Gram+ Cocci Tests

During my 2nd week of the S-STEM program, I worked more with my unknown bacteria, enterococcus faecalis. I performed 6 different tests on it to verify that I indeed identified the bacteria correctly. These tests involved glucose fermentation, lactose, tryptone, TSI, gelatin, TSB and a MSA plate (respectively, as shown below). However, the 1st MSA plate that I streaked on Tuesday, February 21, 2017 did not grow any colonies so I streaked another plate. Still, 2 days later, both of these plates did not show any changes. Nonetheless, the other tests worked as expected. For the glucose fermentation, before the 24 hours (as shown below), the color of glucose was orange and the durham tube (glass tube inside the glucose tube) did not have any air bubbles, which meant a gas was produced. However, over a day, the color changed to yellow and the durham tube still did not have an air bubble (as shown below). This meant that my bacteria produced an acid and did not produce gas. In addition, the lactose tube also changed color from pink to yellow and had no air bubble. Again, the change in color and no air bubble present in the durham tube meant that my bacteria produced an acid and did not produce a gas. To continue, for the tryptone test, I added indole reagent to test if indole was present in my bacteria. If the top layer turned red, indole was present but if the top layer turned yellow, indole was not present. In this case, indole was not present because the top layer of tryptone is yellow (shown below in the 2nd image). As for the TSI tube, I made an “s” shape on the inside using a loop that was dipped into my bacteria. As a result, since it did not turn black, it was negative for H2S (hydrogen sulfide) gas. Similar to the previous tests, the TSI tube turned yellow, which also meant an acid was produced. Next, the gelatin tested whether my bacteria had gelatin hydrolysis. After the 24 hours, the gelatin melted and was now a liquid. To test if it had gelatin hydrolysis, I put the gelatin in the fridge for 10 minutes. If it went back into its solid form, it was negative but if it stayed as a liquid, it was positive. For my bacteria, after the 10 minutes, it went back into its solid form and, thus, was negative for gelatin hydrolysis. Finally, the TSB tube ended up looking cloudy, which meant that bacteria successfully grew. All in all, the 6 tests that I performed showed a change over a course of a day, except for the MSA plates.

6 gram+ cocci tests before 24 hours

6 gram+ cocci tests after 24 hours

STEM Beginnings

I started my internship on Monday, February 13, 2017. In my first week, I was introduced to the basics. For example, I watched safety videos, learned how to clock in/out, received my lab notebook, began working in the lab and identified an unknown bacteria. In order to identify my unknown, I used a plastic loop to streak it onto a TSA plate (top image). Once I was done with that, I left it in a Biohazard fridge for 24 hours. The next day, colonies (the small circles) of bacteria were successfully formed (2nd image). In order to identify my bacteria, I used these colonies to perform gram staining and a catalase test. When working on gram staining, the chemicals used were crystal violet, iodine, alcohol decolorizer and safranin. The purpose of the gram staining was to determine if it were gram+ or gram- (if it were purple, it would be gram+; if it were pink, it would be gram-). Some portion of my bacteria had both pink and purple present, but, since the majority of it was purple, I concluded that it was gram+ (3rd image). Not only did I have to find if it was gram+ or gram-, but I had to figure out if it were coccus (circle) or bacillus (rod) shaped. After closely examining the bacteria, I determined that it was coccus (bottom image). After that, I did a catalase test, which involved using a drop of hydrogen peroxide. Basically, after adding the drop, if it bubbled, I had to follow other tests to ID my bacteria, but, luckily, it did not bubble so I identified it as Enterococcus faecalis. All in all, my first week was a new experience and I cannot wait to see what this semester holds!

TSA plate before 24 hours.

TSA plate after 24 hours.

Unknown bacteria after gram staining.

Enterococcus faecalis (gram+ & coccus shaped).