1. Introduce this lesson:
   “Food safety is a very important issue that we will be pursuing in this lesson. Essentially, food safety is everyone's responsibility—everyone involved in growing, processing, transporting, and handling our food along all the points in our complex food distribution system. Food safety is a serious issue that affects the wellbeing of every individual. We all must eat so we are all at risk of becoming ill if our food becomes contaminated.”
   
2. State: (modify if only using one lesson)
   “In the two laboratory lessons that follow, you will start to understand that bacteria are everywhere and that various surfaces have different levels of organisms. It is very important to keep in mind that bacteria can spread from hands to food, from food to food, and from surfaces to food. This cross-contamination can be controlled by the simple measure of thoroughly washing hands and surfaces.”

• Wash hands thoroughly before and after the lab.
• Disinfect all lab surfaces before and after working in the lab (see page 9, Science and Our Food Supply: Investigating Food Safety from Farm to Table: Teacher's Guide for High School Level Science Classrooms).
• Wear safety gloves.
• Seal inoculated Petri dishes using Parafilm or masking tape (see page 9, Science and Our Food Supply: Investigating Food Safety from Farm to Table: Teacher's Guide for High School Level Science Classroom).
• Remind students never to open a dish with organisms growing in it. Some organisms could be dangerous pathogens.
• After the experiment is completed, discard all disposable dishes using safe techniques (see page 8, Science and Our Food Supply: Investigating Food Safety from Farm to Table: Teacher's Guide for High School Level Science Classrooms).

2. Explain:
“I would like you to try to test for bacteria in as many different areas as possible. If you are going to test hands and under fingernails for bacteria, wash your hands after you have swabbed these areas.”

3. State:
“Each team should talk quietly among themselves and hypothesize which areas you might test that will have the most bacteria. State why. State how fast the bacteria will grow in the areas you are selecting and why.”

4. Explain:
“Now, I would like you to design an experiment that will test your hypothesis.”

5. Ask each team:
“Are you ready to explain your hypothesis to the class? If so, let us begin.”

6. Encourage the teams by saying:
“Please discuss the merits of each test you are suggesting. I would like the teams to exchange helpful information and ideas for the experiments of each team.”

7. After group discussion, give the teams time to revise their hypotheses and design.

8. Demonstrate:
Show students how to swab a surface (on dry surfaces use a moist swab) and inoculate a Petri dish (see page 9, Science and Our Food Supply Investigating Food Safety from Farm to Table: Teacher's Guide for High School Level Science Classrooms, Laboratory Procedures). These procedures will be used throughout these two laboratory lessons.

9. Review:
Review with students the information related to the important rules of lab safety, especially handling of bacteria in Petri dishes(see page 8, Science and Our Food Supply Investigating Food Safety from Farm to Table: Teacher's Guide for High School Level Science Classrooms, Laboratory Procedures).

10. Give instructions:
After giving each team three Petri dishes, provide the following instructions:

• Label the dishes on the bottom (agar side).
• Divide the control dish into thirds. Label the control plate: agar, wet swab, and dry swab. Then swab the control plate.
• Divide and label the other two dishes with the areas they want to test.
• Label the dishes with the date, their team name, class, and hour to avoid mix-ups. Label along the side, so you can see bacterial growth in the center.
• For easy and fun identification, students can swab the plates using their initials.

1. Explain:
   “Please tape your Petri dishes closed.” (If your lab has an incubator, place dishes in incubator at 35° C (95° F). If not, indicate that Petri dishes can sit in room temperature.)
2. Challenge your students:
   “How many days or hours do you think it will take for the bacteria to grow?”