What is Tryptic Soy Agar ?
A tryptic soy agar is a general growth medium used to isolate and cultivate microorganisms.
It is also intended to store, maintain, and transport pure cultures of microorganisms. It is a universal medium because it supports the growth of different types of microorganisms including Gram positive and Gram negative bacteria.
It was in 1955 that Leavitt and his group discovered tryptic soy agar. They facilitated the growth of aerobic and anaerobic microorganisms.
Basically, tryptic soy agar is a general purpose medium; a medium perfect to support fastidious heterotrophs. Additives can be used to make tryptic soy agar selective.
Without interventions, there is no way for tryptic soy agar to be a selective medium. (1, 2, 3, and 4)
Picture 1: Above is the image of a tryptic soy agar plate, which is a general growth medium.
Image Source: microbeonline.com
Picture 2: Tryptic soy agar can cultivate and isolate the growth of microorganisms.
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Other terms for tryptic soy agar are the following:
- Soybean casein digest agar
- Trypticase soy agar
- Tryptone soya agar
- Trypticase soy broth
- Tryptone soya broth (4, 5)
Picture 3: A tryptic soy agar containing lecithin and polysorbate 80.
Image Source: emdmillipore.com
Picture 4: A disinhibitor is added to the tryptic soy agar medium.
Image Source: fishersci.com
A tryptic soy agar is a nutritious base because you can add a variety of supplements in order to enhance the function of the medium.
Usually, nutrients are added to find out the hemolytic reaction of bacteria. Some of the compositions added to tryptic soy agar are:
- Tween 80
- 5% sterile defibrinated sheep, horse, and rabbit blood (5)
Tryptic soy agar ingredients
Tryptic soy agar has soybean meal and casein digest, which makes it perfect for the growth of various forms of fastidious and non-fastidious microorganisms.
Both soy and casein peptones serve as the source of organic nitrogen in amino acid and polypeptides forms, which makes the medium nutritious. A sodium chloride is also added to maintain the osmotic balance. The addition of salt can help in assessing the halotolerance level of microorganisms. A solidifying agent is added in the form of agar.
Glucose is the primary source of energy. Dipotassium phosphate is the buffer that maintains the pH level. Tryptic soy agar medium can be supplemented with blood to permit the growth of fastidious bacteria so as to allow the selection of various microbial groups.
Tryptic soy agar is also used as a base medium for other agar plate types. A perfect example is the blood agar plate. It is created by enriching the tryptic soy agar plate with defibrinated sheep blood.
Additional cooking of blood agar plate with the help of tryptic soy agar is used to create chocolate agar. (6, 7, and 8)
Picture 5: The components of tryptic soy agar.
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The contents of tryptic soy agar includes the following:
Note: The ingredients are based on per liter of deionized water.
- Pancreatic digest of casein and soybean meal
- Sodium chloride
- Agar (9)
- At least 3 grams of tryptic soy broth powder should be dissolved in a 100 ml of distilled water.
- Mix the medium by placing the bottle on a magnetic stirrer.
- About 10 ml of the medium is aliquot to each glass of spiral tubes.
- Place the tube into an autoclave for about 15 minutes at 121 degree Celsius.
- Remove the tube making sure that the tube’s cap is tightly closed.
- Allow the tube to cool at a room temperature and place in a refrigerator at a 4 degree Celsius. Make sure you keep it away from light.
- Before using the medium, pre-warm it at a room temperature. (8, 9, and 10)
Picture 6: S. aureus and P. aeruginosa microorganisms on a tryptic soy agar medium.
Image Source: microbiologyinpictures.com
Picture 7: A tryptic soy agar plate containing lecithin tween.
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What is tryptic soy agar used for?
- It is used to isolate and cultivate microorganisms.
- It enables the growth of non-fastidious and semi-fastidious microorganisms.
- It is used to cultivate, store, maintain, and transport pure culture of microorganisms.
- Tryptic soy agar can be used as the ain isolation medium in clinical microbiology when supplemented with blood. A perfect example is the addition of 5% sheep blood.
- It can be used to determine, X, V, and XV factor in Hemophilus species. To do so, all you need are strips that have the factors X, V, and XV in the inoculated plates.
- Tryptic soy agar with the addition of salt can be helpful in determining the halotolerance level of microorganisms. (2, 4, 6, and 7)
Are there any limitations?
The application of tryptic soy agar in microbiology is limited because it does not promote the growth of some types of fastidious bacteria. It cannot be used to isolate pathogens from clinical specimens. However, it can be used to maintain and subculture bacterial strains. (1, 3)
Tryptic soy agar vs Nutrient agar
What are the differences between a tryptic soy agar and a nutrient agar? The detailed differences are as follows:
- Nutrients agar
- It is a general medium primarily used in the teaching environment.
- It grows on a large number of non-fastidious microorganisms which makes it helpful in different fields such as fuel testing, cutting of metals, cooling water, potable water, food and beverages, packaging, wastewater paint, and environmental education.
- Tryptic soy agar
- It is a nutrient-rich medium and can be used for general purposes.
- It can test both aerobic and anaerobic fastidious and non-fastidious microorganisms.
- It is commonly used for environmental testing in the pharmaceutical field.
- It is helpful in testing water, cosmetics, industrial, food, and beverages.
- It is extremely helpful in performing laboratory works. (3, 6, 9, and 10)
Is tryptic soy agar a differential or selective medium?
A tryptic soy agar is a general purpose media. It is not selective or differential. Its primary purpose is to grow various types of bacteria. (5, 7)
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