Culture media are solid, semisolid, or liquid preparations containing essential nutrients and minerals vital for microorganisms’ survival and growth. They are also called growth media. They provide nutritional requirements and a place to grow the microorganisms in the laboratory. Based on physical state, culture media are classified as solid, semi-solid, and liquid culture media. Similarly, based on their function (intended use), they are classified as general purpose (supportive) media, selective media, differential (indicator) media, enriched media, enrichment media, sugar media, and transport media.
Transport media are those culture media that are used to maintain the viability of pathogenic microorganisms present in a clinical sample and to prevent the potential pathogens to be overgrown by other commensals or contaminants in the specimen during the transportation of the clinical specimen to the clinical/diagnostic laboratory.
Transport media are typically buffer solutions with minimum nutrients like carbohydrates, peptones, and salts, excluding growth factors. Some also contain selective inhibitory components. Due to this minimum nutrient and lack of carbon, nitrogen, and organic growth factors, microorganisms present in the specimen do not multiply but remain viable.
Principle of Transport Media
Transport media only contains enough energy sources like peptone and carbohydrates to maintain the viability of microorganisms potentially present in a specimen. They are well buffered and pH maintained so the present organisms do not suffer from chemical stress.
No additional carbon, nitrogen, and other organic and inorganic (ions and minerals) growth factors are incorporated in the medium. Some may also contain inhibitory substances that selectively inhibit the growth and multiplication of microorganisms. Due to this, the microorganisms can’t multiply but remain viable for a certain duration under optimum physical conditions. Hence, the transport media tends to preserve the microbiome of the specimens in their original condition till they are processed in a lab.
Uses of Transport Media
- To maintain the specimen and its microbiome in their original state after specimen collection to the processing period.
- To maintain the viability of specific pathogenic microorganisms potentially present in a clinical specimen.
- To prevent commensals and contaminants from overgrowing the pathogenic microorganisms potentially present in a clinical specimen.
Types of Transport Media
- Based on their physical state, transport media may be classified as semi-solid or liquid transport media.
- Based on their utility, they can be classified as bacterial transport media, viral transport media, and parasite transport media. Specimens for fungal culture are generally transported without any transport media.
Some Common Transport Medium and Intended Use
|Transport Media||Type||Intended Use|
|Alkaline Peptone Water||Liquid bacterial transport medium||Recovery and transport of V. cholerae|
|Amies Transport Medium||Liquid or Semi-solid bacterial transport medium||Recovery of aerobes and anaerobes|
Transport of swab specimens
|Amies Charcol Transport Medium||Semi-solid bacterial transport medium||Recovery of Neisseria gonorrhea|
Recovery of anaerobesTransport of swabs
|Anaerobic Transport Medium||Semi-solid bacterial transport medium||Recovery of anaerobic, microaerophilic, and facultative bacteria|
|Buffered Glycerol (Buffered Glycerol Saline) Medium||Liquid bacterial transport medium||Transport of fecal and rectal samples for recovery of enteric pathogens|
Recovery of Salmonella spp., Shigella spp., and E. coli in fecal sample
|Cary-Blair Medium||Semi-solid bacterial transport medium||Transport of fecal and rectal samples for recovery of enteric pathogens|
Recovery of Vibrio cholerae, V. parahaemolyticus, Salmonella spp., Shigella spp., and E. coli O157:H7
|Chlamydia Transport Medium||Liquid bacterial and viral transport medium||Transport of swab for recovery of Chlamydia trachomatis and Herpes Simplex Virus|
|5% to 10% Formalin Solution||Liquid parasites transport medium||Recovery and transportation of intestinal parasites|
|Leibovitz Emory Transport Medium||Liquid Viral Transport Medium||Recovery and transport of viruses|
|Mycoplasma Transport Broth||Liquid bacterial transport medium||Transportation of swabs or body fluid for recovery of Mycoplasma, Ureaplasma, Trichomonas vaginalis, Gardenerella vaginalis, etc.|
|Stuart Transport Medium||Semisolid bacterial transport medium||Transportation of swabs for recovery of fastidious, non-fastidious, and anaerobic bacteria|
|Universal Transport Medium||Liquid viral transport medium||Transport of specimens for recovery of viruses, Mycoplasma, Ureaplasma, and Ricketssiae.|
|Viral Transport Medium||Liquid viral transport medium||Transport of specimens for recovery of viruses|
Applications of Transport Media
- They are used for transferring clinical specimens from the collection center to diagnostic laboratories; especially from remote or resource-limited places to a laboratory.
- They are used to preserve clinical specimens if there is some delay in processing/culturing clinical specimens.
- They are used while sharing or transferring microbial cultures which are highly sensitive to environmental change.
- They are used to suppress the growth of contaminants and other microbial species of non-interest in clinical samples.
- They are used to maintain the viability of anaerobes and fastidious organisms and obligate pathogens in the specimen.
- They are also used in transporting food samples, water samples, and other biological samples for analysis.
Limitations of Transport Media
- As the transport mediums are limited in nutrients, they do not support the survival of organisms for a longer duration.
- Though the transport medium inhibits and prevents the overgrowth of many contaminants, some contaminants having similar metabolic, physical, and chemical requirements also remain viable.
- Physical conditions like temperature and pressure must be maintained.
- Specimens must be cultured in another culture medium for isolation and diagnosis.
- Clinical microbiology procedures handbook / editor in chief, Amy L. Leber. 4th edition. | Washington, DC : ASM Press,  | ?2016 |
- Textbook of Microbiology and Immunology, 2/e. Subhash Chandra Parija. Elsevier Publication, 2012.
- PRESCOTT’S MICROBIOLOGY, TENTH EDITION. / Joanne M. Willey, Hofstra University, Linda M. Sherwood, Montana State University, Christopher J. Woolverton, Kent State University.—Tenth edition.
- Johnson, F. B. (1990). Transport of viral specimens. Clinical Microbiology Reviews, 3(2), 120-131. https://doi.org/10.1128/cmr.3.2.120
- Nahmias A, Wickliffe C, Pipkin J, Leibocitz A, Hutton R. Transport media for herpes simplex virus types 1 and 2. Appl Microbiol. 1971 Sep;22(3):451-4. doi: 10.1128/am.22.3.451-454.1971. PMID: 4330319; PMCID: PMC376331.
- Suitability of new chlamydia transport medium for transport of herpes simplex virus. D L Barnard, K Farnes, D F Richards, G F Croft, and F B Johnson