Soyabean Casein Digest Agar (SCDA) / Tryptic Soy Agar (TSA): Composition, Principle, Preparation, and Uses

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Soyabean Casein Digest Agar (SCDA) / Tryptic Soy Agar (TSA): Composition, Principle, Preparation, and Uses

Soyabean Casein Digest Agar (SCDA), also known as Tryptic Soy Agar (TSA), is a widely used general-purpose medium that supports the growth of a wide variety of microorganisms including bacteria and fungi. It is a nutritionally rich medium used for microbial limit testing, environmental monitoring, and sterility testing in pharmaceutical and food industries.

🔬 Principle of Soyabean Casein Digest Agar (SCDA)

The principle of SCDA or TSA lies in providing essential nutrients for microbial growth. The combination of enzymatic digest of soybean meal and casein provides amino acids, peptides, and nitrogenous compounds. Dextrose serves as an energy source, while sodium chloride maintains osmotic balance. The solidifying agent agar provides a firm surface for colony development. This nutrient-rich medium supports both fastidious and non-fastidious organisms.

🧫 Composition of Soyabean Casein Digest Agar (per 1000 mL)

  • Pancreatic Digest of Casein – 15.0 g
  • Papaic Digest of Soybean Meal – 5.0 g
  • Sodium Chloride – 5.0 g
  • Dextrose – 2.5 g
  • Dipotassium Hydrogen Phosphate – 2.5 g
  • Agar – 15.0 g
  • Final pH (at 25°C) – 7.3 ± 0.2

⚗️ Preparation Procedure

  1. Weigh 45 g of Soyabean Casein Digest Agar powder and suspend it in 1 liter of distilled water.
  2. Mix thoroughly and heat gently with frequent agitation until the medium is completely dissolved.
  3. Adjust the pH to 7.3 ± 0.2 if necessary.
  4. Dispense into flasks or tubes as desired.
  5. Sterilize by autoclaving at 121°C (15 lbs pressure) for 15 minutes.
  6. Cool the medium to 45–50°C and pour into sterile Petri dishes under aseptic conditions.
  7. Allow plates to solidify and store them at 2–8°C.

🧪 Uses and Applications

  • 1. Sterility Testing: SCDA is the standard medium used for detecting microbial contamination in sterile pharmaceutical products.
  • 2. Environmental Monitoring: Used for surface, air, and personnel monitoring in cleanrooms and controlled areas.
  • 3. Microbial Limit Testing: Employed to determine the bioburden in raw materials and finished products.
  • 4. General Microbial Cultivation: Supports the growth of a wide range of microorganisms including both aerobic and facultative anaerobic bacteria.
  • 5. Subculture and Maintenance Medium: Suitable for maintaining microbial cultures in quality control laboratories.

🧫 Quality Control of SCDA / TSA

Quality control of SCDA ensures reliability and consistency. The growth promotion test (GPT) must be performed using standard ATCC strains:

  • Staphylococcus aureus ATCC 6538 – Good growth
  • Bacillus subtilis ATCC 6633 – Good growth
  • Escherichia coli ATCC 8739 – Good growth
  • Candida albicans ATCC 10231 – Good growth
  • Aspergillus brasiliensis ATCC 16404 – Good growth

🌡️ Storage and Shelf Life

  • Store the dehydrated medium at 10–30°C in a tightly closed container.
  • Prepared media plates should be stored at 2–8°C.
  • Do not use media beyond the expiry date or if any signs of contamination, dehydration, or color change are observed.

⚙️ Precautions

  • Ensure the medium is sterilized properly before use.
  • Avoid overheating during preparation to prevent nutrient degradation.
  • Always use aseptic techniques to avoid contamination.
  • Perform growth promotion tests periodically to validate performance.

📘 Conclusion

Soyabean Casein Digest Agar (SCDA) or Tryptic Soy Agar (TSA) is one of the most versatile and widely used culture media in microbiology. Its balanced nutrient composition supports a broad range of microorganisms, making it essential for sterility testing, environmental monitoring, and general microbial studies. Regular quality checks and proper storage ensure its optimal performance in every microbiological laboratory.

💬 About the Author

Siva Sankar is a Pharmaceutical Microbiology Consultant and Auditor with extensive experience in sterility testing, validation, and GMP compliance. He provides consultancy, training, and documentation services for pharmaceutical microbiology and cleanroom practices.

📧 Contact: siva17092@gmail.com
/small>Mobile: 09505626106

📱 Disclaimer: This article is for educational purposes and does not replace your laboratory’s SOPs or regulatory guidance. Always follow validated methods and manufacturer instructions.

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