Microbiology lab quiz 2

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quizes

What are the three main types (in terms of their physical forms) of microbiological culture media?

a) liquid/broth
b) semi-solid (gel like)
c) solid

Define culture medium

composed of known amounts of pure chemicals

Define defined or synthetic medium.

composed of complex materials that are rich in vitamins and nutrients

Define complex or non-synthetic medium

composed of known amounts of pure chemicals

Why are culture media sterilized before use?

To make sure the surface is free of all forms of life.

Why is culture medium cooled to about 48 to 50 degrees Celsius before it is poured into petri plates?

to minimize the amount of condensation

What is the source of carbon in the chemically defined medium in table 13.1?
The source of nitrogen?

Carbon-glucose
N2-ammonium sulfate

When is a negative stain used?

when the bacteria doesn't stain well or when it is desirable to confirm observations made on the shape and size of bacteria, also good for viewing capsules.

Name three stains that can be used for negative staining.

nigrosin, india ink,eosin

Why do the bacteria remain unstained in the negative staining procedure?

due to repulsion between the negative charge of the stains and the negatively charged bacterial wall. Instead , these stains either produce a deposit around the bacteria or produce a dark background so that the bacteria appear as unstained cells with a clear area around them. ex. chaulk outline

What is an advantage of negative staining?

you can see the capsules

Why is negative staining also called either direct or background staining?

because the stain goes around the organism like a chalk outline

When streaking with the second slide, why must it be held at a 45 degree angle?

So the bacteria-nigrosin solution spreads over the bacteria

What are the two purposes of heat fixation?

a) to adhere the organism to the slide
b) to kill the organism without serious distortion of the cell structure

What is the purpose of simple staining?

when information about cell shape, size, and arrangement is desired.

Why are basic dyes more successful in staining bacteria than acidic dyes?

they bind to bacterial cells by ionic interactions.

Name three basic stains

Crystal violet, carbolfuchsin, methylene blue

Why is time an important factor in simple staining?

because it can produce a false reaction also you don't want to over/under stain

How would you define a properly prepared bacterial stain?

Is a dried preparation of bacterial cells on a glass slide.
1) The bacteria is evenly spread out on the slide in such a concentration that they are adequately seporated from from each other.
2) The bacteria is not washed off the slide during staining.
3) Bacterial form is not distorted.

Why should you use an inoculating needle when making smears from a solid media? An inoculating loop for liquid media?

To control how much microorganism you put on the slide/

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