What kills fungi?

Project 1, Part 2: What kills yeast?

diffusion disk assayBaker’s yeast is a common fungal species called Saccharomyces cerevisiae in the phylum Ascomycota. We use it to make bread, but it is also a very useful model for understanding human biology and human disease. In this experiment, we will perform a Diffusion disk assay to identify different materials that can prevent the growth of Saccharomyces cerevisiae. These materials can be fugistatic –meaning they slow or prevent growth but don’t kill Saccharomyces cerevisiae-or fungicidal –meaning they kill Saccharomyces cerevisiae. This type of assay is commonly used to test new drugs and figure out dosage.

Materials:

1 nutrient agar plate
5 diffusion disks
Potential fugicidal or fungistatic agents

Procedure

  1. Place 1 drop of the yeast suspension onto the agar plate.
  2. Use the cell spreader to spread the yeast around the whole plate. Spread out from the center and make sure to cover the edges. Allow the plate to dry for 10 minutes.
  3. Using tweezers, place 5 diffusion disks around the plate. Space them out evenly in a circle.
  4. Select 5 agents to test. When choosing these agents, think about what you need to design a good experiment. What controls should you include?        Possible agents:

i.     Rubbing alcohol

ii.     Hydrogen peroxide

iii.     Iron oxide (Fe2O3), Cobalt carbonate (CoCO3), Copper Carbonate (CuCO3), Sodium Chloride (NaCl)

iv.     OR find something to test from your environment. For example, are there plants that you think might have
fungicidal activity? If so, collect samples, grind them up using a mortar and pestle, and suspend in a small volume of water. Pass the suspension through a sterile filter using a syringe.

5.   For each agent, place 1 drop onto the diffusion disk.
6.   Incubate the plates at room temperature for 48 hours.
7.    Record your results by photographing the plate

Record your results:

What agents did you choose and why?

Which agents prevented growth? Which agents failed?

Bonus: How can you test if the effect is fungistatic or fungicidal?

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