Sierra College Department of Biological Sciences

Microbiology Diagnostic Tests: Triple Sugar Iron (TSI) Medium (Set #2)

The TSI medium can be used to test the ability of bacteria to ferment three sugars (glucose, sucrose and lactose) and to form an end product that reacts with the iron present.


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1. Are the organisms growing in these tubes capable of forming hydrogen sulfide? How do you know?

2. Which tube contains organisms that can ferment glucose and probably sucrose with the production of acid and gas? How do you know?

3. Which tube contains organisms that cannot ferment lactose? How do you know?

4. What is the name of the pH indicator in the TSI medium?

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