Module 15: Biochemical Tests to Identify Gram Negative Bacilli

What does IMViC stand for

Indole, Methyl Red, Vogues Proskauer, and Citrate

series of four individual tests that are useful for differentiating the family Enterobaceriaceae

IMViC

the indicator reagent that reacts with indole and turns solution red (positive)

Korvac’s

indole positive vs indole negative

positive= red and negative=beige/yellow

Indole Test A-H Reaction

A- Substrate= Tryptophan

B- Enzyme= Tryptophanase

C- Product= Indole + pyruvic acid + ammonia

D- Indicator/indication= Kovac’s indicator/azo red ring

E- All Positive Organisms= Escherichia coli

F- Differential Agent= Tryptophan

G- Selective agent= none

H- Name= Indole test/TSB

what is the genus and species of the organism that is Indole positive

Escherichia coli

can produce lactose, succinate, formate, and acetate

MR +

bacteria can produce acetoin, acetyl-methyl carbinol, ETOH

VP +

Determine whether the organism is glucose fermenter and whether it produces an acid, alcohol, or both

MR/VP test

organism that only tests positive for citrate

Pseudomonas fluorescens

medium used to differentiate between acid and alcohol fermenting specimen

Methyl Red (MR)

Methyl Red A-H Reaction

A- Substrate= glucose

B- Enzyme= too many

C- Product= many; acidic

D- Indicator/indication= methyl red pH indicator/red(+)

E- All positive organisms= Escherichia coli, Salmonella enterica, Serratia marcescens

F- Differential agent= glucose

G- Selective agent= none

H- Name= Methyl Red(MR) broth

test determines the presence of acetyl-methyl-carbinol(acetoin)

Voges-Proskauer

VP A-H Reaction

A- Substate= glucose

B- Enzyme= many

C- Product= acetoin and butandiol

D- Indicator/indication= Barrett’s A&B/red color(+)

E- All Positive organisms= Enterobacter aerogenes

F- Differential agent= glucose

G- Selective agent= none

H-Name= Voges-Proskauer broth

used to determine an organisms ability to use citrate as a sole carbon source

Simmon’s Citrate agar

pH indicator

Bromothymol blue (BTB)

positive vs negative for Citrate experiment

Blue- positive

Green= negative

Citrate A-H Reaction

A- Substrate= citrate

B- Enzyme= citrase

C- Product= pyruvic acid + acetic acid = CO2

D- Indicator/indication= bromthymol blue pH indicator/agar changes from green to blue

E- All positive organisms= Enterobacter aerogenes, Serratia marcescens, Pseudomonas fluorescens

F- Differential agent=. citrate

G- Selective agent= none

H- Name Citrate test