YEPD Agar (Yeast Extract Peptone Dextrose) 50 FAQs and 30 MCQs
YEPD Agar (Yeast Extract Peptone Dextrose) is a nutrient-rich medium essential for culturing Saccharomyces cerevisiae and other yeasts. This guide covers its principles, preparation, applications in genetics and diagnostics, and troubleshooting—tailored for medical students and lab professionals. Test your knowledge with 30 MCQs and clarify doubts with 50 detailed FAQs.
Introduction to YEPD Agar
YEPD Agar is a complete medium for yeast cultivation, composed of:
- Yeast Extract: B vitamins and amino acids.
- Peptone: Nitrogen source.
- Dextrose (Glucose): Energy.
- Agar: Solidifying agent.
Its near-neutral pH (6.5–7.0) supports robust yeast growth and is widely used in molecular biology, fermentation studies, and clinical mycology.
Core Concepts
- Purpose:
- Cultivating Saccharomyces cerevisiae, Candida spp., and fungal strains.
- Routine maintenance, transformation assays, and antimicrobial testing.
- Key Components:
- Yeast Extract: B-complex vitamins & nucleotides.
- Peptone: Organic nitrogen for protein synthesis.
- Dextrose: Fermentable energy source.
- Agar (15–20 g/L): Solidifies at ~45°C.
- Preparation Protocol:
- Suspend 10 g yeast extract, 20 g peptone, 20 g dextrose, 15 g agar in 1L H₂O.
- Autoclave (121°C, 15 mins), cool to 50°C, pour plates.
- pH: 5.6–6.0 (natural acidity inhibits bacteria).
- Quality Control:
- Growth validation using S. cerevisiae ATCC 9763.
- Reject if dehydrated, contaminated, or >30 days old.
YEPD Agar (Yeast Extract Peptone Dextrose) 50 FAQs
What is YEPD Agar?
YEPD (Yeast Extract Peptone Dextrose) Agar is a growth medium used for cultivating yeasts, including Saccharomyces cerevisiae.
What does YEPD stand for?
YEPD stands for Yeast Extract Peptone Dextrose.
Is YEPD Agar selective or non-selective?
YEPD Agar is a non-selective, complete medium for yeast growth.
What type of organisms grow on YEPD Agar?
It supports the growth of yeasts and some heterotrophic microorganisms.
Why is YEPD Agar commonly used in labs?
It is widely used for maintenance, propagation, and routine cultivation of yeasts.
What is the role of yeast extract in YEPD Agar?
Yeast extract, peptone, dextrose (glucose), and agar.
What is the role of yeast extract in YEPD Agar?
It provides B-complex vitamins, amino acids, and essential nutrients for yeast growth.
What does peptone contribute to YEPD Agar?
Peptone supplies nitrogen, vitamins, and minerals necessary for yeast metabolism.
Why is dextrose added to YEPD Agar?
Dextrose acts as the primary carbon and energy source.
What is the final pH of YEPD Agar?
The pH is adjusted to 6.5 ± 0.2.
Can YEPD Agar support mutant yeast strains?
Can YEPD Agar support mutant yeast strains?
How much YEPD powder is needed per liter?
65 grams per liter of purified water.
How should YEPD Agar be dissolved?
Heat with frequent agitation and boil for 1 minute to dissolve completely.
What sterilization method is used for YEPD Agar?
Autoclave at 121°C for 15 minutes.
At what temperature should YEPD Agar be poured into plates?
Cool to 45-50°C before pouring.
Can YEPD Agar be prepared as a broth?
Yes, by omitting agar, it can be used as YEPD broth.
Which yeast species grow well on YEPD Agar?
Saccharomyces cerevisiae, Candida albicans, Kluyveromyces lactis, etc.
What does Saccharomyces cerevisiae growth look like on YEPD?
Luxuriant, smooth, moist, and glistening colonies.
Does Candida albicans grow on YEPD Agar?
Yes, it shows luxuriant growth.
Can bacteria grow on YEPD Agar?
Some heterotrophic bacteria may grow, but it is primarily for yeasts.
How fast do yeasts grow on YEPD Agar?
Growth is rapid, especially during the exponential (log) phase.
What is YEPD Agar used for?
It is used for culturing, maintaining, and propagating yeasts.
Is YEPD Agar used in genetic studies?
Yes, it is used in molecular genetics and microbiology procedures.
Can YEPD Agar be used for auxotroph selection?
No, because it is a complete medium and does not select for auxotrophs.
Is YEPD Agar suitable for industrial yeast cultivation?
Yes, it is commonly used in research and industrial yeast production.
