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Section: _____________
MCB101 Introductory Microbiology Lab
Exam – 1
Fall 2007
For each question choose the one best answer.
Multiple Choice
(20 Questions, 3 points each)
1) Which one of the following statements about bacteria in the environment is false?
A.
B.
C.
D.
E.
A single gram of garden soil may contain a billion bacterial cells.
There are no bacteria found on clean, healthy human skin.
There are bacteria and mold spores drifting in the air, mostly on dust particles.
There are bacteria living in your mouth, even if you brush your teeth regularly.
A Petri dish of medium can become contaminated if you leave it open for too long.
2) When Staphylococcus epidermidis is incubated on a Petri dish of Phenolethanol agar,
individual cells grow into visible colonies. But when Esherichia coli is plated on this
medium, it dies. In this respect phenolethanol agar is an example of:
A. a general purpose medium
C. a selective medium
E. a complex medium
B. a differential medium
D. a defined medium
3) Many Gram negative bacteria can grow on MacConkey agar but the growth of
most Gram positive bacteria is inhibited.
What ingredient is used in MacConkey agar to cause this inhibition?
A. agar
D. lactose
B. an antibiotic
E. phenolethanol
C. bile salts
4) When describing a bacterial colony growing on an agar plate, the elevation of
the colony is one of the traits that can be noted.
What is the term used to describe a colony that has this sort of elevation profile?
A. raised
B. pulvinate
C. craterform
D. convex
E. umbonate
5) Agar is:
A.
B.
C.
D.
E.
a polymer extracted from algae that has no nutritional value.
a common source of nitrogen in liquid media.
toxic to most medically important bacteria.
a protein extracted from the hooves of cows.
degraded by most medically important bacteria.
6) What substance(s) in sucrose fermentation broth can act as a carbon source?
A.
B.
C.
D.
E.
The carbon source in sucrose fermentation broth is carbon dioxide.
The only source for carbon in sucrose fermentation broth is sucrose.
There are two carbon sources in sucrose fermentation broth, sucrose and glucose.
There are two carbon sources in sucrose fermentation broth, sucrose and amino acids.
There are three carbon sources in this broth, sucrose, ammonium sulfate and vitamins.
7) 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 is clear and does not change color.
The medium is cloudy and greenish-blue.
The medium is cloudy and yellow.
The medium is red.
The pH indicator dye has turned a color that reveals the presence of base.
8) The type of microscopy we use to examine bacteria that are stained by the
Gram stain procedure is called:
A. bright-field microscopy.
C. dark-field microscopy.
E. phase-contrast microscopy.
B. fluorescent microscopy.
D. transmission electron microscopy.
9) You are looking at an insect with a compound microscope. The eyepiece has a
magnification of 8X and the objective lens has a magnification of 2X.
What is the total magnification?
A. 2X
B. 4X
C. 8X
D. 10X
E. 16X
10) What is the diameter a typical coccus bacterium?
A. 1 x 10-5 meters
D. 1 x 10-8 meters
B. 1 x 10-6 meters
E. 1 x 10-9 meters
C. 1 x 10-7 meters
11) Which of the following statements about using amino acids in media for the
culturing of bacteria is true?
A.
B.
C.
D.
E.
Amino acids can be used as a source of carbon by many common bacteria.
Amino acids can be used as a source of nitrogen by many common bacteria.
Amino acids can be broken down to provide energy.
All of the above (A – C) are true.
Responses A and B are true, but not C.
12) What would be the term used to describe the shape of these bacteria?
A. sarcina
D. vibrio
B. streptobacillus
E. spirilla
C. diplococci
13) Which one of the following statements about the Gram stain is false?
A.
B.
C.
D.
E.
In the Gram stain, a dye called crystal violet is used to stain the cells purple.
Gram negative cells have thinner cell walls than Gram positive bacteria.
In the Gram stain, alcohol is used to kill the bacteria.
Gram positive cells end up being stained purple.
Gram negative cells end up being stained pink.
14) The Gram stain divides microorganisms into two groups, purple vs. red, on the basis
of differences in the:
A.
B.
C.
D.
E.
presence of a capsule.
presence of an outer membrane.
thickness of the peptidoglycan layer of the cell wall.
presence of waxy mycolic acids in the cell wall.
presence of endospores.
15) What is the correct order in which these reagents are used in the Gram stain?
A.
B.
C.
D.
E.
