Part 1: Introduce the Lab

1. Ask students:
   • "Where in your kitchen could bacteria be growing?"
   • "Could bacteria be on the kitchen items that you or your parents use when preparing food?" Make a list of students’ responses.
     • Some probable answers:
       • Sponges
       • Dishcloths
       • Dish towels
       • Pot scrubbers
       • Vegetable brushes
       • Can-opener blades
       • Sink stoppers or disposal covers
       • Paper towels
       • Utensils
       • Cutting boards
       • Dishes
2. Next, ask students to hypothesize about which kitchen items contain the most bacteria and which contain the least bacteria. Make 2 lists, “Most Bac” and “Least Bac.” Ask them, "Why would/wouldn’t bacteria be found on these items?
3. Give each student one copy of the Lab Report Outline to record each step of the lab.
4. Then ask students to vote on the items most and least likely to harbor bacteria. List the Top 5 items in each category. Keep the Top 5 lists on the board through the next few labs to allow students to compare their lab results with the lists.
5. Group students into teams of 3 to 4. Ask each team to choose at least 3 or 4 kitchen items they want to inspect.
   • Students should include items they think will have lots of bacteria as well as those they think will have fewer bacteria. For example, they may want to compare new sponges or just-washed dishcloths with dirty or just-used sponges or dishcloths.
   • Items don’t have to be chosen only from the class list. Teams can pick their own items to investigate. Try for as many different items as possible but make sure the important ones, such as sponges, dishcloths and dish towels, are included by at least 2 teams.
6. Give each team 1-gallon storage bags to take home. Ask them to bring in kitchen items from home to test. Remind students to ask their parents’ permission to bring the items to class. Ask them to put in 1 item per bag, seal the bag, and bring it to class. Mention that they should bring in some items, like dishcloths, “as is” rather than washing them first.
   • Note: This lab should be set up to avoid any comparing and critiquing of items from students’ homes. Put a number on each bag as students give the bags to you. Write each student’s name on a list with their corresponding bag number. The lab should be a general learning experience about how to avoid cross-contamination in the kitchen, not a specific review of individual items. For example, students should look for common items that are most likely to harbor bacteria.

Part 2: Develop, Hypothesize, and Conduct Lab

1. Ask each student to label his/her storage bags by the type of item (e.g., sponge, can opener, etc.). Students’ names should not be put on the bags.
2. Have each team develop a hypothesis and design a lab to test the hypothesis.
3. Pose these questions to guide students through their labs:
   • Which type of kitchen items might have the most/least bacteria? Why?
   • How can you find out which items have the most/ least bacteria? (Swab the items and inoculate the Petri dishes.)
   • What’s a good way to get a sample of the bacteria in these items? (Swab the item directly, or add water to the bags and sample the water.)
   • What kind of water would be best to use? (Sterile or distilled water)
   • How can you transfer bacteria from the kitchen item to the water? (Squeeze/massage the item in the bag.)
   • What does the water look like after you squeeze/massage the item? (The water in some bags will appear very dirty. Water in other bags will appear clean.)
   • Is the appearance of the water an indication that bacteria are present? (Not necessarily.)
   • How can you be sure you’re not introducing new bacteria to the test samples? (Use sterile dishes and swabs. Use a control bag with distilled or sterile water.)
4. Demonstrate how to sample the water and inoculate agar dishes (see the attached Lab Procedures sheet for more details).
5. Discuss the importance of a control dish. To test for bacteria in the water, swab half of the control dish with distilled water. Leave the other half untouched.
6. Review the important rules of lab safety, especially the handling of inoculated Petri dishes.
7. Let each team develop its own hypothesis and design its own experiment.
8. Let the students conduct their experiments.

Part 3: Observe and Record Results

1. Have teams observe their Petri dishes and record the results on a data table.
2. Ask each team to present their findings to the class. List the class results and have the students compare their findings to the “Most Bac” and “Least Bac” lists from Part 1. (Be sure to focus the discussion on the categories of items rather than on specific items.)
3. Pose questions to guide students through a discussion. For example,
   • How did your original lists compare to the test results? Were there any surprises? What are your conclusions?
   • Could bacteria transfer from kitchen items to your food? Your hands? What might happen in these cases?
   • Why do certain kitchen items have more bacterial growth than others?
   • How do the data you collected relate to the 4 Cs of Food Safety? Which of the 4 Cs?
   • How could you reduce the bacteria on the items you tested?
   • What are your suggestions for avoiding cross-contamination in the kitchen?
   • What advice would you give to family members to help them prevent the spread of foodborne bacteria?