Culture Media

Cary Blair Transport Medium Composition, Principle, Preparation, Results, Uses

Cary-Blair Transport Medium is simple, semi-solid, and non-nutritive medium that is used to collect and storage of samples of microbiological organisms. The...

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This article writter by MN Editors on January 22, 2022

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Cary Blair Transport Medium Composition, Principle, Preparation, Results, Uses
Cary Blair Transport Medium Composition, Principle, Preparation, Results, Uses

Cary-Blair Transport Medium is simple, semi-solid, and non-nutritive medium that is used to collect and storage of samples of microbiological organisms. The low levels of nutrients in the medium aid in the life of the organisms, without multiplication. The semisolid consistency facilitates the ability to transport easily and the medium is able to be stored for up to a year after its preparation at temperatures of room temperature. Cary-Blair Transport Medium is a modification to Stuart’s Medium which is comprised of a more effective buffering system that replaces sodium glycerophosphate by organic phosphates. This new formulation helps prevent the growth of Enterobacteriaceae and aids in the long-term conservation for Salmonella as well as Shigella for extended durations. It is employed for the transport of clinical specimens believed to have enteric pathogenssuch as Shigella, Salmonella, Vibrio Cholerae, and Escherichia Coli O157 H7.

Principle of Cary Blair Transport Medium

Semi-solid medium for Cary-Blair Transport medium that has minimal nutrients. The calcium and sodium chloride levels of the medium help in limiting cell permeability. They also ensure an osmotic equilibrium to preserve viable bacteria. The sodium thioglycollate is a lower potential for oxidation and reduction. Additionally disodium hydrogen phosphate assists to maintain a stable pH and prevents the formation of pH fluxes that could harm the organisms found in clinical samples. The medium’s alkaline pH helps to prevent bacterial death because of the production of acid. Because this medium is acidic and has a pH high (8.4) which means that it is able to sustain Vibrio cultivars can be sustained for longer periods of time and is considered to be the preferred medium for the transport and preservation of Vibrio cholerae.

Composition of Cary Blair Transport Medium

Ingredients        gm/litre
Disodium hydrogen phosphate          1.1
Sodium thioglycollate          1.5
Sodium chloride          5.0
Calcium chloride          0.1
Agar          5.0
pH8.4 ± 0.2 @ 25°C

Preparation of Cary Blair Transport Medium

  1. Suspend 13.3 grams within 1 liter distillate water. Bring it to a boil in order to dissolve the Agar.
  2. Distribute mediums in 7 ml portions in screw-cap bottles with 9ml capacity (large size Bijou bottles).
  3. Sterilize with steaming using caps loosening (do not use autoclave) at 100degC for fifteen minutes.
  4. Cool and tighten the caps on the screw cap to stop loss of water. Label the bottles.
  5. Keep in a cool, dark location by screwing the tops of the bottles securely.

Appearance of Cary Blair Transport Medium

  • Dehydrated medium: Off-white color, free-flowing powder 
  • Prepared medium: Light amber color, semi-solid gel

Quality Control

Positive controlsExpected results
Shigella flexneri  ATCC 12022Good growth on subculture
Salmonella Typhimurium  ATCC 14028Good growth on subculture
Negative control 
Uninoculated mediumNo change

Uses of Cary Blair Transport Medium

  • It is suggested to use it for the transport and preservation of the clinical specimens , particularly stool and rectal swabs.
  • It’s used to carry pathogens that are enteric which include Shigella, Salmonella, Vibrio cholerae, as well as Escherichia O157:H7 coli.

Limitations of Cary Blair Transport Medium

  • It is intended only to be used for transportation purposes. Therefore long delays in the transport or processing of specimens can cause a decrease in viability of bacterial cells , and permit, in a certain degree the contaminating flora to reproduce within the medium. Thus, a rapid shipping and processing of the sample is vital for the accurate and definitive lab results.
  • The prompt plating, refrigeration, or freezing of the specimens that are in the Cary Blair medium is crucial in the identification of Shigella which is significantly more vulnerable than other enteric bacteria.
  • Cary-Blair Transport Medium is prone to extreme temperatures, and as such the medium hasn’t been autoclaved. Therefore, the sterilizability of this product has been verified, but it is not 100%.
  • The specimens obtained following the initiation of antibiotic therapy could be incongruous to the healing of the enteric pathogens.
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Microbiology Notes is an educational niche blog related to microbiology (bacteriology, virology, parasitology, mycology, immunology, molecular biology, biochemistry, etc.) and different branches of biology.

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