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Do Antimicrobial Agents Slow the Growth of Microbes on Potatoes?

Revised June 2012

Background

By: Carla Easter, Russell Winters, and Ryden Winters | National Human Genome Research Institute, NIH | Grade Level: Elementary School | June 6 2012

Potato slices can be used as a solid medium (that is, as food for bacteria) for isolating bacteria that can grow on them. We were interested in finding out whether antimicrobial agents would hinder the growth of bacteria on potato slices, just like they are supposed to hinder the growth of microbes on our hands. We have all been told that we need to wash our hands or use antimicrobial agents to keep our hands clean in order to stop the spread of various microbes like bacteria and viruses.

We can use a number of things to stop the growth of microbes on the skin, such as hand sanitizers, soap, and dishwashing liquid. In this experiment, we will explore the effectiveness of various materials in stopping the growth of microbes, mainly bacteria and mold, on potatoes.

Objective

To test the effectiveness of various antimicrobial agents and their ability to slow the growth of microorganisms on potato slices.

Hypothesis

Students may hypothesize that exposure to antimicrobial agents will slow the growth of microbes on the potato slices and that certain antimicrobial agents will be more effective than others.

Duration

Total actual in-class time: 90 minutes
Set-up time: 60 minutes
Experiment’s run time: 5 days
Take-down time: 10 minutes

Materials

  • One large baking or sweet potato (depending on your region of the country; $1 per lb.)
  • Paper towels ($1 per roll)
  • Tap water
  • Various antimicrobial agents (dishwashing detergent, hand sanitizers, alcohol wipes; varying prices ranging from $1 to $3 per container, which should be enough for the entire class)
  • Clear, resealable plastic sandwich bags ($2 per box of 20)

Safety Considerations

This experiment is not considered hazardous.

Procedure

  1. Slice a potato in ¼-inch slices and place in a pot. Add enough tap water to cover the potato slices. Bring the water to a boil, and let the potatoes cook for 10 minutes in the boiling water. Be very careful not to burn yourself, and have an adult assist you.
  2. Let the potato slices cool for at least 30 minutes.
  3. Carefully check the potato slices to make sure they are cool enough to handle.
  4. Decide which antimicrobial agents you would like to test.  
  5. Take one of the potato slices and place it in one of the plastic bags and seal. This will be our control. Using a permanent marker, mark the bag with a “C.”
  6. For our experiment, we decided to use hand sanitizer, dishwashing liquid, and an alcohol wipe, but any number of materials, including baby wipes and hand soap, can be chosen.
    1. Place half a teaspoon of hand sanitizer on one side of the potato slice, and use a paper towel to rub it into the potato. Repeat the process on the other side using another half a teaspoon of hand sanitizer. When done, place the potato slice in a clear plastic bag and seal. Make sure to label the bag. Write “HS” on the bag with a permanent marker.
    2. Place half a teaspoon of dishwashing liquid on one side of the potato slice, and use a paper towel to rub it into the potato. Repeat on the other side of the potato using half a teaspoon of dishwashing liquid. When done, place the potato slice in a bag and seal. Make sure to label the bag “DL” with the permanent marker.
    3. Rub one side of the potato slice with an alcohol wipe, and repeat on the other side of the potato. When done, place the potato in a bag and seal. Make sure to label the bag “AW” with the permanent marker.
  7. Let the potato slices in the bag sit in a warm space for five days. Avoid placing in an area where they will be exposed to direct sunlight.
  8. Check the potato slices each day and record what you see on the data table. Observe the slices through the plastic. Do not open the bag! 

Results

Record the following for each sample in Table 1:

  1. Describe what the potato looks like (color, shape, size) on each side.  
  2. Without opening the bag, can you detect a smell?  
  3. Do you notice anything growing on the potato? If so, describe.

Data Analysis

Compare each of the potatoes treated with the various antimicrobial agents and describe what is the same or different about them.

Conclusions

Draw some conclusions about how well the antimicrobial agents worked for inhibiting the growth of microbes on the potatoes. Discuss the purpose of antimicrobial agents and whether we can infer anything from the growth of microbes on potatoes about their growth on human skin.  

Helpful Resource

How to make bacteria media from potatoes, http://www.disknet.com/indiana_biolab/b029.htm

Relevant OSE Supplement

  • Open Wide and Trek Inside

Relevance to NIH Mission

The experiment ties in directly with the mission because it explores a health-related issue (microbes on food or skin) and addresses one way participants can help prevent infection.

Table 1. Results of putting antimicrobial agents on potato slices

Day Control Dishwashing liquid Hand sanitizer Alcohol wipes
         
         
         
         
         

This page was last updated June 2012