Science and Our Food Supply: Investigating Food Safety from Farm to Table

6. 

Review the important rules of lab safety, especially the 

handling of bacteria in Petri dishes (see page 7). 

7. 

Give each team 3 Petri dishes. Ask them: Is there anything 

you should do with these dishes before you start your lab? 

Have the students:

• 

Label the dishes on the bottom (agar side). 

• 

Divide the control dish into thirds. Label the control 

dish: agar, wet swab, and dry swab. Then, swab the 

control dish. 

• 

Divide and label the other 2 dishes with the areas they 

want to test. 

• 

Label the dishes with the date, their team name, class, 

and hour to avoid mix-ups. Remind them to label along 

the side, so that they’ll be able to see the bacterial 

growth in the center.  

• 

For easy and fun identification, students can swab the 

dishes using their initials. 

8. 

Give the students 10 to 15 minutes to gather their  

samples and inoculate their dishes. 

• 

Seal Petri dishes closed with Parafilm.  

• 

Place dishes in an incubator at 35° C (95° F) or let the 

dishes sit at room temperature for the appropriate 

amount of time. 

• 

Ask students to set up time parameters — the number 

of hours or days they think it will take for the bacteria 

to grow.