Everything You Need To Know About Cary-Blair Transport Medium

Woman researcher performing examination of bacterial culture plate

Cary-Blair Transport Medium has become an indispensable tool in the field of microbiology. It plays a crucial role in the preservation and transportation of bacterial specimens, particularly those related to enteric pathogens. As microbiological analysis relies on accurate and timely diagnosis, the use of an appropriate transport medium is essential for ensuring the integrity of the collected samples.

This article provides a brief overview of the Cary-Blair Transport Medium and highlights its importance in the field of microbiology. In the sections that follow, we will delve deeper into the history, composition, and various applications of this transport medium, as well as discuss best practices for specimen collection and handling. By understanding the significance of Cary-Blair Transport Medium in modern laboratory diagnostics, we can better appreciate its impact on improving the accuracy and efficiency of microbial analysis.

I. History and Development of Cary-Blair Transport Medium

Cary-Blair Transport Medium has its roots in the early 20th century when microbiologists were seeking better ways to transport and preserve bacterial specimens for analysis. The development of this medium was based on the earlier Stuart's Transport Medium, which was created by Dr. Stuart in 1943 for the purpose of maintaining the viability of pathogenic bacteria during transport.

As the demand for more effective transport media grew, researchers Dr. Cary and Dr. Blair introduced a modified version of Stuart's medium in 1964. This new formulation, named Cary-Blair Transport Medium, offered improved preservation of bacterial viability, particularly for enteric pathogens such as Salmonella and Shigella species. The key difference between the two media was the replacement of glycerophosphate with sodium thioglycolate, which helped to maintain a more stable pH and reduce the risk of bacterial overgrowth.

Over time, the Cary-Blair Transport Medium has undergone various refinements and modifications to further enhance its performance in preserving bacterial specimens. Today, it is widely recognized as the gold standard for transporting enteric pathogens and other bacteria, and its use has contributed to significant advancements in the field of microbiology and laboratory diagnostics.

II. Composition and Properties of Cary-Blair Transport Medium

The effectiveness of Cary-Blair Transport Medium in preserving bacterial specimens can be attributed to its unique composition and properties. The medium consists of a carefully balanced mixture of chemicals designed to maintain the viability of bacterial cells while preventing overgrowth of non-target organisms.

One of the key components of Cary-Blair Transport Medium is sodium thioglycolate, which serves as a reducing agent. This substance helps to maintain a stable pH and creates an environment that favors the survival of target bacteria while inhibiting the growth of unwanted microorganisms. Other ingredients in the medium include sodium chloride, which helps to regulate osmotic pressure, and calcium chloride, which supports the structural integrity of bacterial cells.

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

Preparation of Cary-Blair transport medium

Follow the manufacturer's instructions for preparation:

1. Suspend 12.6 grams of powder in 991 ml of distilled water.
2. Heat to boiling to dissolve the medium completely.
3. Cool to 50°C and aseptically add 9 ml of 1% aqueous calcium chloride solution. (Note: Various commercially available dehydrated formulations of Cary-Blair are available, some of which require calcium chloride addition and some that do not.)
4. Adjust pH to 8.4 if necessary.
5. Dispense 7 ml of the medium into 9 ml capacity screw-cap bottles (large size Bijou bottles), ensuring at least 4 cm of medium covers the swabs.
6. Sterilize by steaming with loosened caps (do not autoclave) at 100°C for 15 minutes.
7. Once cooled, tighten the bottle caps and label the bottles.
8. Assign a date, batch number, and expiry date (6 months from preparation) to each bottle.
9. Store the bottles in a cool, dark place with the caps tightly screwed.

III. Specimen Collection and Handling with Cary-Blair Transport Medium

Cary-Blair Transport Medium is particularly well-suited for the collection and transportation of a variety of specimens, especially those associated with enteric pathogens. To ensure the integrity and accuracy of microbial analysis, it is crucial to follow proper specimen collection and handling procedures.

When using Cary-Blair Transport Medium, it is essential to select appropriate specimen types, such as fecal samples or rectal swabs, for the detection of enteric pathogens. The collection process should be carried out aseptically to avoid contamination and minimize the risk of introducing non-target microorganisms into the sample.

SPECIMEN COLLECTION

Caution: Prior to specimen collection, patients should avoid using antacids, barium, bismuth, antibiotics, anti-malarial agents, antidiarrheal medications, or oily laxatives. Specimen collection should be postponed for 5 to 10 days or at least two weeks after taking barium or antibiotics.

1. To ensure the recovery of organisms, examine several specimens collected intermittently over multiple days.
2. Proper specimen collection is crucial to prevent contamination with urine or water (refer to collection instructions). It is best to collect specimens in a bedpan. Alternatively, use a clean, dry container, such as a milk container with the top removed and washed thoroughly, or place plastic wrap over the toilet seat opening.
3. Using the provided collection spoon, select a suitable area (e.g., bloody, slimy, watery) from the sides, ends, and middle of the stool. Fill the container with enough stool to reach the "Fill" line, resulting in approximately 5 mL of sample.
4. Stir each specimen using the provided spoon, secure the cap, and shake vigorously until the specimen is well-mixed. The specimen should appear uniform once mixing is complete.
5. Fill out the label on each vial and place the vials back in the plastic bag. Transport the specimen to the laboratory. The specimen can be refrigerated or stored at room temperature.

