Direct Stain, Negative Stain, Gram Stain

Question 1

What does staining provide?

Answer 1

contrast to view the bacteria

Question 2

What three characteristics of bacteria are we able to see when we stain?

Answer 2

morphology, sizze, arrangement

Question 3

How many reagents are used in a simple stain?

Answer 3

1

Question 4

What do direct stains stain?

Answer 4

bacteria

Question 5

What do negative stains stain?

Answer 5

the background, not the bacteria

Question 6

What are dyes?

Answer 6

charged colored ions in a solution

Question 7

How are basic dyes charged?

Answer 7

positive

Question 8

How are acidic dyes charged?

Answer 8

negative

Question 9

How are bacterial cytoplasm’s charged?

Answer 9

slightly negative

Question 10

Do basic dyes dye the bacteria or the background?

Answer 10

Bacteria

Question 11

Do acidic dyes dye the background or the bacteria?

Answer 11

Background

Question 12

What is the procedure for a direct stain?

Answer 12

Prepare a smear, let it air dry, heat fix, add basic due for 2 minutes, rinse with water, air dry

Question 13

What is heat fixing?

Answer 13

passing a smear through a Bunsen Burner

Question 14

What are the two functions of heat fixing a smear?

Answer 14

it adheres bacteria to the slide and it kills bacteria

Question 15

What is the procedure for a negative stain?

Answer 15

Add one drop of acidic dye on one end of a slide, mix in two loopfuls of culture, push smear slide, air dry

Question 16

What is an example of an acidic dye?

Answer 16

India ink

Question 17

What is an example of a basic dye?

Answer 17

Methylene Blue

Question 18

What are the two advantages of negative stain?

Answer 18

fast, no heat fixing so more accurate morphology

Question 19

What are two disadvantages of a negative stain?

Answer 19

Less safe, bacteria is sometimes difficult to find

Question 20

What do differential stains involve?

Answer 20

more than one reagant

Question 21

What do differential stains do?

Answer 21

it differentiates between various bacteria or brings out specific structures

Question 22

What does the Gram stain depend on?

Answer 22

the bacterial cell wall properties

Question 23

What is the gram stain used for?

Answer 23

identifying and classifying bacteria

Question 24

What are bacterial cell walls composed of?

Answer 24

peptidoglycan

Question 25

What does peptidoglycan consist of?

Answer 25

repeating disaccharides

Question 26

What are the names of the disaccharides?

Answer 26

N-acetyl glutamine and N-acetyl muramic acid

Question 27

What is the cell wall of a Gram (+) bacteria like?

Answer 27

Thick, many layers of peptidoglycan

Question 28

What type of acid is found in the cell wall of a Gram (+) bacteria?

Answer 28

Techoic acid, specifically wall techie acid and lipotechoic acid

Question 29

What links the disaccharides in bacterial cell walls?

Answer 29

polypeptide chains

Question 30

What does techoic acid link?

Answer 30

it links together stacked peptidoglycan fibers from different layers

Question 31

What do gram - bacteria not have?

Answer 31

techoic acid

Question 32

What is the cell wall of a gram - bacteria like?

Answer 32

thing layer or peptidoglycan, contains an outermsmbrane with lipopolysaccharides

Question 33

What are lipopolysaccharides composed of?

Answer 33

lipid A and o-polysaccharide

Question 34

What is the order of dyes used for gram stain?

Answer 34

crystal violet, grams iodine, 95% ethanol, safranin

Question 35

What are the times for each dye used in a gram stain?

Answer 35

Crystal violet, grams iodine, safranin = 2-3 minutes; 95% ethanol 3-8 seconds

Question 36

What is the function of crystal violet in a gram stain?

Answer 36

Primary stain

Question 37

What is the function of grams iodine in a gram stain?

Answer 37

mordant

Question 38

What is the function of 95% ethanol in a gram stain?

Answer 38

decolonizing agent

Question 39

What is the function of safranin in a gram stain?

Answer 39

counterstain

Question 40

In a gram (+) bacteria, what color would the bacteria be with any of the dyes?

Answer 40

purple

Question 41

In a gram negative bacteria, what color would the bacteria be after crystal violet and grams iodine?

Answer 41

purple

Question 42

In a gram negative bacteria, what color would the bacteria be after 95% ethanol?

Answer 42

clear

Question 43

In a gram negative bacteria, what color would the bacteria be after safranin?

Answer 43

Red

Question 44

What is a mordant?

Answer 44

binding agent

Question 45

What does grams iodine bind to?

Answer 45

Crystal violet

Question 46

What step can cause innacurate results?

Answer 46

step 3. too long= false negative, too long= false positive

Question 47

What is a pure culture?

Answer 47

contain a single type of microbe

Question 48

What is a pure culture required for?

Answer 48

studying growth, metabolism, pathogenicity, antibiotic sensibility

Question 49

What is a streak plate?

Answer 49

sample is streaked over a pretriplate. Bacteria fall off over different areas of the plate= colony.

Question 50

Why is a streak plate good to use?

Answer 50

it is quick and cheap

Question 51

What is a spread plate?

Answer 51

sample will be serially diluted. there will be a known amount transferred from tubes to several plates. The samples will spread of the surface using a spreading rod.

Question 52

Why is a spread plate good to use?

Answer 52

it is more accurate

Question 53

What is a pour plate?

Answer 53

sample serially diluted, known amount transferred to several tubes of molten agar then poured into petri plate.