Unknown Bacteria Essay

Words: 1364
Pages: 6

The Use of Biochemical Tests to Identify Unknown Bacteria

Elizabeth Vittori
Microbiology Laboratory 3444-003; Malini Kotak; November 7th, 2015

Abstract:
In this experiment, we were given a test tube of unknown bacteria that we were then supposed to identify on our own. The main purpose of this experiment was to use various biochemical tests in order to identify this unknown bacteria out of 4 different bacteria: Echerichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, and Salmonella typhimurium. From the broth, a plate was streaked to attain pure colonies and a Gram Stain procedure was carried out to classify the morphology of the bacteria. Then, the unknown bacteria were identified through the use of various biochemical tests and
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In this test, the medium used is known to be a type of utilization media, where the bacteria use citrate as its only source of carbon. Additionally, the bacteria would use ammonium phosphate as its only source of nitrogen. The media contains bromothymol blue dye, which serves as a pH indicator. At a pH of 6.9, the indicator is a green color and at a pH of 7.6, it becomes blue. This change in color is due to the bacteria being able to survive in the media by utilizing the citrate. The citrate is converted from ammonium phosphate to ammonia and ammonium hydroxide. Utilization of this media causes the media to turn more alkaline, therefore raising the pH, and changing the media color to blue. A blue color in the citrate test is considered positive while a green color is …show more content…
Gelatin is a protein that is derived from collagen, which is a part of vertebrae connective tissue. The medium used for the gelatinase test contains gelatin, peptone, and beef extract. Gelatinase activity can be very slow in some organisms, so this test may take up to 7 or 8 days. If bacteria test positive, they contain the enzyme gelatinase and are able to hydrolyze the protein, gelatin. If they are negative, then they do not contain gelatinase and are not able to hydrolyze gelatin. After being chilled for one hour, a positive test would correspond to a liquefied medium while a negative test would correspond to a solidified