Types of stains
Which of the following is an example of a differential stain:
a. Capsule Stain
b. Spore Stain
c. Gram Stain
d. Flagella Stain
What is the primary stain in the gram stain?
a. Alcohol
b. India ink
c. Crystal violet
d. Congo red
What is the purpose of “fixing” a slide?
a. To keep the bacteria alive to see it under the microscope
b. To enlarge the bacteria to see it easier
c. To attach a specimen (like cheek cells or bacteria) to the slide and kill the
microbes
d. To increase the pH of the specimen
With respect to timing the most critical part of the Gram stain is the application of:
a. crystal violet.
b. methylene blue.
c. iodine.
d. safranin.
e. alcohol
Which of the following is NOT TRUE in regards to the purpose of a mordant in the gram
stain?
a. It allows the primary stain to react chemically with the cell
b. It keeps the crystal violet from being washed out of by the alcohol
c. It makes the bacteria (or cell) stick to the slide better
d. It forms a complex with crystal violet and peptidoglycan in the cell wall of
bacteria
What color is S. aureus after decolorizer is used?
a) Purple
b) Pink
c) No color
What color is S. aureus after the counterstain is added?
a) Purple
b) Pink
c) No color
1
What color is E. coli before the primary stain is added?
a) Purple
b) Pink
c) No color
What color is E. coli after the primary stain is added?
a) Purple
b) Pink
c) No color
What color is E. coli after decolorizer is used?
d) Purple
e) Pink
f) No color
What color is E. coli after the counterstain is added?
d) Purple
e) Pink
f) No color
If you did a Gram stain on a culture that came out looking Gram negative even though
you knew it should be Gram positive, which of the following could have caused the
misleading results?
a. the culture was too old
b. you forgot to add ethanol
c. you used too much alcohol during decolorization
d. the organism is Acid fast +
e. two of these are possible reasons for the wrong Gram reaction.
What is the mordant for the Gram stain technique?
a) Crystal violet
b) Malachite green
c) Iodine
d) Heat
e) Safranin
What is the decolorizer for the Gram stain technique?
a) Alcohol
b) Acid alcohol
c) Water
2
What is the counter-stain for the Gram stain technique?
a) Crystal violet
b) Carbol fushin
c) Malachite green
d) Iodine
e) Safranin
What color are endospores after a Gram stain?
a) Green
b) Red
c) Colorless
You are given a culture of E. coli. You do a successful streak for isolation. You select a
single colony and Gram stain it. You see equal numbers of cocci and bacilli, all Gram
negative. The most reasonable conclusion is that ____________.
a. you have contamination
b. you have a pure culture with some looking like cocci because of age
c. you did the gram stain incorrectly
d. you have a coccus that can also look like a rod
e. two of these are reasonable conclusions
List the reagents used in the Gram stain.
PRIMARY STAIN
Color of Gram positive after
primary stain
Color of Gram negative after
primary stain
MORDANT
DECOLORIZER
COUNTER STAIN
Color of Gram positive after
counter stain
Color of Gram negative after
counterstain
Crystal violet
Purple
Purple
Gram’s iodine
Alcohol
Safranin
Purple
pink
What is the function of a mordant?
Forms an insoluble complex with the primary stain in cells that are positive for the
primary stain.
What layer of the cell wall does a primary stain color?
Peptidoglycan layer
3
Explain what is happening to both Gram positive and Gram negative cells during the
Gram stain procedure.
Gram positive bacteria have more peptidoglycan in their cell wall, so they retain the
crystal violet/iodine complex after decolonization with alcohol, and they appear
purple.
Gram negative organisms have less peptidoglycan in their cell wall, plus they have
an outer membrane, so the crystal violet/iodine complex washes away when alcohol
is applied. Therefore, the Gram negative organisms must be counterstained with a
red dye to be visualized. This red dye is not seen through the darker purple in Gram
positive organisms.
How do gram positive and gram negative bacteria differ in their cell wall structure?
