Gram Staining

Question 1

In ____________, the Danish physician __________________
was trying to develop a staining technique that would
differentiate ___________________ from __________________________________________

Answer 1

1884; Hans Christian Gram; bacterial cells; eukaryotic nuclei
in diseased lung tissue.

Question 2

He discovered that certain stains were retained by some types of bacterial cells but removed from others during the staining process.

Answer 2

Hans Christian Gram

Question 3

His published work served as the foundation of what
would become the most important stain in bacteriology, the Gram stain.

Answer 3

Hans Christian Gram

Question 4

the most important stain in bacteriology

Answer 4

the Gram stain

Question 5

is a valuable diagnostic tool used
in the clinical and research setting

Answer 5

Gram staining

Question 6

is still a widely used method for the identification of unknown bacteria

Answer 6

Gram staining

Question 7

It is often the first test conducted on an unknown species in the laboratory, and in some cases, it can provide presumptive identification of the organism.

Answer 7

Gram staining

Question 8

may be used to determine an
appropriate treatment for a bacterial infection

Answer 8

Gram staining

Question 9

is an example of a differential
stain

Answer 9

The Gram stain

Question 10

In the Gram stain, two kinds of cells, _________________________________, are differentiated based on their __________________ and _______________

Answer 10

gram-positive and gram-negative; cell wall structure; composition

Question 11

gram-positive bacteria retain a _____________________

Answer 11

purple dye complex

Question 12

gram-negative bacteria are ________________ and must be counterstained with a ______________ in order to be visualized by microscopy.

Answer 12

decolorized; red dye

Question 13

Initially, both gram-positive and gram-negative cells are stained by the _______________________

Answer 13

primary stain, crystal violet

Question 14

Iodine is a ___________ that combines with the crystal violet and forms an insoluble complex in gram- positive
cells

Answer 14

mordant

Question 15

During _________________ with ________________________________, gram-positive cells _____________ the crystal violetiodine complex, and therefore these cells will appear ______________ under the microscope.

Answer 15

decolorization; alcohol and/or acetone; retain; purple

Question 16

He discovered that certain stains were ____________ by some types of bacterial cells but ____________ from others during the staining process.

Answer 16

retained; removed

Question 17

_____________ is a _______________ that combines with the crystal violet and forms an _________________ in gram- positive
cells.

Answer 17

Iodine; mordant; insoluble complex

Question 18

Alternatively, the dyemordant complex is _______________ from gram-negative cells, leaving them _________________. _________________is applied as a counterstain, coloring the gram-negative cells ___________________

Answer 18

removed; colorless; Safranin ; pink or red

Question 19

The mechanism for how the Gram stain works
is not completely understood, but it is known to be
related to __________________________________________________________________________

Answer 19

structural and chemical differences in the
cell walls of gram-positive and gram-negative bacteria

Question 20

When viewed by electron microscopy, gram-positive cells have a _______________________ that comprises the cell wall of these organisms

Answer 20

thick layer of peptidoglycan

Question 21

the cell wall in gram-negative cells consists
of an _______________________________________________________________

Answer 21

outer membrane that covers a much thinner layer
of peptidoglycan

Question 22

It is believed that the thick, tightly
linked peptidoglycan molecules of gram- positive cells
_________________________________, preventing
their removal when the smear is correctly decolorized.

Answer 22

trap the crystal violet-iodine complexes

Question 23

In contrast, the decolorizer dissolves the __________ in the
outer membrane of gram-negative bacteria, allowing
the dye-mordant complexes to escape through the thin
peptidoglycan layer.

Answer 23

lipids

Question 24

Some bacteria are considered ______________________
because some cells will retain the crystal violet stain,
while others will not and appear red from the counterstain

Answer 24

gram-variable

Question 25

Other bacteria, called _________________, have a
unique cell wall made of “waxy” lipids.

Answer 25

acid-fast bacteria

Question 26

Mycobacteria, the causative agents of tuberculosis and Hansen’s disease (leprosy), are _____________

Answer 26

acid-fast bacteria

Question 27

the causative agents of tuberculosis and Hansen’s disease (leprosy)

Answer 27

Mycobacteria

Question 28

It is important to use cultures that are _________________
old

Answer 28

16–18 hours

Question 29

It is important to use cultures that are 16–18 hours
old. Gram-positive cultures older than this can convert to ____________________________ and give erroneous results

Answer 29

gram-variable or gram-negative

Question 30

It is important to note that gramnegative bacteria __________ convert to gram-positive

Answer 30

never

Question 31

It is critical to prepare ____________ smears

Answer 31

thin

Question 32

allow the observation of individual cells and any
arrangement in which the cells occur.

Answer 32

Thin smears

Question 33

can entrap the primary stain, preventing decolorization.

Answer 33

thick smears

Question 34

is the most critical step in the Gram stain procedure

Answer 34

Decolorization