The purpose of my project is to see which surfaces have the most bacteria on them and which antibacterial agent works best to eliminate this bacteria. I will test multiple household surfaces during this project.
Preparing Dishes When preparing the petri dishes I heated heat and pour agar and poured the agar into the sterile sealed petri dishes. I barely lifted up the lid when pouring the agar onto the plate so to eliminate the risk of contamination by airborne bacteria. Agar works best in small thin sheets so I poured it about ¼ inch thick in the dishes. I also allowed the dishes to cool and become firm which took 2 hours.
Inoculation I inoculated the dishes by opening a sterile inoculating swab while holding a petri dish in the other hand. I swabbed the test surface then immediately opened the dish and lightly ran the swab across the surface of the agar. I held the lid to dish about 2 inches above the dish when inoculating the agar so not to allow airborne bacteria onto the dish.
Growing I allowed the inoculated plates to then grow in a small room I kept at 99 degrees Fahrenheit and 85% relative humidity. I found in my research that bacteria grows best in these conditions so I used a space heater and humidifier along with a thermometer with humidity gauge on it to make sure that the room was kept stable at these conditions. I let the bacteria grow for 96 hours before making observations and analyzing the plates under a USB microscope.
Observing and Analyzing Plates When analyzing the plates I rated them on a percentage scale on how much of the plate was covered with bacteria. I also rated the disinfectants on how well they eliminated the bacteria.
There are many different types of bacteria. The key way of determining bacteria apart is by identifying rather it is gram positive or gram negative. Bacteria grow in many different conditions depending on that strand of bacteria's specific needs. The largest used way of culturing bacteria is by using agar plates. There are many different types of agar. The most easiest form of agar to use is nutrient agar. Nutrient agar is made of: Nutrient Broth Beef Extract Yeast extract NaCI Peptone Nutrient agar works best because the bacteria grows on the surface and is easily noticed even in very small colonies.
Conclusion In conclusion the living room floor had the most surface bacteria. Also the Clorox spray worked best at eliminating this bacteria. My hypothesis was correct partially because the living room floor had more bacteria on it then any other household surface. But it was incorrect in the fact that I thought the Clorox wipes would work best but the Clorox spay actually was the best of the disinfectants tested.
Future Experiment If I was to have the opportunity to redo this experiment in the future there would only be 3 things I would change. That would be to test more disinfectants and to test more surfaces. I may also try using glass petri dishes instead of the disposable plastic ones that I used to see if that makes a difference in the final outcome. I would also test to see if the bacteria I culture is gram positive or gram negative.
Acknowledgements Mr. Burris my biology teacher for some helpful tips he provided me. My mom and dad for some advice on the presentation. Mrs. Cloran for being so supportive. Thank you to the judges and coordinators of this event for giving me such a wonderful opportunity.