What are the limitations of YEPD Agar?
It is non-selective and cannot differentiate yeast species.
Why can’t YEPD Agar be used for auxotroph screening?
Because it contains all necessary nutrients, masking auxotrophic deficiencies.
Are there selective versions of YEPD Agar?
Yes, additives like antibiotics or amino acid dropouts can make it selective.
What is an alternative to YEPD Agar for auxotroph studies?
Minimal media (e.g., SD – Synthetic Dextrose) with specific nutrient omissions.
Can YEPD Agar be used for fungal cultures?
It is optimized for yeasts, but some fungi may grow.
How should YEPD Agar plates be stored?
Store at 2-8°C in sealed bags to prevent drying.
What is the shelf life of prepared YEPD Agar plates?
Typically 4-6 weeks when stored properly.
Can YEPD Agar be reheated after autoclaving?
Yes, but avoid multiple reheating cycles to prevent nutrient degradation.
Should YEPD Agar be protected from light?
Not strictly necessary, but storage in dark conditions is preferred.
Why is my YEPD Agar not solidifying?
Check agar concentration (15 g/L) and ensure proper sterilization.
What if my YEPD Agar is too hard?
Reduce agar to 10-12 g/L for softer consistency.
Why is there poor yeast growth on YEPD Agar?
Possible contamination, expired medium, or incorrect pH.
Can YEPD Agar expire?
Yes, check the manufacturer’s expiration date.
What if my YEPD Agar has precipitation?
Filter-sterilize dextrose separately if autoclaving causes caramelization.
Can antibiotics be added to YEPD Agar?
Yes, for selective yeast transformation assays (e.g., G418, hygromycin).
How to make YEPD Agar selective for plasmids?
Add amino acid dropouts for plasmid selection in auxotrophic strains.
Can YEPD Agar be made without dextrose?
Yes, but growth will be slower (e.g., YP Agar).
What if I need higher yeast yield in YEPD?
Increase peptone (up to 30 g/L) for richer growth.
How does YEPD differ from Sabouraud Dextrose Agar?
Sabouraud has higher dextrose (40 g/L) and lower pH (5.6), favoring fungi.
Is YEPD Agar the same as YPD?
Yes, YPD and YEPD are interchangeable terms.
Can YEPD replace Nutrient Agar for bacteria?
No, Nutrient Agar is optimized for bacteria, while YEPD is yeast-specific.
What is the difference between YEPD and SD Agar?
SD (Synthetic Dextrose) is minimal, while YEPD is nutrient-rich.
Can YEPD Agar be used for yeast transformation?
Yes, but selective media (e.g., SC – Synthetic Complete) are preferred.
Is YEPD Agar suitable for long-term yeast storage?
No, for storage, use glycerol stocks or slant cultures.
Where can I buy YEPD Agar?
Available from microbiology suppliers (e.g., Sigma, Thermo Fisher, HiMedia).
YEPD Agar (Yeast Extract Peptone Dextrose) 30 MCQs
1.What does YEPD stand for?
