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Dehydrated Culture Media

BLOOD AGAR BASE (SHEEP)

Code: CM0854

A Blood Agar Base that has been specifically formulated to give improved haemolytic reactions with sheep blood.

Typical Formula*

gm/litre

Tryptone

14.0

Peptone Neutralised

4.5

Yeast extract

4.5

Sodium chloride

5.0

Agar

12.0

Final pH 7.3 ± 0.2 @ 25°C

 

* Adjusted as required to meet performance standards 

Directions
Suspend 40g in 1 litre of distilled water and bring to the boil to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C and aseptically add 7% sterile sheep blood.

Description
Sheep Blood Agar Base was developed to meet the demand for an especially nutritious blood agar base which would permit the maximum recovery of organisms without interfering with their haemolytic reactions when used with sheep blood. Sheep Blood Agar Base is based on the formulation of Blood Agar Base No.2 CM0271.

Blood Agar Base No.2 when supplemented with sheep blood was occasionally found to result in a mixed haemolytic reaction (alpha and beta haemolysis) for some Group A Streptococci (Streptococcus pyogenes). These mixed haemolytic reactions were due to trace amounts of fermentable carbohydrates in yeast extract and the physiological differences of sheep blood when compared to horse blood1.

Having identified the causes of the mixed haemolytic reactions, the Sheep Blood Agar Base was formulated to be compatible with sheep blood. Comparisons with other blood agar bases supplemented with sheep blood have shown that with Sheep Blood Agar Base the growth of many bacteria - especially the fastidious streptococci - is considerably improved, and the expected beta haemolytic reaction is achieved with Streptococcus pyogenes.

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 medium at 2-8°C.

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

Quality control

Positive controls:

Expected results

Streptococcus pyogenes ATCC® 19615 *

Good growth; colourless/white colonies

Streptococcus pneumoniae ATCC® 6303 *

Good growth; colourless colonies

Negative control:

 

Uninoculated medium

No change

* This organism is available as a Culti-Loop®

Reference
1. Spector W S (1961) Handbook of Biological Data, P51 and 53. In WS Spector (Ed.) Handbook of Biological Data. W B Saunder Company, Philadelphia and London.

 
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