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

What is Cary Blair Transport Medium?

• Cary Blair Transport Medium is a type of non-nutritive, semi-solid, chemically defined medium used for the collection and preservation of clinical specimens for microbiological analysis. It is specifically designed to maintain the viability of organisms during the period between specimen collection and laboratory examination.
• The medium has a simple formulation with minimal nutrients, which prevents the multiplication of test organisms during transport. Cary Blair Transport Medium is a modified version of Stuart’s Medium, where sodium glycerophosphate is replaced with inorganic phosphates to create an improved buffering system. This modification helps prevent overgrowth of Enterobacteriaceae and contributes to the effective preservation of Salmonella, Shigella, Vibrio cholerae, and Escherichia coli O157:H7 for extended periods.
• The main purpose of Cary Blair Transport Medium is to provide a suitable environment that maintains the viability of the collected organisms without promoting their growth. It is particularly used for transporting clinical specimens suspected to contain enteric pathogens such as Shigella, Salmonella, Vibrio cholerae, and Escherichia coli O157:H7.
• The medium is prepared with minimal nutrients to support organism survival without multiplication. Sodium thioglycollate helps maintain a low oxidation-reduction potential, while disodium phosphate acts as a buffer and sodium chloride maintains osmotic equilibrium within the medium.
• To collect specimens using Cary Blair Transport Medium, sterile cotton-tipped swabs on wooden sticks are used. The swabs are pushed down to approximately one-third of the medium depth, and the stick is cut so that when the cap is tightly screwed down, the swab is forced to the bottom of the medium. This ensures proper contact between the specimen and the transport medium.
• Cary Blair Transport Medium, with its simple and effective formulation, provides a reliable means of preserving the viability of organisms in clinical specimens during transportation to the laboratory for further analysis.

Principle of Cary Blair Transport Medium

The principle of Cary Blair Transport Medium lies in its formulation and specific components that facilitate the preservation and viability of bacterial cells in clinical specimens during transportation. Here are the key principles:

1. Semi-solid medium with minimal nutrients: Cary Blair Transport Medium is a semi-solid medium with limited nutrient content. This non-nutritive composition helps prevent the multiplication of organisms during transportation, ensuring that the test organisms remain viable without excessive growth.
2. Sodium chloride and calcium chloride for osmotic balance: The presence of sodium chloride and calcium chloride in the medium helps control cell permeability and maintains an osmotic balance environment. This balance is crucial for the preservation of viable bacterial cells within the transport medium.
3. Sodium thioglycollate for low oxidation-reduction potential: Sodium thioglycollate, an ingredient in the medium, creates a low oxidation-reduction potential. This feature contributes to the preservation of organisms by minimizing oxidative damage and maintaining their viability.
4. Disodium hydrogen phosphate for stable pH: The addition of disodium hydrogen phosphate to Cary Blair Transport Medium helps maintain a stable pH. This stable pH prevents detrimental pH fluctuations that could harm the organisms present in clinical specimens.
5. Alkaline pH for minimizing bacterial destruction: The medium has an alkaline pH (pH 8.4), which helps minimize bacterial destruction caused by the formation of acid. This alkaline environment supports the viability and survival of the organisms during transportation.
6. Viability of Vibrio cultures: The high pH of Cary Blair Transport Medium (pH 8.4) is particularly beneficial for maintaining the viability of Vibrio cultures over an extended period. Therefore, it is considered the preferred medium for the transport and preservation of Vibrio cholerae.

The principle behind Cary Blair Transport Medium is to create an environment that preserves the viability of bacterial cells in clinical specimens during transportation. The combination of minimal nutrients, osmotic balance, low oxidation-reduction potential, stable pH, and alkaline conditions ensures the survival of the organisms, including Vibrio cholerae, for longer durations.

