Micro Unknown Lab Report

2036 words 9 pages
| Gram Negative Unknown | Biology 3444-006 | | Lena Wallace | 11/7/2011 |


The purpose of this lab was to identify an unknown bacteria culture using differential tests. The identification of the unknown culture was accomplished by identifying the bacteria based on its specific metabolic characteristics and morphology. It is suggested that culture 11 is a sample of Enterobacter aerogenes.
This experiment was centered on metabolic and biochemical testing procedures. The rationale of performing these tests was to distinguish six different microbes from one another and to compare how their metabolic and biochemical processes differ from species to species to determine the unknown sample.
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After the VP reagents have been added, a red color is observed, this is a positive result reported as (+), if a copper color develops, the result is negative and reported as (-).
Citrate test uses Simmons citrate agar to see if the organism is able to utilize citrate as a carbon source. Only bacteria that possess the enzyme citrate-permease can transport citrate inside the cell so it can be converted into pyruvate. Simmons citrate agar utilizes sodium citrate as its only carbon source and ammonium phosphate as the nitrogen source. The pH indicator bromthymol blue dye is green at a pH of 6.9 and blue at pH of 7.6. Bacteria that can survive on the agar and utilize the citrate, alkalinize the agar by breaking down the ammonium phosphate to ammonia and ammonium hydroxide, both increase the pH. Any change to a blue color is a positive result reported as (+), and if there is no change and the agar remains green the result is negative and reported as (-).
The Urea hydrolysis is catalyzed by the enzyme urease. Urease catalyzes the hydrolysis of urea into carbon dioxide and ammonia using water. A urea broth is used that contains yeast extract as its only nutrient source, buffers to inhibit alkalinization of the medium, and phenol red as a pH indicator. Phenol red in this solution will be yellow or orange bellow pH 8.4 and pink above, to show any increase in pH. A pink color in the both indicates a positive result and reported as (+), and an orange or yellow


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