Name: _____________________________
Section: _____________
MCB101 Introductory Microbiology Lab
Exam – 2
Fall 2007
For each question choose the one best answer.
Multiple Choice
(25 Questions, 4 points each)
1) Which one of the following statements about carbohydrate fermentation tests is false?
A.
B.
C.
D.
Bacteria that obtain energy by breaking down amino acids excrete basic wastes.
Bacteria that grow by fermenting a sugar usually excrete some acidic waste product.
In MCB 101, the carbohydrate fermentation broth we use contains a Durham tube.
In MCB 101, the carbohydrate fermentation broth we use contains the pH indicator
dye brom-thymol blue.
E. If the bacterium cannot use the sugar in the carbohydrate fermentation broth, they
can’t grow in that medium.
2) What substance(s) in lactose fermentation broth can act as a carbon source?
A.
B.
C.
D.
E.
The only source for carbon in lactose fermentation broth is lactose.
There are two carbon sources in lactose fermentation broth, lactose and glucose.
There are two carbon sources in lactose fermentation broth, lactose and amino acids.
There are three carbon sources in this broth, lactose, ammonium sulfate and vitamins.
The carbon source in lactose fermentation broth is carbon dioxide.
3) Which one of the following statements best describes the appearance of a reliable
positive result for a carbohydrate fermentation test.
A.
B.
C.
D.
E.
The medium has turned red.
The medium is cloudy and yellow.
The medium is clear and does not change color.
The medium is cloudy and greenish-blue.
No bubble appears in the Durham tube.
4) In any bacterial identification scheme, which one of the following procedures must
be done before doing biochemical tests?
A.
B.
C.
D.
E.
Prepare a Gram stain of the bacteria.
Obtain a pure culture of the bacteria.
Incubate a plate of L-agar at 37 degrees C.
Examine the bacteria with a microscope.
Grow the bacteria on PEA agar.
5) A positive result for the catalase test is the appearance of bubbles of oxygen when a
reagent is placed on the bacterial smear. What is the reagent used in the catalase test?
A. methyl red
D. hydrogen peroxide
B. hydrogen sulfide
E. acidified iron chloride
C. Kovac’s reagent
6) Kligler’s iron agar is used to test for the presence of the enzyme cysteine
desulfhydrase, which catalyzes the breakdown of cysteine. What product of this reaction
reacts with the iron that is in the agar, to produce the black precipitate that is the sign of a
positive test?
A. ammonia
D. various acids
B. pyruvate
E. carbon dioxide
C. hydrogen sulfide
7) One of the biochemical tests we used to identify bacteria checks for the synthesis of
the enzyme phenylalanine deaminase. This enzyme causes phenylalanine to break down
to form phenylpyruvate + _______________.
A. ammonia
D. various acids
B. pyruvate
E. carbon dioxide
C. hydrogen sulfide
8) When the amino acid lysine is broken down by lysine decarboxylase,
______________ is formed and the medium turns ______________.
A. cadaverine, purple
C. citrate, green
E. 2-3 butanediol, does not change
B. putresine, yellow
D. ammonia, blue
9) The Methyl Red test is used to check for the production of:
A. tryptophanase.
C. citric acid.
E. starch.
B. acetoin and 2,3-butanediol from glucose.
D. large quantities of acid from fermentation of glucose.
10) Indole is made from:
A. a sugar, lactose.
B. an amino acid, phenylalanine.
C. an amino acid, tryptophan.
D. an amino acid, lysine.
D. a Krebs cycle intermediate, citrate.
11) The Vogues Proskaur test uses the same type of medium as the __________ test.
A. indole
C. lysine decarboxylase
E. amylase
B. methyl red
D. phenylalanine deaminase
12) The Voges-Proskauer test shows if a bacterium can produce _____________.
A. pyruvate from cysteine
B. a mix of organic acids from glucose
C. cadaverine
D. phenylpyruvate from phenylalanine
E. 2,3-butanediol as a fermentation waste product
13) Bacteria in the genus Staphylococcus are Gram positive spheres or cocci.
Bacteria in the genus Streptococcus are Gram positive cocci too.
Which one of the following biochemical tests is the best way to tell the
difference between Streptococcus and Staphylococcus?
A. phenylalanine deaminase test
C. hydrogen sulfide production
E. indole test
B. methyl red test
D. catalase test
14) You set up a ten-tube Minimum Inhibitory Concentration test where the
concentration of the antibiotic in each tube is a 1/2 dilution of the previous tube.
If the concentration of the antibiotic in tube 1 is 3200 micrograms per ml.
What is the concentration of the antibiotic in tube 6?
A. 3200 g/ml
D. 100 g/ml
B. 1600 g/ml
E. 6 g/ml
C. 600 g/ml
15) Serial Dilution: The Final Dilution Factor
In a three step serial dilution:
the first dilution is 1/10,
the second dilution is 1/5,
the third dilution is 1/4.