SPECIMEN PROCESSING

The Cary Blair Medium protocol includes a buffering system that prevents the development of an acidic pH shift, which may negatively impact the recovery of Shigella and Salmonella species. If the buffering capacity is exceeded, a yellow color will appear, indicating that the medium has reached an undesirably acidic pH and should not be used. For optimal recovery of organisms, the medium should be red in color. Store the Cary Blair System vials at 20-25°C. The system accommodates a variety of procedures and should be considered as only one part of a comprehensive examination.

After obtaining the specimen, it should be immediately transferred to a vial or container containing Cary-Blair Transport Medium. The specimen must be thoroughly mixed with the medium to ensure even distribution and proper preservation of the bacterial cells. It is also important to label the container clearly with relevant information, such as patient details, date, and time of collection.

In terms of storage and transportation, samples in Cary-Blair Transport Medium should be kept at ambient or refrigerated temperatures, ideally between 4°C and 25°C. Transportation to the laboratory should occur as soon as possible, preferably within 48 hours of collection, to maximize the chances of recovering viable bacterial cells.

Before Processing:

1. Add enough sample to reach the Fill line.
2. Keep the vial at room temperature, avoiding extreme temperatures.
3. Using the spoon attached to the cap, mix the sample thoroughly until it appears uniform.
4. Important: The pH indicator must be red. If the medium turns yellow, it indicates an acidic pH and is not suitable for use. In this case, a new specimen must be collected.

Processing:

1. Thoroughly mix the contents of the vial.
2. Take off the vial cap and place it on a paper towel soaked in disinfectant.
3. Inoculate the medium from the Cary Blair vial following the laboratory's standard operating procedure.
4. Reseal the vial and dispose of it in accordance with your laboratory's infectious waste policy. Autoclaving or sterilization before disposal is recommended.

IV. Applications and Benefits of Cary-Blair Transport Medium

Cary-Blair Transport Medium has a wide range of applications in microbiology, particularly in the isolation and identification of enteric pathogens. Its unique composition and properties make it the medium of choice for preserving bacterial viability and morphology during transportation and storage, ultimately leading to improved accuracy in microbial diagnostics.

Cary-Blair transport medium is ideal for transporting clinical specimens suspected of containing enteric pathogens, such as Shigella, Salmonella, Vibrio cholerae, and Escherichia coli O157:H7. With its high pH (8.4), the viability of Vibrio cultures can be maintained for extended periods, making Cary-Blair the preferred medium for the transportation and preservation of V. cholerae.

The semi-solid consistency of Cary-Blair medium ensures ease of transport, and the prepared medium can be stored at room temperature for up to one year after preparation. The Cary-Blair medium base is formulated with minimal nutrients to support organism survival without promoting multiplication. The alkaline pH of the medium helps to reduce bacterial destruction caused by acid formation.

V. Limitations and Precautions for Using Cary-Blair Transport Medium

While Cary-Blair Transport Medium is highly effective in preserving the viability and morphology of many bacterial specimens, it is important to acknowledge its limitations and take necessary precautions when using this medium.

Cary-Blair Transport Medium may not be suitable for preserving all types of microorganisms. For example, it is not designed for the preservation of anaerobic bacteria, viruses, or fungi. Therefore, when dealing with specimens that may contain these organisms, alternative transport media or specialized collection methods should be employed.

In terms of potential hazards and safety measures, it is essential to handle Cary-Blair Transport Medium with care, as some of its components, such as sodium thioglycolate, can be harmful if ingested or inhaled. Appropriate personal protective equipment, such as gloves and safety goggles, should be worn during specimen collection and handling to minimize exposure risk.

Limitations

1. pH of the medium: The pH should fall within the range of 8.3-8.5 at room temperature.
2. Shelf life: Cary-Blair transport medium exhibits high stability when stored in tightly-sealed containers in a cool, dark location to prevent drying out. The medium may be used for up to one year, provided there is no loss of volume, contamination, pH alteration, or color change.

Precautions

1. Cary-Blair transport medium is designed specifically for transportation purposes. Prolonged delays in transport or processing of specimens can lead to decreased viability of bacterial cells and may allow contaminating flora to reproduce within the medium. As a result, rapid shipping and processing of samples are crucial for accurate and definitive lab results.

2. The timely plating, refrigeration, or freezing of specimens in Cary-Blair medium is particularly important for the identification of Shigella, which is more vulnerable than other enteric bacteria. Cary-Blair transport medium is sensitive to extreme temperatures and is not autoclaved. While its sterilizability has been confirmed, it is not 100% guaranteed.

3. Specimens collected after the initiation of antibiotic therapy may not accurately reflect the presence or absence of enteric pathogens, potentially affecting the treatment outcomes.

The field of microbiology is continually evolving, and with it comes the potential for advancements and innovations in transport media, including Cary-Blair Transport Medium. Researchers are exploring new formulations, additives, and technologies to further improve the preservation of bacterial specimens and broaden the range of microorganisms that can be accommodated by transport media.

Introducing Mantacc's Cary-Blair Transport Medium and Swab Kit, an ideal solution for microbiological surface monitoring in pharmaceutical environments. With its superior formulation, long shelf life, and ambient storage capability, this compact kit delivers reliable, high-quality surface examination to maintain safety and cleanliness standards in your facility.