Crystal Violet, Ethanol, Iodine, Safranin,
Crystal Violet, Safranin, Ethanol, Iodine
Crystal Violet, Iodine, Ethanol, Safranin
Safranin, Iodine, Crystal Violet, Ethanol
Iodine, Safranin, Ethanol, Crystal Violet
16) You grow a pure culture of an unknown bacteria on a starch agar plate.
After 48 hours you flood the plate with iodine. Most of the plate turns
dark blue except for a clear zone around the bacterial growth.
What does this mean?
A.
B.
C.
D.
E.
The bacteria excrete amylase.
The bacteria excrete acid.
The bacteria excrete basic waste products.
The bacteria degrade agar.
The bacteria degrade amino acids.
17) You streak an unknown bacterium on a blood agar plate. After incubation
you notice a distinct zone around the colonies that is completely clear.
What does this mean?
A.
B.
C.
D.
E.
The bacteria excrete acid.
The bacteria excrete an enzyme that degrades protein.
The bacteria are alpha-hemolytic.
The bacteria are beta-hemolytic.
The bacteria are gamma-hemolytic.
18) All of the following statements describe Escherichia coli except one.
Which one of the following statements is false?
A.
B.
C.
D.
E.
Escherichia coli is a Gram positive coccus.
Escherichia coli is in the same family as Enterobacter and Klebsiella.
Most samples of mammalian feces contain some Escherichia coli.
Escherichia coli is able to hydrolyze lactose.
Escherichia coli produces acid and gas when fermenting sugar.
19) A mutant strain of bacteria that has an additional nutritional requirement that is
not seen in the wildtype strain is called:
A. an autotroph
D. an auxotroph
B. a heterotroph
E. a phototroph
C. a prototroph
20) Which one of the following statements about the O-F glucose test is true?
A. Enteric bacteria like Escherichia coli require oxygen to make acid from glucose.
B. Pseudomonas bacteria produce acid from glucose both with and without air.
C. Pseudomonas bacteria cause neither of the two tubes to turn yellow.
D. Pseudomonas bacteria cause both tubes to turn yellow.
E. Enteric bacteria like Escherichia coli cause both tubes to turn yellow.
Matching (16 Questions, 2 points each)
Some responses are used more than once, others are not used at all.
MATCH each medium with its purpose.
A. O-F glucose tube
B. starch agar
C. gelatin agar
D. lactose broth
E. egg yolk agar
21) used to detect coliform bacteria in water samples
22) used to determine if a bacterium can grow by using fermentative metabolism
23) used to detect the production of extracellular amylase enzyme
24) used to detect the production of extracellular lipase enzyme
MATCH each chemical reagent, media ingredient or item with its purpose.
A.
B.
C.
D.
E.
25)
26)
27)
28)
glucose
ammonium sulfate
sterile mineral oil
iodine
Durham tube
used to detect the hydrolysis of gelatin
used to keep oxygen out of broth or semisolid media
used to detect gas production in sugar fermentation broth
used to detect starch hydrolysis in the amylase test
MATCH each bacteriological test with the appearance of a positive result.
For this section, responses may be used more than once.
Appearance of a Positive Result
A.
B.
C.
D.
29)
30)
31)
32)
a clear zone is seen around the bacterial growth after addition of a chemical reagent
a clear zone is seen around the bacterial growth after incubation
a bubble is seen in the Durham tube
the medium turns yellow
Amylase Test
Test for acid production from sugar fermentation
Hemolysis Test
Lipase Test
In this matching section you are to put the steps of the procedure in the proper order.
The topic is:
Preparation of a Smear of Bacteria on a Microscope Slide for the Simple Stain
A.
B.
C.
D.
33)
34)
35)
36)
the first step
the second step
the third step
the fourth step
Quickly pass the slide through the flame to heat fix the cells to the glass.
Clean the slide and place a small drop of water on the slide.
Allow the slide to dry at room temperature.
Use a sterile inoculating loop to spread a tiny sample of bacteria on the slide.
True- False Questions
( 8 Questions, 1 point each)
37) When you put a Petri dish into an incubator you should always put the agar side up.
38) When you label a Petri dish culture, you should always write the information
on the lid of the plate.
39) Gram negative bacteria that ferment lactose form pale white colonies on EMB agar.
40) At a pH of 7.0, the indicator dye Brom-thymol blue is green
41) Luria agar is a defined medium that contains only glucose and inorganic salts.
42) In the gelatinase test, the plate is flooded with ammonium sulfate after incubation.
43) Iodine forms a blue-black complex when it binds to lipids found in egg yolk.
44) In theMPN test, a positive response for coliforms can be produced by the presence
of as few as one viable E. coli cell in the water sample put in the tube.