You can run, but you can't hide when it comes to bacteria. They can be found everywhere on earth, from Antarctica to the inside of your intestines! Some are good, aiding digestion and giving us tasty food like cheeses and yogurt. Many are harmful, causing serious diseases; these are called pathogenic bacteria. Learn more about what bacteria are, where they live, and how they can help or harm us in our Bacteria: Tiny But Tough article.
You have millions of bacteria living on your skin. While some types are harmless, bacteria are a major source of illness. They spread easily every time you touch something — you leave them and pick them up on doorknobs, telephones, and more. Touching your face (especially eyes, nose, and mouth) with your hands can allow bacteria to get inside you and make you sick. One of the best ways to prevent the spread of illness is just to wash your hands well in soap and water. It seems so simple, but it really does work! With this project, you can experiment to see which hand soaps are most effective in getting rid of bacteria.
While most environmental bacteria are not harmful to healthy individuals, once concentrated in colonies, they can be hazardous. To minimize risk, wear disposable gloves while handling bacteria, and thoroughly wash your hands before and after. Never eat or drink during bacteria studies, nor inhale or ingest growing cultures. Work in a draft-free room and reduce airflow as much as possible. Keep petri dishes with cultured mediums closed—preferably taped shut—unless sampling or disinfecting. Even then, remove the petri dish only enough to insert your implement or cover medium with bleach or 70% isopropyl alcohol. When finished experimenting, seal dishes in a plastic bag and dispose. Cover accidental breaks or spills with bleach or alcohol for 10 minutes, then carefully sweep up, seal in a plastic bag, and discard.
>> Watch our video to learn how to set up a bacteria experiment and see bacteria colonies grown from a kitchen sink!
Three types of hand cleaners (like regular soap, antibacterial soap, and hand sanitizer)
What You Do:
Part 1: Preparing culture dishes
Melt the agar in a hot water bath, using the directions on the bottle. Use a potholder to pick the bottle up.
Let the agar cool to 110-120°F (when the bottle still feels warm but not too hot to touch) before pouring into petri dishes.
Slide open the cover of the petri dish just enough to pour agar into the dish. Pour enough agar to cover 1/2 of the bottom of the dish. Cover the dish immediately to prevent contamination and tilt it back and forth gently until the agar coats the entire bottom of the dish.
Let the petri dishes stand for one hour until the agar has solidified before using them.
Part 2: Hand soap experiment
Using a sterile swab, collect bacteria from the dominant hand of your first helper. Run the swab across the palm, across the back of the hand, and in between the fingers. Remove the cover of a petri dish and lightly rub the swab across the surface of the agar in a zigzag pattern. Turn the dish a half turn and zigzag again for maximum coverage. Cover the dish again immediately. Label it 'Control' with your helper's initials.
Now put a drop of soap in your helper's palm. Time them as they wash their hands thoroughly (rubbing front, back, and in between fingers) in warm water for 30 seconds. Let the hands air dry, and use a new swab to collect and transfer bacteria as you did in step one. Label this dish with the helper's initials and the type of soap.
Repeat steps 1 and 2 with your other helpers and types of soap. Try to use the same amount of soap and the same temperature of water. Have a fourth helper wash their hands with just water, no soap.
Put all the petri dishes in a warm, dark place. Check on them in a couple of days.
The rate of bacteria growth in your dishes will depend on temperature and other factors. Check your cultures after a couple of days, but you'll probably want to wait 5-7 days before recording your data. You will see multiple round dots of growth; these are bacteria colonies. There may be several types of bacteria growing in the dishes. Different types of colonies will have different colors and textures.
For each soap test, count and record the number of bacteria colonies in each dish. To see how effective each soap was, divide the number of colonies in the test dish by the number of colonies in the control dish, then subtract the result from 1 and write the answer as a percentage. For example, if your control dish had 100 colonies and your soap test dish had 30, the soap eliminated 70% of the bacteria: 1 — (30 ÷ 100) = .7 = 70%
According to your results, which type of soap was the most effective at eliminating bacteria? Does "antibacterial" soap really work better than regular soap? How well did washing hands in water without soap work? What further tests could you do to determine which soaps and hand washing methods are most effective at eliminating bacteria?
Explore the fascinating diversity of bacteria in your own environment! With this kit you can experiment with bacteria in the air, on surfaces, and on your hands. You can also test the antibacterial effects of common household cleaners. This experiment/study kit comes with instructions and all the supplies you need for growing 20 bacteria cultures
- Bacteria that love the heat are called thermophiles, and can survive in temperatures as hot as 284° F! Cold-loving bacteria, called psychrofiles, can live in permanently ice-covered lakes in Antarctica.
- A single bacterium is far too small to see without the help of a microscope...except for the Thiomargarita namibiensis ('sulfur pearl of Namibia') which is as big as a period at the end of a sentence!