Resistance to Mouthwash

The object of our experiment was to determine if Streptococcus mutans, the bacteria that causes dental plaque, would form a resistance to mouthwash, and if it did, which active ingredient in mouthwash would hold its effectiveness on the bacteria longest. The mouthwashes that we used were Scope®, whose active ingredient is alcohol, and ACT®, whose active ingredient is fluoride. Streptococcus mutans was cultured and grown in Petri dishes with nutrient agar. We soaked three paper discs in each type of mouthwash, and placed the discs in Petri dishes that were spread with the bacteria. The area around the discs where the bacteria did not grow, the area of inhibition, was measured and the bacteria at the edge of the area of inhibition were taken and cultured in new Petri dishes. Eight trials were run for each kind of mouthwash. At the end of the eight trials, a matched pairs t test was performed for the differences in the area of inhibition from day to day for each kind of mouthwash. Then a two sample t-test was done to compare the difference of the two different kinds of mouthwash to determine if one kept its effectiveness longer than the other. Our results showed that the bacteria formed a resistance to both kinds of mouthwash, but both brands kept its effectiveness for the same amount of time.

Research Done By:

Shannon Henderson
L'Anse Creuse High School

Natalie Reeder
Lake Shore High School