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Micro lab questions

1.

Which one of the following statements about bacteria in the environment is false?

A. A single gram of garden soil may contain a billion bacterial cells.
B. There are no bacteria found on clean, healthy human skin.
C. There are bacteria and mold spores drifting in the air, mostly on dust particles.
D. There are bacteria living in your mouth, even if you brush your teeth regularly.
E. A Petri dish of medium can become contaminated if you leave it open for too long.

B. There are no bacteria found on clean, healthy human skin.

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
B. a differential medium
C. a selective medium
D. a defined medium
E. a complex medium

C. a selective 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
B. an antibiotic
C. bile salts
D. lactose
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?

  1. raised
  2. pulvinate
  3. craterform
  4. convex
  5. umbonate

E. umbonate

5.

Agar is:

  1. a polymer extracted from algae that has no nutritional value
  2. a common source of nitrogen in liquid media
  3. toxic to most medically important bacteria
  4. a protein extracted from the hooves of cows
  5. degraded by most medically important bacteria.

A. a polymer extracted from algae that has no nutritional value

6.

What substance(s) in sucrose fermentation broth can act as a carbon source?

  1. The carbon source in sucrose fermentation broth is carbon dioxide.
  2. The only source for carbon in sucrose fermentation broth is sucrose.
  3. There are two carbon sources in sucrose fermentation broth, sucrose and glucose.
  4. There are two carbon sources in sucrose fermentation broth, sucrose and amino acids.
  5. There are three carbon sources in this broth, sucrose, ammonium sulfate and vitamins.

D. There are two carbon sources in sucrose fermentation broth, sucrose and amino acids.

7.

Which one of the following statements best describes the appearance of a reliable positive result for a carbohydrate fermentation test.

  1. The medium is clear and does not change color.
  2. The medium is cloudy and greenish-blue.
  3. The medium is cloudy and yellow.
  4. The medium is red.
  5. The pH indicator dye has turned a color that reveals the presence of base.

C. The medium is cloudy and yellow.

8.

The type of microscopy we use to examine bacteria that are stained by the Gram stain procedure is called:

  1. bright-field microscopy.
  2. fluorescent microscopy.
  3. dark-field microscopy.
  4. transmission electron microscopy.
  5. phase-contrast microscopy.

A. bright-field microscopy.

9.

You are looking at an insect with a compound microscope. The ocular lens has a magnification of 8X and the objective lens has a magnification of 2X. What is the total magnification?

  1. 2X
  2. 4X
  3. 8X
  4. 10X
  5. 16X

E. 16X

10.

What is the diameter a typical coccus bacterium?

  1. 1 x 10-5 meters
  2. 1 x 10-6 meters
  3. 1 x 10-7 meters
  4. 1 x 10-8 meters
  5. 1 x 10-9 meters

B. 1 x 10-6 meters

11.

Which of the following statements about using amino acids in media for the culturing of bacteria is true?

  1. Amino acids can be used as a source of carbon by many common bacteria.
  2. Amino acids can be used as a source of nitrogen by many common bacteria.
  3. Amino acids can be broken down to provide energy.
  4. All of the above (A – C) are true.
  5. Responses A and B are true, but not C.

D. All of the above (A – C) are true.

12.

What would be the term used to describe the shape of these bacteria?

  1. sarcina
  2. streptobacillus
  3. diplococci
  4. vibrio
  5. spirilla

D. vibrio

13.

Which one of the following statements about the Gram stain is false?

  1. In the Gram stain, a dye called crystal violet is used to stain the cells purple.
  2. Gram negative cells have thinner cell walls than Gram positive bacteria.
  3. In the Gram stain, alcohol is used to kill the bacteria.
  4. Gram positive cells end up being stained purple.
  5. Gram negative cells end up being stained pink or red.

C. In the Gram stain, alcohol is used to kill the bacteria.

14.

The Gram stain divides microorganisms into two groups, purple vs. red, on the basis of differences in the:

  1. presence of a capsule.
  2. presence of an outer membrane.
  3. thickness of the peptidoglycan layer of the cell wall.
  4. presence of waxy mycolic acids in the cell wall.
  5. presence of endospores.

