Dextrose Tryptone Agar is a solid medium used for cultivating thermophilic “flatsour” microorganisms associated with food spoilage (e.g., Bacilluscoagulans). Bacterial growth results in a 0.3 – 0.5 drop in pH, while the ends of the can remain flat. Tryptone provides nitrogenous sources and vitamins. Dextrose is the fermentable carbohydrate. Bromocresol Purple is the pH indicator that shifts from purple to yellow upon medium acidification. Agar is the gelifying agent.