Gram positive have 90% peptidoglycan, Gram negative have 10%
How does culture age affect the results of a Gram stain?
Older cultures can’t hold the purple color as well
Which of the following is the most common type of stain?
a. Iodine stain
b. Gram stain
c. Acid fast stain
d. Capsule stain
True or false: The cell wall of a gram negative organism has many lipids
a. True
b. False
Which of the following is NOT a characteristic of gram positive bacteria:
a. Purple stain coloration
b. Thick peptidoglycan
c. Very little lipids
d. Lots of lipids
Which of the following is NOT a step in the gram stain procedure:
a. Mordant
b. Primary stain
c. Counter stain
d. Sealant
e. Decolorizer
True or false: Gram positive bacteria have thick peptidoglycan
a. True
b. False
4
When you do a Gram stain, what would happen if you use an old culture?
a. Cells will not hold a stain
b. Gram positive cells would be purple and pink because some
peptidoglycan has broken down
c. Gram positive cells would be pink because they still contain peptidoglycan
d. All cells will turn dark brown because no peptidoglycan remains
Match the following Gram stains. Each answer is only used ONCE.
a. Alcohol or acetone
Decolorizer
b. Safranin
Counterstain
c. Crystal violet
Primary stain
d. Iodine
Mordant
What color does a bacteria stain if it is Gram positive?
A. Green
B. Violet
C. Yellow
D. Black
What color will bacteria stain if it us Gram negative?
A. Orange
B. Brown
C. Pink
D. Black
If a bacterium is positive for the acid-fast stain, what does this indicate?
a. It does not have mycolic acid in the cell wall
b. It has mycolic acid in the cell wall
c. It has tartaric acid in the cell membrane
d. It does not have tartaric acid in the cell membrane
What is the primary stain in acid-fast stain?
a. Acetone
b. Carbol fuschin
c. Mycolic acid
d. Safranin
If a bacterium is gram stain positive, it will appear as a ____________ color; gram stain
negative will indicate a ____________ color.
a. blue, red
b. pink, blue
c. red, pink
d. violet, pink
5
What is the first step in preparing a slide for staining?
a. Wash the slide with water
b. “Fix” the slide by passing it over a flame a few times
c. Place the microbes on the slide
d. Place 2-3 drops of acetone alcohol over the specimen on the slide
The simplest way to make a slide of bacteria is to prepare a wet mount. The main
drawback to this method is that________
a. bacteria are generally colorless and transparent
b. all bacteria are pathogenic
c. live bacteria move around too quickly to be observed
d. reverse osmosis occurs, killing and distorting bacteria
e. cover slips are too expensive to use regularly
Before heat fixation, a wet smear must first be
a) Air-dried
b) Blotted dry
c) Rinsed with water
d) Stained with a basic dye
e) None of the answers are correct
What is the purpose of a smear prep?
To prepare an organism for staining
What are two problems that arise when a slide is not heat fixed properly?
a) burn the cells off
b) cells don’t stick
What causes a stain to adhere to bacterial cells?
Charged ions in the dye are attracted to the charges in the bacteria
What is the purpose of using a pure culture technique?
To separate a mixture of organisms into pure cultures
What does TSA stand for?
Triptic soy agar
The purpose of heat-fixing a bacterial smear slide is to:
a. get the bacteria to stick to the surface of the slide so they don’t wash off during
the later staining.
b. kill and preserve the bacteria.
c. break up clumps of bacteria by evenly melting them across the slide.
d. a & b
e. a, b, & c
6
ETOH is
a.
b.
c.
d.
A type of gram stain
An amino acid
Ethanol alcohol
A type of bacteria resistant to stain
What procedure is done when you “Fix” a slide?
A. Pass it through a flame a few times.
B. Clean it with Lysol
C. Glue pieces together
D. Put it away
What is the purpose of “Fixing” a slide?