Principle of Modified Cary Blair Transport Medium

The principle of Modified Cary Blair Transport Medium builds upon the original Cary Blair Medium, which was designed for the collection and transport of clinical specimens. Here are the key principles of the modified version:

1. Minimal nutrients: Modified Cary Blair Transport Medium is prepared with minimal nutrients. This nutrient limitation is intended to increase the survival of organisms during transportation without promoting their multiplication. It helps maintain the viability of the organisms without excessive growth.
2. Sodium thioglycollate for low oxidation-reduction potential: Sodium thioglycollate is incorporated into the medium to provide a low oxidation-reduction potential. This feature helps minimize oxidative damage and contributes to the preservation of organism viability during transport.
3. Relatively alkaline pH: The pH of Modified Cary Blair Transport Medium is relatively alkaline. This alkaline pH minimizes bacterial destruction that could occur due to the formation of acid during transportation. It creates an environment that supports the survival of organisms.
4. Addition of phenol red indicator: Modified Cary Blair Transport Medium includes phenol red as an indicator. Phenol red is red at alkaline pH and yellow at acidic pH. The presence of phenol red allows for visual monitoring of pH changes in the medium, providing an indication of potential alterations in the specimen during transport.
5. Limited viability of fastidious microorganisms: While Modified Cary Blair Transport Medium can maintain viability for a limited period, it may not be suitable for long-term preservation of fastidious microorganisms. For optimal results, direct inoculation of isolates onto enriched media should be performed at the same time the specimen is inoculated into the transport medium.

The principle behind Modified Cary Blair Transport Medium is to provide a nutrient-limited environment with a low oxidation-reduction potential and alkaline pH to enhance the survival and viability of organisms during transportation. The addition of phenol red indicator allows for pH monitoring. However, for the long-term viability of fastidious microorganisms, direct inoculation onto enriched media is recommended in conjunction with the use of the transport medium.

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
pH	8.4 ± 0.2 @ 25°C

Composition of Modified Cary Blair Transport Medium

Ingredients	Gms / Litre
Disodium phosphate	1.100
Sodium thioglycollate	1.500
Sodium chloride	5.000
Phenol red	0.018
Agar	5.000
Final pH (at 25°C)	8.4±0.2
**Formula adjusted, standardized to suit performance parameters

Preparation of Cary Blair Transport Medium

The preparation of Cary Blair Transport Medium involves the following steps:

1. Suspend 13.3 grams of Cary Blair Transport Medium powder in 1 liter of distilled water. Mix thoroughly to ensure proper dissolution of the agar.
2. Gently heat the suspension, bringing it to a boil to completely dissolve the agar. Take care not to overheat or boil vigorously.
3. Dispense the prepared medium in 7 ml amounts into screw-cap bottles. The bottles should have a capacity of 9 ml (large size Bijou bottles). Ensure that the bottles are clean and sterile before dispensing the medium.
4. Sterilize the bottles with the medium by steaming. Loosen the caps of the bottles to allow steam to escape during the sterilization process. Do not autoclave the medium.
5. Steam the bottles with the medium at 100°C for 15 minutes to achieve sterilization. This steaming process helps eliminate potential contaminants while maintaining the integrity of the medium.
6. After sterilization, allow the bottles to cool down. Once cooled, tighten the screw caps of the bottles to prevent water loss and maintain the sterility of the medium.
7. Properly label the bottles with necessary information such as the medium name, batch number, and date of preparation. Clear labeling ensures accurate identification and tracking of the medium.
8. Store the bottles in a cool, dark place with the screw caps tightly secured. This storage condition helps maintain the quality and longevity of the Cary Blair Transport Medium.

By following these steps, Cary Blair Transport Medium can be prepared and stored properly for the collection and transportation of clinical specimens.

Preparation of Modified Cary Blair Transport Medium

The preparation of Modified Cary Blair Transport Medium involves the following steps:

1. Suspend 12.6 grams of Modified Cary Blair Transport Medium powder in 991 ml of distilled water. Mix thoroughly to ensure proper dissolution of the medium.
2. Heat the suspension to boiling to completely dissolve the medium. Boil gently, ensuring not to overheat or boil vigorously.
3. Allow the solution to cool down to approximately 50°C. This temperature is suitable for the next steps of the preparation.
4. Aseptically add 9 ml of a 1% aqueous calcium chloride solution to the cooled medium. This addition helps stabilize the medium and maintain the appropriate osmotic balance.
5. If necessary, adjust the pH of the medium to 8.4 using suitable pH adjusters such as hydrochloric acid or sodium hydroxide. Maintain sterility during the pH adjustment process.
6. Distribute the prepared medium in 7 ml amounts into screw-capped tubes. The tubes should be sterile and suitable for the intended application.
7. Steam the tubes with the medium for 15 minutes. This steaming process is essential for sterilizing the medium and eliminating potential contaminants.
8. Allow the tubes to cool down to room temperature. Once cooled, tighten the caps of the tubes to ensure a tight seal and maintain the sterility of the medium.

