Starch Casein Agar (SCA) 50 FAQs and 30 MCQs
This comprehensive article covers everything you need to know about Starch Casein Agar (SCA)—from composition and uses to interpretation and storage. Ideal for lab professionals, microbiologists, and medical students, this post includes 50 expertly curated FAQs and 30 MCQs to test and enhance your knowledge.
🧪 What is Starch Casein Agar?
Starch Casein Agar (SCA) is a selective medium used for the isolation of actinomycetes, especially Streptomyces species. It contains starch and casein as the primary carbon and nitrogen sources, respectively.
50 Frequently Asked Questions (FAQs) About Starch Casein Agar
Categories Covered:
- Composition and Preparation
- Purpose and Applications
- Storage and Shelf-life
- Actinomycetes Identification
- Troubleshooting Growth Issues
What is Starch Casein Agar (SCA)?
A nutrient medium for growing saccharolytic marine bacteria and actinomycetes.
What is the primary purpose of SCA?
Isolation and cultivation of actinomycetes from soil, marine sediments, and other sources.
Why is starch used in SCA?
It serves as the primary carbohydrate source for saccharolytic bacteria.
What role does casein play in SCA?
It provides a protein source for bacterial growth.
Why is seawater included in SCA?
It supplies essential nutrients, vitamins, and salts for marine bacteria.
What is the pH of SCA?
Around 7.0–7.3 (varies slightly based on preparation).
Can SCA be used for fungi?
It supports some fungi-like bacteria (actinomycetes) but is not ideal for true fungi.
What type of bacteria grow best on SCA?
Saccharolytic marine bacteria and actinomycetes.
Is SCA selective or differential?
It is a general-purpose medium but favors actinomycetes.
How does SCA compare to Nutrient Agar?
SCA is richer in nutrients, supporting fastidious marine bacteria that may not grow on Nutrient Agar.
What are the main ingredients of SCA?
Starch, casein, seawater, agar, KNO₃, MgSO₄, K₂HPO₄, NaCl, CaCO₃, and FeSO₄.
How much agar is used in SCA?
15–18 g/L (varies between formulations).
Why is KNO₃ added to SCA?
It acts as a nitrogen source for bacterial growth.
What is the role of MgSO₄ in SCA?
Provides essential magnesium and sulfur for metabolism.
How is SCA prepared?
Dissolve 63g powder in 1L distilled water, boil, autoclave (121°C, 15 mins), and pour into plates.
Can distilled water replace seawater in SCA?
Yes, but seawater is preferred for marine bacteria.
What is the sterilization method for SCA?
Autoclaving at 121°C for 15 minutes.
How should SCA be stored?
Powder: 10–30°C in a tightly closed container. Prepared plates: 2–8°C.
What happens if SCA absorbs moisture?
It may form lumps; store in a dry place.
Can SCA be reheated after autoclaving?
Yes, but avoid repeated melting to prevent nutrient degradation.
What is SCA mainly used for?
Isolating actinomycetes from marine and terrestrial sources.
Why is SCA useful for marine bacteria?
Seawater provides essential ions and nutrients.
Can SCA detect antibiotic-producing bacteria?
Yes, especially actinomycetes known for antibiotic production.
Is SCA used in environmental studies?
Yes, for studying microbial ecosystems in soil and water.
Can SCA be used for long-term culture storage?
Yes, it helps preserve actinomycetes cultures.
Does SCA support Vibrio cholerae growth?
Yes, it shows good growth with mucoid colonies.
What industries use SCA?
Pharmaceutical (antibiotic research), environmental, and marine microbiology.
Can SCA be used for clinical samples?
Not typically; it’s mainly for environmental and marine isolates.
How long does it take for actinomycetes to grow on SCA?
1–7 days (powdery colonies appear after 7 days).
What color are actinomycetes colonies on SCA?
White to light yellow, powdery or mucoid.
What are the limitations of SCA?
Some strains may show poor growth due to nutritional variations.
Why might bacteria not grow on SCA?
Incorrect pH, expired media, or unsuitable bacterial type.
How can contamination be avoided in SCA?
Use sterile techniques and proper autoclaving.
What should be done if SCA doesn’t solidify?
Check agar concentration and ensure proper sterilization.
Can SCA be used for anaerobic bacteria?
No, it is designed for aerobic or facultative anaerobic bacteria.
How should moisture on SCA plates be removed?
Dry in a hot air oven at low heat before use.
What if colonies appear atypical on SCA?
Confirm with biochemical tests; SCA alone is not diagnostic.
Does SCA expire?
Yes, check the label for the expiry date.
Can SCA be reused after melting?
Yes, but repeated melting may degrade nutrients.
What alternative media can be used if SCA fails?
Glycerol-Yeast Extract Agar (GYEA) for actinomycetes.
Why are actinomycetes important?
They produce antibiotics, anticancer agents, and aid in organic matter recycling.
Are marine actinomycetes different from terrestrial ones?
Yes, marine strains often produce novel bioactive compounds.
How does SCA help in antibiotic discovery?
It isolates actinomycetes, which are prolific antibiotic producers.
What is the role of CaCO₃ in SCA?
Acts as a pH buffer and calcium source.
Why is FeSO₄ added to SCA?
Provides iron, essential for bacterial enzymes.
Can SCA be modified for specific bacteria?
Yes, by adjusting starch/casein ratios or adding selective agents.
How does SCA compare to ISP Media for actinomycetes?
ISP media are more specialized, while SCA is general-purpose.
