Spring Exhibitions: Focus on Microbes

For spring Exhibitions, students showed a range of projects, including Division III's SHEWASSA (or Simple Human Experiment with a Sound Statistical Analysis), Division II's Ferdinand work, and Division IV's Ethnography Project. In Division I MST, students showed their original antimicrobial research in several formats: oral presentations, journal articles, and blog posts. Below, read a blog post by Division I student Jesse about her group's process and findings:

Antimicrobial Research Series: What Bacteria Does Soap Kill?
Have you ever wondered exactly how well handsoap actually works? We did an experiment to find out how much bacteria softsoap really kills.

Our motivating question was: How much bacteria from a lunch table, the inside of a microwave, a keyboard, and a toilet handle does softsoap kill?

We swabbed each of the areas, and rubbed it all over a petri dish. The petri dishes were split into two halves: one was the experimental side, and one positive control. On the experimental side, we took a mixture of two parts soap and one part water, and swabbed it on top of the bacteria. On the control side, we swabbed water over the bacteria. We also had one more pertri dish. This one was for negative controls. We had one negative control that just had water on it, and one that had the soap mixture on it. Positive controls were a key part of our experiment. Without them, we wouldn’t have known how much bacteria there was to begin with on the experimental petri dishes, so we wouldn’t have have known how much bacteria the soap actually killed. We also used negative controls, which tell you if the water or in our case soap mixture already had bacteria in it. This is helpful if you have bacteria on the experimental petri dishes, because you can say that it came from the water, not the place you swabbed.

What we finally found from our third round of doing the experiment was that the soap works very well. There was no bacteria on the experimental sides of the petri dishes, and the positive controls were covered in bacteria. (as you can see in the pictures below)

It’s not as easy as it seems to answer this question. In our first experiment, we didn’t have any softsoap, so we used Gojo soap and we were not sanitary about putting it into the petri dishes. There also wasn’t much bacteria at all on our positive controls, so we couldn’t say much about what we found. We tried the experiment again and swabbed longer parts of the areas, and got better results, but they were still not perfect. This was because we decided that because there was soap on top of the experimental bacteria, and nothing on top of the positive control, the fact that there was almost no bacteria in the experimental could have been because the bacteria was being smothered by the soap. To solve this, we put a layer of water over the positive controls. This didn’t affect our results, so we are sure now that the bacteria weren’t just being smothered and our results meant something. Lastly, on the third round, there was bacteria on our negative control, but we decided that our negative control was not very important, given our results, so we let it go. Because there was no bacteria on the experimental side, it showed that even if there was bacteria in the water, the soap killed it.

The experimenters all agreed that the most frustrating thing about this experiment was having to redo the experiment multiple times and not getting conclusive results.

Isabel, one of the experimenters, said that “after doing this experiment, I would like to do another experiment to see if there are types of bacteria that this soap can’t kill.”