A. So that you can see it.
B. To attach the cells (or the bacteria) to the slide and kill the microbes.
C. To fix the slide so it is not broken.
D. To get it ready for the next class.
If an ion has a positive charge it is called a:
A. A. Cation
B. Prion
If an ion has a negative charge it is called a:
A. Prion
B. Anion
A simple stain uses:
A. One stain
B. Two stains
C. Three stains
D. Four stains
What is the first step when preparing a slide for staining?
A. Clean the slide
B. Pass the slide through a flame a few times
C. Put dye on the slide
D. You don’t need to do anything, it should be ready to view
If an ion has a positive charge it is called a cation.
A. True
B. False
If an ion has a negative charge it is called an anion.
A. True
B. False
7
What kind of dye does a cation create?
A. an acidic dye (pH lower than 7)
B. colored dye
C. a basic dye (pH higher than 7)
D. doesn’t create a dye
An acidic dye is also called a negative stain?
A. True
B. False
What is the purpose of heating a slide?
A. to make the cells stick to the slide so they don’t rinse off when the stain is applied
B. to give to cells more color
A. to allow light to pass through
B. you don’t need to heat a slide
15. Smears from a slant are:
a. placed directly onto a clean slide and spread into a dime-sized area.
b. placed onto a drop of water on a clean slide and spread into a dime sized area.
c. made by using as much culture as can be lifted with a loop to insure a good
smear.
d. made by using a sample from a broth culture.
e. Both B and C are correct
Which of the following morphological shapes classify a round bacterium?
a) Coccus
b) Bacillis
c) Helical
A rod-shaped bacterium that occurs in strands is which classification?
a) Streptococcus
b) Streptobacillus
c) Spirochete
A bacterial colony shaped like a cluster of grapes is which classification?
a) Streptococcus
b) Streptobacillus
c) Spirochete
What are the two different types of basic stains?
A. negative and positive
B. simple and differential
C. colored or non colored
D. cation and anion
8
What does a negative stain do?
a. Stains the bacteria
b. Creates a more negative charge
c. Stains the background instead of the bacteria
d. Stains the cell membrane of the bacteria
What is the purpose of using a negative stain?
a) Determine the size of an organism
b) Determine the shape of an organism
c) Counting the number of cells present
d) A and B are correct
e) A, B, and C are correct
Which of the following are true about negative stains?
a) It is acidic and has a positive charge
b) It is acidic and has a negative charge
c) It has a basic pH and a positive charge
d) It has a basic pH and a negative charge
A stain used to determine the true cell morphology and size is the:
a. negative stain.
b. simple stain.
c. acid fast stain.
d. Gram stain.
Dyes for bacteria contain which of the following?
a) Positively charged chromophores that are attracted to the negative charge of
bacteria
b) Positively charged chromophores that are attracted to the positive charge of
bacteria
c) Negatively charged chromophores that are attracted to the negative charge of
bacteria
d) Negatively charged chromophores that are attracted to the positive charge of
bacteria
Which of the following are negative stains?
a) Nigrosin
b) India ink
c) Congo red
d) Fuschsin red
e) (a), (b), and (c) are correct
f) All of those are negative stains
What is the function of a spore stain? To visualize bacteria that make spores
What is the function of a capsule stain? To visualize bacteria that have a capsule
What is the function of a flagellar stain? To visualize bacterial flagella
9
Basic dyes are used to stain bacteria because they have:
a. positively charged chromophores that are attracted to the negative charge of
bacteria.
b. negatively charged chromophores that are attracted to the positive charge of bacteria.
c. positively charged chromophores that are attracted to the positive charge of bacteria.
d. negatively charged chromophores that are attracted to the negative charge of bacteria.
e. none of the above
What is an example of of a stain that a differential stain uses?