C. thickness of the peptidoglycan layer of the cell wall.

15.

What is the correct order in which these reagents are used in the Gram stain?

  1. Crystal Violet, Ethanol, Iodine, Safranin,
  2. Crystal Violet, Safranin, Ethanol, Iodine
  3. Crystal Violet, Iodine, Ethanol, Safranin
  4. Safranin, Iodine, Crystal Violet, Ethanol
  5. Iodine, Safranin, Ethanol, Crystal Violet

C. Crystal Violet, Iodine, Ethanol, Safranin

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?

  1. The bacteria excrete amylase.
  2. The bacteria excrete acid.
  3. The bacteria excrete basic waste products.
  4. The bacteria degrade agar.
  5. The bacteria degrade amino acids.

A. The bacteria excrete amylase.

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?

  1. The bacteria excrete acid.
  2. The bacteria excrete an enzyme that degrades protein.
  3. The bacteria are alpha-hemolytic.
  4. The bacteria are beta-hemolytic.
  5. The bacteria are gamma-hemolytic.

D. The bacteria are beta-hemolytic.

18.

All of the following statements describe Escherichia coli except one. Which one of the following statements is false?

A. Escherichia coli is a Gram positive coccus.
B. Escherichia coli can grow on MacConkey agar.
C. Most samples of mammalian feces contain some Escherichia coli.
D. Escherichia coli does not produce amylase, lipase or gelatinase.
E. Escherichia coli is a common inhabitant of mammalian large intestines.

A. Escherichia coli is a Gram positive coccus.

19.

A mutant strain of bacteria that has an additional nutritional requirement that is not seen in the wildtype strain is called:

  1. an autotroph
  2. a heterotroph
  3. a prototroph
  4. an auxotroph
  5. a phototroph

D. an auxotroph

20.

Which one of the following statements about the O-F glucose test is true?

  1. Enteric bacteria like Escherichia coli require oxygen to make acid from glucose.
  2. Pseudomonas bacteria produce acid from glucose both with and without air.
  3. Pseudomonas bacteria cause neither of the two tubes to turn yellow.
  4. Pseudomonas bacteria cause both tubes to turn yellow.
  5. Enteric bacteria like Escherichia coli cause both tubes to turn yellow.

E. Enteric bacteria like Escherichia coli cause both tubes to turn yellow.

21.

Used to determine if a bacterium can grow by using fermentative metabolism:

  1. O-F glucose tube
  2. starch agar
  3. gelatin agar
  4. sucrose fermentation broth
  5. egg yolk agar

A. O-F glucose tube

22.

Used to detect the production of extracellular amylase enzyme:

  1. O-F glucose tube
  2. starch agar
  3. gelatin agar
  4. sucrose fermentation broth
  5. egg yolk agar

B. starch agar

23.

Used to detect the production of extracellular lipase enzyme:

  1. O-F glucose tube
  2. starch agar
  3. gelatin agar
  4. sucrose fermentation broth
  5. egg yolk agar

E. egg yolk agar

24.

Used to see if a bacterial strain can make acid from table sugar when growing anaerobically:

  1. O-F glucose tube
  2. starch agar
  3. gelatin agar
  4. sucrose fermentation broth
  5. egg yolk agar

D. sucrose fermentation broth

25.

Used to detect the hydrolysis of gelatin:

  1. glucose
  2. ammonium sulfate
  3. sterile mineral oil
  4. iodine
  5. yeast extract

B. ammonium sulfate

26.

Used to keep oxygen out of broth or semisolid media:

  1. glucose
  2. ammonium sulfate
  3. sterile mineral oil
  4. iodine
  5. yeast extract

C. sterile mineral oil

27.

Used as a source of vitamins, amino acids and other nutrients in rich complex media:

  1. glucose
  2. ammonium sulfate
  3. sterile mineral oil
  4. iodine
  5. yeast extract

E. yeast extract

28.

Used to detect starch hydrolysis in the amylase test:

  1. glucose
  2. ammonium sulfate
  3. sterile mineral oil
  4. iodine
  5. yeast extract

D. iodine

29.

