Mystery Bacteria TSA Plate [by Emma]

Day 0 of Experiment:

So, the first picture you see is the picture I took before the plates were incubated, on day 0 of the experiment. I divided my plate into three sections, and tested bacteria from my mouth, my hair, and some of a really rancid sample of lemon juice I found (it was way past expiration). I thought it would be fun to see what kind of growth I had with those samples. One plate was then incubated at 24⁰C, and the other at 37⁰C.

                                             Figure 1: TSA Plates on Day 1 of Experiment

Day 2 of Experiment:

After the plates were incubated, I then inspected them on day 2 of the experiment. As you can see by Figure 2, the plates both had growth on them. However, the plate incubated at 37⁰C showed more growth for all the samples then the plate incubated at 24⁰C did. The types of colonies for both were basically the same for each plate, only there weren’t as many colonies for the 24⁰C plate, and two of the three samples completely lacked bacterial growth for this plate. I don’t really know how to explain this difference, but my guess would be that all the bacteria preferred the lovely warm environment of 37⁰C for growth, rather than the cooler environment of 24⁰C. The exception is my mouth sample, which also grew at the 24⁰C.

The plate incubated at 37⁰C had growth on all three samples, especially for my hair sample (I found this really gross!). For my hair sample, I had approximately 30 colonies present of one type (raised circular), for the lemon juice I had approximately 15 colonies present of one type (also raised circular), and for my mouth I had 2 different types of growth, which included approximately 3 colonies (raised circular), and a small lawn growth.  

For the plate incubated at 24⁰C, there was only growth observed for my mouth, and this included approximately 40 small colonies (flat undulate).

    Figure 2: TSA Plates on Day 3 of Experiment

Day 7 of Experiment:

For day 7 of the experiment, the plates both had growth on everything after incubation. The plate incubated at 37⁰C had lots of growth on the hair sample, as seen in Figure 3, and I counted approximately 42 colonies on it, all of one type of colony (raised circular), though some were smaller than others. For the lemon juice sample there were approximately 17 colonies, inclusive of two types; one type was white raised circular, the other was more orange in color. For my mouth sample, I counted approximately 10 big colonies and a small lawn growth. For this sample, there were three types of colonies; one was white and large raised circular, one was orange (raised irregular), and the other was the teeny tiny lawn.

For the plate incubated at 24⁰C, my hair sample grew approximately 12 small colonies (white raised circular), the lemon juice grew approximately 3 colonies (white raised circular), and my mouth sample grew approximately 60 colonies. There were 3 types of colonies for my mouth sample on this plate: one type was big and white (raised circular), one was big and orange (raised irregular), and the other was a small lawn (not too visible in the picture).

Figure 3: TSA Plates on Day 7 of Experiment

My lab mates had very similar results for their plates, in that the plate incubated at the warmer temp flourished more, only their lemon juice samples displayed no growth for either plate on day 3, while my lemon juice did grow on the warmer plate. Their lemon juice samples did grow, however, by day 7.

I am not at all surprised by any of the outcomes, as I expected growth for all the bacteria on at least the warmer plate, and my mouth sample to grow for both plates, which did indeed happen. I am, however, slightly disturbed by the knowledge that I have bacteria growing in my hair, but now I know that bacteria grows literally everywhere anyway, so that fact makes it less disturbing.