Bacillus Cereus in Organic and Regular Milk

The purpose of the experiment was to determine if organic or regular milk had a higher content of bacteria as the expiration date approached. To test the hypothesis that organic milk would have a lower count of Bacillus cereus, the bacteria found in milk, three different samples of Horizon Organic Half and Half, and Land O'Lakes Regular Half and Half were tested on four separate days. After preparing a Nutrient Broth solution and incubating a mixture of each of the milks and the nutrient broth for one day, the solutions were diluted and poured into Petri dishes with Nutrient Agar, and again incubated for 24 hours. The next day the Petri dishes were removed from the incubator and the number of bacteria colonies present in each sample were counted. Four two-sample t tests were performed to compare the difference in bacteria content in organic and regular milk, as the expiration date approached. The statistics failed to support the hypothesis that organic milk had less bacteria than regular milk. The statistics showed there is no difference in the bacteria content, as the expiration date approached, of organic and regular milk.

Research Done By:

Valerie Mika
Warren Mott High School

Alexandra Penz
Cousino High School