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microreport24 - Introduction The IMVic tests stand for...

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Introduction The IMVic tests stand for Indole, Methyl red, Voges-Proskauer, Citrate, Simmons. These are biochemical tests that help to “differentiate morphologically and physiologically similar organisms.” (Barnett, p. 120) They are used mostly to separate coliforms which are “gram-negative, aerobic or facultatively anaerobic, non-endospore-forming, aerobic or facultatively anaerobic, non-endospore- forming, rod-shaped bacteria that produce acid and gas from lactose within 48 hours at 35” (Barnett, p. 120) degrees Celcius. These coliform often live in intestines and are called enterics. Escherichia coli is a fecal coliform while Enterobacter aerogenes is not necessarily associated with feces. In the indole test, coliforms that produce tryptophanase which hydrolizes tryptophan into indole and other components are identified by a red layer on the surface of the medium which appears after Kovacs’ reagent, “an acid solution of para-dimethylaminobenaldehyde in alcohol” (Barnett, p. 120) is added to the culture. The 1% tryptone in water is used as the medium because it is rich in tryptophan. The Methyl Red and Voges-Proskauer medium has dextrose. Coliforms often convert dextrose to acids and sometimes go on to have “mixed acid fermentation.” Others create more netural products via butanediol fermentation. Methyl red pH indicator turns red at pH 4.4 or less. It is yello at pH 6.2 and greater. If the bacteria have created much acid, the culture broth will be red. Otherwise, it will be orange or yellow.
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This note was uploaded on 04/17/2008 for the course BIOL 402 taught by Professor Faurot during the Spring '08 term at Kansas.

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microreport24 - Introduction The IMVic tests stand for...

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