Food and Beverages - Safe Food Practices

Hand Washing: Grades 5 - 8

Growing Micro-organisms

Students learn that micro-organisms can be everywhere by making cultures on agar plates. Cultures of washed and unwashed hands are compared to show that micro-organisms are everywhere and that hand washing reduces the amount of bacteria on hands.


  • Petri dishes with nutrient agar (get these from a science teacher)
  • Masking and Scotch tape
  • A marker
  • Cotton swabs
  • A sink with hot and cold running water
  • Liquid soap
  • Paper towels

Lesson Description:

  1. Explain to students that the petri dishes will help grow bacteria so that they can be seen without the use of a microscope.
  2. Have students inoculate petri dishes with a different bacterial source for each plate. Suggestions are:
    1. Hair - remove hair from the head of a student and place into the dish.
    2. Cough - hold a petri dish 6 cm (about 3 inches) away from the mouth of a student and have him/her cough onto the plate.
    3. Saliva - place a clean cotton swab into a mouth and moisten it with saliva, rub the swab over the agar.
    4. Nose - place a clean cotton swab into a nose and gently move it around, rub the swab over the agar.
    5. Counter - have a student drag his/her fingers on a counter top then trace an "S" on the agar.
  3. Ask a student who hasn't washed their hands to place his fingertips in the agar.
  4. Ask a student to wash their hands properly and to place her fingertips in the agar of a different dish.
  5. Label the bottom of each dish using the masking tape and marker.
  6. Tape each dish closed by running scotch tape around the edge.
  7. Place the dish in a warm dark place for three to five days. Check the dishes daily for growth. Refrigerate once the desired amount of bacterial growth is seen.
  8. When bacterial growth can be seen, have students examine dishes and discuss how bacteria were present even though they couldn't be seen.
  9. Review the types of bacteria and viruses that can be found in the areas used for inoculating the dishes and the different routes of transmission that occurred when inoculating the petri dishes.
  10. Compare the dishes that contained the washed and unwashed hands. Explain how hand washing reduces the amount of bacteria on hands.
  11. Properly dispose all of the used petri dishes.

Source: Wellington-Dufferin Guelph Health Unit. Down With Germs - An educational kit to promote handwashing in schools.

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Revised: Wednesday November 23 2011

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