Quick facts
- Tryptic soy agar is a general-purpose, non-selective medium; it grows a wide range of organisms rather than selecting one group.
- In the United States this kind of medium is a named Class I entry at 21 CFR 866.2300.
- An enriched medium such as chocolate agar is a different entry, 21 CFR 866.2330, and a non-selective, differential medium such as blood agar another, 21 CFR 866.2320, all Class I.
- In Canada a general-purpose culture medium is a Class I in-vitro diagnostic device under the Medical Devices Regulations.
- The medium's performance and its use in environmental monitoring are set by standards: ISO 11133 for preparation and performance testing, CLSI M22 for quality control, and USP general chapter 1116 for microbiological control of the environment.
- The entries and rule text quoted here were checked against the openFDA device classification API and the Regulations on 2026-10-06.
A tryptic soy agar plate is the general-purpose plate a laboratory keeps on the bench for routine recovery and for environmental monitoring. It is used to count organisms in a sample, to check a surface, and as the base that other media are built from. It is non-selective, and that single fact decides which entry it sits under.
What is tryptic soy agar and where is it used?
The medium is also called soybean-casein digest agar, because its two nutrients are a casein digest and a soy digest. It has no selective agent, so it will grow a broad range of bacteria and fungi, which makes it the plate a laboratory uses when it does not know yet what it is looking for. A general-purpose plate is the base for environmental monitoring, for a bioburden count before sterilisation, and for blood agar when red cells are added to it.
There are two formats that a buyer should keep apart. A settle plate is left open to the air for a set time to capture what falls onto it. A contact plate, often called a RODAC plate, is pressed onto a surface to sample what is already there. Both use a general-purpose medium, and both are read the same way.
How do Canada and the United States classify the medium?
The two countries reach the same class from different directions, and the entry depends on the medium.
| Medium | Canada | United States |
|---|---|---|
| Tryptic soy agar (general purpose) | Class I in-vitro diagnostic device | Class I, 21 CFR 866.2300 |
| Blood agar (differential) | Class I | Class I, 21 CFR 866.2320 |
| Chocolate agar (enriched) | Class I | Class I, 21 CFR 866.2330 |
| Medium supplement | Class I | Class I, 21 CFR 866.2450 |
| Basis of the class | General-purpose medium, low individual risk | The named entry it is filed under |
In the United States each medium is a named Class I entry, and a product filed under that entry reaches the market without premarket notification where the entry is exempt. In Canada a general-purpose culture medium is a Class I in-vitro diagnostic device, and a Class I device is not licensed device by device; the manufacturer keeps an establishment licence and the records the Regulations require.
The distinction that matters to a buyer is between the base medium and any neutraliser added to it. A plate that also contains lecithin and polysorbate is still a general-purpose medium, but the neutraliser changes what the plate is validated against, because it is there to stop a residual disinfectant from inhibiting the growth the laboratory is trying to see.
How is the medium used in environmental monitoring?
The format follows the question the laboratory is asking.
| Format | Method | What it measures |
|---|---|---|
| Settle plate | Dish left open for a fixed time | What falls out of the air |
| Contact plate | Dish pressed on a surface | What is on the surface |
| Swab and plate | Surface swabbed, then plated | What is on an irregular surface |
| Bioburden plate | Product washed, wash plated | What is on a product before sterilisation |
Read together, the four rows show why a laboratory cannot report a surface result from a settle plate. The two formats measure different things, and a report that does not say which format was used is not a result that can be compared with a limit.
Which standard decides whether the plate performs?
The plate's performance is a standard question rather than a class question. ISO 11133 sets out how a culture medium is prepared, produced and performance-tested, including the productivity check that shows the medium supports growth. CLSI M22 covers quality control of commercially prepared media, and USP general chapter 1116 covers microbiological control of the environment in which the plate is used.
For a laboratory the practical step is to keep the certificate of analysis with the lot and to record the quality-control organism and the outcome on receipt. That record is what turns a plate into a traceable item when a count is questioned.
What do the two rulebooks actually say?
The entries are short, and the difference between them is the point of this article.
| Entry | Wording in the source | Effect on a tryptic soy agar plate |
|---|---|---|
| 21 CFR 866.2300, US | Culture media, non-selective and non-differential | Named Class I entry |
| 21 CFR 866.2320, US | Culture media, non-selective and differential | Blood agar, Class I |
| 21 CFR 866.2330, US | Culture media, enriched | Chocolate agar, Class I |
| MDR section 45, Canada | An establishment licence for the activity | Who may import or sell |
| Rule 7(1), Canada | all other non-invasive devices are classified as Class I | Class I where a device |
Read together, the five lines explain why a supplier cannot move the class by relabelling a plate. A general-purpose plate described as a selective plate while it carries no selective agent is described against the text, not against the lid.
