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Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, Deanne Erdmann, MS, Sonia Rahmati Clayton, PhD, and James Denk, MA.

Where are Microbes Found?

Session 1: Getting Started (cont.)

5. Review “Safety Issues” (see PDF) with students. Then, give each group five Petri dishes. One dish will be a control. The remaining four dishes will be used to grow cultures (one per student). Have students label the bottom of all five dishes using masking tape and a marker, or by writing directly on the dishes using a permanent marker or wax pencil. (You may grow more than one culture per dish. Simply divide each dish in half or quarters, drawing lines on the outside with a permanent marker.) 

6. Have students use a different clean cotton swab dipped in boiled or distilled water for each sample. You may want to have students think about why the water needs to be boiled or distilled. (Otherwise, the water may contain microbes.) Have students rub the moist swab several times over the area to be tested.

7. Instruct students to open the Petri dishes only enough to swab the gel surface. Tell them to rub the swab gently in a zigzag pattern over the surface of the nutrient agar without breaking the surface of the agar gel. Students may repeat the pattern in another direction. Have students close and seal the dishes by taping around the edges. Tell students that they will not be able to see streaks on the plate after swabbing. Have students rub (inoculate) the control dish with a clean, moist swab. 

8. Collect used swabs from students and discard as instructed in “Safety Issues.” Clean all work areas with paper towels and disinfectant. 

9. Collect and store sealed Petri dishes. 

Funded by the following grant(s)

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605