1. Module 4 Preparation of solid media for culture and DST
Exercise

2. Good- or poor-quality media?
Different dye bubbles

3. Explain possible reasons for poor quality of media.

4. Answers Bubbles (problems in the coagulation process).
Non-homogeneous dye (non-homogeneous melting).
Discoloured (problems in the coagulation process).
Contamination (problems in sterilization and/or during the procedure).
≥8 weeks old (expired, may give false-negative results).
Not properly stored (may give false-negative results).

5. Scenario 1
You have prepared a batch of LJ medium. After 24 hours of incubation at 37 °C, colonies have appeared on the surface of the medium.
Find out possible causes and propose solutions.

6. Scenario 2
You have prepared a batch of plain medium. After coagulation, the medium remains soft/liquid.
Find out possible reasons and propose remedies.

7. Scenario 3
You have prepared a batch of plain medium. After coagulation, the medium has bubbles.
Find out possible reasons and propose remedies.

8. Scenario 4
You have prepared a batch of plain medium. After coagulation, the medium has a non- homogeneous dye.
Find out possible reasons and propose remedies.