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Unknown Lab Report Essay

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Unknown Lab Report April 25th, 2006 Introduction The purpose of this lab was to identify two unknown bacteria cultures using various differential tests. The identification of these unknown cultures was accomplished by separating and differentiating possible bacteria based on specific biochemical characteristics. Whether the tests performed identified specific enzymatic reactions or metabolic pathways, each was used in a way to help recognize those specifics and identify the unknown cultures. The differential tests used to identify the unknown cultures were oxidase, catalase, lactose and sucrose fermentation, Kugler/iron agar, nitrate reduction, gelatin hydrolysis, starch hydrolysis, manitol salt, MR-VP, citrate, bile esculin, …show more content…

An inverted Durham tube was used again to test for the production of any gas. Adding 10 drops of both sulfanilic acid and á-napththylamine to the medium if the first test to see if nitrite is present. If nitrite is present, the medium turns red, indicating a positive test. However, if the medium does not change, a second test is performed to see if nitrite was further reduced. In this second test, zinc powder is added to the broth to catalyze the reduction of any nitrate present to nitrite. If nitrate is present when the zinc is added the reduction of this compound will cause the medium to turn red, from the previously added reagents. Red medium on the second addition indicates nitrate was not reduced and a negative test result. However, if the medium does not change after the addition of the zinc, the unknown is positive for nitrate reduction, as the nitrite has just been further reduced, preventing its detection. A gelatinase test was performed using nutrient gelatin to determine the ability of the bacteria to produce gelatinases. The gelatin was inoculated with the unknown cultures and incubated. The tubes were then placed on ice to reform the warm gelatin. If the gelatin remained solid after inoculation, the bacteria did not produce the gelatinase enzymes to liquefy the agar, constituting a negative test. However, if the gelatin was liquefied, the enzymes were secreted and the bacteria were positive. A starch test

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