70% ethanol only without flaming
• Expose the loop to UV light for 5 seconds
• Rinse the loop in sterile water and use immediately

Correct Answer: Flame the loop until it is red hot and allow it to cool briefly before use

Q4. What is the main advantage of the streak plate technique in subculturing?

• Isolation of single colonies from a mixed or dense culture
• Maximizing overall biomass yield in a single plate
• Precise quantification of viable cells per mL without dilution
• Creating uniform lawns for antibiotic testing

Correct Answer: Isolation of single colonies from a mixed or dense culture

Q5. For obtaining accurate viable cell counts before subculture, which technique is most appropriate?

• Serial dilution followed by pour or spread plate counting
• Direct streaking without dilution
• Microscopic counting only, without plating
• Measuring optical density (OD) without calibration to CFU

Correct Answer: Serial dilution followed by pour or spread plate counting

Q6. From which growth phase should cells ideally be subcultured to obtain healthy, reproducible cultures?

• Exponential (log) phase
• Late stationary phase
• Early death phase
• Lag phase

Correct Answer: Exponential (log) phase

Q7. What is the recommended short-term storage method for bacterial cultures between regular subcultures?

• Maintaining cultures on agar slants at 4°C
• Leaving cultures at room temperature on plates
• Long-term cryopreservation at -80°C with glycerol
• Desiccation on filter paper at ambient temperature

Correct Answer: Maintaining cultures on agar slants at 4°C

Q8. Which procedure is most suitable for long-term preservation of microbial strains without frequent subculturing?

• Cryopreservation at -80°C in a cryoprotectant such as 15% glycerol
• Continuous subculturing every 24 hours on rich media
• Storage of agar plates at room temperature wrapped in parafilm
• Periodic UV exposure to maintain genetic stability

Correct Answer: Cryopreservation at -80°C in a cryoprotectant such as 15% glycerol

Q9. Which observation on a streaked plate most directly indicates potential contamination of a supposedly pure culture?

• Presence of colonies with distinctly different morphologies
• Uniform colony size and pigmentation across the plate
• Absence of any colonies after incubation
• Confluent lawn growth consistent with single species

Correct Answer: Presence of colonies with distinctly different morphologies

Q10. Which colony characteristics are routinely assessed to help distinguish microbial strains during subculture?

• Size, shape, margin, elevation and pigmentation
• Only size and margin are informative
• Growth rate in liquid medium only
• Antibiotic resistance pattern only

Correct Answer: Size, shape, margin, elevation and pigmentation

Q11. When maintaining plasmid-bearing strains after transformation, what subculture practice is essential?

• Include the appropriate selective antibiotic at the correct concentration in the growth medium
• Avoid any selective agent to reduce stress on cells
• Subculture only on rich non-selective media
• Increase incubation temperature to speed plasmid propagation

Correct Answer: Include the appropriate selective antibiotic at the correct concentration in the growth medium

Q12. In which situation is an inoculating needle preferred over an inoculating loop?

• For stab inoculation of semisolid media to assess motility or microaerophily
• For streaking plates to isolate single colonies
• For transferring liquid volumes greater than 1 mL
• For plating dilutions in spread plate technique

Correct Answer: For stab inoculation of semisolid media to assess motility or microaerophily

Q13. How often should rapidly growing laboratory bacterial strains typically be subcultured to maintain vigor and prevent overgrowth?

• Every 24–48 hours
• Once every two weeks
• Only when obvious contamination appears
• Every 6 months by default

Correct Answer: Every 24–48 hours

Q14. What is an appropriate method for handling obligate anaerobes during subculture?

• Use an anaerobic chamber or anaerobic jar with oxygen-scavenging systems during transfers
• Perform subculture on open bench in atmospheric oxygen to acclimate cultures
• Incubate in high-CO2 incubators without oxygen control
• Use flaming extensively to remove oxygen from media surface

Correct Answer: Use an anaerobic chamber or anaerobic jar with oxygen-scavenging systems during transfers

Q15. Compared to the spread plate method, what primary advantage does the streak plate method provide during subculture?

• Rapid isolation of discrete colonies from a small inoculum without preparing serial dilutions
• More accurate quantitative enumeration of viable cells
• Better for growing strict anaerobes on the surface
• Produces uniform lawns suitable for plaque assays

Correct Answer: Rapid isolation of discrete colonies from a small inoculum without preparing serial dilutions

Q16. How does increasing the inoculum size generally affect the lag phase during subculture?

• A larger inoculum usually shortens the lag phase
• A larger inoculum always prolongs the lag phase
• Inoculum size has no effect on lag phase
• A larger inoculum prevents cells from entering exponential phase

Correct Answer: A larger inoculum usually shortens the lag phase

Q17. To minimize genetic drift and phenotypic changes during repeated subculturing, which practice is recommended?

• Limit the number of passages and store master stocks for recovery
• Continuously culture the strain without freezing to maintain adaptation
• Always use selective antibiotics at high concentrations to force stability
• Increase incubation temperature to select for robust mutants

Correct Answer: Limit the number of passages and store master stocks for recovery

Q18. What is the quickest routine laboratory method to detect contamination in a bacterial broth culture?

• Perform a Gram stain on a sample and inspect for mixed cell morphologies
• Incubate the broth for another 48 hours to observe changes
• Measure OD600 and assume purity if value is within expectations
• Sequence the entire genome of the culture

Correct Answer: Perform a Gram stain on a sample and inspect for mixed cell morphologies

Q19. Which tool is most appropriate for transferring small, precise liquid volumes (>1 µL) during subculture procedures?

• Pipette (micropipette) with sterile disposable tips
• Flamed inoculating loop
• Sterile glass spreader
• Metal inoculating needle alone

Correct Answer: Pipette (micropipette) with sterile disposable tips

Q20. What incubation temperature is standard for subculturing human pathogenic bacteria to mimic host conditions?

• 37°C
• 25°C
• 4°C
• 50°C

Correct Answer: 37°C

Download