Milk Agar Plate
Differential media
Tests for the presence of the enzyme caseinase
(Hydrolyzes casein (a milk protein) --> amino acid products)
(+) = Clearing
(-) = no clearing -
Starch Agar Plate
Differential media --> amylase
Hydrolyses starch --> simple sugars that can be tra...
MCB 3020 Lab Practical Exam Questions
and Answers
Milk Agar Plate
Differential media
Tests for the presence of the enzyme caseinase
(Hydrolyzes casein (a milk protein) --> amino acid products)
(+) = Clearing
(-) = no clearing -
Starch Agar Plate
Differential media --> amylase
Hydrolyses starch --> simple sugars that can be transported into the cell
Indicator= grams iodine
Iodine + starch = purple color
(+) = No color change/ colorless
(-) = purple around the colony
Lipase Plate
Differential media --> lipase
Hydrolyzes fats --> glycerol and fatty acids
Indicator: spirit blue dye
(+) = blue color
(-) = no color
Oxidase Test
Differential test -->cytochrome c oxidase
(oxidize aromatic amines)
Indicator: dimethyl-p-phenylenediamine hydrochloride DMPD (an aromatic amine)
In the presence of cytochrome c oxidase, the reagent will be oxidized and turn dark blue
to black
(+) = dark blue/black
(-) = colorless
Catalase Test
Differential test --> catalase
Converts hydrogen peroxide (H2O2) --> water and oxygen
Anaerobic (no O2) growth produces hydrogen peroxide which is toxic to the cell
Cell produces catalase to get rid of hydrogen peroxide
Add 3% hydrogen peroxide to the edge of the colony
, Oxygen product will be seen as bubbles coming from the sample
(+) = bubbles
(-) = no bubbles
Litmus Milk
Litmus pH indicator (turns pink at acidic pH)
Acid production
Alkaline production
Curd
Reduction
Proteolysis
Results
(+) Moderate Fermenter= pink
(+) Heavy Fermenter= Curd reaction
(-) Alkaline = blue
Clearing= Casinase +
Labeled Litmus results --
PR Sugar Broth (test for specific sugar fermentation - either glucose, lactose or
mannitol)
Reagent: phenol red and a Durham tube
(+) yellow color = acid
(+) gas + yellow color = acid + gas
(-) Red
(-) Cerise = alkaline -
OF Glucose Media
Tests for Glucose fermentation (Obligate anaerobic fermentation
vs Facultative anaerobic fermentation vs Strict aerobes)
Indicators: Bromthymol blue pH indicator
(closed- adding oil to make anaerobic environment)
Both tubes blue/green = no result
Both tubes yellow = fermentative (F)
Open yellow/closed green = oxidative (O) - Answer-
Vogues Proskauer (VP)
tests for 2,3-butanediol fermenters
Glucose -->AMC-->2,3-butanediol
2,3-butanediol fermenters produce the acetylmethylcarbinol (AMC)/acetoin intermediate
Reagents:
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