By following these steps, Modified Cary Blair Transport Medium can be properly prepared for the collection and transport of clinical specimens. Ensure proper labeling and storage of the tubes to maintain the quality and efficacy of the medium.

Recommended Procedure for Test on Cary Blair Transport Medium

The recommended procedure for using Cary Blair Transport Medium is as follows:

1. Swab Collection: If the clinical specimen is collected using a swab, carefully insert the swab into the upper third portion of the medium. Ensure that the swab is fully immersed in the medium. Aseptically cut or break the protruding portion of the swab, leaving only the handle outside the tube. Recap the tube tightly to maintain sterility.
2. Solid Sample Collection: If the clinical sample is solid, such as a tissue sample, fully immerse the sample in the Cary Blair Transport Medium. Ensure the sample is fully submerged. Recap the tube tightly to maintain sterility.
3. Labeling: Clearly label the tube with appropriate information to avoid any ambiguity regarding the identity of the specimen. Include relevant patient information and specimen details.
4. Transport: As soon as possible after collection, transport the sealed specimen tube to the laboratory for processing. Prompt transportation helps maintain the viability of the organisms and minimizes the risk of contamination.
5. Laboratory Processing: Once the specimen arrives in the laboratory, it should be processed promptly. The Cary Blair Transport Medium should be sub-cultured onto an appropriate medium suitable for the recovery of the specific organism of interest. This step allows for further growth and isolation of the target organism.

By following this recommended procedure, the integrity and viability of the clinical specimen, as well as the target organisms within it, can be maintained during transportation and subsequent laboratory processing.

Appearance of Cary Blair Transport Medium

The appearance of Cary Blair Transport Medium can be described at two different stages: as a dehydrated medium and as a prepared medium.

Dehydrated medium: Cary Blair Transport Medium in its dehydrated form is an off-white colored, free-flowing powder. It is typically packaged in containers or pouches.

Prepared medium: When the dehydrated medium is reconstituted and prepared according to the instructions, it transforms into a light amber colored, semi-solid gel. The prepared medium has a smooth and gel-like consistency, allowing it to maintain its shape while remaining semi-solid.

It is important to note that the appearance may vary slightly depending on the specific manufacturer or brand of Cary Blair Transport Medium. However, in general, the dehydrated medium is an off-white powder, while the prepared medium is a light amber semi-solid gel.

Quality Control Organisms for Cary Blair Transport Medium

Quality control of Cary Blair Transport Medium involves testing the medium using specific control organisms to ensure its performance meets the required standards. Here is an overview of the quality control process:

1. Testing of control organisms: All lot numbers of Cary Blair Transport Medium with Indicator undergo testing using established laboratory quality control procedures. This testing involves the use of control organisms to evaluate the growth performance of the completed medium.
2. Checking pH, color, depth, and sterility: Before testing with control organisms, the medium is checked for correct pH, color, depth, and sterility. These parameters ensure that the medium is within the acceptable range and free from contamination.
3. Inoculation and incubation: Control organisms, such as Campylobacter jejuni, Salmonella enterica serovar Typhimurium, Shigella flexneri, Escherichia coli, and Bacteroides fragilis, are inoculated into the medium. The inoculated medium is then incubated under specific conditions.
4. Growth evaluation: After a 24-hour incubation period at room temperature, the medium is sub-cultured onto a nutrient medium to assess the viability and growth of the control organisms. Expected results for each organism are established based on their known growth characteristics.
5. Interpretation of results: The growth performance of the control organisms is evaluated to ensure they exhibit the expected growth on subculture. If the quality control results deviate from the expected outcomes, it may indicate issues with the medium, and patient results should not be reported until the issue is resolved.

