R2A Agar

EMD Cat. No. 1.00416.0500
500 g


Nutrient medium for the determination of the heterotrophic total bacterial count in drinking water.

R2A Agar is a medium with a low nutrient content, which, in combination with a low incubation temperature and an extended incubation time, is specially suitable for the recovery of stressed and chlorine-tolerant bacteria from drinking water.
 The nutrient medium conforms with recommendations of the standard methods ( US-EPA ) for the examination of water.

Experimental Procedure and Evaluation Quality Control
Typical Composition (g/liter) Literature
Picture/Image


Mode of Action
 The low concentration of yeast extract, casein hydrolisate, peptone and glucose allows a wide spectrum of bacteria to grow without the fast-growing bacteria suppressing the slow-growing species, such as would be the case on richly nutritious media like e.g. Plate Count Agar.
 The content of starch and pyruvate allows particularly the injured bacteria to grow again more quickly.
Preparation
 Suspend 15.2 g in 1 liter purified water and heat in a boiling water bath or flowing steam until the medium has completely dissolved. Autoclave for 15 min. at 121°C, cool to 4550°C and pour into sterile Petri dishes.
 pH : 7.2 ± 0.2 at 25°C
 The prepared medium is clear to slightly opalescent and colorless.
In correct storage conditions ( +2 +8°C, protected from light and dehydration) the plates can be stored for 4 weeks.
Experimental Procedure
The determination of the total bacterial count using R2A agar can be carried out with the pour plate, spread plate and membrane filter methods.
 If an incubation time of more than 3 days is used, the plates should be protected from dehydration.
Incubation
 temperature
 		Minimum
Incubation time
 		Optimum
Incubation time
35°C
 		72 hours
 		5-7 days
20 or 28°C
 		5 days
 		7 days

Evaluation
 The number of colonies is counted and the bacteria count/ml is calculated noting the incubation temperature and incubation period.
Quality control

Test strains
 Growth
 35 °C / 24 h
 		Growth
 20 °C / 72 h



Escherichia coli ATCC 25922
 		+
 		+
Pseudomonas aeruginosa ATCC 27853
 		+
 		+
Staphylococcus aureus ATCC 25923
 		+
 		+
Bacillus cereus ATCC 11778
 		+
 		+

Typical Composition (g/liter)
 Yeast extract 0.5; proteose peptone 0.5; casein hydrolysate 0.5; glucose 0.5; soluble starch 0.5; sodium pyruvate 0.3; dipotassium hydrogenphosphate 0.3; magnesium sulphate 0.05; agar-agar 12.0.
Literature
Eaton, A. D., L.S. Clesceri, and A.E. Greenberg (ed.). 1995. Standard methods for the examination of water and wastewater, 19th. Ed. APHA, Washington D.C.
 Fiksdal, L., E.A. Vik, A. Mills, and T. Staley. 1982. Non-standard methods for enumerating bacteria in drinking water. Journal AWWA. 74:313-318.
 Means, E.G., L. Hanami, H.F. Ridgway, and B.H. Olson. 1981. Evaluating mediums and plating techniques for enumerating bacteria in water distributing systems. Journal AWWA. 53:585-590.
 Reasoner, D.J., and E.E. Geldreich. 1979. A new medium for the enumeration and subculture of bacteria from potable water. Abstracts of the Annual Meeting of the American Society for Microbiology 79th Meeting, Paper No. N7