Your laundry can make you sick: one teen searches for ways to zap illness-causing germs that lurk in your clothes.

Many people believe that a spin in a washing machine turns dirty clothes sparkly clean. Aarthi Shankar did too, until she came across a study by Charles Gerba, a microbiologist at the University of Arizona, which showed that household washers contain a shocking amount of bacteria.

In his study, Gerba swabbed the insides of 100 empty washers and found that more than 60 percent of the machines contained fecal coliforms, or bacteria associated with human or animal wastes. One type of the bacteria, E. coli, can cause people to develop abdominal cramps and diarrhea. The main source of the machines' fecal coliforms: dirty underwear. To prevent the bacteria from spreading from one laundry load to another--and to people, Gerba recommends separating underwear from the rest of the laundry and washing the load with germ-killing bleach.

Aarthi was grossed out by the findings, but she faced a dilemma: Her chores include doing her own laundry. "I do not have enough clothes to do separate loads of colored and white clothes," says the 15-year-old from Colorado Springs, Colorado.

Using strong chemical bleach in her mixed load of wash could ruin the colored clothing. So she wondered if there are natural antibacterial agents that could serve as alternatives to harsh bleach. That thought sparked an idea for a science project, and Aarthi's germ-busting experiment earned her a spot as a national finalist of the Discovery Channel Young Scientist Challenge 2006.

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CLEANING SOLUTIONS

Aarthi began her project by researching natural antibacterial agents. She read that apple cider vinegar, grapefruit seed extract, and olive leaf extract are known for having germ-killing abilities. She also learned that some people use extracts from tea trees and neem trees to zap bacteria. Based on this information, Aarthi developed a hypothesis, or a possible answer to a scientific question.

AARTHI'S HYPOTHESIS

Using natural antibacterial agents will eliminate fecal bacteria found in mixed laundry.

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Aarthi, an aspiring microbiologist, wanted her experiment to follow the standards that professional scientists use. So she sought guidance from professors at Colorado College near her home. Microbiologist Mark Wilson agreed to mentor Aarthi and even allowed her to work in his lab.

After getting pointers from Wilson, Aarthi created a detailed procedure. Having a clear list of steps to an experiment is important because other people who are unfamiliar with your project will be able to repeat your experiment, says Aarthi. Here's how she prepared for, and then set up, her procedure.

CHECKLIST

* What materials do you need for your experiment? Make a detailed list that includes specific amounts and measurements.

* Define your control, or standard against which you will compare your results. Aarthi compared various natural antibacterial agents to bleach, which has been proven to eliminate fecal coliforms.

* Identify your independent variable, or the factor that you change during your experiment. For Aarthi's science experiment, the independent variable is the type of natural antibacterial agent.

* Determine your dependent variable, or the factor that responds to the change in the independent variable. Aarthi's dependent variable is bacterial growth.

* Keep all other variables constant, The independent variable should be the only changing factor in your experiment. Aarthi kept her lab station clean to keep microorganisms--besides the bacteria she was testing--from contaminating her experiment.

* Repeat the experiment Conduct several trials. If you get similar results among the trials, your conclusions will be more reliable. Aarthi worked on her science experiment for more than four months.

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SPOTLESS RESULTS

Aarthi repeated her experiment several times. After studying the results, she found evidence to prove her hypothesis correct.

Grapefruit seed extract and tea tree oil eliminated all seven types of bacteria found in the dirty underwear. Apple cider vinegar was effective against some types of bacteria, but olive leaf extract and neem extract didn't work very well. Has Aarthi started adding natural antibiotic agents to her laundry? "Not yet," she says. "I still need to find out how well the agents work alongside of laundry detergents."

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nuts & bolts

How to write a procedure

AARTHI'S PROCEDURE

HER LIST OF MATERIALS

4 pairs of dirty underwear * 1 bucket * distilled water * 1 sterile (germ-free) water bottle * 8 agar plates (gel-filled petri dishes used for growing bacteria) * pipette (dropper used for measuring and dispensing liquid) * incubator * 7 sterile test tubes * 42 paper disks * bleach * natural antibacterial agents: apple cider vinegar, grapefruit seed extract, olive leaf extract, tea tree oil, neem extract * tweezers * ruler

AARTHI'S STEPS

1. Place four pairs of dirty underwear in a bucket. Pour distilled water on the underwear and let them soak for 24 hours.

2. Pour the dirty water into a sterilized bottle.

3. Using a pipette, place 0.1 milliliters of the dirty water onto an agar plate.

4. Put the agar plate in an incubator for two days so the bacteria can grow. (Seven different types of bacteria grew on Aarthi's agar plate.)

5. Isolate each type of bacteria: Place a small amount of one type of bacteria into a test tube. Add distilled water to the tube and mix well. Repeat this step for each type of bacteria.

6. Using a pipette, place 0.1 milliliters of each liquid bacteria sample onto a separate agar plate (Now Aarthi had seven plates, with each containing a different type of bacteria.)

7. Soak seven paper disks in bleach. Soak another seven disks in apple cider vinegar. Do the same with grapefruit seed extract, olive leaf extract, tea tree oil, and neem extract.

8. Use tweezers to place one of each type of paper disk onto an agar plate. (Now Aarthi had seven agar plates, each containing six disks soaked in different liquids.)

9. Put the agar plates into the incubator.

10. After two days, examine the areas around each of the 42 paper disks. (The more effective an antibacterial agent is at eliminating bacteria, the larger the bacteria-free zone will be surrounding the disk.)

11. Use a ruler to measure the diameter of each bacteria-free zone. Record the data.

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Interested in a science project on bacteria? Start your research here: www.microbeworld.org/microbes