Deck 6: Role of Microscopy

Question 1

Which of the following statements is true concerning dark-field microscopy?

A) This type of microscopy uses specific stains to enhance the contrast of certain bacteria.
B) The condenser does not allow light to pass directly through the specimen but directs the light to hit the specimen at an oblique angle.
C) Dark-field microscopy allows the visualization of larger viruses.
D) Dark-field microscopy can differentiate various difficult-to-grow organisms by using immunofluorescence.

Answer 1

B
Dark-field microscopy does not allow light to pass directly through the specimen but directs light to hit at an oblique angle thus making the background a dark field.

Question 2

The acid-fast stain is specifically designed for bacteria whose cell walls contain:

A) teichoic acids.
B) mycolic acids.
C) peptidoglycan.
D) disaccharide-pentapeptide subunits.

Answer 2

B
Mycolic acids render the bacterial cells resistant to decolorization and thus cause acid-fast organisms to maintain the primary stain in the acid-fast staining procedure.

Question 3

A mordant that is applied after the primary stain to bond chemically the alkaline dye to the bacterial cell wall is:

A) safranin.
B) crystal violet.
C) Gram's iodine.
D) Gram's decolorizer.

Answer 3

C
Gram's iodine serves to stabilize the crystal violet in the cell wall of gram-positive bacteria.

Question 4

In microscopy, resolution can be defined as the:

A) magnification power.
B) extent to which detail in the magnified object is maintained.
C) ability of objects to stand out from the background.
D) ability to see objects against a black background.

Question 5

The first step in the Gram-stain sequence is the application of _______, which is the primary stain.

A) safranin
B) crystal violet
C) Gram's iodine
D) Gram's decolorizer

Question 6

Bacterial cells with thick peptidoglycan and numerous teichoic acid cross-linkages are Gram stained.The organisms stain pink.Which one of the following statements explains this discrepancy?

A) The bacterial cells were most likely not heat-fixed to the slide.
B) The bacterial cells were subjected to the decolorizer too long and were overdecolorized.
C) The lot of Gram-stain reagent is most likely expired.
D) No discrepancy exists; cells with this composition stain pink on Gram stain.

Question 7

An organism such as Mycobacterium tuberculosis would absorb which stain in its cell wall?

A) Crystal violet
B) Methylene blue
C) Carbolfuchsin
D) Malachite green

Question 8

The most critical step in the Gram stain is the application of the:

A) safranin.
B) crystal violet.
C) Gram's iodine.
D) Gram's decolorizer.

Question 9

The fluorochrome stain used to study a fungus is:

A) calcofluor white.
B) acridine orange.
C) auramine.
D) immunofluorescence.

Question 10

In the Kinyoun acid-fast staining method, ______ replaces _____ in the primary stain solution.

A) increased phenol; heat
B) heat; increased phenol
C) mycolic acid; heat
D) carbolfuchsin; phenol

Question 11

The fluorochrome stain that can be used to detect mycobacteria is:

A) calcofluor white.
B) acridine orange.
C) auramine.
D) immunofluorescence.

Question 12

Contrast in microscopy is most commonly achieved by:

A) changing objectives for various specimens.
B) increasing the resolution or resolving power.
C) staining techniques.
D) adding a blue filter to the light path.

Question 13

After which step in the Gram-stain procedure are gram-positive bacteria first distinguished from gram-negative bacteria?

A) Crystal violet
B) Iodine mordant
C) Gram's decolorizer
D) Safranin

Question 14

Magnifications in excess of 100,000 ´ are achieved by ________ microscopy?

A) bright-field
B) electron
C) dark-field
D) phase-contrast

Question 15

Of the different types of staining and microscopic techniques, which one of the following is basically the most sensitive?

A) Chromogenic
B) Fluorescence
C) Phase contrast
D) Light field