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Microbiology Lab Quiz #5, 23

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IMViC reactions

test is 4 in 1 biochemical related tests


breakdown/end product of tryptophan



Sugar used as the basis for the methyl red test



name two media that can be used to detect citrate utilization

Koser's citrate broth and Simmon's citrate agar


medium used to test for indole production

Tryptone broth


medium used to test for methyl red and Voges-Proskauer

MR-VP broth


medium used to test for citrate in this lab

Simmon's Citrate agar


Chemical reagent used in indole test

Kovac's indole reagent; let stand 10 minutes


positive methyl red test pH

pH below 4.4


name two major end products produced by Voges-Proskauer positive organisms

2, 3 butanediol and acetonin


reagents used in the Voges-Proskauer test

Barritt's solution A and B


members of the Enterobacteriaceae or the enteric bacilli for which the IMViC tests are most useful belong to

coliform group


Enterics that do not fall into the two distinctive categories formed by E. coli and E. aerogenes are collectively referred to as



Methyl red test

tests for fermentation of glucose by looking for acid production


when must indole production test be read

after 24 hour incubation, but no longer!


positive indole test

alcohol in Kovac's reagent separates out and turns red


negative indole test

alcohol in Kovac's reagent remains and color is unchanged


Media used in Methyl red test and Voges-Proskauer test

contains peptone, glucose and a phosphate buffer


Methyl red: if glucose has been fermented to acid

methyl red will be red, below pH of 4.4


Methyl red: if glucose has not been fermented

methyl red will be yellow, above pH of 4.4


Voges-Proskauer test

reaction results in red color complex formed by oxidation of 2, 3 butanediol and acetonin and presence of creatine and alpha-napthol


Voges-Proskauer: detection of glucose

red color complex forms if creatine and alpha-napthol are produced; may take 2 hours to develope


Citrate utilization

tests whether an organism can use 6-carbon citrate as its sole source of carbon


what must a cell need to carry citrate into cell

transport protein


Citrate test agar

Simmon's Citrate agar (green colored agar)


detection of citrate use

growth is observed on a slant and is accompanied by a change of the bromothymol blue indicator from green to deep blue


positive for citrate use

color of medium becomes bright blue


negative for citrate use

color stays the same green color


why are IMViC tests useful in differentiation?

differentiates subset of Gram negative, enteric bacteria known as the coliforms; helpful in spotting fecal contamination


Indole test

most E. coli strains produce indole

Enterobacter-Klebsiella group does NOT


Methyl red test

most E. coli strains are mixed acid fermenters

Enterobacter-Klebsiella group converts fermented glucose into neutral products


Voges-Proskauer test

most E. coli strains produce a negative result (no end products)

Enterobacter-Klebsiella group produce a positive result (end products)


Citrate test

E. coli strains cannot use citrate as a carbon source

Enterobacter-Klebsiella group can use citrate as a carbon source

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