By performing quality control tests using specific control organisms, laboratories can verify the performance and reliability of Cary Blair Transport Medium. This helps maintain the integrity of the medium and ensures accurate and consistent results when using it for the transportation and preservation of clinical specimens.

Positive controls	Expected results
Shigella flexneri  ATCC 12022	Good growth on subculture
Salmonella Typhimurium  ATCC 14028	Good growth on subculture
Negative control
Uninoculated medium	No change

Uses of Cary Blair Transport Medium

Cary Blair Transport Medium has specific uses in the transportation and preservation of clinical specimens, particularly stool and rectal swabs. Here are the key uses of Cary Blair Transport Medium:

1. Transportation of clinical specimens: Cary Blair Transport Medium is recommended for use in the transportation of clinical specimens, especially those obtained from stool and rectal swabs. The medium helps maintain the viability and integrity of the collected organisms during transit to the laboratory for further analysis.
2. Preservation of enteric pathogens: The primary use of Cary Blair Transport Medium is for the transportation and preservation of enteric pathogens. It is particularly effective in preserving the viability of various enteric pathogens, including Shigella, Salmonella, Vibrio cholerae, and Escherichia coli O157:H7. These pathogens are responsible for causing gastrointestinal infections and can be found in stool samples.
3. Maintaining viability during transportation: Cary Blair Transport Medium provides an optimal environment that supports the survival and viability of enteric pathogens during the transportation phase. The minimal nutrient content of the medium prevents the growth and multiplication of organisms, while the specific formulation and pH help maintain their viability for an extended period.

By using Cary Blair Transport Medium, clinical laboratories can ensure the integrity and viability of enteric pathogens during the transit of clinical specimens, particularly those obtained from stool and rectal swabs. This medium is specifically designed to preserve the viability of these pathogens, allowing for accurate and reliable diagnostic testing and analysis.

Limitations of Cary Blair Transport Medium

Cary Blair Transport Medium has certain limitations that should be taken into consideration. Here are the key limitations:

1. Intended for transport only: Cary Blair Transport Medium is specifically designed for use as a transport medium and should not be used as an enrichment medium or for long-term storage of specimens. It is optimized to maintain the viability of organisms during transportation, but its effectiveness may diminish over time.
2. Impact of antibiotic therapy: Specimens collected after the initiation of antibiotic therapy may not be suitable for successful recovery of organisms. Antibiotics can inhibit the growth and recovery of targeted organisms, potentially affecting the accuracy of results.
3. Acidic stool specimens: Some stool specimens may be highly acidic, which can overcome the buffering capacity of the medium. This may cause the red indicator in the medium to shift to a yellow color. If the medium turns yellow, it indicates a pH change and should be discarded. In such cases, it is advisable to request another specimen.
4. Temperature control for certain pathogens: Proper transport and storage of fecal specimens at temperatures between 2-8°C (refrigeration) are crucial for the recovery of certain enteric pathogens like Shigella and Campylobacter. Maintaining the appropriate temperature during transport is essential to preserve the viability and integrity of these pathogens.
5. Avoid contamination with urine: It is important to avoid contamination of the specimen with urine. Urine can introduce unwanted microorganisms and potentially interfere with the analysis of the target enteric pathogens.

Considering these limitations, it is essential to use Cary Blair Transport Medium according to its intended purpose and adhere to proper specimen collection, handling, and storage protocols. Following the recommended procedures and avoiding potential sources of contamination can help ensure accurate and reliable results.

FAQ

References

• https://exodocientifica.com.br/_technical-data/M202.pdf
• https://exodocientifica.com.br/_technical-data/M1660.pdf
• https://assets.thermofisher.com/TFS-Assets/LSG/manuals/IFU60450.pdf
• https://www.puritanmedproducts.com/cb-200.html
• https://www.wakemed.org/assets/documents/pathology/microbiology-specimen-collection-and-transport.pdf
• https://assets.fishersci.com/TFS-Assets/MBD/Instructions/IFU21610.pdf
• http://www.dalynn.com/dyn/ck_assets/files/tech/AN280.pdf