Which consumables does an environmental monitoring round restock?
A monitoring round runs on the same supplies as any other bench. The sterile screw-cap specimen containers carry the wash or dilution fluid for a bioburden check, and the sterile graduated specimen cups handle the sampling that comes before a plate is opened. A laboratory that also monitors its own steriliser pairs the sterilization monitoring collection with the 24-hour monitoring five-pack trial. Laboratories and multi-site groups ordering at case level use the wholesale ordering page, and the B2B wholesale collection lists the lines held for institutional buyers. Reselling? become a distributor.
What incubation temperature is used?
The temperature follows the organism the plate is meant to recover. A general-purpose plate for a clinical or environmental count is usually incubated near thirty-five degrees Celsius, while a plate used to recover organisms from a room or a water system is often incubated lower, near thirty degrees, to suit a different range. The setting is part of the method, and a count is not comparable to a limit unless the temperature and the time are the same.
The time matters as much as the temperature. A plate read too early will miss a slow grower, and a plate left too long will overgrow and hide the colonies a reviewer wants to count. Both settings belong on the monitoring log next to the result, because a count without its incubation conditions cannot be repeated by the next person who reads the sheet.
A laboratory that prints the temperature and the time beside each count is able to compare one month with the next without re-reading the method, and that comparison is what makes a trend visible before it becomes a finding.
Sources
- 21 CFR 866.2300, Culture media, non-selective and non-differential
- 21 CFR 866.2320, Culture media, non-selective and differential
- 21 CFR 866.2330, Culture media, enriched
- 21 CFR 866.2450, Supplement, culture media
- Medical Devices Regulations, SOR/98-282, full text
- openFDA device classification API
- ISO 11133:2014, preparation of culture media
- CLSI M22, quality control of commercially prepared culture media
- USP, general chapter 1116, microbiological control
- ISO 13485:2016, medical devices quality management
- ISO 14971:2019, risk management for medical devices
- Health Canada, medical devices guidance
- Public Health Ontario, laboratory services test index
- CLSI, clinical and laboratory standards
- Standards Council of Canada
- CCOHS, OSH answers
- US FDA, medical devices
- Canadian Dental Association
A count of how many plates a monitoring round opens is a count that is hard to rebuild later. The printable environmental monitoring log is a blank form with columns for the site, the format, the incubation time and the count, so a result above a limit is visible on the day. The monitoring log generator on the same page sizes the form to the number of rooms a site runs. No account and no sign-up are needed to open either one.
Every monitoring setup is different. Ask a compliance specialist and you will get a written answer specific to your equipment and province, with the regulation or standard it is based on cited.
Related reading
- Microscope Slides in Canada vs the US: Which Size and Finish?
- Blood Culture Bottles in Canada vs the US: Which Rules Apply?
- Microcentrifuge Tubes in Canada vs the US: Which Standards?
CliniEco Medical supplies eye care, laboratory and dental consumables of the kind described in this article. MDEL #35334. This article is written for optometry, laboratory and procurement professionals and is not legal advice; the class of a device and the records kept by a clinic belong to the manufacturer and to the requirements that apply to it.
Frequently Asked Questions
Is tryptic soy agar a selective medium?
No. It is a general-purpose, non-selective medium, which is why it grows a broad range of organisms and is used as the base for other media.
How is it classified in the United States?
It is a non-selective, non-differential medium and is filed as a Class I entry at 21 CFR 866.2300.
Is blood agar the same entry?
No. Blood agar is a non-selective, differential medium filed at 21 CFR 866.2320, and an enriched medium such as chocolate agar is filed at 21 CFR 866.2330.
How does Canada classify the same medium?
In Canada a general-purpose culture medium is a Class I in-vitro diagnostic device, and a Class I device sits under an establishment licence and records rather than a device licence.
What is the difference between a settle plate and a contact plate?
A settle plate is left open so organisms fall onto it from the air, while a contact plate is pressed onto a surface. The two measure different things and are not interchangeable.
Why add lecithin and polysorbate to a plate?
The two neutralisers stop a residual disinfectant from inhibiting growth, so a surface sampled soon after cleaning still gives a true count rather than a falsely low one.
What does the class change for a supplier?
In Canada a Class I device sits under an establishment licence and records rather than a device licence, while a Class II device needs a licence under section 32 supported by an ISO 13485 certificate. In the United States a Class I entry reaches the market without premarket notification where the entry is exempt.
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