LAB Flashcards Preview

Microbiology > LAB > Flashcards

Flashcards in LAB Deck (99)
0

Why is the gram stain considered a differential stain?

Because it differentiates 2 different types of bacteria having different cell wall compositions

1

How do gram-positive and gram- negative bacteria differ in cellular structure, and how does this contribute to their differential staining properties?

Gram positive = thick cell wall layer of peptidoglycan and retains the crystal violet dye better in the presence of of a decolourizer with alcohol or acetone

Gram negative = has less peptidoglycan and thus the cell wall is thinner and the alcohol and acetone removes the crystal violet.

2

How does the age of a culture affect the gram stain reaction? What is the optimum culture age for a valid gram reaction?

Old culture of gram-positive cells can concert to gram variable or gram-negative and give erroneous results. They may also not retain as well as young cultures.

Optimum culture age = less than 16-18 hours

3

What step in the gram stain more prone to error?

Decolonization

Over decolonization will result in the lost of the primary stain, causing the gram positive it appear negative

4

What is the function of a mordant? And heat reagent is the mordant is the gram stain?

Iodine

It complexes with the crystal violet and forms an insoluble complex in the gram positive cells walls.

5

List the reagents of the gram stain technique in order and the amount of time they take

Crystal violet - 1 minute
Iodine - 1 minute
Alcohol/acetone - 20 seconds
Safranin - 1 minute

6

In what type of cell will you find lipopolysaccharide in the cell wall?
a) gram positive
b) gram negative

Gram negative because thee is an additional outer membrane composed of phospholipids and lipopolysaccharide in their cell wall

7

Gram positive cell is stained
a- pink
b- green
c- purple
d- yellow

Purple

8

What is the decolourizing agent in the gram stain technique ?

Acetone alcohol ( ethanol)

9

What is the counter stain agent used in the gram stain technique?

Safranin

10

What causes the different reactions between the gram positive and gram negative organisms?

The larger amount of peptidoglycan in the gram positive cell walls

11

If you did not do the last step of the gram stain technique ( counter stain ) what colour would your gram negative organisms appear?
- purple
- blue
- colourless
- red

Colourless

12

A __________ contains only a single kind of organism.

Pure colony
Pure culture
Mixed culture
None of the above

Pure culture

13

What contains more than 1 single kind of organism?

Mixed culture

14

What is a contaminated culture?

Contains a desired organism and also unwanted organisms

15

What is a pure colony?

An individual colony which raised from a single cell of an organism

It grows into a discrete mound of cells

16

Which method is most used to isolate colonies?

Streak plate

17

Why do we incubate the inoculated plate upside down ( with e bottom facing up)?

To eliminate condensation formed from dripping down into the media and spreading all of the organisms all over the media which will defeat our reason for obtaining single colonies

18

Which method takes less time but requires more skill?
- streak plate
- pour plate

Streak plate method

19

What type of media has nothing but nutrients to support the growth of most bacteria in it?

Non-selective

20

What is an example of non-selective media?

-blood agar
- trypticase soy broth and soy agar

21

What are some examples of selective media?

Neomycin and macConkey agar

22

True or false

Selective media prevent the limit of certain organisms to allow the pathogenic organism to grow

True

23

Does MacConkey agar promote gram negative or gram positive agar to grow? And why

Allows gram negative to grow because it contains bile salts and crystal violet which inhibits the gram positives to grow.

24

What are examples of differential media?

MacConkey agar
XLD agar
Blood agar
Triple sugar iron

25

name some cultural characteristics or observations that are used to identify organisms

- production of hemolysis
- color
- smell
- shape
- consistency
- atmospheric requirements

26

True or false
The use of these different medias eliminate the need for further identify organisms

FALSE

It just shortens the identifying process

27

At what temperature and how long do we incubate the organism?

