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MCIM 224 > Lab Exam > Flashcards

Lab Exam Flashcards

1
Q

3 types of hazards in the lab:

A
  1. Microbial hazards
  2. Chemical hazards
  3. Physical/mechanical hazards
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2
Q

Define “biohazard”

A

microbial infectious agents or other biological materials that present a risk or potential risk to the health of humans or animals

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3
Q

Describe a microorganism that is classified under Risk Group 1.

A

One that is unlikely to cause human/animal disease

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4
Q

Describe a microorganism that is classified under Risk Group 2.

A

One that MIGHT cause human/animal disease, but is unlikely to be a serious hazard.

Lab exposure may cause mild to moderate illness > effective treatments and preventative measures are available

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5
Q

Our lab is a Containment Level ___ lab

A

2

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6
Q

What is one of the greatest risks of working in a microbio lab?

A

Accidental exposure to aerosolized suspension of microorganisms.

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7
Q

Define “sterilization”

A

Complete destruction/removal of ALL microorganisms by chemical or physical means

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8
Q

Define “disinfection”/”decontamination”

A

The destruction of specific types of organisms, usually by chemical means

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9
Q

Diff b/w sterilization and disinfection?

A

Sterilization: complete destruction of ALL microorganisms
Disinfection: reduces the amt of microorganisms on a surface

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10
Q

Purpose of WHMIS?

A

To reduce the incidence of illness and injury caused by hazardous materials in the workplace

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11
Q

3 key elements of WHMIS?

A
  1. Labels
  2. MSDS’s
  3. Worker Education
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12
Q

What is brightfield microscopy?

A

Microscopy where a dark image is observed on a bright background

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13
Q

Two types of lens are utilized in compound microscopes:

A
  1. ocular lens

2. objective lens

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14
Q

What’re the three objective lens magnifications? Which lens can be used w/ oil immersion?

A

10x, 40x, and 100x

100x = oil immersion

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15
Q

Total magnification = ?

A

Total magnification =

ocular magnification x objective magnification

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16
Q

Define resolution (microscopy).

A

The ability of a microscope to distinguish two objects as being separate and distinct if they are v. close together.

Essentially, it’s a measure of how clearly objects can be seen.

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17
Q

How does oil immersion improve resolution?

A

It reduces light from scattering > more light passes through specimen > improves resolution

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18
Q

Gram stain rxn, cellular morphology, and cellular arrangement of Staphylococcus aureus?

A

gram positive, coccus, and clusters

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19
Q

Gram stain rxn, cellular morphology, and cellular arrangement of E. coli?

A

gram negative, bacillus, and singles

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20
Q

Gram stain rxn, cellular morphology, and cellular arrangement of Bacillus cereus?

A

gram positive, bacillus, chains

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21
Q

Gram stain rxn, cellular morphology, and cellular arrangement of Streptococcus pyogenes?

A

gram positive, coccus, chains

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22
Q

What colour do gram positive bacteria stain?

A

blue to purple

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23
Q

What colour do gram negative bacteria stain?

A

pink to red

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24
Q

What type of stain is used for Mycobacterium sp.?

A

acid-fast stain

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25
Q

Are E. coli motile?

A

Yes, E. coli are motile (they have a true direction of motion)

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26
Q

What’s the purpose of a hanging drop?

A

To observe living bacteria in their natural habitats, and to observe features of living microbes (such as motility)

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27
Q

Purpose of staining bacteria before observation?

A

increase contrast b/w bacteria and the background > allows for easier observation of bacteria and special structural features

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28
Q

Purpose of air-drying and heat fixing of bacteria on slide? (3)

A
  1. Kill bacteria > no infection risk
  2. Bacterial surface accepts stain more readily
  3. Bacteria become firmly stuck to glass surface > less likely to be washed away
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29
Q

More gram positive or negative cells found in oral cavity?

A

More gram positive bacteria

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30
Q

When gram staining an oral cavity specimen, large, flat, pink-staining material are also seen. What could these be?

A
  1. Plaque

2. Epithelial cells

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31
Q

Why’s staining needed in brightfield microscopy?

A

Microscopic organisms = transparent > staining contrasts bacteria w/ the background of the slide

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32
Q

When would you use a simple stain (methylene blue)? What’s an advantage of the simple stain?

A

When you only want to know whether organisms are present, and their shapes

Advantage of simple stain: It’s simple!

