Name________________________
Medgar Evers College
Lab Interpretation sheet
Prof. Santos
Bio 261, Microbiology
Arrange your tubes and plates according to the tests conducted last week.
Test I Starch test
Add enough Iodine to cover the plate and then after a couple of minutes slowly
remove the Iodine and look for a clear zone indicating presence of starch hydrolysis.
organism
B. subtilis
unknown
Presence of clear zone of starch hydrolysis
yes
Test II Skim milk proteases
Look for a clear zone indicating the hydrolysis of milk proteins.
organism
B. subtilis
unknown
Presence of clear zone of milk protein
hydrolysis
yes
Test III Triglyceride hydrolysis
Look for a halo around the bacterial growth. Spirit Blue agar contains olive oil and the
organism hydrolyzes the olive oil giving you the halo appearance.
organism
S. aureus
unknown
Presence of clear zone of lipid hydrolysis
yes
Test IV Tryptophan test
Add drops of Kovac’s reagent and look for a red ring. The control organism will
break down the amino acid into an indole ring, pyruvate, and ammonia. We are detecting
the indole ring through kovac’s reagent.
organism
E.coli
unknown
Presence of red ring/indole ring
yes
Test V Urease test
Look for a nice cheesy pink color that indicates that the organism produced ammonia
and thus raised the pH causing the medium to change from orange to pink. The indicator
in the medium is phenol red! The control has the enzyme Urease that breaks down urea
into ammonia and carbon dioxide. We detect the ammonia.
organism
P. vulgaris
unknown
Pink color
yes
Test VI Phenylalanine test
Add drops of 10% FeCl3 and look for a green precipitate. The control organism has the
enzyme, phenylalanine deaminase that breaks down the substrate into phenylpyruvic acid
and ammonia. The phenylpyruvic acid will react with the 10 % ferrous chloride to give
you a green precipitate.
organism
P. vulgaris
unknown
Green precipitate
yes
Test VII Kliger’s Iron Agar
Look for the fermentation of glucose, lactose, and the production of hydrogen sulfide.
If glucose was fermented, the butt should be yellow, if lactose was fermented look for the
entire tube being yellow, and if hydrogen sulfide was produced, look for a black
precipitate.
organism
Glucose
Lactose
Hydrogen sulfide
fermentation
fermentation
production
P. vulgaris
E.coli
unknown
Test VIII SIM
Look for the indole ring by adding kovac’s reagent to the tube containing E.coli, look
for motility by observing if organism grew only on stab or all over, and finally look for
hydrogen sulfide production (black precipitate).
Organism
Motility
E. coli
S. aureus
P. vulgaris
unknown
yes
No
Hydrogen sulfide
production (black
precipitate)
Indole ring
indicating
breakdown of
tryptophan
Test IX Litmus milk
Tough one here! Refer to your book for the diagram indicating the different test
results.
Reaction
Unknown
Acid formation due to fermentation (pink)
Alkaline reaction due to formation of
ammonia as a result of protein breakdown
(purple)
Litmus reduction (white)
Coagulation of proteins (curds)
Peptonization (clear or translucent)
Formation of slime (ropiness)