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Lab Practicum, Micro 200, study guide

When you did your hand wash experiment, you decided a variable to test, say, hot vs cold water, you called this variable an “experimental variable” since it was the variable you were testing experimentally. In order to get meaningful data, you need to keep other things the same, for example the washing time had to be the same for both, you called the washing time a _Control_______ variable.

Through the semester, you have used two bacteria that produce colorful colonies: one produce yellow colonies, another one pink. What are the names of these two bacteria? Are they Gram+ or Gram-?

Micrococcus Luteus, yellow colonies, gram +

Serratia Marcescens, pink colonies, gram -

There was one bacterial species for which the colonies were waxy, thus you had to be very patient when making smears to do staining, what is the name of this bacteria?

Mycobacterium

Different types of agar plates are used to culture different types of microbes: What (microbes) is Sabourand agar used for? NA,TSA and Blood agar plates are all used to culture bacteria, but the costs are very different, when do you use the cheapest one (NA), the more expensive one (TSA), the most expensive one (Blood agar)?

Sabourand agar: fungus, collects bacteria from the air, selective medium.

NA: Bacteria in things (eg. table, floor, door knob)

TSA: Bacteria outside our bodies (hands, fingernails)

Blood agar: Bacteria inside our bodies ( throat, blood)

Plates are used according to bacterias natural habitat.

The temperature at which you incubate your plates is important, what temp would you incubate microbes harvested from your desk top? From your tongue?

Desk top: room temp, 25-30 celsius

Tongue: body temp, 37 celsius

What is a wet mount? What is a hanging drop? When do you do the former, when the later?

Wet mount: a drop of bacteria covered with a plastic slip to observe the shape of the bacteria (no staining)

Hanging drop: observes motility of bacteria.

Different types of microscope are used for different purposes, what microscope is used to observe the motility of bacteria? Which to observe the cell membrane/nuclear membrane of a cell (microbe)?

Dark field: Motility

Electron Microscope: cell membrane and nuclear membrane.

On each lens of your microscope, there is a # showing the magnification power (4X, 10X, 40X, 100X), there is another # (_____numerical_____ aperture) you use to calculate the resolution power of that lens, do you know the difference between “magnification” and “resolution” power?

Magnification: Makes image bigger to see detail.

Resolution: Clarity of an object, resolution is more important than magnification.

You have learnt many staining techniques through the lab exercises: What dye did you use in simple stain? Crystal Violet
What dyes did you used in Gram stain? Crystal violet, gram’s iodine, and safranin violet.

Why did you have to heat up the slide when you did the acid fast stain and the spore stain?

To open the spores and allow the dye to enter and stain. Once cooled down the spores closed trapping the dye inside.

What color is a “+” in acid fast stain? Which bacteria are “+” for acid fast stain? What color is a “+” in spore stain? Which bacteria are “+” for acid fast stain?

green, Mycobacterium

purple/red, Bacillus

Why did you have to do “negative stain” to look at bacterial capsules? What is “negative stain”?

Negative stain: Staining of the background of the slide.

The bacterial capsule is not stain and the capsule appears as a halo.

In lab exercise #8, you were trying to determine the “generation time” (= doubling time) of a bacterial culture. Knowing the different phases of a bacterial culture, which phase the bacterial culture should be in when you did the experiment?

Lag phase, log phase, stationary phase, death phase.

Log phase

When you used all those paper pieces to...
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