R2a agar

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R2A agar (Reasoner´s 2A agar) is a culture medium[1] developed to study bacteria which normally inhabit potable water.[2] These bacteria tend to be slow-growing species and would quickly be suppressed by faster-growing species on a richer culture medium.

Since its development in 1979,[3] it has been found to allow the culturing of many other bacteria that will not readily grow on fuller, complex organic media.

Typical Composition (g/l)[edit]

Proteose peptone, 0.5
Casamino acids, 0.5
Yeast extract, 0.5
Dextrose, 0.5
Soluble starch, 0.5
Dipotassium phosphate, 0.3
Magnesium sulfate 7H2O, 0.05
Sodium pyruvate, 0.3
Agar, 15
Final pH 7 ± 0.2 @ 25 °C


  1. ^ van der Linde K, Lim BT, Rondeel JM, Antonissen LP, de Jong GM (October 1999). "Improved bacteriological surveillance of haemodialysis fluids: a comparison between Tryptic soy agar and Reasoner's 2A media". Nephrol. Dial. Transplant. 14 (10): 2433–7. doi:10.1093/ndt/14.10.2433. PMID 10528669. 
  2. ^ Sandle, T. (July 2004). "An approach for the reporting of microbiological results from water systems". PDA J Pharm Sci Technol 58 (4): 231–7. 
  3. ^ Reasoner DJ, Blannon JC, Geldreich EE (August 1979). "Rapid seven-hour fecal coliform test". Appl. Environ. Microbiol. 38 (2): 229–36. PMC 243471. PMID 42349.