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MCB 101 Lab > Exercise 6_ Bacterial Cell Wall > Flashcards

Exercise 6_ Bacterial Cell Wall Flashcards

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1
Q

primarily provides a protective shield to bacteria against hostile environment, allow communication with its surroundings to find optimal conditions for growth and development of the bacterial cell

A

bacterial cell wall

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2
Q

role of bacterial cell wall

A
  • protective shield to bacteria against hostile environment, - allow communication with its surroundings to find optimal conditions for growth and development of the bacterial cell - its rigidity maintains the shape of the bacterium - enables transport of large molecules into and out of the cell
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3
Q

who developed gram stain

A

Danish scientist and physician, Hans Christian Joachim gram

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4
Q

when was gram stain developed?

A

year 1884

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5
Q

gram staining is what type of staining method

A

differential staining

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6
Q

advantages of using gram staining

A
  • rapid turnaround and generation of information about the organism’s gram rxn - available inexpensive reagents
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7
Q

2 divisions of bacteria according to gram staining method

A

gram + gram -

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8
Q

what can be seen under the light microscope after staining the cells with gram stain

A

cell shape cell size cell arrangement

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9
Q

what differentiates the gram reaction of a bacterium when stained with gram stain

A

surface layer composition (cell wall)

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10
Q

Gram ____ are decolorized by alcohol, losing the purple color of crystal violet

A

negative

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11
Q

Gram ____ are not decolorized by alcohol, can retain the purple color of crystal violet

A

positive

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12
Q

True or false: a bacterium with a thick peptidoglycan can retain crystal violet after decolorization of alcohol

A

true

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13
Q

True or false: a bacterium with a thin peptidoglycan can retain crystal violet after decolorization of alcohol

A

false

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14
Q

counterstain medium of gram stain

A

safranin

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15
Q

what color does safranin impart to the cells of the decolorized gram negative bacterium?

A

red or pink

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16
Q

which gram bacterium will manifest red/pink colored cells after decolorization

A

gram negative

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17
Q

which gram bacterium will manifest violet or blue colored cells after decolorization

A

gram positive

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18
Q

what method can be used to determine the gram rxn of an unknown bacterium

A

gregersen’s method

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19
Q

if the bacterium mounted in KOH turns viscous it is gram

A

gram negative

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20
Q

if the bacterium mounted in KOH turns watery it is gram

A

gram positive

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21
Q

control organisms utilized in this exercise

A

B polymyxa E coli

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22
Q

gram negative control organism

A

E coli

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23
Q

E coli’s gram reaction

A

gram negative

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24
Q

gram positive control organism

A

B polymyxa

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25
Q

B polymyxa’s gram reaction

A

gram positive

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26
Q

percent concentration of KOH

A

0.03

27
Q

mounting medium of gram stai

A

distilled water

28
Q

mounting medium of gregersen’s method

A

3% KOH

29
Q

3% KOH is the mounting medium of which method?

A

gregersen’s method

30
Q

distilled water is the mounting medium of which method?

A

gram stain

31
Q

During gregersen’s test, do you heat fix samples?

A

NO

32
Q

During gram staining, do you heat fix samples?

A

yes

33
Q

1st staining agent utilized during gram staining

A

crystal violet

34
Q

time requirement in staining cells with crystal violet

A

1 min

35
Q

after staining with crystal violet, what’s next?

A

wash smear with tap water

36
Q

next stain after crystal violet

A

gram’s iodine

37
Q

time requirement in staining cells with gram’s iodine

A

1-2 min

38
Q

decolorizer of gram staining

A

95% ethanol

39
Q

percent concentration of the decolorizer

A

0.95

40
Q

time requirement in decolorizing cells

A

10-15 secs

41
Q

counter stain used in gram staining

A

safranin

42
Q

time requirement in staining cells with safranin

A

45 secs

43
Q

where does crystal violet binds to?

A

peptidoglycan

44
Q

gram’s iodine serves as the ____ which combines the stain with the peptidoglycan of the bacterial cell wall forming a complex

A

mordant (fixing agent)

45
Q

false gram stain results can be because of

A
  • excessive heat fixation - concentration of primary stain - smear is too thick - faulty smear prep - age of culture - use of antibiotics - insufficient iodine exposure - prolonged decolorization - excessive counterstain - lack of experience
46
Q

this bacteria cannot be stained using gram staining due to the lack of a peptidoglycan in the cell wall

A

Mycoplasma

47
Q

Mycoplasma cannot be stained by gram staining because of what

A

absence of peptidoglycan in the cell wall

48
Q

the viscous sample in gregersen’s test contains

A

cell wall debris and DNA

49
Q

the outer membrane of the gram-negative bacteria interact with ____ ____ causing the hydrolysis of the ____ bonds breaking down the cell wall including the peptidoglycan

A

hydroxide ions, ester

50
Q

hydroxide ions interact with what part of the gram negative bacterium

A

outer membrane

51
Q

what does the gram negative has that is not found in gram positive bacteria

A

outer membrane thick peptidoglycan

52
Q

what aids the cell wall of gram positive bacteria to not be degraded during gregersen’s method?

A

thick peptidoglycan

53
Q

as a control organism, what is expected to be the color of the cells of E coli after gram staining

A

pink/re

54
Q

as a control organism, what is expected to be the color of the cells of B polymyx after gram staining

A

purple/blue

55
Q

alternatives for crystal violet as the primary stain for gram staining

A

methyl violet/gentian violet

56
Q

methyl violet/gentian violet can be alternative of what stain in gram staining method?

A

primary stain

57
Q

staining alternatives for safranin as the counterstaining agent in gram staining

A

dilute carbol fuchsin or neutral red

58
Q

dilute carbol fuchsin or neutral red can be alternative of what stain in gram staining method?

A

counterstain/safranin

59
Q

effect of replacing iodine with other oxidizing agents (eg. bromine, chlorine/fluorine)

A

can cause decolorization unnecessary cell wall interaction not form complexes with the primary stain

60
Q

importance of using freshly prepared KO

A

-KOH degrades over time as it reacts with the environment which can affect its ability to differentiate the gram positive and gram negative bacteria -Remains pure from contaminants (eg carbon dioxide)

61
Q

KOH stands for

A

potassium hydroxide

62
Q

higher concentrations than the 3% optimum concentrations of the KOH it will produce false ____ results

A

negative

63
Q

lower concentrations than the 3% optimum concentrations of the KOH it will produce false ____ results

A

positive

MCB 101 Lab (7 decks)

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