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33
Q

When would you use a gram stain?

A

When you want to know whether there’re gram positive or gram negative bacteria present

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34
Q

What can be seen in a hanging-drop that can’t be seen in a stained prep?

A
  1. Living organisms

2. Motility

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35
Q

Why do we discard stained slides and hanging drops in a disinfectant soln?

A

They contain biohazardous material > potential danger to lab demonstrators

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36
Q

Why don’t we perform a spore stain on E. coli or S. aureus?

A

These two bacteria do not form spores

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37
Q

What bacterium forms spores?

A

Bacillus cereus

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38
Q

Which microscope objective is most satisfactory for studying bacteria? Why?

A

100x oil immersion bc it allows for the best visualization of bacteria

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39
Q

Purpose of heating and steaming during the spore stain?

A

Drives spore stain into spore coat (which is usually v. impermeable under normal conditions)

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40
Q

What is agar?

A

solidifying agent which provides a physical support for bacterial growth - it’s not used nutritionally by bacteria

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41
Q

In order to grow bacteria, what must be understood about them?

A

Their nutritional needs

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42
Q

Define autotroph bacteria.

A

Those who obtain their carbon from inorganic sources

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43
Q

Define heterotroph bacteria.

A

Those who obtain their carbon from organic sources.

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44
Q

4 categories of culture media:

A
  1. Basic media
  2. Enriched media
  3. Selective media
  4. Differential media
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45
Q

This category of media contains additional components (e.g. blood, serum, or meat infusions) due to the need to support bacteria who have special nutritional needs.

A

Enriched media

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46
Q

This category of media has substances added to it in order to inhibit certain bacteria, while still allowing the growth of others.

A

Selective media

47
Q

This category of media allows all bacteria to grow, but has certain substances added to it which allows the differentiation of one species of bacteria from another.

A

Differential media

48
Q

Mannitol salt agar has a high salt conc, and inhibits the growth of most bacteria except _____

A

Staphylococci

49
Q

What is MacConkey’s agar used for?

A

To isolate Enterobacteriaceae away from other bacteria in mixed pops (e.g. stool samples), and to differentiate b/w lactose fermenters from non-fermenters (thus, MacConkey’s agar = selective AND differential)

50
Q

In nitrogen-free agar, where do bacteria get their nitrogen from?

A

The air

51
Q

Define “pure culture”

A

a pop of bacteria consisting of only a single bacterial species

52
Q

How can you tell whether or not there’s bacterial growth in a tube of nutrient broth?

A

If it’s cloudy, then there’s growth

53
Q

Why must the loop be cooled before touching it to a culture of bacteria? (2)

A
  1. Avoid aerosol formation

2. Avoid killing the bacteria

54
Q

Why should we invert the petri plates during incubation?

A

Less chance of plates drying out

55
Q

How could you tell whether a colony on a streaked plate was a contaminant?

A
  1. If the colony grows outside of streak lines

2. For pure cultures, each colony should be the same > if diff colony appears, then it’s a contaminant

56
Q

What would happen if the streak plates had been incubated for a week at 37ºC instead of only 24 h?

A

The bacteria would’ve grown over that time into larger colonies (though not indefinitely)

57
Q

Two ways of measuring bacterial numbers?

A
  1. Bacterial suspension turbidity (absorbance)

2. Plate count method

58
Q

T or F: Higher turbidity and absorbance is correlated w/ lower bacterial cell numbers.

A

F

It’s correlated w/ HIGHER bacterial cell numbers

59
Q

Disadvantage of measuring the turbidity of bacterial suspensions w/ a spectrophotometer?

A

Can’t differentiate b/w living and dead cells

60
Q

If 0.1 mL of dilution is plated and 35 bacteria are counted on the plate, how many organisms were in the original solution (assuming a final dilution factor of 10^-6)?

A

35 * 1/0.1 * 1/(10^-6) = 3.5*10^8 cells/mL

61
Q

Higher absorbance = ?

A

higher cell #

62
Q

T or F: It’s possible for a suspension of bacteria to have a high absorbance value yet give zero CFU/mL on a plate count

A

T

Dead bacteria can block light

63
Q

Why might pour and spread plating give diff CFU/mL values?

A

Pour plating allows anaerobes to grow in addition to aerobes, hence it’s expected to result in higher CFU/mL values

64
Q

What’s plate count agar? What’s it usually used for?

