This study introduces R2A, a new low-nutrient agar medium designed for the enumeration and subculture of bacteria from treated potable water, addressing the limitations of the standard plate count agar. The formulation of R2A includes yeast extract, proteose peptone, casamino acids, glucose, soluble starch, and sodium pyruvate. Comparative studies demonstrated that R2A medium consistently yields significantly higher bacterial counts than plate count agar. The research found that bacterial recovery is inversely proportional to incubation temperature, with maximal counts achieved at 20°C after 14 days, which also enhances the detection of pigmented bacteria. For practical application in monitoring water treatment and distribution systems, the authors recommend using R2A with a spread or membrane filter plate, incubated at 28°C for 5 to 7 days.
Key Findings on R2A Agar for Potable Water Analysis
Limitation of Standard Media: The standard medium, plate count agar, is insufficient for recovering many bacteria present in treated potable water supplies.
A New Formulation: R2A Agar: A new, low-nutrient medium was developed to improve bacterial recovery. Its key ingredients per liter are 0.5 g each of yeast extract, proteose peptone no. 3, casamino acids, glucose, and soluble starch, along with salts and sodium pyruvate.
Superior Bacterial Recovery: In parallel studies using spread, membrane filter, and pour plate methods, R2A medium yielded significantly higher bacterial counts compared to the standard plate count agar.
Optimal Incubation Conditions: Maximal bacterial counts were achieved with longer incubation times (up to 14 days) at lower temperatures. The highest yields were observed after 14 days at 20°C.
Recommended Protocol for Water Monitoring: As a practical tool for routine water quality monitoring, the study recommends using R2A spread or membrane filter plates incubated at 28°C for a period of 5 to 7 days.