Presence-Absence Broth, PA

Presence-Absence Broth is a selective enrichment medium, which was created especially for the presumptive detection of coliform bacteria in water samples.
Peptones and meat extract are among the nutrients included in the medium’s composition, which promotes the growth of a variety of microorganisms. As the main carbon source, lactose is fermented by coliforms to create acid and frequently gas, which is an indication of a positive result. The selective agent sodium lauryl sulfate increases the medium’s specificity for coliforms by preventing the growth of many Gram-positive bacteria and some Gram-negative non-coliforms. Because lactose fermentation produces acid, bromocresol purple functions as a pH indicator, visually indicating the presence of coliforms by changing color from purple to yellow. Gas production, often observed in Durham tubes, further confirms the presence of coliforms.
Presence-Absence Broth is regarded as a presumptive test even though it is a quick and effective way to find coliforms. To positively identify coliform species, positive results usually need to be confirmed by additional testing, like the Membrane Filter or Multiple Tube Fermentation procedure.

Storage
Keep the container at 15-30 °C and prepared medium at 2-8 °C.