A

It’s a non-selective nutrient media used for enumerating aerobic bacteria

65
Q

What’s MacConkey agar? What can it be used for?

A

Selective media for gram negative bacteria (due to bile salts and crystal violet).
Differential media as well > lactose fermenters (pink or purple colonies) from non-fermenters (no colour change)

It can be used for determining a coliform count

66
Q

What does a high coliform count indicate?

A

Fecal contamination of meat

67
Q

What’s an “indicator organism”?

A

It indicates that there’s bacterial contamination of food (e.g. coliforms indicate fecal contamination)

68
Q

Equation for calculating the number of organisms per mL in the original sample?

A

= # of colonies on plate * 1/vol of sample plated * 1/final dilution factor

69
Q

In a soil envir, how might the production of an antibiotic benefit the producer organism?

A

Less competition > Uninhibited growth

70
Q

Why was it necessary to use a 10-day old culture (as opposed to a fresh 24h culture) of the Penicillium, Bacillus polymyxa, and Streptomyces in order to demonstrate the production of antibiotics?

A

Antibiotic production is a secondary metabolism that occurs only when access to nutrients is reduced

Thus, as cultures get older, antibiotic production increases

71
Q

What vars might alter the zone of inhibition around an antibiotic disc in the disc diffusion assay?

A
  1. Too few or too many bacteria plated

2. Different incubation temperatures

72
Q

What does it mean when colonies are observed growing within the zone of inhibition in a disc diffusion assay?

A

It means that these cells are spontaneous mutants that’re resistant to the antibiotic

73
Q

Despite the tube dilution test for antibiotic sensitivity being more accurate than the diffusion method, what is a major advantage of the disc diffusion method?

A

It’s MUCH easier to do!

74
Q

What does it mean when the minimum bactericidal and minimum inhibitory concentrations are the same?

A

The antibiotic is bactericidal

75
Q

What does it mean when the minimum bactericidal and minimum inhibitory concentrations are different?

A

The antibiotic is bacteriostatic (at lower concentrations)

76
Q

Is tetracycline bactericidal or bacteriostatic?

A

Bacteriostatic

77
Q

Is penicillin bactericidal or bacteriostatic?

A

Bactericidal

78
Q

Compare and contrast b/w sterilization, disinfection, and antisepsis.

A

All three = reducing viable microbes on/in s.th.

Sterilization: destroy ALL microbial life and spores
Disinfection: reduce level of microorganisms on an inanimate surface (maybe spores too)
Antisepsis: reduce level of microorganisms on living tissue

79
Q

Which is more effective at killing bacteria and spores - autoclaving (moist) or dry heat?

A

Autoclaving (moist heat)

80
Q

How does pasteurization affect bacteria?

How would the effects of pasteurization differ b/w pure culture broths and milk?

A

Pasteurization doesn’t completely kill all the bacteria.

In milk, there’re organic materials that can protect bacteria, and so even less would be killed in milk compared to a pure culture broth.

81
Q

Would B. cereus or E. coli be more sensitive to heat?

A

E. coli would be. B. cereus is more resistant due to it being a spore-forming bacterium.

82
Q

How does the length of time an organism is exposed to the disinfectant affect how readily it’s killed?

A

Longer = more killing, but more toxic

83
Q

Are disinfectants designed to be more or less potent than antiseptics? Why?

A

They are designed to be MORE potent bc they’re meant to be used on non-biological surfaces

84
Q

Why is a glass rod that is coated with nutrient broth bacteria not a good representation of what might be encountered in real-life settings, and hence not represent a disinfectant’t true effectiveness in the real-world?

A

Bc in the real-world, bacteria are usually present along with other organic matter (e.g. in feces, blood, etc.)

85
Q

Why does the Use-Dilution test used for disinfectants NOT mimic real-life conditions?

A

Bc we exposed the bacteria to disinfectants for a much longer duration than usual

86
Q

Define “oligodynamic action”

A

The ability of small amts of heavy metals to exert a lethal effect on bacteria

87
Q

Which metals are effective at inhibiting bacterial growth?

A

Zn and Ag

88
Q

Which metals are ineffective at inhibiting bacterial growth?

A

Fe, Mg, Cu, Pb

89
Q

Does oligodynamic action also apply to fungi or viruses? Why or why not?

