Yeast Lab: Antifungal Agents

What tiny organism is a great chef’s assistant? It’s yeast. And what does yeast eat? You may already know that yeast has a voracious appetite for sugar. This yeast lab pits yeast against powerful antifungal agents. Who will win?

Yeast is an essential ingredient in many different foods, including fresh bread. However, humans have a love-hate relationship with fungi. Fungi are prominent in our diets and our ecosystems, where they break down old materials and turn them into energy. However, fungal diseases, such as athlete’s foot, can also be quite annoying! In this experiment, you’ll determine whether different chemicals act to stop the growth of fungi. These chemicals are known as antifungals.

Problem

How do antifungal agents affect yeast growth?

Materials

• Baker’s yeast
• 7 clear plastic cups
• 7 teaspoons white sugar
• Cup
• Warm water
• Liquid athlete’s foot medicine
• Liquid ringworm medicine
• Tea tree oil
• Citronella oil
• Cinnamon oil
• Oil of oregano
• 7 identical eye droppers
• Camera
• Masking tape
• Permanent marker
• Stopwatch

Procedure

1. First, create your antifungal solutions. Look at the packages of antifungal agents and look for the active ingredient in each one. What percentage of the liquid is the active ingredient? Figure out which one of the antifungal preparations has the lowest percentage of active ingredient. Let’s pretend that this antifungal has 1 percent active ingredient. You’ll want to adjust all of your other solutions to achieve the same concentration.
2. Dilute each of the other antifungal agents until they have an active ingredient concentration that’s the same as your most diluted antifungal. For example, if one of the antifungal agents contains 10 percent active ingredient, you will need to add 9 eyedroppers of water to 1 eyedropper of the existing solution to get a concentration that’s closer to 1 percent.
3. Label the cups with the names of the different antifungal agents. Label the last one Control. Add additional masking tape labels to the table next to the cup so that you can see the labels from above.
4. Place a teaspoon of white sugar and 1/2 a cup warm water into each cup. Add ½ a teaspoon of baker’s yeast. Add an eyedropper full of antifungal solution to each different cup. Make sure that you put a different antifungal into each cup.
5. Set your timer. When it has been two minutes, look down on the cups and take a photo of the growth of the yeast. Take a photo of all of the cups at the same time. At four minutes, take another photo. Continue taking a photo every two minutes until the yeast looks like it has stopped growing.
6. Now, take the photos and place them side-by-side. Which cup had the most yeast growth? Which one had the least? Why do you think that this is the case?

Results

The cups with the antifungal agents will have produced less yeast growth than the control cup.

Why?

When a fungus grows, it releases digestive enzymes. These enzymes go out into the environment around the fungus and help the fungus get energy from carbohydrates. In this case, the carbohydrate was sugar.

There are many different ways to change the growth of a fungus. Taking away yeast’s source of food will make it harder for the yeast to grow. Chemistry can also change the way that yeast grows. Chemicals called azoles are used in liquid athlete’s foot medications to prevent fungal growth. Allylamines are used to treat ringworm, another fungal infection.

Different antifungal agents work in different ways. Antifungals target different parts of the fungal cells. For example, some antifungals target ergosterol, a component of the fungal cell membrane. Tea tree oil makes the membranes of the cells more permeable so that it’s easier for them to be damaged. Cinnamon oil eats away at the surface of fungal cells and damages what’s inside.

Extend your experiment by investigating your top two antifungal agents. Conduct some research. What behavior do these agents exhibit that classify them as antifungals?