Disinfectants, Antiseptics,and a Gross Little Petri Dish

We recently completed a lab on disinfectants and antiseptics, and my results were surprizing (and gross!). Disinfectants are chemicals used to kill bacteria on non-living objects like surfaces, whereas antiseptics are chemicals used to kill bacteria on the body. Antiseptics are usually much less harsh, but sometimes lack the power to kill all the bacteria because of this. In this lab, we used the disinfectants alcohol and bleach, and the antiseptic soap to see if the difference in effectiveness of the products. We were to take samples of both our hands and a surface of our choice.

First, I divided my petri dish into six sections. For the first section, I swabbed a portion of my finger and streaked the petri dish with it. Then I put my swab in alcohol and swabbed a different finger, again streaking the petri dish with the swab. Then I washed my hands with soap and swabbed another finger, applying it to the petri dish once again. Next, I tested a water fountain at the school. I swabbed it once with distilled water, once with an alcohol tip, and once with bleach. Everytime I streaked the petri dish with the swab. After about 72 hours, I had growth in my dish. Growth was low with my skin control, none with my alcohol section, and moderate with my soap section. In my surface sections: the control had low growth, and the alcohol and bleach sections had no growth at all.

http://www.123rf.com/photo_2672554_isolated-black-and-white-cartoon-drawing-of-bacteria-bugs-floating-in-a-petri-dish.html

I concluded that the best disinfectants for surfaces are alcohol and bleach. The least effective is water. The best antiseptic is alcohol. Soap had the least effect, so I conclude that it is the least effective antiseptic. It's also nice to know that our water fountains are clean! Good job janitors! =)

Things that could have effected or scewed the results of my experiments: the janitors clean the fountain everyday, I was not able to dry my hands after washing them, and the length of time I washed my hands was not recorded.