A

Yes bc heavy metals act against proteins > viruses and fungi also have proteins that can be disrupted/denatured

90
Q

Resident flora are…

A

bacterial species that’re permanently colonized in or on some part of the body

91
Q

Transient flora are…

A

bacterial species that’re present for only hours or days in or on the body

92
Q

Why might washed hands have MORE bacteria than unwashed ones?

A

Warm water brings resident bacteria to the surface from the pores

93
Q

Are antimicrobial soaps or Isagel more effective at removing bacteria than reg soap?

A

They should be due to added chemicals being used

94
Q

Can our experiments that dealt with hand washing’s effects upon bacteria tell us anything about how effective these treatments might be against other microbes, such as fungi or viruses?

A

No

95
Q

How would increased time exposed to UV light affect bacteria?

A

It would be more lethal

96
Q

Which species of bacteria are more sensitive to UV?

Which are less sensitive? Why?

A

More sensitive: E.coli and Staph. aureus

Less sensitive:
Mycobacterium (due to its mycolic acid that prevents penetration of UV rays)
B. cereus (due to being a spore-forming bacterium)

97
Q

Why’s it necessary to remove the lid from the plate when exposing it to UV?

A

UV cannot pass through ordinary plastic or glass

98
Q

A solution that’s been passed through a bacterial filter is “sterile” (in quotes). What does this mean?

A

The solution is free from bacteria, but NOT from smaller organisms and viruses

99
Q

Describe an experiment, using only bacterial filters and nutrient agar plates, that would allow you to estimate the approximate size of a bacterial cell.

A
  1. Have different filters of diff sizes
  2. Filter bacteria through each of them
  3. Plate each of the filtrates
  4. If there’s no growth, then we would conclude that the bacteria are larger than the diameter of the particular filter used
100
Q

Predominant organisms in throat cultures?

A

Streptococcal species

101
Q

What’s the purpose of the “Catalase Test”?

A

To tell the difference b/w Staphylococcus and Streptococcus species of bacteria

102
Q

What are the 3 possible hemolysis rxns in blood agar? Describe each.

A
  1. alpha hemolysis: partial breakdown of RBCs in the agar > media turns greenish around the colonies
  2. beta hemolysis: complete breakdown of the RBCs > complete clearing of media around the colonies
  3. gamma hemolysis: no change/no rxn on the media
103
Q

Which species is catalase negative? Which species is catalase positive?

A

Catalase negative: Streptococcus species (no gas production)

Catalase positive: Staphylococcus species (gas production)

104
Q

Why would a gram stain not be useful for stool samples - why?

A

There’re thousands of bacterial species in feces > impossible to tell the diff b/w pathogenic and normal bacteria under a normal gram stain

105
Q

What type of stain is used on blood to visualize white blood cells? What’s it composed of?

A

Wright’s Giemsa stain

It’s made up of methylene blue (basic) and eosin (acidic)

106
Q

5 types of white blood cells?

A
  1. Basophils
  2. Eosinophils
  3. Monocytes
  4. Lymphocytes
  5. Neutrophils
107
Q

When observing the 5 diff types of white blood cells, some of them weren’t seen (or not seen as much). Why?

A

Some of the WBCs are lower in percentage in the blood compared to others

108
Q

Define serology

A

Study of antigen and antibody rxns in vitro

109
Q

Describe agglutination rxns

A

A rxn used to demonstrate an antibody-antigen interactions

It involves antibodies interacting w/ antigens, forming an immune complex consisting of many cells cross-linked to e/o by antibody molecules > eventually, this cross-linking is able to be seen w/ the naked eye

110
Q

Suppose you suspected that a pt had a Salmonella infection. How would you test for this?

A

Use an agglutination rxn by using the pt’s serum and anti-Salmonella antibodies

111
Q

Media most commonly used to isolate and grow fungi? What specific characteristics allow it to select for fungi?

A

Sabouraud’s agar

It has reduced pH (inhibits bacterial growth)
It has a high level of dextrose (a sugar that’s readily fermented by fungi)

112
Q

What dye is used for fungi?

A

Lactophenol cotton blue dye

113
Q

If a fungus w/ hyphae is observed, we’re dealing w/ a _____

A

mold

114
Q

If a fungus reproduces by budding, then it’s a _____.

A

yeast

MCIM 224 (25 decks)

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