A) Yeast Extract Protein Dextrose
B) Yeast Extract Peptone Dextrose✔
C) Yeast Ethanol Peptone Dextrose
D) Yeast Extract Phosphate Dextrose
2. Which of the following is NOT a component of YEPD Agar?
A) Peptone
B) Yeast extract
C) Dextrose
D) Sodium chloride✔
3. What is the primary carbon source in YEPD Agar?
A) Peptone
B) Yeast extract
C) Dextrose✔
D) Agar
4. What is the final pH of YEPD Agar?
A) 5.0 ± 0.2
B) 6.5 ± 0.2✔
C) 7.0 ± 0.2
D) 7.5 ± 0.2
5. YEPD Agar is a:
A) Selective medium
B) Differential medium
C) Complete medium✔
D) Minimal medium
6. Which of the following yeasts grows luxuriantly on YEPD Agar?
A) Escherichia coli
B) Saccharomyces cerevisiae✔
C) Staphylococcus aureus
D) Pseudomonas aeruginosa
7. What is the role of peptone in YEPD Agar?
A) Carbon source
B) Nitrogen source✔
C) Solidifying agent
D) pH indicator
8. Which component supplies B-complex vitamins in YEPD Agar?
A) Dextrose
B) Agar
C) Yeast extract✔
D) Peptone
9. How many grams of YEPD powder are needed per liter?
A) 20 g
B) 50 g
C) 65 g✔
D) 100 g
10. At what temperature should YEPD Agar be autoclaved?
A) 100°C for 10 minutes
B) 115°C for 20 minutes
C) 121°C for 15 minutes✔
D) 130°C for 5 minutes
11. YEPD Agar CANNOT be used for:
A) Growing Saccharomyces cerevisiae
B) Cultivating Candida albicans
C) Selecting yeast auxotrophs✔
D) Routine yeast propagation
12. What is the solidifying agent in YEPD Agar?
A) Gelatin
B) Agar✔
C) Starch
D) Carrageenan
13. Which phase of yeast growth is supported best by YEPD Agar?
A) Lag phase
B) Exponential (log) phase✔
C) Stationary phase
D) Death phase
14. What is the main limitation of YEPD Agar?
A) It is too expensive
B) It is non-selective✔
C) It inhibits fungal growth
D) It requires anaerobic conditions
15. Which of the following is a correct application of YEPD Agar?
A) Antibiotic susceptibility testing
B) Viral culture
C) Yeast transformation✔
D) Bacterial sporulation
16. What type of medium is YEPD Agar?
A) Synthetic minimal medium
B) Nutrient-rich complex medium✔
C) Selective and differential medium
D) Chemically defined medium
17. Which yeast is likely to show luxuriant growth on YEPD Agar?
A) Kluyveromyces lactis✔
B) Escherichia coli
C) Bacillus subtilis
D) Aspergillus niger
18. Why is YEPD Agar unsuitable for auxotroph selection?
A) It lacks essential amino acids
B) It contains all required nutrients✔
C) It inhibits mutant strains
D) It is toxic to auxotrophs
19. What is the alternative to YEPD for auxotroph studies?
A) LB Agar
B) MacConkey Agar
C) Synthetic Dextrose (SD) Agar✔
D) Blood Agar
20. How should YEPD Agar plates be stored?
A) At room temperature
B) At -20°C
C) At 2-8°C✔
D) Under direct sunlight
21. Which component provides amino acids in YEPD Agar?
A) Dextrose
B) Yeast extract✔
C) Agar
D) Peptone
22. What happens if YEPD Agar is not autoclaved properly?
A) It solidifies too quickly
B) It may remain contaminated✔
C) It turns blue
D) It loses all nutrients
23. Which of the following is a chemoorganotroph?
A) Yeast✔
B) Cyanobacteria
C) Nitrosomonas
D) Purple sulfur bacteria
24. What is the function of dextrose in YEPD Agar?
A) Nitrogen source
B) Carbon and energy source✔
C) Solidifying agent
D) pH buffer
25. Which organism would NOT grow on YEPD Agar?
A) Saccharomyces cerevisiae
B) Candida albicans
C) Escherichia coli✔
D) Kluyveromyces lactis
26. What is the purpose of boiling YEPD Agar during preparation?
A) To sterilize it
B) To dissolve the powder completely✔
C) To change its color
D) To reduce its pH
27. Which vitamin is supplied by yeast extract in YEPD Agar?
A) Vitamin C
B) B-complex vitamins✔
C) Vitamin D
D) Vitamin K
28. Why is YEPD Agar preferred for yeast culture?
A) It is selective against bacteria
B) It supports fast yeast growth✔
C) It changes color with yeast metabolism
D) It only allows mutant yeast growth
29. What is the agar concentration in YEPD Agar?
A) 5 g/L
B) 10 g/L
C) 15 g/L
D) 20 g/L✔
30. Which of the following is a limitation of YEPD Agar?
A) It cannot grow wild-type yeasts
B) It cannot differentiate yeast species✔
C) It is toxic to Saccharomyces cerevisiae
D) It requires UV light for growth
YEPD Agar Preparation
- Recipe per liter:
- Yeast extract: 10g
- Peptone: 20g
- Dextrose: 20g (sterilized separately)
- Agar: 15–20g
- Steps:
- Dissolve yeast extract, peptone, and agar in 800ml H₂O. Autoclave (121°C, 15 min).
- Autoclave dextrose solution (20g/200ml H₂O) separately.
- Mix post-cooling (50°C), adjust pH to 6.5–7.0, pour plates.
Best Practices
- Quality Control: Test plates with control strains (e.g., S. cerevisiae S288c).
- Storage: Wrap plates to prevent dehydration.
- Contamination Check: Incubate 1–2 plates per batch at 30°C for 48h pre-use.
Conclusion
YEPD Agar remains a gold standard for yeast studies due to its simplicity and versatility. This guide bridges theory with practical lab know-how—equipping students to ace exams and professionals to optimize protocols. Combine the FAQs for quick problem-solving and MCQs for self-assessment!
Pro Tip: For long-term yeast storage, use YEPD + 20% glycerol at -80°C
