PRESENCE ABSENCE BROTH
Presence-Absence Broth is used for the detection of coliform bacteria in water from treatment plants or distribution systems using the presence-absence coliform test. Enzymatic Digest of Gelatin, Enzymatic Digest of Casein, and Beef Extract provide amino acids, peptides, carbohydrates, vitamins, and trace elements. Lactose is the fermentable carbohydrate. Dipotassium Phosphate and Monopotassium Phosphate serve as pH buffers. Sodium Chloride maintains the osmotic balance. Sodium Lauryl Sulfate is the selective agent, inhibiting many organisms except coliforms. Bromocresol Purple is used as an indicator dye. Lactose-fermenting organisms acidify the medium, thus causing a color shift from purple to yellow with or without gas production.