R2a agar

R2A agar (Reasoner's 2A agar) is a culture medium developed to study bacteria which normally inhabit potable water. 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, it has been found to allow the culturing of many other bacteria that will not readily grow on fuller, complex organic media.