35 degrees Celsius
18 hours

28

Before determining which identification process to set up on bacteria, one must determine the __________ reaction of the bacteria

Gram stain

29

what is simple staining?

use of a strain to colour a bacterial cell

30

what are that are negatively charged called?

anionic

31

what are positively charged bacteria called ?

cationic

32

are positive dyes basic or acidic?

basic

33

are negative dies basic or acidic?

acidic

34

what type of microscope do we use in the lab
a) fluorescence
b) brightfield
c) plate microscope


brightfield

35

the arm and the base of the microscope are part of the __________

Frame

36

What are the 3 lenses of the microscope?

oculars
objectives
condenser

37

the oculars consist of 2 or more internal lenses and usually have a magnification of
a) 10 x
b) 100x
c) 1000x
d) none of the above

a) 10x

38

the objectives are attached to the _________ which is rotatable

nosepiece

39

match the magnification with the objective
a) 10x 1) oculars
b) 40x 2) high dry
c) 100x 3) oil immersion
d) 10 x 4) low power

a) 1 or 4
b) 2
c) 3
d) 1 or 4

40

which part of the microscope works like the iris diaphragm of your eye?

condenser ; it determines the amount of light that reaches the slide

41

What should you do to maximize the resolving power?

- use a blue filter because this will shorten the wavelength of the light

- the condenser should be kept at the highest position to allow the most amount of light to enter the objectives

- the iris diaphragm should not be closed down too much

42

Good quality microscopes require little focus adjustment when changing objectives from low power to higher power is called
a) fine focusing
b) resolution
c) parfocal
d) none of the above

c) parfocal

43

the limit resolution of light in a microscope is _________ where as the unaided eye is ________.
a) 0.2 mm
b) 0.2 cm
c) 0.2 mcg
d) 0.2 dm

c, a

44

as the power of the objective __________ the distance to the lens/stage ________.
a) increase
b) decrease

increases, decreases

45

the resolving power of a microscope is a function of
a) the magnifying power of the lenses
b) the numerical aperture of the lenses
c) the wavelength of light
d) both a and b
e) both b and c

both b and c

46

the coarse and fine focus knobs adjust the distance between
a) the objective and ocular lenses
b) the ocular lenses
c) the ocular lenses and your eyes
d) the stage and the condenser lens
e) the stage and the objective lens

the stage and objective lens

47

why is it important to limit the quantity of cells used to prepare a smear?

thick smears can become clumpy and obscure details about individual cells.

if its too thick it can hold on to too much stain and lead to wrongful results

48

What does Universal Precautions mean?

means the worker must treat all patients and samples as though they are infectious

49

why is it necessary to air-dry a slide before heat fixing it?

cells might splatter during heating if not dried first

50

Name the 3 differential staining techniques

- endospore
- acid fast
- gram stain

51

In what stage are endospores produced?
a) mating stage
b) reproducing stage
c) resting stage
d) all stages
e) none of the above

resting stage

52

What is very resistant to heat?
a) negative bacteria
b) positive bacteria
c) endospore
d) both a & b
e) none of the above

Endospore

53

Are endospore difficult or easy to stain? and why?

Difficult because of the resistant properties

54

What would you see if you did the gram stain technique on bacteria containing endospore?

clear holes in the bacteria

55

What is mycolic acid composed of?

fatty acids and fatty alcohols

56

What are some test that can be done on gram POSITIVE bacteria to help identify them?

Catalase Test
Coagulase Test (slide or tube methods)
Antibiotic disks
Latex Test Kits
Manual Biochemical tests
Miniaturized Multitest Systems

57

When aerobic organisms grow by respiration, they use _________ as a terminal electron acceptor, converting it to water.
a) sugar
b) bacterias
c) oxygen
d) heat

c) Oxygen

58

What do aerobic organism produce ( other than water)

hydrogen peroxide

59

To prevent damage to essential molecules in the bacterias, which enzyme to the aerobes produce?

CATALASE

60

What does Catalase do?
a) nothing
b) degrades hydrogen peroxide into oxygen and water
c) kills the microorganisms as a defines mechanism
d) none of the above

b it degrades hydrogen peroxide into oxygen and water which is why you will see Bubbles if catalase is present.

