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Microbiology Unknown Essay

The purpose of this report was to identify an unknown bacterium by applying methods that were previously learned and conducted in microbiology lab class. It is possible to identify a mixed culture by running experiments on the unknown bacteria and taking what we already know and applying it to the results. It helps to slowly eliminate any bacteria that do not correspond with the results of certain tests. An unknown test tube labeled 94 was given to me b my instructor. The first procedure performed was an isolation of my unknown bacteria with the goal of obtaining a pure culture. This was done by streaking the unknown onto a nutrient agar plate using the streak method. The plates were incubated for two days and the bacterium was able to grow. I studied the bacteria based of its physical characteristics of how it grew on the agar.

I began my quest by conducting a Gram stain on my bacteria. I prepared a smear by placing a drop of water onto the center of a slide and then removed a loop full of bacteria to place within the water droplet. I use the aseptic treatment while doing this making sure to flame the inoculating loop before and after transferring bacteria. It was important to get this done correctly because the test determines the stain as well as the shape of the cells. After looking at my stain under the microscopic I came to the conclusion that my bacteria was a positive cocci. After the gram stain I performed specific tests based of those results of the stain to determine what my unknown could be.

The first test I did was the catalase test. It had a positive reaction meaning the bacteria produced the enzyme catalase. This helped me narrow my unknown down to Micrococcus and Staphylococcus. I inoculated my unknown onto a mannitol salt agar. The growth and color change to yellow indicated mannitol fermentation because acid was produced. The acid fermentation is a characteristic of the pathogen Staphylococci. Then a nitrate broth test was performed. This test also had a positive reaction meaning the reduction to nitrates occurred. From these results I was able to indicate that my unknown was Staphylococcus. To make sure of my decision I performed a triple sugar iron agar test. The results show that glucose, lactose, and sucrose fermentation with acid accumulated in the test tube. With the results of all the tests I performed, I came to the conclusion that my unknown was Staphylococcus aureus.


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