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Microbiology > lab practical > Flashcards

lab practical Flashcards

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Biology 101 flashcards
1
Q

parts of a microscope

A 
ocular lens
nosepiece
objectives
stage
slide holder
condenser 
diaphragm
light source
lock screw
coarse and fine adjustment
mechanical stage control
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2
Q

what function does the condenser have?

A

focuses light onto the specimen

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3
Q

what function does the diaphragm have?

A

changes the intensity of the light

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4
Q

equation for resolution

A

wavelength of light / (2 x numerical aperture)

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5
Q

define numerical aperture

A

how far away they need to be from each other to be able to see 2 separate things (want the smallest number)

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6
Q

why do we use oil immersion?

A

in order to capture all the light and not let it escape

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7
Q

how do you get maximum resolution for a lens system?

A

correct alignment & adjusted to focus & oil

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8
Q

cleaning tissue used for microscope

A

lens paper

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9
Q

solvent used on a microscope

A

alcohol

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10
Q

how can you extend lamp life?

A

keeping oil out

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11
Q

brightfield microscopy

A

live & preserved stained specimens
specimen is dark, field is white
provides for cellular detail

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12
Q

dark field microscopy

A

live unstained specimens
specimen bright, field black
provides outline of specimen with reduced internal cellular detail

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13
Q

phase contrast microscopy

A

live specimens
contrasted against gray background
internal cellular detail

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14
Q

fluorescence microscopy

A

illuminates specimen
antibodies with fluorescent dyes emit visible light only if antibody recognizes and binds to cell
diagnostic tool

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15
Q

transmission electron microscopy

A

best resolution
to view internal structure of cells and viruses
for small specimens

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16
Q

scanning electron microscopy

A

produce 3d image
surface of cell
for small specimens

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17
Q

smear prep

A

heatfix, in order to ensure microorganisms are attached to slide and will not wash off during staining. cells are also killed in the process.
problem- may distort cells

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18
Q

simple staining (positive)

A

chromophore is positively charged, on inside of cell
requires heat fixing
need oil
distorted

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19
Q

negative staining

A

chromophore is negatively charged, on outside of cell
requires NO heat fixing
no oil
better shape

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20
Q

how does a smear prep of cells from a liquid medium differ from prep of cells from a solid medium?

A

must add a drop of water to slide before adding solid medium

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21
Q

what causes a stain to adhere to bacterial cells?

A

charge attraction

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22
Q

what is the difference between basic and acidic dyes?

A

Basic dyes have a positive charge and acidic dyes have a negative charge.

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23
Q

what are chromophores?

A

color bearing ions

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24
Q

shape of: bacillus

A

rod

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25
Q

shape of: coccus

A

spherical

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26
Q

shape of: spirochetes

A

spring

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27
Q

shape of: spirilla

A

cork screw

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28
Q

shape of: coccobacillus

A

short rods

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29
Q

shape of: vibrios

A

curved rod

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30
Q

arrangement of: strepto

A

chains

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31
Q

arrangement of: staphylo

A

clusters

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32
Q

arrangement of: tetrads

A

packets of 4

33
Q

arrangement of: sarcinae

A

packets of 8, 16, 32

34
Q

arrangement of: palisade

A

ununiformed clusters

35
Q

advantages and disadvantages to a negative stain

A

not kiling cells

cant differentiate between cells

36
Q

advantages and disadvantages to a positive stain

A

can use oil immersion

kill cell

37
Q 
Gram stain colors: postive
crystal violet
gram's iodine
ethyl alcohol
safranin
A

crystal violet: purple
gram’s iodine: purple
ethyl alcohol: purple
safranin: purple

38
Q 
Gram stain colors: negative
crystal violet
gram's iodine
ethyl alcohol
safranin
A

crystal violet: purple
gram’s iodine: purple
ethyl alcohol: white
safranin: pink

39
Q

gram positive

A

coccus

40
Q

gram negative

A

rod, more disease because thinner peptidoglycan layer

41
Q

why is the gram strain considered a differential stain?

A

differentiates between two kinds of bacterial cells based on their cell wall structure and composition

42
Q

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

A

a gram positive cell- has a thick cell wall, retains the crystal violet dye better in the presence of a decolorizer gram negative cell- which has a thin wall

43
Q

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

A

old cultures of gram positive cells may not retain stain as well as younger cultures and could give false negative results. 16-18 hours are best

44
Q

Which step in the Gram stain procedure is most prone to error? If done incorrectly, how might that step affect the end result?

A

The decolorizer step is very important because it is the step in which the cells become differentiated (gram-positive cells are purple and gram-negative cells are colorless). If too much decolorizer is used, gram-positive cells will lose the primary stain and be counterstained pink. If too little decolorizer is used, gram-negative cells will not lose the primary stain and will remain purple after counterstaining.

45
Q

In what type of cell, gram positive or gram negative, would you find lipopolysaccharides in its cell wall?

A

gram negative

46
Q

what is the function of a mordant? and which reagant serves this purpose in the gram stain procedure?

