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Dehydrated Culture Media

Sector: Clinical

CARY-BLAIR MEDIUM

Code: CM0519

A transport medium for Gram negative and anaerobic organisms.

Typical Formula*

gm/litre

Disodium hydrogen phosphate

1.1

Sodium thioglycollate

1.5

Sodium chloride

5.0

Calcium chloride

0.09

Agar

5.6

pH 8.4 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards 

Directions
Suspend 13.3g in 1 litre of distilled water and bring gently to the boil to dissolve the agar. Distribute into small, screw-cap bottles and sterilise by immersing in free-steam for 15 minutes. Allow to cool and tighten the screw caps to prevent water loss.

Description
Oxoid Cary-Blair Medium is a transport medium for the collection and shipment of clinical specimens based on the formulation of Cary and Blair1.
The low nutrient content of the medium and utilisation of phosphate as a buffering agent instead of sodium glycerophosphate, prevents bacterial overgrowth by Escherichia coli, Citrobacter freundii and Klebsiella aerogenes.

This sometimes happens when using Stuart Transport Medium CM0111 because these organisms possess specific glycerophosphate dehydrogenases2. The low oxidation-reduction potential of the medium ensures bacterial survival over long periods3.

Cary and Blair1 reported recovery of cholera vibrios up to 22 days, salmonellae and shigellae after 49 days and Yersinia pestis up to 75 days storage at 28°C.

Cary-Blair Medium is particularly suitable in field epidemiological surveys for Vibrio parahaemolyticus, especially where rectal swabs are to be transported to a central diagnostic laboratory4,5. Survival of Vibrio parahaemolyticus in Cary-Blair medium has been reported after a 35-day period at a temperature of 70-80°F6.

The medium can be modified to improve the transport and survival of Campylobacter species.
(i) by the addition of 1% w/v sodium pyruvate (10 g/litre) to the formula7.
(ii) reducing the agar content from 5g to 1.6g per litre8.

For the transport of fastidious anaerobic bacteria the medium may be prepared as directed and filled into long narrow screw-capped tubes9. It may also be prepared as a pre-reduced anaerobic sterilised medium (PRAS)10. Methods of producing PRAS media are described by Holdeman and Moore11.

Technique
Use sterile, cotton-tipped swabs on wooden sticks to collect the specimen. Push the swabs down one third of the medium depth and cut the stick. Screw the cap firmly on the bottle.

Label the bottle and send it to the laboratory without delay.

The recovery of Shigella species is higher when the transport medium is held at 4°C or frozen12.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
The prepared medium should be stored away from light at 2-8°C or at room temperature (22-25°C) up to 19 months13.

Appearance
Dehydrated medium: Off-white coloured, free-flowing powder
Prepared medium: Light straw coloured, semi-solid gel

Quality control

Positive controls:

Expected results

Shigella sonnei ATCC® 25931 *Good growth on subculture

Vibrio parahaemolyticus NCTC 11344

Good growth on subculture

Negative control:

 
Uninoculated medium

No change

* This organism is available as a Culti-Loop®

Precautions
The medium should not be incubated to check sterility, prior to use. This should be carried out on separate quality control samples.
The medium can maintain the viability of fastidious organisms for transport purposes but it should not be used as a storage or enrichment medium.
The results obtained from the medium are dependent on the quality of the specimen material. Commensal anaerobic organisms may overgrow in the medium and cause misleading results.

References
1. Cary S. G. and Blair E. B. (1964) J. Bact. 88. 96-98.
2. Crookes E. M. and Stuart R. D. (1959) J. Pathol. Bacteriol. 78. 283-288.
3. Stuart R. D. (1959) Public Health Reports 74. 431-438.
4. Cary S. G., Fusillo M. H. and Harkins C. (1965) Am. J. Clin. Path. 43. 294-295.
5. DeWitt W. E., Gangarosa E.J., Huq I. and Zarifi A. (1971) Amer. J. Trop. Med. Hyg. 20. 685-688.
6. Neumann D. A., Benenson M. W., Hubster E. and Tuan N. T. N. (1971) Am. J. Clin. Path. 57.
7. Patton C. M., Mitchell S. W., Potter M. E. and Kauffmann A. F. (1981) J. Clin. Microbiol. 13. 326-328.
8. Luechtefeid M.W., Wang W. L. L., Blaser M. J. and Reller L. B. (1981) J. Clin. Microbiol. 13. 438-439.
9. Wren M. W. D., Baldwin A. W. F., Eldon C. P. and Sanderson P. J. (1977) J. Med. Microbiol. 10. 49-61.
10. Wren M. W. D. J. Med. Microbiol. 10. 195-201.
11. Holdeman L. V. and Moore W. E. C. (1975) Anaerobe Laboratory Manual, Virginia Polytechnic Institute Anaerobe Laboratory, 3rd Ed.
12. Wells J. G. and Morris G. K. (1981) J. Clin. Microbiol. 13. 789-791.
13. Morris G. K and Heck J. (1978) J. Clin. Microbiol. 8. 616-617.

 
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