Which carbohydrate source is found in small concentrations in tsi media, allowing the investigator to differentiate between organisms that can only ferment this monosaccharide and those that are able to ferment other available carbohydrate sources?

The carbohydrate is Glucose. TSI agar or Tripple sugar agar medium is a differential medium that contains lactose, sucrose, a small amount of glucose, ferrous sulfate, and the pH indicator phenol red. It is used to differentiate enterics based on the ability to reduce sulfur and ferment carbohydrates.