Introduction
Tryptic Soy Agar as a laboratory medium that creates a suitable environment for the growth of several microorganisms. Scientists also refer to it as soybean casein digest media (SCDM) or Soybean Casein Digest Agar Medium. TSA is a general-purpose, no selective growth medium that promotes the development of Gram-negative and non-fastidious Gram-positive bacteria, as well as many yeasts and molds. TSA has a variety of functions in the laboratory.
Researchers often use it as a beginning growth medium to examine colony morphology and generate pure microbial cultures. The medium contains enough nutrients for a diverse range of bacteria to develop, making isolation and identification possible. It is also used to conduct additional biochemical tests on microbes and to store bacterial cultures. TSA slopes are extremely useful for storing and transporting bacterial cultures.
Principle
TSA works by providing a diverse supply of nutrients for the development of a broad range of bacteria. Tryptone and soybean meal provide critical amino acids, carbohydrates, vitamins, and minerals, resulting in an environment favourable for bacterial development. The sodium chloride concentration maintains osmotic balance, protecting against cell injury. Furthermore, the agar solidification of the medium enables the separation and quantification of distinct bacterial colonies.
Composition
| Ingredients | Gms/liter | Function |
| Pancreatic digest of casein | 17.00 | Provides peptides and amino acids as a nitrogen and carbon source |
| Papaic digest of soybean meal | 3.00 | Supplies vitamins, nitrogen compounds, and carbohydrates for microbial growth. |
| Sodium chloride | 5.00 | Maintains osmotic balance |
| Dextrose (Glucose) | 2.50 | Serves as a readily available energy and carbon source. |
| Dipotassium hydrogen phosphate | 2.50 | Acts as a buffering agent to maintain stable pH |
| Agar | 15.0 | Solidifying agent |
Preparation of Tryptic Soy Agar (TSA)
- Weigh all components according to the preceding recipe.
- Using gentle heat and stirring, dissolve them in 1000 mL of pure water.
- If necessary, adjust the pH to 7. 3 using 1N NaOH or HCl.
- Distribute the media into appropriate flasks or tubes as required.
- Autoclave to sterilize at 121°C for 15 minutes at a pressure of 15 psi.
- Before using or storing, cool the sterilized broth to room temperature.
Image Source: Thermo Fisher
Examples of microorganisms
Escherichia coli, staphylococcus aureus, enterococcus faecalis, pseudomonas aeruginosa, bacillus subtilis
Colony appearance
| Bacterium | Appearance |
| Escherichia coli | Small, smooth, and pale colonies |
| Staphylococcus aureus | Large, golden-yellow colonies |
| Enterococcus faecalis | Small, grayish-white colonies |
| Pseudomonas aeruginosa | Large, greenish colonies with a fruity odor |
| Bacillus subtilis | Large, cream-colored colonies with wrinkled appearance |
Uses
- A general-purpose medium for culturing a wide range of bacteria and certain fungi.
- It is utilized in clinical, food, pharmaceutical, and water microbiology.
- Excellent for routine bacterial enumeration and isolation.
- When properly supplied, it is used in antibiotic sensitivity testing.
- It serves as a foundation medium for enriched and selective agars.
- Used in the quality control of microbiological media and sterility testing.
Precautions
- To avoid contamination, utilize sterile procedures during preparation and inoculation.
- Sterilize the medium for 15 minutes at 121°C under 15 psi pressure.
- Avoid overheating, since it can destroy nutrients and impair performance.
- Check the pH before sterilizing; it should be 7. 3 ± 0. 2.
- Store prepared dishes at 2–8°C and utilize within the shelf life.
- Only give supplements such as blood or antibiotics after cooling to 45-50°C.
Limitations
- Non-selective: Does not harm non-target creatures.
- Lacks indicators, meaning it does not distinguish between bacterial species.
- Some fastidious organisms may not grow without enrichment.
- Fungal growth is not adequately supported as compared to PDA or SDA.
- May need additional supplements for certain diagnostic applications.
