Total Coliform Bacteria Kit...

Charlie, Technical Service, replies to a request for more information on what causes a positive Total Coliform Test using LaMotte tablets.

The tablets used to detect the presence of total coliforms contain nutrients (a proprietary cocktail!) that support the growth of coliform bacteria, a casein gelling substance (like Jell-O), and a pH indicator.

If coliform bacteria are present in the sample, a sequence of events occurs:

1. The bacteria metabolize the nutrients in the tablet, releasing CO2 gas and acids as by-products.
2. CO2 gas is trapped in the gelling substance, causing the gel to rise in the tube.
3. Acid by-products lower the pH of the sample, changing the phenol red pH indicator from red to yellow.
4. Both CO2 and acids have to be produced to detect the presence of Total Coliforms.

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