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microbiology lab > Week 2 Labs > Flashcards

Week 2 Labs Flashcards

1
Q

What is a macronutrient? Give an example. How might a cell use macronutrients?

A

Nutrients needed in larger quantities like amino acids. They are broken down into smaller parts to provide energy.

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2
Q

What is a micronutrient? What are some ways a cell uses micronutrients?

A

Vitamins and minnerals needed in very small amounts. Used as coenzymes and cofactors of enzymatic reactions.

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3
Q

What is a growth factor? Give example.

A

Organic compounds required for cell growth like vitamins.

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4
Q

What are the two main purposes of the media used in a microbiology lab?

A

Facilitate growth of microorganisms and aid identification.

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5
Q

What is complex media? Defined media? How are they similar and how are they different.

A

Complex media contains nutrients in unknown quantities. Defined media contained specific chemicals in known consecrations. Similar in that they both contain nutrients needed for microorganisms to grow, different in the specific composition of those nutrients.

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6
Q

Selective Media

A

Supports the growth of some types of microorganisms while purposefully suppressing the growth of other types.

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7
Q

Differential media

A

Allow one to visually differentiate between multiple species growing on the medium.

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8
Q

Tryptic soy agar (TSA)

A

general-purpose agar capable of supporting the growth of a wide range of bacteria. It is neither selective nor differential.

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9
Q

Glucose mineral salts (GMS/GSA)

A

Defined medium containing glucose as the only carbon and energy source. Also called a minimal medium. Not differential, selective for organisms able to synthesize all their organic molecules from glucose.

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10
Q

Bacillus subtilis

A

Gram-positive rod incapable of fermenting lactose. This bacterium requires no growth factors.

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11
Q

Enterobacter aerogenes (or Klebsiella aerogenes)

A

Gram-negative rod capable of fermenting lactose. This bacterium requires no growth factors

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12
Q

Escherichia coli

A

Gram-negative rod capable of fermenting lactose. This bacterium requires no growth factors

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13
Q

Pseudomonas aeruginosa

A

Gram-negative rod incapable of fermenting lactose. This bacterium requires no growth factors.

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14
Q

Staphylococcus aureus

A

is a salt-tolerant Gram-positive coccus capable of fermenting lactose. This bacterium requires certain organic growth factors in its medium.

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15
Q

Staphylococcus epidermidis

A

is a salt-tolerant Gram-negative coccus capable of fermenting lactose. This bacterium requires certain organic growth factors in its medium.

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16
Q

What can grow on TSA?

A

It contains all the nutrients needed so anything can grow.

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17
Q

What can grow on GMS/GSA?

A

Selective for organisms that can synthesize their own organic molecules from glucose. Organisms that require no growth factor. Think of it as can they work with just glucose and make due with that? If yes then they can grow on this.

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18
Q

Mannitol salt agar (MSA)

A

Selective and differential. selective for salt-tolerant organisms that can live in media with a 6.5% NaCl concentration. Most species die in this media as water is removed from their cells through osmosis.

Organisms capable of using mannitol as a food source will produce acidic byproducts of fermentation that will lower the pH of the media. The acidity of the media will cause the pH indicator, phenol red, to turn yellow.

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19
Q

Salt (NaCl) concentration of most media?

A

0.5%

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20
Q

What can grow on MSA?

A

Salt tolerant species. Gram positive spaces will also change the color to yellow.

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21
Q

Which of these three types of media are complex? Which are synthetic? How do you know?
TSA
GMS/GSA
MSA

A

Complex- TSA
Synthetic- GMS/GSA and MSA
Defined= synthetic
Complex= non- synthetic

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22
Q

Why might a bacteria species be unable to grow on GMS media?

A

Because it needs a growth factor. Bacteria unable to synthesis their organic molecules from glucose will not grow.

23
Q

Why might a bacterial species be unable to grow on MSA media?

A

Because they are not salt-tolerant. MSA has a high NaCl concentration and most speices dye from water loss.

24
Q

Why is MSA media red? What is the importance of this chemical.

A

Its red because it is a differential media. Bacteria able to ferment the mannitol in the agar will produce acid waste changing the color from red to yellow.

25
Q

If a particular bacterium does not form clonies on MSA, does that mean it cannot ferment mannitol?

A

No, it means it’s not salt tolerant.

26
Q

Why can different bacterial species look different when growing on MSA media?

A

Organisms capable of using mannitol as a food source will produce acidic byproducts of fermentation that will lower the pH of the media. The acidity of the media will cause the pH indicator, phenol red, to turn yellow.

27
Q

What is a complex medium? What is a defined medium? How do they Differ?