A. methylene blue
B. Gram stain
C. positive stain
D. negative stain
The negative stain _________________.
a. stains the organisms’ cell walls and protoplasm.
b. allows you can estimate pathogenicity
c. stains the background surrounding the organisms.
d. causes the flagella to become visible
e. two of these
Which of the following is a differential stain?
a) Congo red
b) India ink
c) Gram stain
d) Methylene blue
Which of the following are basic dyes?
a) Methylene blue
b) Crystal violet
c) Eosin
d) (a) and (b)
e) All of the above
Which of the following are acidic dyes?
a) Methylene blue
b) Crystal violet
c) Eosin
d) All of the above
Which of the following are differential stains?
a) Gram stain
b) Spore stain
c) Acid-fast stain
d) All are correct
Which species of bacteria produce endospores?
10
a.
b.
c.
d.
e.
Bacillus anthracis.
Streptococcus mutans
Mycobacterium smegmatis
Staphylococcus aureus
two of these are spore formers
What is the primary stain for the acid-fast technique?
a) Crystal violet
b) Carbol fuschin
c) Malachite green
d) Iodine
e) Safranin
What is the mordant for the acid-fast technique?
a) Crystal violet
b) Malachite green
c) Iodine
d) Heat
e) Safranin
At what temperature is a motility stab incubated?
a) Body temperature
b) Room temperature
c) 50 °C
What external structure makes Mycobacterium different from other organisms?
a) It has a capsule
b) It has mycolic acid in the cell wall
c) It has a larger amount of peptidoglycan than most
Endospores are produced by bacteria in the genus
a) Bacillus
b) Clostridium
c) Mycobacterium
d) Both (a) and (b)
e) Both (a) and (c)
Acid-fast staining is useful for identifying the causative agent of
a) Leprosy
b) Tetanus
c) Tuberculosis
d) Both (a) and (c)
e) All of the above
What are the three purposes of a spore stain?
11
To show endospore presence, location, and size
Name an organism which can be identified with an acid-fast stain
Mycobacterium
What is the purpose of a motility test?
To determine the presence of a flagella to assist with identifying the organism
Why is Bacillus more resistant than Staph to environmental conditions?
Can produce endospores when environmental conditions are not favorable.
What is the difference between true motility and Brownian motion?
In true motility, the organism moves from one location to another. Brownian motion
is just water molecules hitting the organism, causing it to bounce around. It is not
true motility.
Multiple Choice: Select the single best answer to the following.
Tuberculosis and leprosy are both disease caused by:
a. viruses.
b. Streptococcus.
c. Klebsiella.
d. Mycobacterium.
e. Bacillus.
Endospores are:
a. the result of sexual conjugation in bacteria.
b. found only in gram negative bacteria.
c. resistant to chemicals and heat.
d. all of the above are correct statements about endospores.
e. none of the above
Matching: Match the organisms listed in Column 1 with the appropriate description in
Column 2.
Descriptions in column 2 may be used once, more than once, or not at all.
COLUMN 1
COLUMN 2
36. Mycobacterium E
A. Gram negative bacillus
37. S. aureus
D
B. Gram positive bacillus
38. B. cereus
B
C. Gram negative coccus
39. E. coli
A
D. Gram positive coccus
E. Tuberculosis
What color do Acid fast bacteria stain if they are positive for being Acid fast?
12
A.
B.
C.
D.
Blue
Red
Pink
Yellow
Match the stain to the result of color for each
A. Purple
1.
2.
3.
4.
5.
6.
B. Pink
Gram + with Crystal Violet
Gram + with Iodine
Gram - with Alcohol-acetone
Gram - with Safranin
Gram + with Alcohol-acetone
Gram + with Safranin
C. Colorless
A-PURPLE
A-PURPLE
C-COLORLESS
B-PINK
A-PURPLE
A-PURPLE
MATCH THE IMAGE WITH THE FLAGELLA ARRANGEMENT BELOW:
7. Monotrichous
8. Lophotrichous
9. Amphitrichous
10. Peritrichous
A
B
C
D
What is an acidic stain used for?
A. When you want to stain the cell
B. When you can’t see the cell
C. When you want the cell to change color
D. when you want to stain the background instead of the cells
A differential stain uses methylene blue.