Appearance of a positive Amylase Test:

  1. a clear zone is seen around the bacterial growth after addition of a chemical reagent
  2. a clear zone is seen around the bacterial growth after incubation
  3. the medium turns blue
  4. the medium turns yellow

A. a clear zone is seen around the bacterial growth after addition of a chemical reagent

30.

In the appearance of a positive test, the bacteria make acid because they ferment a sugar.

  1. a clear zone is seen around the bacterial growth after addition of a chemical reagent
  2. a clear zone is seen around the bacterial growth after incubation
  3. the medium turns blue
  4. the medium turns yellow

D. the medium turns yellow

31.

Appearance of a positive Hemolysis Test:

  1. a clear zone is seen around the bacterial growth after addition of a chemical reagent
  2. a clear zone is seen around the bacterial growth after incubation
  3. the medium turns blue
  4. the medium turns yellow

B. a clear zone is seen around the bacterial growth after incubation

32.

Appearance of a positive Lipase Test:

  1. a clear zone is seen around the bacterial growth after addition of a chemical reagent
  2. a clear zone is seen around the bacterial growth after incubation
  3. the medium turns blue
  4. the medium turns yellow

B. a clear zone is seen around the bacterial growth after incubation

33.

In the appearance of a positive Test, the bacteria grow on Simmon’s citrate agar:

  1. a clear zone is seen around the bacterial growth after addition of a chemical reagent
  2. a clear zone is seen around the bacterial growth after incubation
  3. the medium turns blue
  4. the medium turns yellow

C. the medium turns blue

34.

Clean the slide and place a small drop of water on the slide.

  1. the first step
  2. the second step
  3. the third step
  4. the fourth step

A. the first step

35.

Allow the slide to dry at room temperature.

  1. the first step
  2. the second step
  3. the third step
  4. the fourth step

C. the third step

36.

Use a sterile inoculating loop to spread a tiny sample of bacteria on the slide.

  1. the first step
  2. the second step
  3. the third step
  4. the fourth step

B. the second step

37.

Quickly pass the slide through the flame to heat fix the cells to the glass.

  1. the first step
  2. the second step
  3. the third step
  4. the fourth step

D. the fourth step

38.

When you label a Petri dish culture, you should always write the information on the lid of the plate.

False

39.

Gram negative bacteria that ferment lactose form pale white colonies on EMB agar.

False

40.

At a pH of 7.0, the indicator dye bromthymol blue is green.

True

41.

Luria agar is a defined medium that contains only glucose and inorganic salts.

False

42.

In the gelatinase test, the plate is flooded with ammonium sulfate after incubation.

True

43.

Iodine forms a blue-black complex when it binds to lipids found in egg yolk.

False

44.

There are no vitamins or amino acids in Simmon’s citrate agar.

True

45.

When you put a Petri dish into an incubator you should always put the agar side up.

True

46.

Used as a mordant for the flagella stain:

  1. congo red
  2. malachite green (with heat for 5 minutes)
  3. tannic acid
  4. safranin

C. tannic acid

47.

Used to stain endospores:

  1. congo red
  2. malachite green (with heat for 5 minutes)
  3. tannic acid
  4. safranin

B. malachite green (with heat for 5 minutes)

48.

Used as a counterstain:

  1. congo red
  2. malachite green (with heat for 5 minutes)
  3. tannic acid
  4. safranin

D. safranin

49.

Used to stain the background in the capsule stain:

  1. congo red
  2. malachite green (with heat for 5 minutes)
  3. tannic acid
  4. safranin

A. congo red

50.

Which of the following bacterial species can make heat resistant endospores and be grown in aerobic conditions?

  1. Pseudomonas aeruginosa
  2. Bacillus cereus
  3. Clostridium tetani
  4. Streptococcus pyogenes
  5. Esherichia coli

B. Bacillus cereus

51.

Which of the following bacterial species makes a capsule which is an important virulence factor?

  1. Streptococcus pneumonia
  2. Klebsiella pneumonia
  3. Pseudomonas aeruginosa
  4. Neisseria meningitidis
  5. all of the above

E. all of the above