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Microbiology Lab Practicum 1 > Direct Stain, Negative Stain, Gram Stain > Flashcards

Direct Stain, Negative Stain, Gram Stain Flashcards

1
Q

What does staining provide?

A

contrast to view the bacteria

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2
Q

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

A

morphology, sizze, arrangement

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3
Q

How many reagents are used in a simple stain?

A

1

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4
Q

What do direct stains stain?

A

bacteria

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5
Q

What do negative stains stain?

A

the background, not the bacteria

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6
Q

What are dyes?

A

charged colored ions in a solution

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7
Q

How are basic dyes charged?

A

positive

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8
Q

How are acidic dyes charged?

A

negative

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9
Q

How are bacterial cytoplasm’s charged?

A

slightly negative

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10
Q

Do basic dyes dye the bacteria or the background?

A

Bacteria

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11
Q

Do acidic dyes dye the background or the bacteria?

A

Background

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12
Q

What is the procedure for a direct stain?

A

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

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13
Q

What is heat fixing?

A

passing a smear through a Bunsen Burner

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14
Q

What are the two functions of heat fixing a smear?

A

it adheres bacteria to the slide and it kills bacteria

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15
Q

What is the procedure for a negative stain?

A

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

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16
Q

What is an example of an acidic dye?

A

India ink

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17
Q

What is an example of a basic dye?

A

Methylene Blue

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18
Q

What are the two advantages of negative stain?

A

fast, no heat fixing so more accurate morphology

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19
Q

What are two disadvantages of a negative stain?

A

Less safe, bacteria is sometimes difficult to find

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20
Q

What do differential stains involve?

A

more than one reagant

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21
Q

What do differential stains do?

A

it differentiates between various bacteria or brings out specific structures

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22
Q

What does the Gram stain depend on?

A

the bacterial cell wall properties

23
Q

What is the gram stain used for?

A

identifying and classifying bacteria

24
Q

What are bacterial cell walls composed of?

A

peptidoglycan

25
Q

What does peptidoglycan consist of?

A

repeating disaccharides

26
Q

What are the names of the disaccharides?

A

N-acetyl glutamine and N-acetyl muramic acid

27
Q

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

A

Thick, many layers of peptidoglycan

28
Q

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

A

Techoic acid, specifically wall techie acid and lipotechoic acid

29
Q

What links the disaccharides in bacterial cell walls?

A

polypeptide chains

30
Q

What does techoic acid link?

A

it links together stacked peptidoglycan fibers from different layers

31
Q

What do gram - bacteria not have?

A

techoic acid

32
Q

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

A

thing layer or peptidoglycan, contains an outermsmbrane with lipopolysaccharides

33
Q

What are lipopolysaccharides composed of?

A

lipid A and o-polysaccharide

34
Q

What is the order of dyes used for gram stain?

A

crystal violet, grams iodine, 95% ethanol, safranin

35
Q

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

A

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

36
Q

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

A

Primary stain

37
Q

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

A

mordant

38
Q

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

A

decolonizing agent

39
Q

What is the function of safranin in a gram stain?

A

counterstain

40
Q

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

A

purple

41
Q

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

A

purple

42
Q

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

A

clear

43
Q

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

A

Red

44
Q

What is a mordant?

A

binding agent

45
Q

What does grams iodine bind to?

A

Crystal violet

46
Q

What step can cause innacurate results?

A

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

47
Q

What is a pure culture?

A

contain a single type of microbe

48
Q

What is a pure culture required for?

A

studying growth, metabolism, pathogenicity, antibiotic sensibility

49
Q

What is a streak plate?

A

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

50
Q

Why is a streak plate good to use?

A

it is quick and cheap

51
Q

What is a spread plate?

A

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.

52
Q

Why is a spread plate good to use?

A

it is more accurate

53
Q

What is a pour plate?

A

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

Microbiology Lab Practicum 1 (15 decks)

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