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Dehydrated Culture Media

Sector: Clinical

TRYPTOSE BLOOD AGAR BASE

Code: CM0233

A highly nutritious medium specially developed for the preparation of a blood agar which will support the growth of fastidious organisms.

Typical Formula*

gm/litre

Tryptose

10.0

`Lab-Lemco’ powder

3.0

Sodium chloride

5.0

Agar

12.0

pH 7.2 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards

Directions
Suspend 30g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes.

For blood agar, cool the basal medium to 45-50°C and add 7% of sterile blood. Mix thoroughly, taking care to avoid incorporation of air bubbles, and dispense into Petri dishes or other containers.

Description
A highly nutritious medium specially developed by Casman1,2 for the preparation of a blood agar which will support the growth of many fastidious organisms.

The original formulation included 0.3g dextrose per litre which interfered with the haemolytic reactions. It is now used without dextrose as a standard medium3.

Tryptose Blood Agar Base with added blood gives good haemolytic reactions and without blood it will sustain good to excellent growth of many demanding organisms. However, to improve the growth of certain organisms e.g. Neisseria meningitidis and Streptococcus pneumoniae, the addition of 1g of yeast extract (LP0021) to one litre of Tryptose Blood Agar Base can be made.

Technique
Lightly inoculate the surface of the medium and incubate aerobically at 35°C for 18-24 hours in 5-10% carbon dioxide (if necessary) or incubate anaerobically at 35°C for 48 hours to enhance haemolysis and to restrict unwanted commensal growth.

Carry out microscopy and other identification tests on the isolated colonies.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared plates of medium at 2-8°C.

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured gel       

Quality control

Positive controls:Expected results
Staphylococcus aureus ATCC® 25923*Good growth; white colonies   
Streptococcus pyogenes ATCC® 19615*Good growth; pale straw coloured colonies; zone of ß-haemolysis
Negative control:  
Uninoculated mediumNo change
* This organism is available as a Culti-Loop®

References
1. Casman E. P. (1942) J. Bact. 43. 33-37.
2. Casman E. P. (1947) Amer. J. Clin. Path. 17. 281-282.
3. American Public Health Association (1970) Diagnostic Procedures and Reagents. 5th Edn. APHA Inc. New York.

 
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