What Is the Dirtiest Place in the House?

Overview

Objectives/Goals I wanted to find the dirtiest place in my house. I chose 9 places in my house. I bought petri dishes and agar to grow samples of what actually lives at these places. By growing these samples and recording their size, I found the dirtiest place. Methods/Materials Method: Melt agar in microwave. Pour into petri dishes and number each dish. Cool overnight. Rinse swab with distilled water. Swab chosen areas. Swab into petri dish by making Z formation without contaminating petri dish. Place petri dishes into plastic bags under a hear lamp to replicate a homemade incubator. Each day take out all petri dishes and record their growth. Also clean bags of excess condensation. Continue for seven days. Materials: 4 agar bottles, 40 petri dishes, 20 swabs/20 loops, gallon of distilled water, microwave, 3 gallon plastic bags, heat lamp, thermometer, clock, paper towels, measuring pies, pen, paper, gloves, kitchen mitts, and camera. Results I made measuring pies for the petri dishes so I could compare and contrast the growth each day. In agar bottle D all of the samples did not grow because of the agar bottle not being melted enough. I had 9 places that I recorded and a 10th petri dish that was considered my control sample. The phone had no growth. The toilet seat, TV remote, and door knob had only 5% growth. The toothbrush had 3 positive results but not a tremendous amount of growth. The computer keyboard had 2 positives but a large mold growth and possible contamination. The kitchen counter had 3 positive results with multiple types of microorganisms. Inside the microwave there were 3 positive results two of which took 25% of the petri dish and the same bacteria. The corner of the room had the most growth and variety of microorganism in each dish. Conclusions/Discussion The corner of the room had the most variety and biggest size of all the samples. It rejected my hypothesis that the doorknob was dirtiest. The toothbrush had 3 positive results and did not have quite as big growth as the corner of the room but the toothbrush grew exactly where I swabbed. The microwave had 2 positive results, no significant growth. The toothbrush and microwave both seemed to have bacteria growth only. If I had to do the experiment all over i would have made sure all of my problems including not boiling the agar in bottle D enough were fixed. Contamination was also a small problem in that it could change the results.

Competition history

• CSEF 2012 Microbiology (General) · Entry S1508

Resources

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