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introduction to microbiology > Microscopy, Culturing, and Counting (Lab) > Flashcards

Microscopy, Culturing, and Counting (Lab) Flashcards

1
Q

What is resolution?

A

The ability to distinguish separate objects as actually being separate

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2
Q

How do you improve resolution?

A

Use a smaller wavelength

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3
Q

Are smaller or larger resolutions better?

A

Smaller

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4
Q

Why do we use oil immersion?

A

Causes the light to travel in a straight path instead of being refracted by the air, which causes more light to enter the objective

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5
Q

Why do we use Koehler illumination?

A

Provides the best possible image by setting up the light path correctly

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6
Q

What are the 2 purposes of aseptic technique?

A

To protect yourself and the environment from your experiment
To protect your experiment from yourself and the environment

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7
Q

What are 5 ways to do aseptic technique?

A
  1. Wash your hands
  2. Ethanol the bench
  3. Keep lids on
  4. Don’t put lids down on contaminated surfaces
  5. Flame culture tubes
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8
Q

Why do we streak plates for single colonies?

A

Allows us to purify colonies to get a culture of genetically identical cells

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9
Q

What are 2 ways to sterilize stuff?

A

Dry heat: flaming with bunsen burners

Moist heat: autoclave - high pressure and heat

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10
Q

Which method of sterilization can kill endospores? Dry heat or moist heat?

A

Moist heat (the autoclave)

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11
Q

Are plates labelled on the lid or the bottom?

A

Bottom. Labelling on the lid would become difficult if the lids accidentally became switched

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12
Q

Why do we do serial dilutions?

A

Determine the appropriate dilution that gives between 30-300 colonies when plated, then using that to calculate the original cell density

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13
Q

Why would we use a pure liquid culture over a pure culture on an agar plate?

A

Much easier to get DNA or proteins out of a cell suspension than a plate

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14
Q

What are the 6 different types of medium?

A
  1. Defined
  2. Minimal
  3. Complex
  4. Enriched
  5. Selective
  6. Differential
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15
Q

What is defined medium?

A

We know the exact nutrient composition of both organic and inorganic compounds

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16
Q

What is minimal medium?

A

A specific type of defined medium where only prototrophic cells can grow. Contains inorganic salts, ions, and a carbon source. Everything else needs to be synthesized de novo by the cells

17
Q

What is complex medium?

A

Highly nutritious medium full of organic and inorganic energy sources made from a digest of plant, animal, or microbial products (Casein, soy, yeast, beef). Don’t know the exact nutrient composition

18
Q

What is enriched medium?

A

Complex medium + a few other things like blood or serum that supports the growth of fastidious microorganisms

19
Q

What is selective medium?

A

Medium that only allows the growth of certain microorganisms

20
Q

What is differential medium?

A

Complex medium containing some sort of dye that will allow different properties to be distinguished

21
Q

Why is all growth medium somewhat selective?

A

No medium will support the growth of every single bacterial species

22
Q

What are endospores?

A

A differentiated dormant cell type produced by some species that are resistant to desiccation, radiation, heat

23
Q

How do you break the dormancy on an endospore?

A

High heat treatment

24
Q

What are total cell counts?

A

All cells are counted, whether alive, dead, or dormant

25
Q

What are viable cell counts?

A

Only cells that are alive and capable of forming colonies are counted

26
Q

What are 3 direct ways to get a total cell count?

A
  1. Microscopy to look at the cells
  2. Hemocytometer without methylene blue
  3. Petroff-Hausser counter
27
Q

What are 3 indirect ways to get a total cell count?

A
  1. Turbidity measurements with OD
  2. Dry weight
  3. Measurements of cell components (ex. DNA)
28
Q

What is the direct way to get a viable cell count?

A

Hemocytometer with methylene blue

29
Q

What are 2 indirect ways to get a viable cell count?

A
  1. Serial dilution and plate count

2. Measurement of incorporation of an indicator molecule

30
Q

How do you calculate the original viable cell concentration from a plate count? What are the units?

A

Average # of colonies on a plate/dilution factor x volume of dilution plated
Units are CFU/ml

31
Q

Why can plate counts sometimes be inaccurate?

A

One colony didn’t necessarily stem from 1 cell. Lots of bacteria show clumping, and it is impossible to distinguish different colonies

32
Q

Why does the methylene blue dye stain alive and dead cells differently?

A

Dead cells have compromised membranes, so the dye can get in

33
Q

How do you get a viable cell count from a hemocytometer?

A

of alive cells - # of dead cells/# of total cells

introduction to microbiology (18 decks)

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