What biochemical tests follow SCA isolation?
Gram staining, catalase, oxidase, and specialized actinomycetes tests.
Can SCA be used for biofilm studies?
Not ideal; specialized biofilm media are better.
Where can I buy SCA?
From microbiological suppliers like HiMedia, Thermo Fisher, or Sigma-Aldrich.
30 Multiple-Choice Questions (FAQs) About Starch Casein Agar
Categories Covered:
- Composition and Preparation
- Purpose and Applications
- Storage and Shelf-life
- Actinomycetes Identification
- Troubleshooting Growth Issues
What is the primary purpose of Starch Casein Agar (SCA)?
A) Cultivation of fungi
B) Isolation of actinomycetes✔
C) Detection of viruses
D) Growth of anaerobic bacteria
2. Which component serves as the primary carbon source in SCA?
A) Casein
B) Starch✔
C) KNO₃
D) NaCl
3. Why is seawater included in SCA?
A) To provide essential nutrients for marine bacteria✔
B) To inhibit fungal growth
C) To increase agar solidification
D) To reduce pH
4. What is the typical pH range of SCA?
A) 5.0–6.0
B) 6.0–6.5
C) 7.0–7.3✔
D) 8.0–9.0
5. Which organism is MOST likely to grow on SCA?
A) Escherichia coli
B) Streptomyces praecox✔
C) Saccharomyces cerevisiae
D) Mycobacterium tuberculosis
6. What is the role of casein in SCA?
A) Carbon source
B) Nitrogen source✔
C) Solidifying agent
D) pH indicator
7. How should prepared SCA plates be stored?
A) Frozen at -20°C
B) At 2–8°C✔
C) At room temperature
D) Under UV light
8. What is the sterilization method for SCA?
A) Filtration
B) Autoclaving at 121°C for 15 mins✔
C) Boiling for 5 mins
D) UV radiation
9. Which of the following is a limitation of SCA?
A) Supports only anaerobic bacteria
B) Poor growth for some strains due to nutritional variations✔
C) Cannot detect gram-negative bacteria
D) Turns blue upon bacterial growth
10. What color are actinomycete colonies on SCA?
A) Blue
B) Pink
C) White to light yellow✔
D) Green
11. Which salt in SCA acts as a pH buffer?
A) NaCl
B) CaCO₃✔
C) KNO₃
D) FeSO₄
12. What is the incubation period for actinomycetes on SCA?
A) 1–3 days
B) 1–7 days✔
C) 10–14 days
D) 24 hours
13. Which of these is NOT a component of SCA?
A) Agar
B) Glucose✔
C) MgSO₄
D) K₂HPO₄
14. Why is KNO₃ added to SCA?
A) As a nitrogen source✔
B) To inhibit gram-positive bacteria
C) For color indication
D) To increase viscosity
15. Which bacteria form mucoid colonies on SCA?
A) Vibrio cholerae✔
B) Streptococcus pneumoniae
C) Bacillus subtilis
D) Pseudomonas aeruginosa
16. What is the solidifying agent in SCA?
A) Gelatin
B) Agar✔
C) Silica gel
D) Carrageenan
17. Which of these is a key application of SCA?
A) Blood culture
B) Antibiotic discovery✔
C) Viral plaque assay
D) Protozoan isolation
18. What should be done if SCA powder absorbs moisture?
A) Discard it
B) Dry it in an oven
C) Store in a tightly closed container
D) Both B & C✔
19. Which organism would NOT grow well on SCA?
A) Streptomyces
B) Saccharolytic marine bacteria
C) Obligate anaerobes✔
D) Vibrio species
20. What confirms actinomycete identity after SCA isolation?
A) Gram staining & biochemical tests✔
B) Hemolysis on blood agar
C) Motility test
D) Oxidase test
21. What is the weight of SCA powder needed for 1L of media?
A) 10 g
B) 37 g
C) 63 g✔
D) 100 g
22. Which component provides iron in SCA?
A) FeSO₄·7H₂O✔
B) MgSO₄·7H₂O
C) K₂HPO₄
D) CaCO₃
23. How does SCA help in environmental studies?
A) By isolating pathogens from clinical samples
B) By studying microbial decomposition of organic matter✔
C) By detecting viral loads
D) By identifying photosynthetic bacteria
24. Which of these is a HiMedia SCA ingredient?
A) Peptone
B) Yeast extract
C) Sea water (37 g/L)✔
D) Glucose
25. What is the colony morphology of Streptomyces praecox on SCA?
A) Mucoid and translucent
B) Golden-yellow, circular, and opaque✔
C) Pink and irregular
D) Green and fuzzy
26. Why is autoclaving necessary for SCA?
A) To melt the agar
B) To sterilize and dissolve components✔
C) To change the pH
D) To activate antibiotics
27. Which of these is NOT a use of SCA?
A) Preserving actinomycete cultures
B) Isolating marine bacteria
C) Diagnosing tuberculosis✔
D) Studying soil microbes
28. What precaution prevents lump formation in SCA powder?
A) Storing in a dry place
B) Keeping the container tightly closed
C) Avoiding moisture exposure
D) All of the above✔
29. What is the appearance of prepared SCA plates?
A) Red and opaque
B) Clear to slightly opalescent✔
C) Blue and transparent
D) Green and fluorescent
30. Which component in SCA provides sulfur?
A) KNO₃
B) MgSO₄·7H₂O✔
C) NaCl
D) CaCO₃
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