Overview:
Cary-Blair Transport Medium is a semi-solid, non-nutritive, chemically defined transport medium developed by Cary and Blair in 1946 for the collection, preservation, and transportation of clinical specimens, particularly fecal samples containing enteric pathogens. It features an improved phosphate buffering system to maintain a high alkaline pH (8.4), which minimizes acid production by bacteria and supports prolonged viability of delicate organisms like Vibrio cholerae, Salmonella spp., Shigella spp., and Escherichia coli O157:H7 without promoting overgrowth or multiplication. Sodium thioglycollate reduces the oxidation-reduction potential to protect against oxygen toxicity, while minimal nutrients ensure organism survival during transit (up to several days at room temperature). This medium is recommended by APHA, CDC, and ISO standards for shipping specimens to reference labs, outperforming simple saline by reducing desiccation and pH shifts.
Applications:
?? Preservation and transport of fecal specimens for isolation of Salmonella, Shigella, Vibrio, and other enteric pathogens in clinical diagnostics
?? Collection of rectal swabs, urine, or nasopharyngeal samples suspected of bacterial infections per FDA-BAM and ISO 6579/10273 protocols
?? Shipment of specimens from remote sites to microbiology labs without refrigeration (viable for 24-72 hours at ambient temperature)
?? Maintenance of fragile pathogens like Shigella sonnei after antibiotic exposure or environmental stress
Key Features:
?? Alkaline pH (8.4) and phosphate buffer prevent acidification, enhancing Vibrio recovery (>90% viability after 48 hours)
?? Low redox potential from thioglycollate protects anaerobes and microaerophiles during transit
?? Osmotic balance via NaCl and CaCl? minimizes cell lysis; semi-solid agar (0.5%) prevents drying
?? Non-selective and non-nutritive to avoid contaminant overgrowth; validated for ATCC strains like Shigella flexneri 12022
?? Room-temperature stable prepared medium (up to 1 year); compatible with swabs, stools, or bulk samples in screw-cap tubes
Composition (per liter):
Disodium Hydrogen Phosphate � 1.10 g
Sodium Thioglycollate � 1.50 g
Sodium Chloride (NaCl) � 5.00 g
Agar � 5.00 g
Calcium Chloride (1% aqueous solution) � 9.00 mL (equivalent to 0.09 g anhydrous CaCl?)
Final pH: 8.4 � 0.2 at 25�C
Preparation:
Suspend 12.6 g of the dehydrated base in 991 mL of purified/distilled water. Heat to boiling with agitation until completely dissolved (do not overheat). Cool to 45�50�C in a water bath. Aseptically add 9 mL of 1% sterile calcium chloride solution. Mix thoroughly and adjust pH to 8.4 if necessary. Dispense into screw-capped tubes or bottles (typically 5�7 mL per tube for swabs or 10�20 mL for bulk feces). Steam sterilize at 100�C for 15 minutes (do not autoclave to avoid agar degradation). Allow to cool and solidify at room temperature; tighten caps to prevent evaporation. The prepared medium should appear light amber, slightly opalescent, and semi-solid without bubbles or separation.
Storage:
Dehydrated medium: Store in a tightly closed container at 10�30�C, protected from moisture, light, and humidity; stable until expiry date (typically 3�5 years).
Prepared medium: Store at 15�30�C (room temperature) in sealed tubes; use within 1 year or discard if dehydrated, contaminated, discolored, or volume loss occurs. Refrigerate (2�8�C) for extended hold if needed, but avoid freezing.
?? For laboratory and research use only. Not for diagnostic procedures without proper validation. Not for human or veterinary consumption. Handle under biosafety level 2; wear gloves, lab coat, and eye protection�use Universal Precautions for clinical specimens. Autoclave all waste and contaminated materials before disposal per local regulations. Prolonged transit (>72 hours) may reduce viability; inoculate promptly upon receipt. Not suitable for strict anaerobes like Clostridium without anaerobic packaging. Specimens post-antibiotics may yield false negatives.