Which of the Following Is an Example of a Differential Stain

Which of the following is an example of a differential stain:

1. Capsule Stain
2. Spore Stain
3. Gram Stain
4. Flagella Stain

If a bacterium is positive for the acid-fast stain, what does this indicate?

1. It does not have mycolic acid in the cell wall
2. It has mycolic acid in the cell wall
3. It has tartaric acid in the cell membrane
4. It does not have tartaric acid in the cell membrane

What is the primary stain in the gram stain?

1. Alcohol
2. India ink
3. Crystal violet
4. Congo red

What is the primary stain in acid-fast stain?

1. Acetone
2. Carbolfuschin
3. Mycolic acid
4. Safranin

If a bacterium is gram stain positive, it will appear as a ______color; gram stain negative will indicate a ______color.

1. blue, red
2. pink, blue
3. red, pink
4. violet, pink

What is the first step in preparing a slide for staining?

1. Wash the slide with water
2. “Fix” the slide by passing it over a flame a few times
3. Place the microbes on the slide
4. Place 2-3 drops of acetone alcohol over the specimen on the slide

What is the purpose of “fixing” a slide?

1. To keep the bacteria alive to see it under the microscope
2. To enlarge the bacteria to see it easier
3. To attach a specimen (like cheek cells or bacteria) to the slide and kill the microbes
4. To increase the pH of the specimen

What type of dye will we primarily be using in the lab?

1. Complex dye
2. Basic dye
3. Acidic dye
4. Solvent dye

What does a negative stain do?

1. Stains the bacteria
2. Creates a more negative charge
3. Stains the background instead of the bacteria
4. Stains the cell membrane of the bacteria

Which of the following is NOT TRUE in regards to the purpose of a mordant in the gram stain?

1. It allows the primary stain to react chemically with the cell
2. It keeps the crystal violet from being washed out of by the alcohol
3. It makes the bacteria (or cell) stick to the slide better
4. It forms a complex with crystal violet and peptidoglycan in the cell wall of 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

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

16. 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.

18. 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

19. 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

21. Which of the following is a differential stain?

a)Congo red

b)India ink

c)Gram stain

d)Methylene blue

22. Which of the following are basic dyes?

a)Methylene blue

b)Crystal violet

c)Eosin

d)(a) and (b)

e)All of the above

23. Which of the following are acidic dyes?

a)Methylene blue

b)Crystal violet

c)Eosin

d)All of the above

24. 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

25. 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

26. Which of the following are differential stains?

a)Gram stain

b)Spore stain

c)Acid-fast stain

d)All are correct

27. Which species of bacteria produce endospores?

a. Bacillusanthracis.

b. Streptococcusmutans

c. Mycobacteriumsmegmatis

d. Staphylococcus aureus

e. two of these are spore formers

28. 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

29. What color is S. aureus after decolorizer is used?

a)Purple

b)Pink

c)No color

30. What color is S. aureus after the counterstain is added?

a)Purple

b)Pink

c)No color

31. What color is E. coli before the primary stain is added?

a)Purple

b)Pink

c)No color

32. What color is E. coliafter the primary stain is added?

a)Purple

b)Pink

c)No color

33. What color is E. coliafter decolorizer is used?

d)Purple

e)Pink

f)No color

34. What color is E. coliafter the counterstain is added?

d)Purple

e)Pink

f)No color

35. What is the primary stain for the acid-fast technique?

a)Crystal violet

b)Carbolfuschin

c)Malachite green

d)Iodine

e)Safranin

36. What is the mordant for the acid-fast technique?

a)Crystal violet

b)Malachite green

c)Iodine

d)Heat

e)Safranin

39. 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

43. 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.

44. What is the mordant for the Gram stain technique?

a)Crystal violet

b)Malachite green

c)Iodine

d)Heat

e)Safranin

45. What is the decolorizer for the Gram stain technique?

a)Alcohol

b)Acid alcohol

c)Water

46. What is the counter-stain for the Gram stain technique?

a)Crystal violet

b)Carbolfushin

c)Malachite green

d)Iodine

e)Safranin

48. At what temperature is a motility stab incubated?

a)Body temperature

b)Room temperature

c)50 °C

51. What color are endospores after a Gram stain?

a)Green

b)Red

c)Colorless

52. 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

53. Endospores are produced by bacteria in the genus

a)Bacillus

b)Clostridium

c)Mycobacterium

d)Both (a) and (b)

e)Both (a) and (c)

54. 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

55. 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 or viewing angle

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

62. What is the purpose of a smear prep?

To prepare an organism for staining

63. What are two problems that arise when a slide is not heat fixed properly?

a) burn the cells off

b)cells don’t stick

64. What causes a stain to adhere to bacterial cells?

Charged ions in the dye are attracted to the charges in the bacteria

65. What are the three purposes of a spore stain?

To show endospore presence, location, and size

66. Name an organism which can be identified with an acid-fast stain

Mycobacterium

67. What is the purpose of using a pure culture technique?

To separate a mixture of organisms into pure cultures

68. What does TSA stand for?

Triptic soy agar

69. What is the purpose of a motility test?

To determine the presence of a flagella to assist with identifying the organism

70. What is the function of a mordant?

Forms an insoluble complex with the primary stain in cells that are positive for the primary stain.

71. What layer of the cell wall does a primary stain color?

Peptidoglycan layer

72. How do gram positive and gram negative bacteria differ in their cell wall structure?

Gram positive have 90% peptidoglycan, Gram negative have 10%

73. How does culture age affect the results of a Gram stain?

Older cultures can’t hold the purple color as well

74. Why is Bacillus more resistant than Staph to environmental conditions?

Can produce endosporeswhen environmental conditions are not favorable.

75. 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.

12. Tuberculosis and leprosy are both disease caused by:

a. viruses.b. Streptococcus.c. Klebsiella.d. Mycobacterium.e. Bacillus.

13. 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

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

31. 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

32. 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

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. MycobacteriumEA. Gram negative bacillus

37. S. aureusDB. Gram positive bacillus

38. B. cereusBC. Gram negative coccus

39. E. coliAD. Gram positive coccus

E. Tuberculosis

56-63. List the reagents used in the Gram stain. [8pts]

64-65. Explain what is happening to both Gram positive and Gram negative cells during the Gram stain procedure. [2pts]

Gram positive bacteria have more peptidoglycan in their cell wall, so they retain the crystal violet/iodine complexafter 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.