IMViC Tests Flashcards
What are IMViC tests used to test for
Used to differentiate between gram-negative bacilli, particularly those in the Enterobacteriaceae family
What does the Citrate utilization test do
Determines an organisms ability to use citrate as its sole carbon source
How is Citrate produced
Citrate is produces when acetylene coenzyme A reacts surge oxaloacetate in the beginning of the Kreb’s cycle
What is the purpose of citrate permease
Bacteria with citrate permease take in citrate and convert it to pyruvate which can be transformed into different products.
What does a citrate-positive organism test look like, why does this occur
Citrate-positive organisms show growth and a blue slant, Thor is occurs because bacteria that use citrate convert ammonium phosphate to ammonia and ammonium hydroxide which alkalinize the agar, turning it blue
What is SIM agar used for
Sulfur, indole, motility agar tests for sulfur reduction, indole production, and motility
How is a sulfur reducing organism indicated (SIM, TSIA)
Anaerobic of sulfur to hydrogen sulfide by reducing thiosulfate or hydrolyzing cysteine into pyruvate. Hydrogen sulfide reacts with ferrous iron to form ferrous sulfide, a black precipitate in the butt
- acidic conditions must exist for reduction, so hydrogen sulfide presence also indicates fermentation
What does the indole test do
Differentiates bacteria that produce indole by hydrolyzing the amino acid tryptophan using tryptophanase.
Indole production results from bacteria with tryptophanase hydrolyzing tryptophan into pyruvate, ammonia, and indole
What are kovac’s reagents and why are they utilized
Dimethylaminobenzaldehyde (DMABA) and hydrochloric acid in amyl alcohol
Kovac’s reagents form a liquid layer on the agar and turn red if DMABA reacts with indole, undergoing a dehydration reaction
What does the methyl red test detect
The ability to produce acid end products from mixed-acid fermentation of glucose
What is MRVP broth
Methyl red voges-proskauer broth, contains glucose, peptone, and phosphate as a buffer
How’s is a methyl red positive organism indicated
MR positive organisms produce stable acids such as lactis acid, acetic acid, and Formic acid which lower the pH, turning the broth red
How is a MR negative organism indicated
MR negative organisms convert the acids in the broth into non-acidi end products 2,3-butanediol and acetoin, raising the pH and causing it to turn yellow
What does the voges-pro skater test identify
Organisms that ferment glucose and transform the organic end products acetoin & 2,3-butanediol
What are Barrett’s reagents, why are they added
5% alpha-naphthalene in ethanol and 40% potassium hydroxide
- barritt’s reagents oxidize any acetoin present in the broth into diacetyl, allowing diacetyl to react with any guanidine nuclei from the peptone to produce a reddish-pink complex
