Cary-Blair medium is a specialized transport medium designed to preserve enteric bacteria during transit, ensuring reliable diagnostic results for gastrointestinal infections. Originally developed in 1964, this medium remains a gold standard for stool and rectal swab specimen transport, particularly in cases of foodborne illness outbreaks. By maintaining bacterial viability while preventing overgrowth, Cary-Blair medium is essential for public health, clinical microbiology, and food safety applications.
In this guide, we’ll explore what Cary-Blair medium is, how it works, when to use it, and why it remains a crucial tool for laboratories and healthcare providers worldwide.
What is Cary-Blair Medium?
Cary-Blair medium is a widely used transport medium designed to preserve enteric bacteria for clinical and laboratory testing. Its primary function is to maintain the viability of gastrointestinal pathogens, such as Salmonella, Shigella, Vibrio, and Campylobacter, during transportation from collection sites to diagnostic laboratories. Originally developed by Cary and Blair in the 1960s, this medium has since become a gold standard for stool and rectal swab sample transport, particularly in cases of foodborne illness, gastrointestinal infections, and outbreak investigations.
Unlike nutrient-rich media that promote bacterial growth, Cary-Blair medium is formulated to minimize metabolic activity, preventing overgrowth of commensal flora while preserving the target pathogens. It is an essential tool in public health, clinical microbiology, and food safety industries, ensuring that viable bacteria reach the laboratory for accurate diagnosis and treatment guidance.
Why is it Named “Cary-Blair” Medium?
Cary-Blair medium is named after its developers, Sylvia G. Cary and Eugene B. Blair, who formulated it in 1964. Their research focused on improving the transport and viability of enteric pathogens like Salmonella, Shigella, Vibrio, and Pasteurella, which often degrade quickly in traditional transport media. Through their work, Cary and Blair created a low-nutrient, high-pH formulation that significantly extended the survival of these bacteria, making it an essential tool in clinical and public health microbiology.
Composition and Properties of Cary-Blair Medium
Cary-Blair medium consists of a semi-solid, low-nutrient formulation that provides an optimal environment for bacterial survival without promoting excessive replication. The key ingredients include:
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Sodium Thioglycolate: Reduces oxidation, helping maintain an anaerobic or microaerophilic environment, which is particularly important for preserving Campylobacter and Vibrio species.
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Disodium Hydrogen Phosphate and Monopotassium Phosphate: Act as buffering agents, maintaining a stable pH to prevent bacterial degradation.
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Sodium Chloride: Helps maintain osmotic balance to prevent bacterial stress.
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Calcium Chloride: Supports cellular stability during transport.
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Agar: Provides a semi-solid consistency, preventing sample desiccation while ensuring uniform distribution of bacteria.
One of the distinguishing features of Cary-Blair medium is its highly alkaline pH (~8.4-8.5), which inhibits bacterial degradation and neutralizes acidic byproducts that could harm the specimen. This alkaline environment is particularly beneficial for preserving Vibrio cholerae, a pathogen that is highly sensitive to acidic conditions.
How Does Cary-Blair Medium Work?
Cary-Blair medium functions by creating an environment that supports bacterial survival while limiting excessive growth. Its semi-solid nature prevents sample desiccation, ensuring that bacteria remain viable over extended transport times. Unlike enriched growth media, Cary-Blair medium provides minimal nutrients, preventing the rapid multiplication of bacteria that could outcompete the target pathogens.
The medium’s high pH level helps stabilize bacterial cell structures, preventing degradation during storage. Sodium thioglycolate reduces oxidation, which is especially crucial for microaerophilic organisms like Campylobacter, allowing them to survive transport without significant loss of viability.
By maintaining bacterial stability, Cary-Blair medium extends the window of opportunity for reliable pathogen detection, allowing laboratories to process samples with greater confidence.
When and Why is Cary-Blair Medium Used?
Cary-Blair medium is primarily used for stool and rectal swab samples in suspected cases of bacterial gastroenteritis. It is recommended by the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) for transporting enteric pathogens, particularly in outbreak investigations or routine clinical diagnostics. It is widely used in hospitals, clinical laboratories, food safety programs, and epidemiological investigations where rapid and reliable pathogen detection is critical.
The medium is especially useful when:
Testing for Foodborne Illnesses
Foodborne illnesses caused by Salmonella, Shigella, Vibrio, and Campylobacter require quick and accurate diagnostic testing to confirm outbreaks and prevent further spread. Since these bacterial pathogens can degrade rapidly outside the body, Cary-Blair medium helps ensure their viability from the point of collection to laboratory analysis. Whether in hospitals, public health departments, or food safety laboratories, Cary-Blair plays a crucial role in confirming infections, guiding treatment decisions, and informing outbreak response efforts.