What is the total dilution factor of this three step serial dilution procedure?
A. 0.05
B. 0.005
C. 1/19
D. 19
E. 200
16) If a viable plate count of a 0.1 ml sample yields 210 colonies
and the dilution factor was 104,
what was the concentration of cells in the original sample?
A. 2.1 x 104 cells/ml
D. 210 x 104 cells/ml
B. 2.1 x 106 cells/ml
E. 210,000 cells/ml
C. 2.1 x 107 cells/ml
17) A bacterial culture is started with 60,000 cells and is allowed to grow for 30
generations. Determine the final number of cells in the culture.
A. 1.80 x 105
D. 1.20 x 1035
B. 6.44 x 1013
E. 6.44 x 1036
C. 6.00 x 1034
Questions 18 and 19 refer to the information given in this table.
18) You are attempting to identify an unknown enteric bacterium that is one of the 12
species shown in the biochemical test key that is given above. Your unknown bacterium
is positive for the Voges-Proskauer test and positive for lactose fermentation. Which one
of the following tests would allow you to unambiguously determine the identity of the
unknown?
A. arabinose fermentation
D. dulcitol fermentation
B. indole test
E. esculin hydrolysis
C. urease test
19) You are attempting to identify an unknown enteric bacterium that is one of the 12
species shown in the biochemical test key that is given above. Your unknown bacterium
is positive for dulcitol fermentation, negative for raffinose fermentation and positive for
Simmon’s citrate.
Which one of the following would you expect to be true?
A. Your unknown is positive for the indole test.
B. Your unknown produces a black precipitate in Kligler’s iron agar.
C. Your unknown is Citrobacter freundii.
D. Your unknown is positive for lactose fermentation.
E. Your unknown can create a clear zone around the area of growth on egg yolk agar.
20) What is the generation time for the bacteria depicted in this growth curve?
A. 30 minutes
B. 60 minutes
C. 90 minutes
D. 5.5 hours
E. 7 hours
21) For the growth curve depicted below, the bacterial culture called ________ grows
the fastest while the bacterial culture called ________ shows the greatest number
of doublings during the experiment.
A. P, P
B. P, S
C. S, S
D. S, P
22) Which one of the following bacteria is the best fit to this description?
It is purple in the Gram stain. The cells are shaped like little round balls.
The cells are arranged in chains. It is negative for the catalase test.
The normal habitat for this bacterium is the mammalian large intestine.
A. Bacillus subtilis
B. Enterococcus faecium
D. Pseudomonas aeruginosa
E. Staphylococcus aureus
C. Escherichia coli
23) Which one of the following statements about the Kirby-Bauer disc diffusion test
for antibiotic susceptibility is true?
A. If the bacterium is resistant to an antibiotic there is a big clear zone around that disc.
B. If there is any clear zone at all around a given antidiotic disc, even a very small one,
the bacterium is considered to be resistant to that antibiotic.
C. The concentration of the antibiotic on a disc has no effect on the size of any clear
zone that may be seen around that disc.
D. If there is a big clear zone around a given antibiotic disc, that drug might be clinically
useful in treating an infection caused by the bacteria being tested.
E. If the bacterium is susceptible to any of the antibiotics on the discs it won’t grow on
the agar plate at all
24) You perform a MIC test using a new antibiotic, Hexacycline, against an old nemesis,
Bordetella pertussis the bacterium that causes whooping cough.
From the data shown, determine the MIC for Hexacycline against this bacteria.
Antibiotic Concentration (g/ml):
Growth?:
A. 500 g/ml
B. 250 g/ml
1000 500
C. 125 g/ml
250
-
125 62.5
+
D. 62.5 g/ml
31.3 15.6
+
+
7.8
+
E. 31.3 g/ml
25) Which one of the following statement about bacterial growth in broth culture is false?
A. After inoculating the broth, there may be a delay before you begin to see growth.
B. Calculations of the growth rate require data from the exponential phase.
C. A shorter generation time equals a faster growth rate.
D. The generation time is the time it takes for the bacterial population to double.
E. The bacterial population is at its’ maximum density during the middle of the log
phase.
MCB101 Microbiology
Exam – 2
Answer Key
1) __ E ___
8) ___ A ___
15) ___ E ___
22) ___ B __
2) __ C ___
9) ___ D ___
16) ___ C ___
23) ___ D __
3) __ B ___
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17) ___ B ___
24) ___ C __
4) __ B ___
11) ___ B ___
18) ___ C ___
25) ___ E __
5) __ D ___
12) ___ E ___
19) ___ B ___
6) __ C ___
13) ___ D ___
20) ___ C ___
7) __ A ___
14) ___ D ___
21) ___ B ___