R2A agar

A low-nutrient medium used to recover stressed, slow-growing bacteria from water systems. Organisms adapted to pure water often grow poorly on rich media, so R2A with longer incubation, typically 5–7 days, gives more accurate counts. It is used for Purified Water and WFI testing, often by membrane filtration. As with any medium, the choice and incubation conditions should be supported by a comparison study and growth promotion testing.