61

TRUE or FALSE
Red cells produce Catalase?

TRUE, so don't touch the media if the organism is taken form blood agar!

62

Staphylococcus species are Catalase ______________
a) positive
b) negative
c) it depends

positive

63

Streptococcus species are Catalase ______________
a) positive
b) negative
c) it depends

negative

64

Why does hydrogen peroxide bubble when it is used to cleanse a cut on one's hand?

because there is aerobic bacteria on your hands.

65

What does the Coagulase test differentiate?

Staphylococcus AUREUS from other Staphylococcus SPECIES

66

True or False
Pathogenic Staphylococcus will not produce the enzyme coagulase?

False
Yes, it will.

67

What are the 2 Coagulase tests methods?

Slide Method
Tube Method

68

___________ indicates the presence of Coagulase?
a) clumping
b) bubbles
c) change of color
d) all of the above

a) clumping

69

True or False
If the Slide method indicates the absence of coagulase, the test must be repeated using the tube method to confirm coagulase negative results?

True

70

Why do you have to verify the tubes every hour once incubated?

Because the Staph Aureus can also produce an enzyme which dissolves the clot.

71

Which of these are coagulase positive?
a) Staph Species
b) Staph Aureus
b) both
c) neither

b) Stap Aureus is coagulase positive

72

The antibiotic used to identify Strptococcus pneunomiae is called:

optochin disk

73

Which test may be done on Gram Negative bacteria to help identify them?

- Oxidase test
- TSI
- ONPG-Pam Sulphate
- API 20E (Miniaturized Multitest System)

74

Cytochrome oxidase is an enzyme produced by gram positive or gram negative bacteria?

gram NEGATIVE

75

What test is done to test for the enzyme cytochrome oxidase?

Oxidase Test

76

What colour is oxidase positive ?
a) pink
b) yellow
c) green
d) dark blue/purple

d) dark blue purple

77

Which organisms are oxidase positive?
a) E.Coli
b) Enterobacteriaceae
c) Pseudomonas Species
d) All of the above
e) only A and B

c) Pseudomonas

78

What does TSI stand for?

Triple Sugar Iron

79

What is TSI useful for screening?

stool cultures for enteric pathogens

80

What are the 3 sugars in TSI?

Lactose
Sucrose
Glucose

81

When the TSI media is uninoculated, it is what colour?

red

82

When sugars are fermented by the organism, the indicator (phenol red) will change to what colour?

yellow

83

When the organism produces H2S, there will be ________ in the medium?
a) bubbling
b) blackening
c) clumping

b) blackening

84

How can you tell if an organism produces gas?

it will be demonstrated in the medium as bubbles, cracks/splits, and by the pushing up of the medium in the tube.

85

Glucose is in the __________, Sucrose is in the _________ and Lactose is in the ________ of the TSI tube.
a) slant
b) mid-way
c) butt

glucose = butt
sucrose = mid-way
lactose= slant

86

True or False
All H2S producers are glucose producers?

TRUE

87

Yellow butt / Red slant =

glucose fermenting organism

88

Red butt / Yellow slant =

lactose fermenting organism

89

Red butt/ Red slant =

organism which does not ferment glucose, sucrose or lactose

90

Yellow butt / yellow slant =

organism ferments glucose, sucrose and lactose

91

Black butt / yellow slant =

organism ferments glucose and produces H2S

92

Black butt / Yellow slant =

organism ferments glucose, sucrose and lactose and also produces H2S

93

What does it mean if there is bubbles, splits/cracks or displaced media (motility)?

the organism produces gas

94

True or False
All H2S producing organisms are considered motile?

TRUE

95

What are the 4 different tests used in the ONPG Pam Sulphate Media?

Motility
Beta-Galactosidase production
Phenylanine deaminase production
H2S production

96

If the ONPG tube turns yellow what does it mean?

there is production of beta-galactosidase

97

How is motility observed?

Spreading out from the stab line and the blackening of the media ( from the H2S)

98

What colour is indicative of phenylalanine?

green