4) Micro Bio Lab Practical (IMViC)

What three broths are inoculated in IMViC?

1) Indole (tryptone broth)

2) MRVP (MRVP Broth)

3) Citrate (use needle)

What is significant about IMViC test?

It is the 2nd most important medical procedure (after gram stain)

What is the purpose of the indole test?

To determine whether bacteria can produce indole from tryptophan

What endoenzyme is used in indole test?

Tryptophanase

What is the reagent in Indole test and what does it do?

Kovac’s reagent - detects the presence of indole

What do the (+) & (-) results look like in indole test?

(-) = stays yellow (no indole produced)

(+) = turns pink (indole produced)

What is the purpose of the MRVP test?

To determine whether bacteria ferment glucose into mixed acids or acetoin

What is the reagent (pH indicator) in the Methyl Red test?

Methyl Red reagent (3 drops)

Turns pink/red if low pH ((+) result)

What is the reagent in the Voges-Proskauer test?

VPA (15 drops) & VPB (5 drops)

Turns pink/red if acetoin is present ((+) result)

What are the end products of Methyl Red test?

Mixed acids

What are the end products of Voges-Proskauer?

Acids (24 hours)

Acetoin (48 hours)

What is the purpose of the citrate test?

To determine whether bacteria can utilize citrate as a sole carbon source

What is sodium citrate used for in citrate test?

Sole source of carbon

What is Ammonium dihydrogen phosphate used for in citrate test?

Source of nitrogen (metabolized if bacteria can’t utilize sodium citrate)

What is dipotassium phosphate used for in citrate test?

pH buffer

What is the pH indicator in the citrate test?

Bromothymol blue

yellow = acidic

green = neutral

blue = alkaline

What are the 2 endoenzymes used in the citrate test?

1) Citrate permease

2) Citrate lyase

What is a (+) result in citrate test?

Blue OR green w/ growth

What is a (-) result in citrate test?

Green w/ no growth