13
C. True
D. False
Immuno compromised patients include the following
A. Elderly people or infants
B. AIDS or HIV infection
C. Immunosuppressing agents for organ transplant recipients
D. Chemotherapy for cancer patients
E. Malnutrition
F. Medicine (some antibiotics)
G. Medical procedures
H. All of the above
Special stains are
A. Spore or endospore, capsule, and flagella
B. Primary and mordant
C. decolorize and counter stain
D. B and C
Only sterilization can kill a spore. T
Spores are only produced by
A. Cocci bacteria
B. Bacillus bacteria
C. Cocci bacteria and Bacillus bacteria
D. None of the above
When the environment becomes too harsh to survive, some bacteria have the ability to
eliminate all their cytoplasm and condense all their essential DNA and organelles in to a
highly resistant structure called a spore. T
Spores are metabolically inactive. T
Spores or endospores stain are
A. Primary stain
B. Mordant
C. Decolorize
D. Counter stain
E. All of the above
Streptococcus pneumoniae are bacteria which have a capsule which resists phagocytosis.
T
Flagella stain reveals bacterial flagella, the tail which not easily seen in ordinary stains. T
14
Capsule stain colors the background but the capsule remains clean. This reveals the
presence of a capsule, assisting in the diagnosis. T
What 2 colors of dye are used to stain a slide to determine gram positive or gram
negative?
A. Red
C. Blue
B. Purple
D. Pink
E. None of them
What is the name of the primary stain used for a gram stain?
A. Crystal light
C. Crystal white
B. Crystal red
D. Crystal violet
To determine a gram positive stain, the color must be:
A. Pink
C. Purple
B. Colorless
D. Blue
A Gram negative stain will show what color?
A. Purple
C. colorless
B. Pink
D. Red
Name the order of staining for the Gram Stain.
A. Alcohol-acetone, safranin, iodine, Crystal violet
B. Safranin, alcohol-acetone, crystal violet, iodine
C. Crystal violet, alcohol-acetone, safranin, iodine
D. Crystal violet, iodine, alcohol-acetone, safranin
A flagella that has a tail at one end is called:
a. Lophotrichous
c. monotrichous
b. Pertitrichous
d. amphritrichous
A flagella that has a tail at both ends is called:
a. Peritrichous
c. amphitrichous
b. Lophotrichous
d. monotrichous
A flagella that has many tails at one end is called:
A. Momotrichous
c. pertrichous
B. Lophotrichous
d. amphitrichous
A flagella that has many tails at either end is called:
A. Peritrichous
C. amphitrichous
B. Monotruchous
D. Lophotrichous
15
What is the primary stain for gram positive bacteria?
a. Crystal violet
b. Blue
c. Green
d. clear
True or False. The mordant for gram negative bacteria is iodine.
True.
What is the mordant for an acid fast stain?
a. Heat
b. ETOH
c. crystal violet
d. safranin
What is the counter stain for an acid fast stain?
a. Acid alcohol
e. water
f. Methylene blue
g. safranin
The primary stain for spore stain is _________.
a. Malachite green
b. Crystal violet
c. Heat
d. acid
What color will the gram positive bacterial cell be after the decolorizer is used?
a. Purple
b. safranin
c. water
d. acid
True or False. The gram negative bacterial cell be pink after the counter stain.
True
True or False. Iodine is the decolorizer used in an acid fast stain?
False
What is the primary stain used in an acid fast stain?
a. carbol fuschia
b. safranin
c. methylene blue
d. water
True or False. Water is the decolorizer used in a spore stain.
True
16
The first step in preparing a slide for staining is to “fix” the slide, this means
A. scrapping the inside of the cheek
B. passing the slide through a flame a few times.
C. cleaning and drying the slide.
D. dyeing the slide with ink.
The purpose of fixing a slide is to
A. attach the cells, or bacteria to the slide and kill the microbes.
B. be able to see the bacteria under a microscope
C. repairing it before viewing
D. measure the size of cells
An acidic dye is also known as a negative stain.
True
False
A positive charged ion is known as an anion.
