R2A Broth

Principle And Interpretation

The total bacterial count of drinking water is determined by plate count on a nutritionally rich medium. However all organisms present are not able to grow on them, either because they are slow growers or because they cant grow on that media (1). For this reason a nutritionally reduced medium was described. R-2A Agar is a modification of this medium (2,3). R-2A Agar is an alternative medium used for the heterotrophic plate counts and for subculturing isolates from potable waters (1). R-2A Agar is also recommended by APHA (4) for pour plate, spread plate and membrane filter technique. R-2A Broth is similar to R-2A Agar except agar. Total count recommended for the bacterial examination of potable waters gives an estimate of the aerobic and facultatively anaerobic bacteria, which grow best at 35°C in a rich medium (3). R-2A Broth enables better recovery of these bacteria from treated waters under different incubation conditions. Many bacteria from natural waters, which contain limited nutrients at ambient temperature, grow best on the media with less nutrient levels. They grow better at the temperatures below the routine laboratory incubation temperatures of 35 to 37°C(3). This medium contains acicase, yeast extract, proteose peptone as source of essential growth factors required for metabolism of the bacteria. Dextrose/glucose is the energy source. Starch acts as a neutralizer that neutralizes any toxic metabolites, if present. Phosphate buffers the medium while sodium pyruvate supplies additional nutrition. Magnesium sulphate serves as a source of ions. Due to the presence of the above mentioned ingredients these media allow the growth of stressed and chlorine tolerant bacteria present in treated waters.