My AP Biology class was given a great opportunity to attend the U of R on October 31 and November 1, to take part in a microbiology experiment hosted by Professor John Stavrinides. Here are a few things that I learned from my experience:

A microbe is a microscopic living organism, it includes bacteria, archaea, fungi and protists.  Focusing more on the bacteria side of things, we were taught about Gram-positive and Gram-negative bacteria.  A Danish scientist devised a test where bacteria that maintain the crystal violet stain do so because of a thick layer of peptidoglycan and are called Gram-positive bacteria.  Whereas, Gram-negative bacteria do not retain the Gram stain and stay colourless.  Compared with Gram-positive bacteria, Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall.  I found it very interesting how the microbes can be differentiated based on the structural differences in their cell walls with this unique technique.  It was a concept initially I knew nothing about.

Diagram of Gram-positive and Gram-negative bacteria via:

In our experiment, we had three types of agar dishes to choose from. Mannitol Salt, MacConkey, and Lysogeny Broth. Different types of agar are used to encourage the growth of certain bacteria while inhibiting the growth of others. Mannitol Salt Agar is selective for Gram-positive bacteria, an example we were told about is staphylococcus, which often reside normally on the skin. MacConkey is designed to selectively isolate Gram-negative bacteria, an example would be diplococcus, which is a bacteria that occurs in pairs. Lysogeny Broth is the most widely used medium for the growth of bacteria, and it isn’t selective for Gram-positive or Gram-negative.

My Results

Phone Receiver- I used a MacConkey agar dish. This plate came back and had 3 visible microbes on it, one of them being fairly big.

Water Fountain Button- I used a Mannitol Salt agar dish. Kira and I both swabbed a different button but from the same fountain. We then split a Mannitol Salt plate in half so we could compare the results. Neither had any visible results.

Toilet Seat- I used a Lysogeny Broth agar dish. Kira and I split the plate in half so we could compare the results from the toilet seat I swabbed and the toilet seat Kira swabbed. Both sides did not have any visible microbes.

Recycling Bin- I used a MacConkey agar dish. The swab I took from the recycling bin was quite dirty, so one microbe started growing off of a piece of dirt.

Hand Sanitizer Button- I used a Lysogeny Broth agar dish. When I got this plate back I noticed 1 visible microbe.

I also comprised a group of 8 individuals, including myself, and divided a Lysogen Broth plate into eighths. Each individual dampened a swab and swabbed their hand. Essentially we did this to see who had the dirtiest hands. 4/8 people had dirty hands while the other 4/8 had clean hands.

What surprised me the most was that when I swabbed my iPhone, no visible microbes showed up. I thought for sure there would have been a few since I take my iPhone everywhere and I’m always carrying it. A few of my dishes had no noticeable microbe growth on them, and there is a couple reasons for this. 24 hours might not have been  enough time to for the microbes to culture, the surface could have just been cleaned, the plate I picked could have selected against the bacteria on it, or the temperature might have been either too cold or hot.

Typical Bacteria Cell Via Wikieducator 

At the end of day two we had a group discussion on how bacteria is everywhere. When we were asked, what do you think is the single dirtiest item in your house?  Lots of great answers were thrown out there, some examples were the tooth brush, cutting boards, toilet seat, etc. But believe it or not, it is the kitchen sponge which contains around 10 million bacteria per square inch. Gross right? It instantly made me want to throw out every sponge at my house.

This lab really opened my eyes to this whole other microscopic world that is often forgotten about. I am thankful for being given the opportunity to do this experiment, I learned so much as it was very informative.