Bacteria Essay, Research Paper

Enterobacter Aerogenes

Identifying bacteria may seem like a daunting task, but if approached slowly and methodically it can be achieved. The objective assigned to each individual in Dr. Robbins microbiology lab was to identify a randomly chosen bacterium. I chose test tube number forty-six. Upon selection, I immediately conducted a gram stain to determine if the unknown was gram negative, gram positive, and find out cell morphology. I discovered that my unknown was a gram-negative bacillus with a rod like morphology. From this point, I was guided through a series of tests that led me to my final conclusion.

I first had to establish if my unknown was a glucose fermentor. Two tests that helped me decide were the phenol red carbohydrate test and the triple sugar agar test. The phenol red carbohydrate test was the most helpful. In this test I had to make a decision as to whether my unknown could ferment glucose, lactose, or sucrose with the production of acid or gas. In this experiment my primary concern was the fact that my unknown was indeed a glucose fermentor, which was indicated by a yellow color in the test tube. These results led into the importance of the Simmons citrate agar test.

The Simmons citrate agar test is used to test an organism’s ability to grow on citrate as a lone carbon source. If my unknown could grow on the citrate, then it would produce an alkaline reaction in which the color of the medium is changed from green to blue. My unknown did exactly that. The positive reaction from this test made the eosin methylene blue agar (EMB) test the next important experiment in my search for the identification of my unknown

The next significant factor in my quest was whether or not my unknown was a lactose fermentor. The EMB test would answer this question. The EMB test is a selective and differential medium that isolates Gram-negative intestinal organisms. Differentiation of organisms is based on their ability to ferment lactose. My unknown turned out to be a weak fermentor, because I had slightly black colonies. The positive results of this test made the results of the methyl red test necessary in order to narrow my remaining possibilities.

Methyl Red is a test that is performed with the Voges Proskauer experiment. Both tests are intended to indicate whether or not the unknown can ferment glucose. More specifically, the methyl red test is to indicate the high production of acid due to glucose fermentation. Which in my case, the unknown tested negative, because the test tube remained yellow. At this point I was ready to for the results of one more test to get a definitive identity for my bacteria. The deciding test would be that of motility.

Motility is determined by the SIM (sulfide-indole-motility) test. The SIM media is a softer agar because it has less agar than other media. So, this allows for motile organisms to swim in it. After conducting the entire SIM test I found that my unknown was slightly motile. The results from this test allowed me to conclude that my unknown was Enterobacter aerogenes.

The genus enterobacter is widely distributed in nature. It can be found in fresh water, soil, sewage, plants, vegetables, and human and animal feces. The species enterobacter aerogenes is most notable for being an opportunistic pathogen, causing burn, wound, and urinary tract infections. Sometimes, E. aerogenes can cause septicemia or meningitis. Identifying my bacteria was not an easy task. But after a little perseverance and patience I was able to come to a conclusion as to the identity and occurrence of my bacteria.