A

it causes the primary stain to adhere better or be taken up by the cell so that it is not removed during the decolorizing step. Gram’s Iodine

47
Q

if you omit the mordant step while gram-staining Staphylococcus areus, what color will it stain?

A

pink

48
Q

if you omit the decolorizing step while gram-staining Escherichia coli, what color will it stain?

A

purple

49
Q

What are the functions of endospores in bacteria?

A

Endospores are resting stages that allow bacteria to survive conditions unfavorable for growth.

50
Q

what is the mordant in the spore stain?

A

boiling, It causes the endospore to expand allowing stain to penetrate the structure

51
Q

what unique chemical compound is important in the heat resisitance of endospores?

A

calcium dipicolinate is found only in endospores and not in vegetative cells. it is associated with heat resisitance

52
Q

what conditions are necessary to destroy endospores? in what device are these conditions achieved?

A

endospores must be exposed to 121 degrees C, 15 pounds of pressure for at least 15-20 mins. these conditions are achieved in the autoclave

53
Q

identify some spore-forming bacteria that may be responsible for disease

A

Clostridium, Bacillus

clostridium tetani, Bacillus anthracis

54
Q

Escherichia coli

A

gram reaction: gram negative
shape: bacillus
arrangement- none

55
Q

Staphylococcus epidermidis

A

gram reaction: gram postive
shape: cocci
arrangment- staphylo

56
Q

advantages and disadvantages to standard plate count

A

can see living cells

time consuming

57
Q

equation for calculating the number of cells in culture tube

A

number of bacteria per ml = number of colonies X dilution factor

58
Q

equation for total number of cells in original culture tube

A

total number of cells in original culture = number of bacteria / ml X volume of broth in culture tube

59
Q

advantages and disadvantages to turbidity

A

quick

see both living and dead cells

60
Q

methylene blue

A

simple stains/ postive

61
Q

malachite green

A

spore

62
Q

crystal violet

A

gram stain

63
Q

india ink

A

negative staining

64
Q

if forget mordant

A

pink

65
Q

Staphylococcus aureus (gram type, shape)

A

gram-positive, coccus

66
Q

sugar fermentation reactions

A
  • can the organism break down certain sugars
  • does it produce acid and/or gas
  • phenol red
  • fermentation tubes catch gas
  • positive: yellow (orange- slow)
  • negative: red or pink
67
Q

mixed acid fermentation

A
  • determines if mixed acids are produced in the presence of glucose
  • methyl red
  • MR-VP test tube
  • positive: red
  • negative: remain yellow
68
Q

Voges Proskauer test

A
  • determines if butanediol (acetylmethylcarbinol or acetoin) is produced by the fermentation of glucose
  • MR-VP tube &broth
  • reagent A&B
  • positive: red within 5 mins
  • negative:
69
Q

Simmons Citrate test

A
  • determines if bacteria can use citrate as sole source of energy and carbon
  • citrate agar slant (bromothymol blue)
  • positive: blue
  • negative: green
70
Q

catalase test

A
  • indicates the presence of catalase in an organism (enzyme)
  • dribble H2O2 down slant of agar to see bubbling (reagent)
  • positive: bubble (gas produced)
  • negative: no bubbling
71
Q

nitrate reduction

A
  • determines if bacteria can reduce nitrate to nitrite or other nitrogenous compounds
  • A & B reagent
  • reduced: pink/red
  • add reagent C (Zn dust) if no color develops
  • negative: pink/red, clear: positive
72
Q

urea hydrolysis

A
  • detect the presence of enzyme urease (degrades urea to ammonia)
  • phenol red (reagent)
  • positive: pink
  • negative: orange
73
Q

tryptophan degradation

A
  • determines presence of enzyme tryphtophanase (converts tryptophan into indole and pyruvic acid)
  • reagent: Kovac’s reagent
  • positive: red layer at top
74
Q

gelatin

A
  • detects presence of gelatinase (degrade gelatin from solid to liquid)
  • positive: liquid after ice bath
  • negative: solid
75
Q

O2 requirements

A
  • thyglycolate test
  • obligate aerobes: growth at top
  • obligate anaerobes: growth at bottom
  • facultative anaerobes: heavy growth at top, throughout
  • aerotolerant anaerobes: equal growth
  • microaerophiles: growth in middle
76
Q

motility

A
  • determines if bacteria is motile
  • wet mount: look for movement under microscope
  • stab method: use needle and stab agar
  • motile: swim away from stab line
  • non-motile: only grow along stab line
77
Q

oxidase test

A
  • indicates the presence of cytochrome oxidase (enzyme)
  • Tryptic soy agar plate
  • Becton Dickinson (oxidase reagent dropper)
  • positive: purple under 30 seconds
78
Q

mannitol salt agar

A
  • selective and differential
  • if significant growth- Staphylococcus because it can handle high salt (gram-positive)
  • plate from red to yellow
79
Q

levine EMB agar

A
  • selective and differential
  • purple: bacteria can ferment sucrose and lactose
  • non-fermenters: normal colored colonies
  • positive: dark red/brown-green
  • gram-negative

Microbiology (3 decks)

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