Putting Disinfectants to the Test

In this two-part lab, students will sample the indoor environment to estimate how many bacteria are living on surfaces, then test the effectiveness of various household disinfectants on bacterial growth. Students use RODAC petri plates to directly sample surfaces such as benches, desks, or cell phones and then can quantify the number of bacteria detected before and after cleaning with a disinfectant. They will also set up a disc diffusion assay to test the potency of household cleaners and other disinfectants against Gram-positive and Gram-negative bacteria.

Intended Audience
Grades 9-12

Learning Objectives
At the completion of this activity, students will be able to:

1. Quantify the number of cultivable bacteria from an environmental surface sample
2. Observe how well different chemical disinfectants can kill bacteria or inhibit bacterial growth
3. Compare the effectiveness of disinfectants on Gram-positive vs. Gram-negative bacteria
4. Discuss the importance of disinfecting surfaces at home, especially in the kitchen

Antimicrobial, Environmental sampling, Disc diffusion

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Putting Disinfectants to the Test