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Short answer: Tryptic soy broth (TSB) is a general-purpose liquid culture medium, also sold as soybean-casein digest broth, that supports growth of a wide variety of microorganisms. Two independent manufacturer documents state the same formula, 30 g of powder per litre of water with a final pH of 7.3 ± 0.2.
Definition and scope
Neogen’s technical specification sheet (FS-TSS-0192, rev 4.0, effective 2023-08-30) describes TSB as a general-purpose medium commonly referred to as Casein Soya Bean or Soybean-Casein Digest broth. The Bigelow National Center for Marine Algae and Microbiota (NCMA) lists the same medium as Medium 11, “Bacto Tryptic Soy Broth (Soybean-Casein Digest Medium)”. So three names circulate for one formulation: tryptic soy broth, soybean-casein digest medium and casein soya bean digest broth. The abbreviation TSB is used for all of them.
Neogen states that the product is used for the cultivation of a wide variety of microorganisms, conforms to harmonized USP/EP/JP requirements, and is not intended for use in the diagnosis of disease or other conditions in humans. The same sheet says the medium was originally developed without blood to determine the effectiveness of sulfonamides against pneumococci and other organisms.
What is in tryptic soy broth, and what each part does
Both documents give the same quantities per litre. Neogen also states the role of each component, which turns the formula into a readable checklist.
| Component | Per litre | Role stated by the manufacturer |
|---|---|---|
| Pancreatic (enzymatic) digest of casein | 17.0 g | Nitrogen source |
| Papaic (enzymatic) digest of soybean meal | 3.0 g | Nitrogen source |
| Dextrose (glucose monohydrate in the Neogen sheet) | 2.5 g | Carbon and energy source |
| Sodium chloride | 5.0 g | Osmotic balance |
| Dipotassium phosphate | 2.5 g | Buffer |
The two documents agree on every quantity and on the final pH of 7.3 ± 0.2 at 25 °C. They differ only in wording, such as “dextrose” versus “glucose monohydrate” and “pancreatic digest” versus “enzymatic digest”. When you compare a spec sheet from one supplier against another, those wording differences are naming conventions rather than different formulas. Confirm the quantities and the pH, not the labels.
How it is used in practice
Both sources describe preparation in one sentence: 30 g of the commercial dehydrated preparation dissolved in 1 litre of water and sterilised by autoclave (Neogen: 121 °C for 15 minutes; NCMA: 15-20 minutes). Neogen refers readers to the safety data sheet and to appropriate references for test procedures. For how autoclave cycles work, see what an autoclave is.
Neogen lists several uses of its TSB:
- Testing for bacterial contaminants in cosmetics.
- Food-industry testing, where the sheet says the medium complies with established standards.
- Detecting viable bacteria in live vaccines, a use for which the sheet says USDA APHIS chose it.
- Growth of clostridia and non-sporulating anaerobes, which the sheet says grow luxuriantly when incubated anaerobically.
Variations and related media
The base formula is often modified. The table lists only the modifications that the two documents state.
| Modification | What the source says it gives you |
|---|---|
| Add 15 g/L agar (NCMA) | A solid version of the medium |
| Add 6.5% sodium chloride (Neogen) | Selective growth of group D streptococci |
| Add SPS and CO2 (Neogen) | “An excellent broth for blood cultures” |
| Incubate anaerobically (Neogen) | Luxuriant growth of clostridia and non-sporulating anaerobes |
Plain TSB is not itself selective. For a different kind of enriched plate medium, see the guide on alpha-hemolysis on blood agar. For mammalian cell culture, which uses an entirely different class of medium, see types of cell culture media.
Where it matters for labs and supply decisions
A TSB specification sheet gives staff several checkable items before a lot is accepted into routine use. These come from the Neogen sheet.
- Intended-use statement. Neogen states the product is not intended for diagnosing disease in humans. A procurement or quality reviewer should read that line against the intended application.
- Conformance statement. The sheet states conformance to harmonized USP/EP/JP requirements. Compendial text itself should be consulted for the test requirements.
- Formula and pH. 17.0 / 3.0 / 5.0 / 2.5 / 2.5 g per litre and pH 7.3 ± 0.2 at 25 °C, as above.
- Physical appearance. The dehydrated powder is specified as homogeneous, free-flowing and light beige. The prepared medium is specified as brilliant to clear, yellow to amber, with none to light precipitate.
- Growth promotion. The sheet reports growth-promotion testing with an inoculum of approximately 10-100 CFU. Two of its organisms are Aspergillus brasiliensis ATCC 16404 (growth within 5 days) and Bacillus subtilis ATCC 6633 (growth at 18-72 hours).
Sterile media preparation is also a quality topic in its own right. The guide on aseptic process simulation (media fill) covers a related quality topic, the simulation of aseptic processes with growth media. Handling cultures grown in broth falls under biosafety practice; see the biosafety level (BSL) entry.
Common misunderstandings
Is tryptic soy broth selective?
No. The manufacturer describes it as a general-purpose medium for a wide variety of microorganisms. Selectivity, such as for group D streptococci, comes from a modification like 6.5% sodium chloride.
Is TSB the same as tryptic soy agar?
Not exactly. NCMA states that adding 15 g/L agar to the broth formula gives a solid medium, so the two share a base but differ in physical form.
Does every supplier use the same formula?
The two documents cited here agree, but a specification sheet remains the reference for any particular product. Check the sheet’s quantities and pH rather than relying on the name alone.
Can a TSB product be used to diagnose infection?
Neogen’s sheet states that its product is not intended for use in the diagnosis of disease or other conditions in humans.
FAQ
What does TSB stand for?
Tryptic soy broth. It is also called soybean-casein digest broth or casein soya bean digest broth.
What is the pH of tryptic soy broth?
Both NCMA and Neogen give a final pH of 7.3 ± 0.2 at 25 °C.
How much powder makes a litre?
Both sources give 30 g of the commercial preparation per litre of water.
What is the broth used for?
Neogen lists cultivation of a wide variety of microorganisms, cosmetics contaminant testing, food-industry use, detection of viable bacteria in live vaccines, and, with supplements, blood culture and group D streptococci work.
Sources
- Neogen, Technical Specification Sheet FS-TSS-0192 rev 4.0, Tryptic Soy Broth (Soybean-Casein Digest Broth), effective 2023-08-30, https://media.neogen.com/m/1b0f165bc191d9c3. Date checked: 2026-10-29.
- NCMA at Bigelow Laboratory, Medium 11 TSB (Bacto Tryptic Soy Broth, Soybean-Casein Digest Medium), https://ncma.bigelow.org/PDF%20Files/NCMA%20Medium%2011%20TSB.pdf. Date checked: 2026-10-29.
