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Compare the rate of bacterial growth in dog versus human saliva

Life Sciences science projects

Suitable For

Grade 8

Difficulty

2

Time Required

 <2 Weeks

Supervision

Advised

What’s it about?

Dogs give you joy. They give you loyalty, and often they give you sloppy kisses. Of course, there is that old saying, “a dog’s mouth is cleaner than a human’s mouth.” Is that true? After all, dogs have to be carrying all kinds of germs in their fur and in their mouths. Are you worried about dog germs? Try the following science experiment to find out the truth:

Topics covered

Bacteria, Saliva, Mycology

What will I need?

  • MAGIC MARKER
  • NUTRIENT AGAR PETRI DISHES
  • SOAP
  • TAP WATER
  • COTTON SWABS
  • BLEACH

Procedure (Method)

Dogs give you joy. They give you loyalty, and often they give you sloppy kisses. Of course, there is that old saying, “a dog’s mouth is cleaner than a human’s mouth.” Is that true? After all, dogs have to be carrying all kinds of germs in their fur and in their mouths. Are you worried about dog germs? Try the following science experiment to find out the truth:

  1. Purchase 4 Petri dishes from your local science supply store or a store that sell school supplies.
  2. Use a magic marker to label two of the dishes ‘Human saliva’ and the remaining two dishes ‘Dog saliva’.
  3. Before taking saliva samples, make sure not to eat anything or to give your dog any treats for at least one hour. Then, use a sterile cotton swab to gently swab on the inside of your dog’s mouth to collect some saliva.
  4. Carefully swipe the first sample of dog saliva in the first Petri dish labelled ‘dog’ on the agar making sure not to press too hard down on the agar. Discard of the used swab properly. Repeat the same process a second time and place the sample in the second Petri dish labelled ‘dog’ and then thoroughly wash your hands with soap and water.
  5. Now, using a new sterile cotton swab, gently swab the inside of your own mouth to collect a saliva sample and place it is the first ‘human’ labelled Petri dish. Repeat the process once again to collect a second ‘human’ sample.
  6. Place the dishes in a room where they will not be disturbed and check them every 24 hours for bacterial growth that will develop over time.
  7. Notice that the samples with human saliva grow bacteria more rapidly than the dog saliva samples!

How does it work?

In this science experiment, it would seem that a dog’s mouth is ‘cleaner’ than a human’s mouth. However, this is more a matter of comparing apples and oranges in many respects. The bacteria in a dog’s mouth are different from the bacteria in a human being’s mouth. When dealing with different bacteria, it’s rather difficult to make a sensible comparison. The germs contained in the mouths of animals tend to be species-specific. For instance, when a dog bites another dog it would be more dangerous to the dog than if a human was bitten by the dog. Similarly, a human bite is more dangerous to another human than it would be to a dog.

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