Product Summary and Explanation
Dextrose Tryptone Agar evolved from research by Williams, while studying the cultivation and enumeration
of thermophilic bacteria caused by “flat-sour” spoilage of canned foods.1
In the 1930’s, the National Canners
Association specified the use of Dextrose Tryptone Agar for isolating “flat sour” organisms from food
products.2
“Flat sour” spoilage of canned foods is caused by Bacillus coagulans (Bacillus thermoacidurans).
Bacterial growth results in a 0.3 – 0.5 drop in pH, while ends of the can remain flat. B. coagulans is a soil
microorganism, found in canned tomato products and dairy products. Conditions favorable for organism
growth can result in spoilage of food products.3
Dextrose Tryptone Agar can be used to isolate other food spoilage bacteria including mesophilic, aerobic
spore-formers and thermophilic “flat sour” spore-formers such as B. stearothermophilus.
3
Principles of the Procedure
Enzymatic Digest of Casein is the carbon, nitrogen, and vitamin sources used for general growth
requirements in Dextrose Tryptone Agar. Dextrose is the carbohydrate source. Bromcresol Purple is the pH
indicator. Agar is the solidifying agent.
Formula / Liter
Enzymatic Digest of Casein...................................