Written and maintained by CASRAI Editorial Board
Last updated
Short answer: A transport medium in microbiology is a semisolid or liquid holding medium that keeps the organisms on a swab or in a stool sample alive, without letting them multiply, between collection and culture. The common bacterial families are Stuart, Amies (a modification of Stuart) and Cary-Blair. Which one is acceptable depends on the target organism and how long the specimen waits, and the labelled hold time matters as much as the medium name. This page is general product information, not medical advice.
Definition and scope
Thermo Fisher’s Remel instructions for use describe Amies Transport Medium as a semisolid medium recommended for qualitative procedures for the transport of clinical swab specimens to the laboratory. In the US a bacterial collection and transport system is regulated as a Class I device under 21 CFR 866.2900. This page covers general bacterial transport media. Virus and universal transport media are covered in viral transport medium, and swab types and culture workflow in throat culture swab. For the physical swab, see sterile swab sticks.
How the media differ in practice
Stuart transport medium and Amies transport medium
Amies medium is described in the Remel instructions as a modification of Stuart transport medium, introduced by Stuart and colleagues in 1954. Cary and Blair determined that the sodium glycerophosphate used in earlier formulations could act as an energy source that let contaminants overgrow pathogens, so Amies substituted an inorganic phosphate buffer. Charcoal was added later to improve survival of gonococci. Sodium thioglycollate and agar provide a reduced environment that suits a variety of bacteria, and the product is 0.3% sodium chloride with a pH of 7.3 ± 0.2 at 25°C. The CDC manual states that Amies and Stuart media are both acceptable for Shigella and E. coli O157:H7.
Cary-Blair transport medium
The CDC laboratory manual on epidemic dysentery and cholera states that Cary-Blair can be used to transport many enteric pathogens, including Shigella, Vibrio cholerae and E. coli O157:H7. It is semisolid, and because of its high pH (8.4) it is the medium of choice for transport and preservation of V. cholerae. The same manual says Amies and Stuart are inferior to Cary-Blair for V. cholerae.
Anaerobic and fastidious organisms
The FDA 510(k) summary for an Amies swab system (K131630) gives the intended use as collection and transport of specimens containing aerobic, anaerobic and fastidious bacteria to the laboratory for bacteriological examination and culture. FDA product codes separate aerobic transport systems (JTW) from anaerobic transport systems (JTX), and swab collection systems more broadly (LIO). A supplier’s anaerobic claim should therefore be read against the product code and the instructions for use, not the medium name alone.
Stuart, Amies and Cary-Blair compared
| Medium | What the source states | Source |
|---|---|---|
| Cary-Blair | Many enteric pathogens (Shigella, V. cholerae, E. coli O157:H7); semisolid; pH 8.4; medium of choice for V. cholerae | CDC |
| Amies and Stuart | Acceptable for Shigella and E. coli O157:H7; inferior to Cary-Blair for V. cholerae | CDC |
| Amies with charcoal | Gonococci survive at least 6 to 12 hours; by 24 hours conditions may prevent recovery | Remel IFU |
| Amies swab system (one 510(k) device) | Viability maintained up to 48 hours for the ten tested strains; N. gonorrhoeae acceptable to 24 hours | FDA K131630 |
Hold times and storage temperatures differ by specimen type and by product, and published documents do not agree on one rule. The Remel instructions for swab specimens state that refrigeration may be detrimental to some organisms. The product’s own instructions for use and the receiving laboratory’s requirements govern.
Where it matters for labs, clinics and supply decisions
How a supplier’s hold-time claim is validated
The FDA summary for K131630 cites CLSI M40-A, Quality Control of Microbiological Transport Systems (2003 edition). In that review, ten ATCC strains were tested by a roll-plate method, held for 0, 24 and 48 hours at 4 to 8°C and at 20 to 25°C. A “48-hour” claim therefore refers to defined test organisms under defined temperatures, and it does not extend to every organism or specimen.
Documents worth asking a supplier for
- The instructions for use, including the intended use and the stated hold times and temperatures
- The list of organisms the product was tested with, and any organisms for which survival is limited (for example gonococci)
- The FDA product code and regulation number for the product (for example 866.2900 and LIO, JTW or JTX)
- The quality-control statement, including whether it references CLSI M40
- The labelled shelf life of the specific product
Shipping of the packed specimen is a separate question; see biological substance Category A vs Category B. For plated media used after transport, see what is an agar plate.
Common misunderstandings
- “Transport medium grows the organism.” It is meant to preserve viability in transit. The Remel instructions describe the phosphate buffer and reduced environment as maintaining survival, and the culture itself happens at the laboratory.
- “Any medium works for any pathogen.” The CDC manual says Amies and Stuart are acceptable for Shigella and E. coli O157:H7 but inferior to Cary-Blair for V. cholerae.
- “One storage temperature suits every specimen.” The Remel instructions warn that refrigeration may be detrimental to some organisms on swab specimens, so the instructions for the specific product apply.
- “Viral transport medium is a bacterial transport medium.” Different products with different intended uses; see the viral transport medium guide.
FAQ
What is a bacterial transport medium?
A holding medium that keeps bacteria from a specimen viable between collection and culture. Examples named by the CDC and Remel documents are Cary-Blair, Amies and Stuart.
What is Stuart transport medium?
The 1954 formulation from which Amies medium was derived, according to the Remel instructions for use. The CDC lists it as acceptable for Shigella and E. coli O157:H7 and inferior to Cary-Blair for V. cholerae.
What is an anaerobic transport medium?
FDA classifies anaerobic transport systems under product code JTX, separately from aerobic systems (JTW). The K131630 summary describes an Amies-based system intended for aerobic, anaerobic and fastidious bacteria.
What is a transport swab?
A swab supplied with a transport medium, usually in a tube, so the specimen stays viable on the way to the laboratory. The K131630 device is a rayon swab with 4 ml of Amies medium, with or without charcoal.
Sources
- CDC, Laboratory Methods for the Diagnosis of Epidemic Dysentery and Cholera, Chapter 2, Collection and Transport of Fecal Specimens (checked 2026-11-01): cdc.gov
- Thermo Fisher Scientific (Remel), Amies Transport Medium with and without Charcoal, instructions for use IFU60060 (checked 2026-11-01): documents.thermofisher.com
- FDA, 510(k) decision summary K131630, Puritan Amies Medium Collection and Transport System (checked 2026-11-01): accessdata.fda.gov
