BIOL 329 Midterm Exam Exercise 16 IMViC Tests

What is the IMViC diagnostic tests used for?

to differentiate members of the Enterobacteriaceae, which is important for identifying intestinal infections

What is the indole test?

used to assay for the presence of bacteria that can hydrolyze the amino acid tryptophan

What is tryptophanase?

converts tryptophan to indole plus pyruvic acid and ammonia

True or False: the indole test involves inoculation of SIM medium with a pure culture of bacteria

True!

What is indole?

a nitrogen-containing heterocylclic ring that forms the R-group of tryptophan

What happens when Kovak's reagent is added to a tube with a bacterium that produces tryptophanase?

indole is extracted from the medium into the reagent and forms a complex with DMABA, producing a cherry color in the ring around the top of the medium

What is Kovac's reagent composed of?

p-dimethylaminobenzaldehyde (DMABA), HCl, and butanol

How can it be evaluated that a culture is indole positive?

cultures produce a red reagent layer following the addition of Kovac's reagent

How can it be evaluated that a culture is indole negative?

the absence of red coloration, which means the substrate tryptophan was no hydrolyzed

What is the purpose of a methyl red test?

determine the ability of organisms to oxidize glucose with the production and stabilization of high concentrations oof acid end products; identifies mixed acid fermentation of glucose

What is the role of methyl red in a methyl red test?

pH indicator that detects the presence of large concentrations of acidic end products; used to separate E.coli from K. aerogenes

What happens to methyl red at a pH less than 4.4?

the indicator turns red, meaning that the test is positive

What happens to methyl red at a pH greater than 6.0?

the indicator turns yellow, meaning that the test is negative

What type of bacteria is present at a pH of 4.4 in a methyl red test?

E. coli

What type of bacteria is present at a pH of 6.0 n a methyl red test?

K. aerogenes

What is the first purpose if the Voges-Proskauer test?

used to identify organisms able to produce acetoin from the degradation of glucose during a 2,3-butanediol fermentation

What is the second purpose if the Voges-Proskauer test?

determine the capability of some organisms to produce nonacidic or neutral end products, such as acetylemthylcarbinol from the organic acids that result from glucose metabolism in other organisms

What does the Voges-Proskauer test differentiate between?

differentiates between the organisms E. coli, K, aerogenes, and K. pneumoniae

What is a positive result in a Voges-Proskauer test?

a deep rose color in the culture following the addition of Barritt's reagent

What is a negative result in a Voges-Proskauer test?

absence of a deep rose color in the culture following the addition of Barritt's reagent

What is the purpose of the citrate utilization test?

allows differentiation among enteric organisms on the basis of their ability to ferment citrate as a sole carbon source by using the enzyme citrase

What is the indicator in the citrate utilization test?

acid-base indicator dye Bromothymol blue

What happens when bromthymol blue turns from green to blue?

change in pH; indicator will turn from green at neutral pH (6.9) to blue when a higher than 7.6 is reached

Why does the indicator in a citrate utilization test turn blue?

acidification of the medium is overcome by large amounts of alkali ammonia generated, which shifts the indicator to blue

What is a positive result in a citrate utilization test?

shift of indicator from green to blue

What is Simmon's citrate agar?

defined medium containing sodium citrate as the sole carbon source and the ammonium ion as the sole nitrogen source

Why would a Simmon's citrate agar turn from green to blue?

citrate is utilized, resulting in alkaline products being produced

What is a positive result in a Simmon's citrate agar?

presence of growth on the surface of the slant with a blue color

What is a negative result in a Simmon's citrate agar?

no growth and the medium remains green