Study Guide for MCB 2010C
Lab Practical Final Exam
Some of these slides were graciously provided by Dr. Gessner
Ex. 5-2: Phenol Red Sugar
Fermentation Broths
• Tube on the left is
negative for sugar
fermentation (red).
• Tube on the right
shows the
fermentation of a
sugar with the
production of acid
(yellow) and gas (gas
bubble in the Durham
tube).
Ex. 5-17: Indole Production (SIM
Agar Deeps)
• The tube on the left
(yellow) is negative
for the production of
indole.
• The tube on the right
(red layer) is positive
for the production of
indole.
Ex. 5-3: Methyl Red Test
• The test on the left is
negative (yellow).
• The test on the right is
positive (red) for the
production of mixed acids
from the fermentation of
glucose.
Ex. 5-3: Voges-Proskauer Test
• The tube on the left is
MRVP broth before
inoculation.
• The tube in the
middle is a negative
test (dirt or mud
color).
• The tube on the right
is a positive test for
neutral end products
(wine color).
Ex. 5-7: Citrate Utilization
• The tube on the left is
negative for citrate
utilization.
• The tube on the right
is “prussian blue” and
is positive for citrate
utilization.
Ex. 5-8: Lysine Decarboxylase
• Tube on the left is
negative for the enzyme
(it ferments glucose to
produce an acid, but
doesn’t have the enzyme
lysine decarboxylase).
• Tube on the right shows
the presence of the
enzyme, a positive result.
• Tube on the right is the
color of uninoculated
media also.
Ex. 5-15: DNA Hydrolysis on
Dnase medium
• The streak on the
bottom is positive
for DNase enzyme
• The streak on the
top is negative for
the DNase enzyme
Ex. 5-12: Urea hydrolysis
• The tube on the left is
negative for the
presence of urease.
• The tube on the right
is positive for the
presence of urease.
Ex. 5-14 Gelatin Hydrolysis:
Some bacteria have enzymes which breakdown the gelatin (which is protein) to
amino acids; as indicated by liquefaction in test tube B.
Remember: Besides the fact that most bacteria are unable to digest agar, agar
is superior to gelatin because it remains solid well above room temperature
(~25°C). Whereas gelatin begins to melt around 25°C.
Ex. 5-9: phenylalanine
deaminase
• The tube on the left
is positive for the
enzyme
• The middle tube is
uninoculated
• The right tube is
negative for the
enzyme
Ex. 5-4: Catalase Production
(cont.)
• The tube on the left is
catalase negative.
• The tube on the right has
bubbles and is catalase
positive.
Ex. 5-20 Blood Agar
Gamma Hemolysis: No destruction of red blood cells
Is blood agar selective, differential or enriched?
Photo: Courtesy of Dr. Kaiser, C.C. of Baltimore County
Blood Agar
Alpha Hemolysis: Partial destruction of red blood cells. Indicated by the greenish
coloration of the media around the bacterial growth.
Photo: Courtesy of Dr. Kaiser, C.C. of Baltimore County
Blood Agar
Beta Hemolysis: Complete destruction of red blood cells. Indicated by the clear area
around the bacterial growth.
Photo: Courtesy of Dr. Kaiser, C.C. of Baltimore County
Ex. 5-18: Kligler’s Iron Agar
• The tube on the left is
uninoculated.
• The second tube shows
glucose fermentation only
(KA--)
• The third tube shows gas
production (see gap in
the bottom of the agar)
and the fermentation of
lactose and glucose
(AA+-)
• The fourth tube shows
glucose fermentation
only, and H2S production
(black) (KA-+)
Ex. 5-21: Coagulase Test
• The tube on top is
positive for the
presence of the
enzyme
• Tube on bottom is
negative for the
presence of the
enzyme
Ex. 5-6: Nitrate reduction
• After addition of reagents A
and B:
– Pseudomonas aeruginosa:
appears negative,
no color change: must test
further
– Escherichia coli: positive,
color change to red
– Corynebacterium xerosis:
appears negative,
no color change: must test
further
Courtesy of Austin Community College
Ex. 5-6: Nitrate reduction, Cont.
After addition of Reagent C (zinc):
Pseudomonas aeruginosa:
Positive (no color change)
Corynebacterium xerosis:
Negative (color change to red)
Courtesy of Austin Community College
Ex. 5-5: Oxidase test
• The streak on the
right is positive for
the oxidase
enzyme
• The streak on the
left is negative for
the oxidase
enzyme
Ex. 5-10: Bile Esculin Agar (BEA)
• Group D Streptococci and
Enterococci darken the
medium around its growth.
Other microbes do not.
•Notice the positive result on
the bottom streak
• The top streak is negative
Enterotube
Figure 10.9