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disposable gloves. Obtain a Petri dish with nutrient agar from your teacher. Divide your Petri dish into four equal quadrants by writing on the outer bottom surface of the dish with the marking pen. Label the quadrants 1, 2, 3, and 4, as shown in the photograph at left. Also label the bottom of the dish with your group name or number. Do not mark on the top of the Petri dish because it will rotate with respect to the agar.

3. Use quadrant 1 as a control. Take a sterile cotton swab, and moisten it with distilled water. Be careful not to touch the cotton swab to any other surfaces, including your fingers. Remove the cover to the Petri dish, and rub the cotton swab across the nutrient agar in quadrant 1. Be careful not to tear the surface of the agar. Replace the cover immediately.

4. Take another sterile cotton swab, and moisten it with distilled water. Swipe the moistened swab across a surface that you have decided to test for the presence of bacteria. Be careful not to touch the cotton swab to any other surface. Touching the swab to other surfaces could contaminate the swab with bacteria other than the bacteria from your selected surface.

5. Remove the cover to the Petri dish, and rub the cotton swab across the nutrient agar in quadrant 2. This process transfers bacteria from the surface you have sampled to the nutrient agar in the Petri dish. Replace the cover immediately.

6. Using a clean cotton swab each time, repeat steps 4-5 for quadrants 3 and 4. Be sure to note in your lab report the areas that you swipe for each quadrant.

7. After you have swiped a sample in each quadrant of the Petri dish, seal the Petri dish with tape. CAUTION Do not open the Petri dish again. Treat the contents of the Petri dish as you would any other pathogens.

8. Place the Petri dish in a warm place with the cover side down for 24 hours or in an incubator at 37°C overnight.

9. ^^ Dispose of the cotton swabs and gloves accord-

13. /ih\ Discard your Petri dish as directed by your ▼ ■

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