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How do Disinfectants Work?

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Author: Nancy Rogers Bosse

Objective:

To investigate how different disinfectants work in killing germs.

Research Questions:

  • Do disinfectants kill germs?
  • Do some disinfectants work better than others at killing germs?

Germs are everywhere. Germs can cause illness and disease. Soap and water get rid of germs. Special disinfectants are produced to remove germs from other surfaces such as kitchen and bathroom countertops.

Materials:

  • Large plastic cutting board
  • Marker
  • Masking tape
  • 3 disinfectant solutions
  • Clean spray bottle
  • Water
  • Latex gloves
  • Raw hamburger or chicken
  • Paper towels
  • Petri dishes with nutrient agar
  • 4 cotton swabs

Experimental Procedure:

  1. Gather the necessary materials.
  2. Use masking tape to divide the cutting board into four equal sections. Number the sections 1 – 4.
  3. Pour water in the spray bottle. Number the water bottle number 1. Number the disinfectants numbers 2 through 4.
  4. Label the petri dishes 1 through 4. Do not open them or you will contaminate them.
  5. Put on the latex gloves. Smear a small bit of raw hamburger or chicken on each space of the cutting board. Try to apply the same amount to each section. Throw the remainder of the hamburger or chicken into the garbage. Let the cutting board sit undisturbed overnight.
  6. Spray some water on a paper towel and rub over section one. Repeat spraying each disinfectant on a separate paper towel. Rub over the appropriate section. Allow the cutting board to dry completely. Throw away the used paper towels.
  7. Using a cotton swab, gently swipe one end across one section of the cutting board.
  8. Do not allow the cotton swab to touch anything else. Open the lid of the petri dish and swipe the cotton swab across the agar surface. Immediately replace the lid. Do not let the lid touch anything else.
  9. Repeat steps 7 with the other sections of the cutting board.
  10. Place the petri dishes in a warm place where they can remain undisturbed from 2 days.
  11. After 2 days, record your findings and draw your conclusion.

Terms/Concepts: germs: tiny bacteria that can cause disease bacteria: small organisms that grow sometimes causing disease or sickness disinfectant: chemical used to kill germs on surfaces; some germs can cause illness and disease; disinfectants can be used to remove germs from surfaces.

References:

“What are Germs? at http://kidshealth.org/kid/talk/qa/germs.html “Germs: Understand and protect against bacteria, viruses, and infection” by Mayo Clinic Staff at http://www.mayoclinic.com/health/germs/ID00002 “What are Germs?” at http://www.coolquiz.com/trivia/explain/docs/germs.asp “How Do Disinfectants and Antiseptics Work?” at http://www.typesofbacteria.co.uk/how-do-disinfectants-antiseptics-work.html

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