Mystery TSA Dish Bacteria by Nhung Nguyen

Day 0

I was curious about how “sterile” my phone screen was so I decided to do a little test, comparing the bacterial culture living on the phone screen to that on the bottom of my shoes and two well-cleaned places in our laboratory (the wall and the table). I expected lots of microorganisms were living under my shoes, while none to only a few bacteria could be found on the laboratory wall and table.

So two TSA plates had been prepared and stored under two different temperature conditions: one was at room temperature and one was at body temperature.

Day 2

As I thought, no bacterial colony grew on the wall and table areas. I was also glad to know my phone screen had none either (or not yet). The only place that had bacteria, obviously, was the shoes. The bacteria on both dish belonged to the same species; however, I was unable to identify the species. Also, only six small bacterial colonies were found on the room temperature dish, but then they grew like crazy at body temperature, even crossed the line I drew out as you can see on the picture! I found this level of growth pretty amazing. I believed these bacteria could grow even more strongly if I let it sit there for a week, therefore I decided to keep these two dishes a few more days. Another reason was I wanted to see if there would be any growth on the other three areas.

Day 7

This time I got some interesting observations. First of all, the table area finally got one tiny yellowish colony on both dish. After doing a quick research on the medical microbe gallery, possibly the bacteria was a type of Staphylococcus aureus. The colony was bigger on the 37^oC dish, meaning this bacteria favors body temperature.

No growth could be observed on the wall and phone screen areas, which was pretty surprising to me since I expected my phone screen would have more bacteria than the table which is cleaned regularly. Anyways, it proved my phone was actually pretty clean, as clean as laboratory areas.

On the other side, the growth on the shoes area got different on two dishes. While the colonies on the 37^oC continued to grow and expand further, trespassing the table/phone screen corners, they did not grow much on the room temperature dish. Instead, many bacterial colonies of other different kinds appeared on this dish as different colors: orange, brown, gray, and black. Unfortunately, I could not identified these species either.

Below are some close-ups taken from the room temperature dish. The first one, whitish with tiny black dots, was the black colony when observed under the dissecting microscope, while the cotton-like organism on the second picture was a close-up of the orange colony lying on the black lines.