True
False
We can measure the cells by using a tiny ruler in the eyepiece of the microscope called an
A. ocular lens
B. ocular ruler
C. ocular micrometer
D. microscopic ruler
Methylene Blue is known as a
A. simple stain
B. gram stain
C. differential stain
D. bacterial stain
A _______ ________ is used to stain bacteria.
A. bacterial stain
B. differential stain
C. gram stain
D. simple stain
What type of cells are we using with methylene blue?
A. buccal
B. tongue
C. cheek
D. none of the above
Stain is applied to slides for what reason?
A. visibility
B. staining
C. bacterial growth
D. adhesive
17
Fill in the missing blanks:
GRAM POSITIVE
GRAM NEGATIVE
pink
Thick peptidoglycan
Very little lipid
Lots of lipid (in the outer membrane)
A) Purple; thin peptidoglycan
B) Pink; thick peptidoglycan
C) Pink; thin peptidoglycan
D) Purple; thick peptidoglycan
The gram stain is used to distinguish between Gram positive and Gram negative bacteria.
Which color will Gram positive bacteria appear?
A) Violet because they are decolorized
B) Violet, because they are not decolorized
C) Pink from the safranin because they are decolorized
D) Pink from the safranin, because they are not decolorized
True or False:
F All differential types of stains have the following steps, with the same order and
chemicals.
What steps are followed in the gram stain procedure (with variations in order and
chemicals)?
A) Primary, Mordant, Colorizer, Stain
B) Primary, Mordant, Decolorizer, Stain
C) Primary, Mordant, Decolorizer, Counterstain
D) None of the above
What are some reasons you might get a Gram positive culture show up with both purple
and pink cells that are all the same size?
A) The culture is too new
B) The culture is too old and decolorizer was left on for too long
C) The sample smear was too thick and the stain did not get through to all of the cells
D) B and C
E) B
True or False:
F If you see purple and pink cells of different shapes, it is a pure culture.
18
If you get four clean slides and prepare one slide of the following cultures that are less
than 24 hours old:
1. E. coli
2. B. Megaterium
3. Staphylococcus aureus
Then used your fourth slide to make one slide of an old culture to compare them, what
complications would occur when you do a Gram stain?
Matching: A) cells would be purple B) cells would be pink C) Gram+cells would be
purple and pink because some PG has broken down
Forgot to used Gram’s iodine-B
Over-colorize-B
Use no alcohol-A
Use an old culture-C
What makes a stain a negative stain?
A. It is acidic with its negative anion on the chromophore (color portion of the dye).
B. It means the color portion of the dye has a negative charge.
C. Bacteria cells also have a negative charge, so the bacteria cells repel the chromophore
(dye). Therefore, the cell will have no color.
D. All of the above
True, or False, when preparing a negative stain, wearing gloves is mandatory.
A.True
B.False
Whenever you look at a slide with oil immersion, you can change the objectives back to
one of the lower two lenses, but do not ever use the hi-dry lens on a slide that already has
oil on it. Why?
A. The slide will break
B. It will get oil on the wrong lens.
C. You will not be able to see anything.
When taking a sample from a pure colony, which type of tool would one use?
A. Loop
B. Toothpick
C. Q-Tip
D. Inoculating Needle
What does morphology mean in relationship to a cell?
A. Size
B. Shape
C. Arrangement
D. All of the above
19
When using Nigrosin to make a bacteria sample stick to a slide, which of the following
methods will work?
A. Let it air dry
B. Use a hair dryer to dry out the liquid
C. Microwave the sample
D. Add salt
What is morphology in relation to a colony mean?
A. Color
B. Margin
C. Elevation
D. All of the above
Staphylo, Tetrads, Strepto, are all examples of what?
A. Bacteria shapes
B. Bacteria Size
C. Bacteria arrangements
D. None of the above
What type of stain is used in the following picture?
A. Negative
B. Positive
What type of stain is used in the following picture?
