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Dehydrated Culture Media

R2A AGAR

Code: CM0906

A medium for the bacterial examination of drinking water.

Typical Formula*

gm/litre

Yeast extract

0.5

Proteose peptone

0.5

Casein hydrolysate

0.5

Glucose

0.5

Starch

0.5

Di-potassium phosphate

0.3

Magnesium sulphate

0.024

Sodium pyruvate

0.3

Agar

15.0

pH 7.2 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards 

Directions
Suspend 18.1g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes. Mix well and pour into sterile Petri dishes.

Description
Standard methods for the enumeration of heterotrophic bacteria in water have traditionally used nutritionally rich media, such as Plate Count Agar, with incubation at 35°C1. Organisms isolated under these conditions may represent only a small percentage of the bacteria present in the sample2.

R2A Agar developed by Reasoner and Geldreich2 is a nutritionally reduced medium. It was demonstrated that using this medium and incubating for longer at lower temperatures enhanced the recovery of stressed and chlorine damaged bacteria from treated waters resulting in higher, more realistic bacterial counts.

Technique
R2A Agar may be used in poured plate, spread plate and membrane filtration procedures. Refer to standard methods for sample collection and testing1,2,4 .

Recommended incubation is for 5-7 days at 20°C or 28°C, or for 3 days at 35°C.

Storage conditions and Shelf life
R2A Agar should be stored tightly capped in the original container at 10-30°C. When stored as directed the medium will remain stable until the expiry date printed on the label.

The prepared medium may be stored for up to 2 weeks at 2-8°C.

Appearance
Dehydrated medium: Pale straw coloured, free-flowing powder
Prepared medium: Light straw coloured gel

Quality control

Positive control:

Expected results

Staphylococcus aureus ATCC® 6538 *

Good growth; white coloured colonies

Negative control:

 
Uninoculated mediumNo change
* This organism is available as a Culti-Loop®

References
1. Greenbreg, Trussell and Clesceri (ed) (1998) Standard Methods for the Examination of Drinking Water and Waste Water. 20th Ed. APHA,
Washington DC.
2. Reasoner and Geldreich (1985). Appl. Environ. Microbiol. 49, 1.
3. Environment Agency- The Microbiology of Drinking Water 2002
4. European Pharmacopoeia 2002, supplement 4.6.

 
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