How to Grow Yeast on Lysine Agar Plates

When testing for infection, scientists and doctors often grow infectious samples on lysine agar plates. This hard, gelatinous substance won't degrade like gelatin and the lysine encourages the growth of fermenting bacteria, such as yeast.

Unlike other bacteria, yeast is a plant. It clones itself into neatly packed, dense colonies. It's also a safe, fast-growing choice for students using agar plates for the first time. Students can observe bacteria growth without the risk of spreading infection.

Warm water
Glass measuring cup
Yeast: bread yeast, vintner's yeast, etc.
Cotton swabs
Lysine agar petri dish

Instructions

- 1
  Fill a glass measuring cup with about one-fourth cup of very warm water, about 130 degrees Fahrenheit. Yeast comes dried and dormant; you have to "wake it up" with a warm water bath, or it won't grow very quickly.
- 2
  Add a single packet, about 2 grams, of yeast to the warm water. Swirl the water around gently and let the solution settle. It should develop foam on the top. This means your yeast is awake and active.
- 3
  Gently remove the lid from a glass petri dish containing lysine agar. The hard gel inside should be pink in color. Do not touch it with your fingers. This will contaminate the agar with other bacteria.
- 4
  Dip a cotton swab into the yeast solution and rub it lightly over the agar. You may create stripes or try drawing shapes to see if your colonies will grow into a design.
- 5
  Cap the agar plate and set it in a warm, dark place. After a day or two, check on the yeast growth. You should see dense, white colonies of yeast forming on the agar.

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