A

Complex contains a wide range of nutrients in unspecified concentrations. Defined contains specific concentrations of specific nutrients.They differ in concentration of the nutrients they contain?

28
Q

What is selective medium? Give an example of an ingredient that could make a medium selective.

A

Selective mediums promote the growth some types of organisms while suppressing the growth of others. High salt concentration is a ingredient that could be added.

29
Q

What is a differential medium? Give and example of an ingredient that could make a medium differential.

A

Differential mediums have some sort of indicator that helps identify microorganism. Mannitol (sugar) can be added to a medium to promote color change.

30
Q

Are all types of media either differential or selective?

A

No, they can be both, neither, one or the other.

31
Q

Can a single media be both differential and selective?

A

Yes, they can have specific nutrient compositions and also a indicator present.

32
Q

Eosin methylene blue (EMB)

A

Selective and differential. Gram-positive bacteria growth is inhibited so only Gram-negative grows. Organisms able to ferment lactose produce a color change.

33
Q

Which of the bacteria below grow on EMB?
Bacillus subtilis
Enterobacter aerogenes
Escherichia coli
Pseudomonas aeruginosa
Staphylococcus aureus
Staphylococcus epidermidis

A

Enterobacter aerogenes
Escherichia coli
Pseudomonas aeruginosa
Staphylococcus epidermidis?

34
Q

MacConkey Agar (MAC)

A

Both selective and differential. Gram positive spaces are inhibited. Lactose-fermenting bacterial colonies turn red/pink.

35
Q

Phenylethyl alcohol agar (PEA)

A

Selective, supresses growth of gram-negative bacteria. Not differential. Light growth of gram-negative bacteria my be observed.

36
Q

Which of the media below is complex? Which are synthetic, how do you know?
Eosin methylene blue (EMB)
MacConkey Agar (MAC)
Phenylethyl alcohol agar (PEA)

A

Complex-
Synthetic- PEA, MAC, EMB
Defined= synthetic
Complex= non- synthetic

37
Q

Why did we test TSA, after already having tested it in the media 1 Lab?

A

Because it is a control, all bacteria being tested should grow on this medium.

38
Q

Is eosin methylene blue (EMB) selective, differential, both?

A

Both. Selective to inhibit gram-positive growth, lactose fermentation causes a color change.

39
Q

Is Macconkey Agar (MAC) selective, differential, both?

A

Both, selective to inhibit gram-positive growth. lactose fermentation causes color change.

40
Q

Is Phenylethyl alchol agar (PEA) selective, differential, both?

A

Selective to suppress the growth of gram-negative. Not differential.

41
Q

Why is MAC agar red? What is the importance of the chemical?

A

It turns red in the presence of lactose fermentation by the bacteria. The red color is a result of pH drop in the presence of acid fermentation products.

42
Q

What is the purpose of pour plates and loop dilution?

A

To separate different members of a mixed sample.

43
Q

Why is it necessary to briefly cool the melted agar deep prior to inoculation?

A

Because if it is too hot it will kill the bacteria.

44
Q

How will you be able to distinguish between Escheribia coli and Serratia marscesns colonies following incubation?

A

Serratia marscesns is red while Escheribia coli is white.

45
Q

If you had a mixed sample and wished to produce pure cultures, which method would you chose: streak for isolation or loop dilution pour plate? Why?

A

Streak for isolation, uses less resorces and only need one plate.

46
Q

What is a bacterial colony?

A

Isolated masses of bacterial groups.

47
Q

What is the goal of streaking for isolation and why is this procedure critical to identifying a bacteria species?

A

The goal is to isolate bacterial colonies for identification.

48
Q

How are streaking plates incubated, augar side up or down? Why?

A

Augar side up (plate is upside down). Done so that condensation does not drip on the plate.

49
Q

Colony characteristics can also be described in terms of the following?

A

Shape, margin, elevation, size.

50
Q

What are the possible sources of contamination that may occur during the streak plate procedure?

A

Not sanitizing the loop properly. media not proper autoclave. Touching the media with anything but the loop.

51
Q

Why must plates be incubated upside down?

A

to avoid condensation dripping onto the inoculated augar.

52
Q

Why is it incorrect to say that the size of an individual colony can be influenced by the size of the inocum?

A
53
Q

What factors do influence the eventual size of a bacterial colony?

A

temperature, pH, oxygen availability, and types of nutrient available.

54
Q

Assume your streak plate contains isolate colonies of both species of bacteria used in this exercise. What steps could you take to efficiently produce two pure broth cultures.

A

microbiology lab (7 decks)

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