Antibacterial Ability of Different Mouthwashes

In the Microbiology Lab, we tested five different mouthwashes, using water as a control, to see which mouthwash was the most effective at killing bacteria. The two types of bacteria used were Staphylococcus epidermidis and Bacillus subtilis. The five mouthwashes we tested were Scope, Rembrandt, Therasol, Cepacol, and Listerine. In testing the mouthwashes, we mixed bacteria and agar together and placed the mixture onto petri plates. We divided our plates into six sections, one for each mouthwash, plus another section for water. After dividing our plates, we took strips of paper that had been soaked in the appropriate mouthwash and placed them onto our plates. We let the plates sit for twenty-four hours to allow the antibacterial ingredients in the mouthwashes to kill the bacteria. After one day, we went back to our plates and measured the “zone of inhibition,” which is the area of the plate where the mouthwash had killed the bacteria. The larger the zone of inhibition was, the more effective that particular mouthwash had been at killing bacteria. We found that different mouthwashes worked well for the two different types of bacteria. For Bacillus subtilis, the #1 mouthwash was Therasol, #2 was Scope, #3 were Rembrandt and Cepacol, and #4 was Listerine. For Staphylococcus epidermidis, the #1mouthwashes were Therasol and Scope, #2 was Cepacol, #3 was Rembrandt, and #4 was Listerine. We determined this ranking by measuring the mean zones of inhibition for each mouthwash and then determining whether the differences were statistically significant.