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S2Media™ Reasoner's 2A (R2A) Agar

S2Media™ Reasoner's 2A (R2A) Agar

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S²Media™ prepared Reasoner’s 2A (R2A) Agar is a low-nutrient culture medium intended for the cultivation and enumeration of heterotrophic bacteria from water and other low-nutrient environments. Originally developed by Reasoner and Geldreich for improved recovery of bacteria from treated potable water, R2A Agar is specifically formulated to support slow-growing, stressed, and chlorine-injured microorganisms that may be poorly recovered on more nutrient-rich media. The reduced nutrient content limits the competitive advantage of rapidly growing organisms, while yeast extract, peptone, casein hydrolysate, and glucose provide nutrients for microbial recovery. Soluble starch and sodium pyruvate aid in the recovery of stressed organisms, and phosphate and magnesium salts support appropriate buffering and cellular metabolism. When used with extended incubation periods and lower incubation temperatures, R2A Agar provides enhanced recovery of heterotrophic bacteria from treated water systems.


S²Media™ R2A Agar is well suited for potable water testing, pharmaceutical and purified water monitoring, environmental microbiology, and microbiological water quality programs. The product is intended for laboratory use and is not intended for use in the diagnosis of disease or other conditions in humans.


Material #5003UL: Plates are not printed with any information, making them suitable for automated readers. (Packs are labeled with batch specific information.)


Also known as:

  • Reasoner’s 2A Agar

  • R2A Agar

  • Reasoner and Geldreich Agar

  • R2A Medium

  • Low-Nutrient R2A Agar

  • Heterotrophic Plate Count Agar (R2A)


👉 Finished product meets the following standards and references:

  • APHA

  • CLSI (for reagent water)

  • EPA

  • EP

  • SM-WW

  • USP-NF


🧫 Application Areas:

  • Potable and drinking water microbiology

  • Heterotrophic plate count (HPC) testing

  • Enumeration of heterotrophic bacteria in water

  • Recovery of stressed and chlorine-injured bacteria

  • Treated water system monitoring

  • Municipal and public water system testing

  • Pharmaceutical water system monitoring

  • Purified Water (PW) monitoring

  • Water for Injection (WFI) system monitoring, where appropriate to the established method

  • Process and laboratory water monitoring

  • Food and beverage processing water testing

  • Cosmetics and personal care manufacturing water monitoring

  • Environmental microbiology and water quality testing

  • Microbiological quality control and contamination investigations

  • Spread plate, pour plate, and membrane filtration applications


Equivalent/Comparable Item Numbers:

  • G54

  • R01722

  • L99480

  • 299480

  • 50-238-8023

  • R1035

  • PO0659A

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