A. Negative
B. Positive
20
Lab Chapter 4 Questions
Inoculated most closely means
A. Cured
B. Contaminated
C. Introduced
D. Sterilized
What technique is used when inoculating a bacteria culture?
A. Scientific Technique
B. Laboratory Technique
C. Microbiology Technique
D. Aseptic Technique
Prior to use, all cultured media is:
A. Inoculated
B. Cured
C. Contaminated
D. Sterilized
Sterilization:
A. Cleans
B. Cures
C. Inoculated
D. Disinfects
E. Renders free of all life
The type of culture that provide for a large number of bacteria in a small space is:
A. Agar
B. Egg White
C. Bacterial
D. Broth
What is it called when test tubes containing solid media are left at a slant while the
media solidifies?
A. Bacteria Slant
B. Cultured Slant
C. Petri Slant
D. Agar Slant
Agar is allowed to solidify in the bottom of a test tube to make:
A. Solid media
B. Solid Culture
C. Agar Deep
D. Petri Slant
21
Aseptic transfer and inoculation are usually performed with a sterile, heat-resistant,
noncorroding Nichrome wire attached to an insulated handle. When the end of the
wire is bent into a loop, it is called:
A. An aseptic hook
B. A Nichrome hook
C. A sterile hook
D. An inoculating loop
Aseptic transfer and inoculation are usually performed with a sterile, heat-resistant,
noncorroding Nichrome wire attached to an insulated handle. When the end of the
wire is straight, it is called:
A. An aseptic hook
B. A Nichrome hook
C. A sterile hook
D. An inoculating loop
E. An inoculation needle
Sterilization is usually accomplished using:
A. Alcohol
B. Soap and Water
C. Handi Wipes
D. Autoclave
A culture media rendered free of all life, prior to use is _______.
A. Sterilized
B.Inoculated
C.Contaminated
D.Aseptic
Bacteria are introduced or ____________ into various forms of culture media to keep
them alive and to study their growth.
A. Inoculated
B. Sterilized
C. Differentiated
D. Transferred
Unwanted microbes on media as known as ___________.
A.Contaminants
B. Bad microbes
C. Agars
D. Mediums
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What is the technique used in microbiology to exclude contaminants?
A. Cleaning with lysol
B. Aseptic Technique
C. Inoculating
D. All of the above
Motile bacteria will move ______ from the point of inoculation, giving the appearance of
an inverted pine tree.
A. Closer
B. Away
C. Medial
D. Circular
Lab Chapter 5 Questions
To stain bacteria, a thin film of bacteria cells, called a ________, must be placed on a
slide.
A) Smear
B) Simple stain
C) Direct Stain
D) Negative Stain
A smear is made by spreading a small amount of a _________ on a ________ and
allowing it to dry.
A)
Agar
Clear slide
B)
Bacterial broth
Clean slide
C)
Bacterial broth
Petri dish
D)
Agar
Petri dish
To heat-fix the bacteria; the dry smear is passed through a Bunsen burner flame only one
time.
A) True
B) False
To chemically fix the bacteria, cover the smear with 95% methanol for 1 minute.
A) True
B) False
Most stains used in microbiology are synthetic aniline dyes derived from what?
A) Methanol
B) Water
C) Chlorine
D) Benzene
Staining procedures that use only one stain are called what?
A) Fixed stains
B) Smear
C) Chromophore
D) Simple Stains
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The smear must be what to kill the bacteria?
A) Dead
B) Alive
C) Fixed
D) Free
A simple stain that stains the bacteria is called a ________ and the simple stain that stains
the background but leaves the bacteria unstained is a _________.
A)
B)
C)
D)
Negative stain
Simple Stain
Direct Stain
Simple Stain
Simple Stain
Negative Stain
Negative Stain
Direct Stain
The ion that is colored in a simple stain is referred to as a what?
A) Chromophore
B) Chemically fixed
C) Acidic
D) Basic
Most bacteria are stained when a basic stain permeates the cell wall and adheres by
_______ ionic bonds to the bacterial cell, which is slightly ________charged.
A) Strong; negatively
B) Weak; positively
C) Strong; positively
D) Weak; negatively
What methods are used to ensure that the smear is fixed?
