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1. Laboratory - Microbiology and Immunology > Microbial Growth > Flashcards

Microbial Growth Flashcards

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Biology 101 flashcards
1
Q

What are most medias based of and why?

2

A

Most growth medias are based on extracts or digests of animal tissues or plant tissues

These are used because they offer the required nutrients to support the growth of bacteria

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2
Q

Describe the range in different requirements needed for different types of microorganisms.

A

Some organisms may only need a carbon source to grow while others might need factors such as vitamins, purines, pyrimidines, specific amino acids etc

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3
Q

What are fastidious organisms?

A

Organisms that require a wide range of factors to grow

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4
Q

What is the name given to organisms that need a wide range of factors to grow?

A

Fastidious organisms

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5
Q

Give an example of some factors fastidious organisms might need to grow.

A

Vitamins
Specific amino acids
Purines
Pyrimidines

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6
Q

What are the main ingredients of general-purpose media?

5

A

Water

Protein derivatives

Yeast extract

Gelling agent

Buffers

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7
Q

Give some examples of what might be part of the growth derivatives used in general-purpose media.
(4)

A

Amino acids

Salts

Minerals

Growth factors

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8
Q

What is found in yeast extract?

A

A wide range of amino acids, carbohydrates, minerals and growth factors

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9
Q

What is the gelling agent found in all medias?

A

Agar

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10
Q

Why is agar used in medias?

A

It creates a solid media and supports the growth of single colonies

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11
Q

List the different types of media.

A

Enrichment media

Selective media

Differential media

Selective and Differential Media (combined)

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12
Q

What are enrichment medias?

A

Medias used to encourage the growth of a desired microbe in a mixed culture

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13
Q

Give two examples of enrichment agars.

A

Charcoal agars

Blood agars

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14
Q

Why is blood agar used often?

A

It improves the growth of a range of fastidious organisms and allows some bacteria to demonstrate haemolysis

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15
Q

What are selective medias?

A

This is where selective antibiotics or chemical inhibitors are added to general purpose agar to inhibit the growth of undesirable microbes while still allowing the growth of the desired microbe

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16
Q

What are differential medias?

A

Medias which are used to show differences among the microbes that grow on it

17
Q

What are selective and differential medias?

A

These are differential medias which incorporate selective agents and

18
Q

What is Mannitol Salt agar selective for?

A

It is selective for members of the genus staphylococcus

19
Q

How is mannitol salt agar selective for members of the genus staphylococcus?

A

This is due to the high concentration of SALT (7.5%), only staphylococcus can tolerate high saline levels like these

20
Q

What is mannitol salt agar differential for?

A

It is differential for staphylococci spps

21
Q

How is mannitol salt agar differential for staphylococci spps?
(2)

A

This is due to the sugar mannitol and the pH indicator phenol red

If an organism can ferment manitol than an acid by-product is formed which will cause the phenol red in the agar to turn yellow

22
Q

Give an example of a staphylococci that will ferment manitol.

A

Staphylococcus aureus

23
Q

What is the general rule of thumb when it comes to staphylococci and mannitol?

A

Most pathogenic staphylococci will ferment mannitol and most non-pathogenic staphylococci will not ferment mannitol

24
Q

What is MacConkey Agar selective and differential for?

A

Gram negative bacilli

25
Q

How does MacConkey Agar isolate and differentiate gram negative bacilli>

A

This is done based on thier ability to ferment lactose

26
Q

What is the selective agents in MacConkey Agar?

A

Bile salts and crystal violet

27
Q

Explain how MacConkey Agar is selective for gram negative bacilli.

A

The bile salts and crystal violet suppress the growth of most gram positive organisms

28
Q

What is the differential agent in MacConkey agar?

A

Lactose and neutral red indicator

29
Q

How does MacConkey differentiate bacteria?

3

A

The lactose present provides a source of fermentable carbohydrate and the neutral red indicator changes colour based on pH

Lactose fermenters produce an acidic environment, the neutral red indicator turns red due to the low pH, red colonies and culture result

Non-lactose fermenters will remain colourless as well as the media

30
Q

What indicator is used in Mannitol salt agar?

A

Phenol red

31
Q

What indicator is used in MacConkey agar?

A

Neutral red

1. Laboratory - Microbiology and Immunology (8 decks)

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