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This page describes products and general use; it is not medical advice.
A TSA plate is a Petri dish of tryptic soy agar (also written trypticase soy agar), a general-purpose, non-selective growth medium used to detect and count microorganisms. It is used by microbiology, quality-control and environmental-monitoring staff in laboratories and cleanrooms. After reading you should be able to tell what is in the plate, which format fits which job, how it is regulated, and how to avoid the usual handling errors.
What is a TSA plate?
A TSA plate holds agar made to the U.S. Pharmacopeia (USP) standard formula for Soybean-Casein Digest Agar. Hardy Diagnostics’ instructions for use (IFU) for its USP-grade plates describe the product as a general growth medium for the detection and enumeration of microorganisms from non-clinical samples, prepared in accordance with USP <62> and meeting the harmonized European, US and Japanese pharmacopoeial requirements for microbial quality of non-sterile products. Several catalogue items in the same IFU are not intended for the diagnosis of human disease, so the IFU for the exact catalogue number decides the intended use.
Who uses it: pharmaceutical and device quality-control labs, cleanroom environmental-monitoring teams, and teaching and research microbiology labs.
What is in a TSA plate (composition)?
Per the Hardy IFU, one litre of medium contains:
| Component | Amount per litre | Role stated in the IFU |
|---|---|---|
| Pancreatic digest of casein | 15.0 g | Amino acids and nitrogen |
| Peptic digest of soybean meal | 5.0 g | Amino acids and nitrogen |
| Sodium chloride | 5.0 g | Osmotic equilibrium |
| Agar | 15.0 g | Solidifying agent |
Final pH is 7.3 ± 0.2 at 25 °C. Because the medium has no selective agents and no indicator, it supports a broad range of organisms rather than separating them. Blood agar is built on this kind of base with added defibrinated blood; see alpha hemolysis on a blood agar plate for how that changes what you read.
What is the difference between TSA and SDA plates?
TSA is the general-purpose medium; Sabouraud dextrose agar (SDA) is a separate medium with its own formula and IFU, usually chosen when fungi are the target. The Hardy TSA IFU itself uses TSA for both groups, with different incubation: bacteria at 30–35 °C for up to 3 days and fungi at 20–25 °C for up to 5 days. Where a procedure or pharmacopoeial method names SDA specifically, use SDA rather than substituting TSA.
Is TSA the same as nutrient agar?
No. They are separate named formulations. TSA’s formula is the casein plus soybean digest recipe in the table above; compare it with the printed formula on a nutrient agar label before treating the two as interchangeable. For the wider plate families, see what is an agar plate.
What bacteria grow on TSA plates?
TSA is described as a general-purpose, non-selective medium that supports moderately fastidious to non-fastidious bacteria (Wikipedia, “Trypticase soy agar”). Fastidious organisms generally need enrichment such as blood, which is why blood agar is built on a TSA-type base. Which specific organisms a given lot must recover is set by the growth-promotion test in the applicable USP chapter, not by this page.
Formats and fill volumes
Hardy lists these plate formats in its TSA, USP IFU:
| Catalogue no. | Format | Fill |
|---|---|---|
| G60 | 15 × 100 mm plate | 18 mL |
| W64 | 15 × 100 mm plate | 26 mL |
| H19 | 15 × 150 mm plate | 69 mL |
| J330 | TSA/CET/MSA triplate | 7 mL per section |
The IFU also lists tube and bottle formats. Plates (G60, G60BX, H19, W64) are stored at 2–8 °C away from direct light; bottle and deep-tube formats are stored at 2–30 °C.
Using TSA plates for environmental monitoring
The IFU points users to USP <1116> for environmental monitoring and to USP <61>, <62> and <71> for enumeration, growth promotion and sterility. Practical points it states:
- Settle plates: expose the agar for 15 minutes or longer according to the established procedure, and do not invert the lid while the plate is open.
- Impact air samplers: use the plate size the sampler specifies.
- Incubation: invert the plates; bacteria 30–35 °C up to 3 days, fungi 20–25 °C up to 5 days.
- Reporting: colonies are reported as colony-forming units (CFU), and recovery should be trended over time rather than judged from a single sample count.
- Growth promotion: inoculate with no more than 100 CFU on solid media; growth should not differ by more than a factor of 2 from the calculated value and should be comparable to a previously approved batch.
Safe use and handling basics
- Warm plates to room temperature and make sure the surface is dry before inoculating.
- Do not use plates that show shrinking, cracking, discoloration, contamination or that are past expiry. Protect from light, heat, moisture and freezing.
- The IFU states that the media may contain animal-origin components and should be treated as potentially infectious; use is for trained laboratory personnel with standard precautions and aseptic technique. Sterilize biohazard waste before disposal (the IFU cites CLSI M29).
- Solid media in tubes or bottles should be re-melted only once, and not in a microwave.
Regulatory status
In the U.S., plain non-selective culture media fall under FDA product code JSG, “Culture Media, Non-Selective and Non-Differential”, a Class I device under 21 CFR 866.2300 (openFDA classification database, read 2026-11-07). The AccessGUDID record for Hardy’s 15 × 100 mm USP TSA monoplate (10 packs per case) lists it as single-use, not packaged sterile, stored at 2–8 °C, with GMDN term 58685 “Basic/simple nutrient agar culture medium IVD”.
Common mistakes
- Assuming every TSA plate is a clinical diagnostic product; check the IFU for the intended use of the specific catalogue number.
- Incubating bacteria and fungi at the same temperature when the procedure specifies different conditions.
- Inoculating cold or wet plates.
- Reading a single count instead of trending recovery.
- Leaving a settle plate uncovered longer or shorter than the validated exposure time.
For liquid-medium counterparts and media quality control, see tryptic soy broth and culture media preparation.
Frequently asked questions
What is a TSA plate?
A Petri dish of tryptic soy agar, a general, non-selective medium for detecting and counting microorganisms, made to the USP Soybean-Casein Digest Agar formula.
What is the difference between TSA and SDA plates?
They are different media with different formulas; SDA is the one typically named for fungi. Follow the medium your method specifies.
Is TSA the same as nutrient agar?
No; they are separate formulations. Check the formula printed on each product.
What bacteria grow on TSA plates?
Moderately fastidious to non-fastidious bacteria; fastidious species need enriched media such as blood agar.
Sources
- Hardy Diagnostics, Instructions for Use, “Tryptic Soy Agar (TSA), USP” (PDF copy hosted by Bioactiva), read 2026-11-07.
- NLM AccessGUDID, device record 00816576025992, read 2026-11-07.
- openFDA device classification, product code JSG (21 CFR 866.2300), read 2026-11-07.
- Wikipedia, “Trypticase soy agar”, read 2026-11-07 (context only).