A. heat fixed
B. chemically fixed
C. (A and B)
D. None of the above
What is the purpose of fixing the smear?
A. Preserves microbes with minimal shrinkage or distortion when stained.
B. Denatures bacterial enzymes, preventing them from digesting cell parts.
C. Allow bacterial growth.
D. All of the above
E. (A and B)
What procedure is used to heat-fix the bacteria?
A. Cover the smear with 95% methanol.
B. Pass the slide through the flame of a Bunsen burner several times.
C. Dry smear can be placed on a 60oC slide warmer for 10 minutes.
D. All of the above
E. (A and B)
F. (B and C)
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What is added to the stain to chemically fix the bacteria?
A. 5% alcohol
B. 2 drops of sterile water
C. 95% methanol
D. Methylene blue
What portion of the stain’s solution is responsible for its color?
A. Agar
B. Broth culture
C. Methanol
D. Chromophore
If the chromophore is a positive ion, the stain is a ____________.
A. acidic stain
B. basic stain
C. direct stain
D. negative stain
E. simple stain
If the chromophore is a negative ion, it is __________________.
A. basic stain
B. simple stain
C. negative stain
D. acidic stain
E. direct stain
Staining procedures that use only one stain are called _____________.
A. simple stains
B. basic stains
C. negative stains
D. direct stains
A simple stain that stains the bacteria is a ________________.
A. negative stain
B. simple stain
C. basic stain
D. direct stain
A simple stain that stains the background but leaves the bacteria unstained is a
______________.
A. acidic stain
B. direct stain
C. negative stain
D. basic stain
True/False
The inoculating loop must be cool before you insert it into the medium. True
Do not fix until the smears are completely dry. True
Blow on the slide to dry it quicker. False
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Lab Chapter 7 Questions
Who invented Gram-staining technique?
Hans Christion Gram
Put the staining technique steps in order
Primary stain (crystal violet)
Mordant (Gram’s iodine)
Decolorizing agent (ethanol or ethanol-acetone)
Secondary stain/counterstain (safranin)
______________ stains the decolorized bacteria red
A Safranin
B primary stain
C mordant
Some common sources of Gram-staining errors are the following
A The loop was to hot
B The decolorizing agent (ethanol) was left on the smear to long
C The smear was too thick
D All of the above
Bacteria that decolorize easily are referred to as
A gram-negative
B gram-positive
Bacteria stain differently because
A peptidoglycans
B compounds in the cell wall
C chemical and physical differences in their cell walls
D layers of lipoprotein
Gram stain is most consistent when done on cultures of bacteria
A less than 48 hours old
B less than 24 hours old
c within 30 days
d none of the above
The alcohol decolorizing agent dehydrates the cell wall of the
A gram-negative cells
B gram-positive cells
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Very thick smears will give inaccurate results
A True
B False
All bacteria are stained purple by this basic dye
A counterstain
B mordant
C primary stain
What is the last step in gram staining?
A. cover the smear with crystal violet for 30 seconds
B. gently wash off the ethanol
C. gently wash the smear with water
D. Blot it dry
True or false. Bacteria differ in their rate of decolorization. True
True or false. Gram-negative bacteria decolorize slowly. False
True or false. Very thick smears on a stain will give inaccurate results. True
Bacterial cell walls are complex lattice structures composed of layers of ________.
A.peptidoglycans
B.lipoproteins
C.phospholipids
D.lipopolysaccharides
What color does basic dye stain bacteria?
A.blue
B.red
C.green
D.purple
When is gram stain most consistent on bacteria?
A. less than 24 hours old
B.2 days
C.3 days
D. 4 days
What color is bacteria dyed when using a primary stain?
a. blue
b. green
c. yellow
d. purple
True or false.
Gram negative decolorizes quickly, while gram negative decolorizes slowly. True
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