YKYW - Nursing Student Blog

Microbiology is coming along fairly well. I just finished my third lecture test, and I’m waiting to go into lab. Our unknown projects are due tomorrow. I was a little apprehensive going into this project, but I’ve had a lot of fun. I don’t know if other schools set up the microbiology unknown projects the same way, but this is how ours works:

We are each given two different specimens in a broth culture. All we know is that we have one Gram positive and one Gram negative. We have to get pure, isolated cultures of each, and properly identify each organism.

My first TSA streak plates didn’t go well, but I did have some growth on both my EMB and blood/PEA plates. These were a big help to narrow down which specimen was Gram positive and which was Gram negative. Gram staining is so tricky!

After isolating my Gram negative specimen, I started running tests on it. The glucose test came back positive: bright yellow, with gas in the vial. The lactose test was also positive with the top of the tube red and the bottom yellow. With these results, I decided to use the citrate and indole tests. In the citrate test, the slant was a bright, Prussian blue — positive! The negative indole test confirmed my results. A positive result on my Voges Proskauer test eliminated a couple possibilities, and I decided my Gram negative bacillus is Enterobacter aerogenes. I ran a few other tests (ornithine, phenylalanine, nitrate, TSI and urea) to confirm my results. So far, all the test results are in line with what is expected of Enterobacter aerogenes.

I made a mistake with my Gram positive specimen, so I had to rerun a test overnight. As of now, I know I have Gram positive cocci. It bubbled like crazy during the catalase test, and it is glucose negative (red) with no gas. I tried to run the nitrate test, but I got a little impatient. I only waited about a minute after putting in the Nitrate I and II drops before I added the zinc. I got a reaction! But, since my Gram positive specimen is such a slow grower, I should have waited a full three minutes. I suspect I have Sarcina lutea (which means it reacted to the zinc, and has NO3-, but I’m not sure. If the reaction was due to the Nitrate I and II drops, then I have Micrococcus luteus. I’m fairly sure I have Sarcina lutea, and will confirm soon.

What a way to spend a summer, hmm?

We start our unknown projects in Microbiology tomorrow. Is this a fairly typical part of Microbiology lab classes? We get a mixture of two different organisms, and we have to isolate them, and figure out what they are without any help from the professor.

It does count for a large percentage of our grade, so I’m a bit nervous.

While studying for my microbiology test, I realized that our microscopes remind me of Johnny 5 from Short Circuit. Ah, the good old days!