How Bacteria Transfer to Food and Surfaces

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Objective

The goal of this experiment is to demonstrate how bacteria can transfer to food and food contact surfaces when hands are not properly washed before food preparation. Students will compare bacterial transfer between washed and unwashed hands using Glow Germ and UV light.

Background

Hand hygiene is a critical factor in preventing the spread of bacteria and reducing the risk of foodborne illnesses. Bacteria and viruses can be transferred from unwashed hands to food, utensils, and surfaces, increasing the likelihood of contamination. The Centers for Disease Control and Prevention (CDC) recommends washing hands with soap and water for at least 20 seconds to effectively remove most harmful microorganisms.

Glow Germ, a simulated germ powder that glows under UV light, is commonly used in hygiene training to visualize contamination. When applied to hands, Glow Germ mimics the behavior of real bacteria, showing how easily microorganisms can spread from one surface to another. In this experiment, students will observe how bacteria transfer from unwashed hands to food and food-contact surfaces, emphasizing the importance of proper handwashing techniques in food safety.

Materials

• Slices of bread (2 per student or group)
• Butter, peanut butter, or jelly
• Plastic knives or spreaders
• Paper plates
• Glow Germ powder
• UV flashlight
• Soap and water
• Paper towels

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Procedure

Preparing Hands

1. Divide students into two groups:
   • Group A: Will wash their hands with soap and water for 20 seconds before handling food.
   • Group B: Will not wash their hands before handling food.
2. Apply a small amount of Glow Germ powder to all students’ hands and have them rub their hands together to evenly distribute it.
3. Use the UV flashlight to observe and document the presence of simulated germs on students’ hands before washing.

Handwashing (For Group A Only)

1. Group A will wash their hands with soap and water for 20 seconds.
2. Dry hands with paper towels and use the UV flashlight to check for remaining Glow Germ.

Food Preparation

1. Each student will take two slices of bread and place them on a paper plate.
2. Using a plastic knife or spreader, they will apply butter, peanut butter, or jelly to one slice and place the second slice on top to make a sandwich.

UV Light Inspection

1. After making the sandwich, use the UV flashlight to check for Glow Germ residue on:
   • The bread
   • The plastic knife/spreader
   • The paper plate
   • The table or work surface
2. Record observations on the visibility of Glow Germ on food and surfaces for both washed and unwashed hands.

Data Collection

Students will use the table below to record their observations:

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Discussion and Analysis

Students will answer the following questions:

1. What did you observe under the UV light before washing your hands?
2. How did your hands look after washing for 20 seconds?
3. What differences did you notice between sandwiches made with washed and unwashed hands?
4. What surfaces showed the most Glow Germ contamination?
5. How does this experiment relate to real-world food safety practices?
6. Why is it important to wash hands before preparing food?
7. What recommendations would you give to someone who wants to improve their handwashing technique?