Bacterial Adventures: A TSA Investigation

By Amy Latimer

DAY ZERO

I decide to test three locations: the back of my phone case, because I figure it will be germy; the door handle to the ‘bio’ study room, because I hope it won’t be germy; and the inside of my mouth, because of burning curiosity.

I hypothesize that my phone case will produce the most colonies overall because I touch it for more than an hour a day, without washing it frequently. It sounds gross, but when was the last time you washed your phone case? See what I mean?

I also hypothesize that on the body temperature plate I will find the most colonies from the mouth sample. My reasoning? There are ten times more bacteria and archaea in our body than cells!

Pic. 1—the setup

DAY TWO: The investigation continues…

My first results are in.

I find no growth on the room temperature plate, save a single colony from the door handle. The body temperature plate presents a completely different story. Bacteria have multiplied like wildfire, eating up their TSA to grow healthy and strong. I count 8 large colonies from the door handle, and see an innumerable amount of small colonies from my mouth. Surprisingly, I find no growth from my phone case but I am hopeful for the next time I encounter my bacterial experiment.

My main takeaway from today is to open the door to the bio study room with a sleeve next time I want to do homework.

Pic. 2—Day 2 results

DAY 7: That’s a wrap?

The final results are intriguing and a bit disgusting.

I find two additional colonies on the room temperature plate, both from the door handle, for a grand total of three colonies! One is yellow, and it could be Staphylococcus aureus. S. aureus is usually harmless, but it can cause sinus infections or food poisoning depending on the strain, or have antibiotic resistance (MRSA).

On the body temperature plate I found several new colonies from the door handle, 13 colonies in all. One colony of particular interest is the largest, slimiest one from the door handle. Not only did it grow tremendously over only four days, it is far larger than all the other colonies. In fact, less colonies and greater growth is what seems to set the door handle bacteria apart from the mouth bacteria. Could it be that the door handle bacteria are better equipped to eat the TSA media than the mouth bacteria? After all, mouth bacteria are accustomed to eating whatever I eat.

Apart from the colony highlighted by the arrow, the colonies from the door handle are rounded and white. A possible identification for these bacteria is Staphylococcus epidermidis, a species common on human skin. This identification would make sense, as the door handle makes contact with skin whenever it is opened.

Also concerning the body temperature plate, the mouth sample does not appear to have much more growth. The colonies are simply a bit more developed. Most surprisingly, no bacterial colonies developed from the phone sample on either of the plates. My only explanation for this is that I must do a good job washing my hands. J Perhaps the touch screen would tell a different story.

Pic. 3—Day 7 results

Pic. 4— A suspected S. epidermis colony up close.

IN CONCLUSION

My hypothesis that the mouth sample would produce the most colonies was correct, and only on the body temperature plate. It proves that bacteria can be picky like us when it comes to living environments.  However, I was surprised to find that my phone case did not produce any bacterial colonies. From what I’ve seen so far, many of you who tested your phone cases found a similar result. Any ideas as to why?

Wishing you germy (and friendly) adventures,

Amy