Surveillance Programs
Public health agencies and epidemiologists rely on Cary-Blair medium as a tool for disease surveillance and antimicrobial resistance monitoring. By collecting and preserving enteric bacteria from individuals, food products, or environmental sources, laboratories can study trends in pathogen prevalence, identify emerging threats, and track antibiotic resistance patterns. Surveillance programs using Cary-Blair are essential in preventing large-scale outbreaks, implementing public health interventions, and improving food safety standards worldwide.
Delayed Specimen Transport
In many clinical and field settings, immediate sample processing is not always possible. Cary-Blair medium provides a stable environment that can preserve bacterial viability for up to 48–72 hours when stored at refrigerated temperatures (2–8°C). This extended preservation time is crucial for rural healthcare facilities, outbreak investigations in remote areas, and international disease monitoring efforts where long transit times are common. By preventing bacterial degradation, Cary-Blair ensures that laboratories receive high-quality specimens for accurate diagnostic testing, even after prolonged transport.
Comparing Cary-Blair Medium to Other Transport Media
While Cary-Blair medium is one of the most reliable options for enteric pathogen transport, other transport media may be used depending on specific testing needs:
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Stuart & Amies Transport Media: Designed for preserving aerobic and anaerobic bacteria from wound, throat, and genital specimens but less effective for enteric pathogens.
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Alkaline Peptone Water: Used primarily for Vibrio cholerae transport but does not support a broad range of enteric pathogens.
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Buffered Glycerol Saline: Suitable for short-term Salmonella and Shigella preservation but lacks long-term viability support.
Cary-Blair remains the preferred choice for gastrointestinal specimens due to its stability, pathogen viability, and ease of use.
Regulatory Guidelines and Quality Control for Cary-Blair Medium
To ensure consistency and reliability, Cary-Blair medium must adhere to strict regulatory standards. The CDC and WHO recommend Cary-Blair medium for stool sample transport in epidemiological investigations. ISO and CLSI (Clinical & Laboratory Standards Institute) guidelines provide specifications for its preparation and use. Laboratories must regularly test Cary-Blair lots for pH stability, sterility, and bacterial viability to maintain quality control. Compliance with these guidelines ensures that Cary-Blair medium continues to provide accurate, reproducible results in diagnostic microbiology.
6 Best Practices for Using Cary-Blair Medium
Ensuring optimal specimen preservation requires following best practices for collection, inoculation, and transport.
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Use a sterile swab or collection spoon to transfer a pea-sized amount of stool or rectal swab specimen into the Cary-Blair transport tube.
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Immerse the sample in the medium, ensuring full contact but avoiding excessive dilution.
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Tighten the cap securely to prevent leakage or contamination.
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Room Temperature (Short-Term): Cary-Blair medium can maintain pathogen viability for up to 24 hours at room temperature.
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Refrigeration (Optimal): Samples should be stored at 2–8°C for best results, ensuring bacterial survival for up to 72 hours before processing.
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Avoid Freezing: Freezing disrupts bacterial cell integrity, compromising diagnostic accuracy.
Commonly Asked Questions about Cary-Blair Medium
How long can a specimen remain in Cary-Blair before testing?
Ideally, specimens should be processed within 24–48 hours for best results, though viability may be maintained up to 72 hours under refrigeration.
Can Cary-Blair medium be used for viral or fungal transport?
No. Cary-Blair is specifically designed for bacterial pathogens and does not effectively preserve viruses or fungi.
Is Cary-Blair medium available in different formulations?
Yes, some variations exist, including pre-filled transport tubes and dehydrated powders for laboratory preparation.
Where can I purchase high-quality Cary-Blair medium?
Cary-Blair medium is available from reputable laboratory suppliers and diagnostic companies that adhere to regulatory quality standards.
Which leads us to…
Puritan Products with Cary-Blair Medium
When it comes to reliable specimen transport, Puritan offers high-quality Cary-Blair medium solutions designed to preserve enteric pathogens for accurate laboratory testing. Our transport systems ensure that Salmonella, Shigella, Vibrio, Campylobacter, and other gastrointestinal bacteria remain viable during transit, supporting precise diagnostics in clinical, public health, and food safety applications.
Puritan Cary-Blair Medium, 2 ml
Cary-Blair transport medium for the preservation of fecal specimens containing enteric pathogenic bacteria
SKU #: CB-200
Puritan Cary-Blair Medium, 5 ml
Cary-Blair Medium for the preservation of fecal and rectal specimens containing enteric pathogenic bacteria
SKU #: CB-500
Puritan Fecal Opti-Swab Collection & Transport System
2 ml Cary-Blair Medium Filled Vial w/ One Sterile Elongated HydraFlock® Swab (25-3506-H)
SKU #: CB-206
Ensure accurate results and reliable pathogen detection with Puritan’s Cary-Blair transport solutions. Contact our sales team today to find the best option for your laboratory needs!
