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Presence Absence (P-A) Test 


Presence Absence (P-A) test with MUG (4-Methylumbelliferyl-β-D-glucuronide): 

The P-A test is frequently used for routine examination of drinking water. Coliform analysis by the P-A test is based on 2 premises: 1) no coliform bacteria should be present in 100 mL of drinking water, and 2) if one viable cell is present it will multiply to give a population of cells that will ferment lactose to produce acid and gas. Thus, P-A broth contains lactose and a pH indicator, which will change from purple to yellow if lactose is fermented and acid is produced. To this P-A broth, the compound 4-Methylumbelliferyl-β-D-glucuronide (MUG) has been added. This initially colorless compound can be hydrolyzed by the E. coli β-glucuronidase enzyme to form a compound (4-methylumbeliferone) that fluoresces under long UV light (336 nm). Observing for fluorescence emission is a sensitive way to confirm the presence of E. coli in water samples. 



Observe the yellow color change in the PA broth. Additionally the presence of coliforms will cause the broth to fluoresce under a UV light.

PA broth negative and positive resultsPA broth negative and positive results under UV light

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