IMViC reactions

test is 4 in 1 biochemical related tests

breakdown/end product of tryptophan

indole

Sugar used as the basis for the methyl red test

glucose

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

intermediates

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