Problem to be Solved:
Does dog saliva kill bacteria?
Hypothesis:
Saliva will be effective at killing bacteria because in ancient times dogs were considered holy because of their ability to treat wounds.
Variables:
The variables are the saliva from three dogs:
Dog 1 - Golden Retriever, age 10
Dog 2 - Golden Retriever, age 7
Dog 3 - Saint Bernard, age 2
Control Group:
The control group is a test to kill the bacteria with bleach on the filter paper, and a test to kill bacteria with no saliva on the filter paper.
Equipment:
Saliva from each of the three dogs
Staphylococcus epidermis bacteria (non-pathogenic)
Sterile tweezers
Sterile scissors
Sterile cotton swabs
Sterile eyedroppers
Four cups
Qualitative filter paper cut into 1 cm squares
Nutrient agar
Six sterile petri dishes
Paper towels
Procedure:
1] Pour nutrient agar into six petri dishes. Let agar cool for 24 hours.
2] Mix freeze-dried Staphylococcus epidermis bacteria with growth medium using a sterile eye dropper.
3] Place five drops of Staphylococcus epidermis bacteria mixture onto agar in a petri dish.
4] Spread bacteria mixture over all of agar with a sterile cotton swab.
5] Label dish with the date it was inoculated.
6] Let bacteria grow in dish for 24 hours.
7] Collect saliva from each of the three dogs in the morning before they have eaten.
8] Cut filter paper into 1 cm squares.
9] Pour bleach into one of the cups. Put each dog saliva into a separate cup.
10] With sterile tweezers, dip filter paper into the cup with bleach and place the filter paper onto the bacteria in one petri dish. Label as bleach.
11] With sterile tweezers, dip filter paper into the cup with saliva from dog #1 and place the filter paper onto the bacteria in the petri dish. Label as dog #1.
12] Repeat step 11 for the saliva from each of the other two dogs. Label as dog #2 and dog #3.
13] With sterile tweezers, place an plain filter paper onto the bacteria in the petri dish. Label as plain.
14] Let dish sit for 24 hours.
15] Lift the filter papers with a sterile tweezers to look underneath. Estimate the percentage of bacteria that disappeared under each filter paper.
16] Repeat steps 3-15 for each of the other five petri dishes.
Notes:
1] All five filter papers should be spaced equally apart in the petri dish.
2] Protective gloves are worn when working with bacteria and petri dishes.
Results:
The amount of bacteria in each petri dish was reduced under all of the filter papers containing dog saliva. Results for the Golden Retrievers were similar. Saliva from the Saint Bernard was more effective at reducing bacteria than the saliva from the Golden Retrievers. Bleach reduced bacteria by 100%. There was no change in the amount of bacteria under the plain filter.
Conclusion:
My hypothesis that dog saliva would kill bacteria was correct. To improve my experiment I could have had more dogs with different ages and breeds because some breeds may have more enzymes in their saliva that kill bacteria.
Biblical Application:
For every beast of the forest is mine, the cattle on a thousand hills. I know ever bird of the mountains, and everything that moves in the field is mine. Psalm 50:10-11
This verse means that God loves His creations including His animals, and takes care of them. He took care of dogs by giving them special healing powers in their saliva to heal wounds or prevent infection. Along with the healing, He gave them the instinct to know what to do with their God-given abilities. God truly knows best.
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2nd Place, 7th Life Science, PCA Science Fair