Do-It-Yourself Experiment

Does Listerine® Actually Kill Bacteria?

We can thank Joseph Lister for introducing the use of germ-killing antiseptics to hospitals, but how about seeing a germ-killing antiseptic at work with your own eyes? Try the experiment below to see if using Listerine® (the antiseptic mouthwash named for Lister) kills more bacteria than brushing alone.

3 agar petri dishes 3 disinfected swabs 1 bottle of disinfected water 3 toothbrushes 1 bottle of Listerine© 1 tube of toothpaste 1 marker pen 1 ruler

• Remove petri dishes from refrigerator and allow them to warm to room temperature.

• Label each dish and each toothbrush either A, B, or C.

• Toothbrush A is used to brush teeth 2 times a day for 5 days with only water. After brushing, the toothbrush is kept in an empty cup.

• Toothbrush B is used to brush teeth 2 times a day for 5 days using toothpaste. After brushing, the toothbrush is kept in an empty cup.

• Toothbrush C is used to brush teeth 2 times a day for 5 days using toothpaste. After brushing, the toothbrush is kept in a cup filled with Listerine®. At the end of five days, dampen each sterilized swab with sterilized water, then brush over corresponding toothbrush. Wipe brush over corresponding petri dish. Cover each petri dish and keep in cool shaded place for bacteria to grow over the course of several days.

• Measure diameter of the bacteria colony in each dish, then record your findings.Which dish had the smallest bacteria colony? Does Listerine® kill more bacteria than toothpaste alone?

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