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From Flashcardlet > Micro Lab Quiz 4 > Flashcards

Micro Lab Quiz 4 Flashcards

1
Q

What is MSA?

A

Mannitol Salt Agar

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2
Q

What is MSA selective for?

A

Salt tolerant and loving microbes

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3
Q

What is MSA differential for?

A

Determining members of the genes Staphylococcus

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4
Q

Which staph is nonpathogenic?

A

Staph epidermidis

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5
Q

Which staph is pathogenic?

A

Staph aureus

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6
Q

Which staph is a resident of skin flora?

A

Staph epidermidis

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7
Q

Which staph is a transient member of skin flora?

A

Staph aureus

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8
Q

What kind of environment does staph epidermidis prefer?

A

Dry, salty environments

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9
Q

What kind of environment does staph aureus prefer?

A

Moist, salty environments

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10
Q

What percentage of people always/never/sometimes carry Staph aureus?

A

Always and never = 20%

Sometimes = 60%

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11
Q

How does someone get a Staph aureus infection?

A

It starts as a skin infection as a pimple (infected hair follicle) which get deeper and wider, turning into a boil (the immune system walls off the infection). It continues to get bigger (carbuncle) until it spreads into the bloodstream causing sepsis.

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12
Q

What ingredients in MSA make the media selective?

A

7.5% NaCl - both species can grow in the salty environment

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13
Q

What ingredients in MSA make the media differential?

A 
Mannitol (fermentation of mannitol produces acid)
Phenol red (pH indicator)
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14
Q

What conclusions can be drawn from an MSA plate?

A

If the organism is positive for mannitol fermentation, the plate will turn yellow due to the acids being released by fermentation reacting with the phenol red pH indicator.

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15
Q

What did our MSA plate look like and why?

A

SA - yellow halo = ferments mannitol
SE - red plate = does not ferment mannitol
EC - did not grow = not salt tolerant

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16
Q

What two bacteria are used to produce yogurt?

A

Lactobacillus bulgaricus

Streptococcus thermophilus

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17
Q

What is the inoculum in the yogurt production?

A

A sample of yogurt (already contains the bacteria)

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18
Q

What do the two yogurt bacteria degrade and produce?

A

They degrade the milk sugar lactose into galactose and glucose

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19
Q

What happens to the glucose that is produced?

A

The glucose is fermented to lactic acid

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20
Q

What happens when lactic acid is present?

A

The pH decreases

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21
Q

What happens to the yogurt when the pH decreases?

A

The milk protein casein denatures in the acidic conditions, and the hydrophobic amino acids are exposed. These phobic regions clump together to protect themselves from aqueous solutions surrounding them, and are responsible for the semisolid consistency of yogurt

22
Q

What is the milk protein?

A

Casein

23
Q

Explain the whole process of yogurt production

A

Condensed milk is added to liquid milk and boiled. The milk is then cooled and the Lactobacillus bulgaricus and Streptococcus thermophilus are added from yogurt inoculum. These bacteria hydrolyze lactose into glucose and galactose. The glucose is then fermented to lactic acid, which lowers the pH of the solution and causes the milk protein casein to denature. When the protein denatures, its hydrophobic portions are exposed and therefore want to clump together, thus producing the consistency of yogurt.

24
Q

What happens to the galactose while glucose is being fermented?

A

It is not fully utilized and therefore gives the yogurt a hint of sweetness

25
Q

Once the yogurt is inoculated, where is it incubated?

A

In the walk in for 48 hours to allow optimal growth of the L. bulgaricus and S. thermophilus, and then the refridgerator to slow any growth of spoiling bacteria

26
Q

What does IMViC test for?

A

Indole production
Methyl red test (MR)
Voges Proskauer test (VP)
Citrate utilization

27
Q

Is E. coli positive or negative for IMViC?

A

++ - -

28
Q

Is Enterobacter aerogenes positive or negative for IMViC?

A
    • ++
29
Q

What does the indole experiment test for?

A

If the organism respires or ferments the amino acid tryptophan

30
Q

What is the reaction for indole?

A

Tryptophan –> fermentation or respiration –> indole

31
Q

What is the media used for indole production tests?

A

A tryptone (protein digest, source of tryptophan) broth

32
Q

What reagents are used for indole production tests?

A

To test for the presence of indole after incubation, add Kovac’s reagent (5 drops) and let it stand for 10 minutes

33
Q

What is the interpretation for the indole production test?

A

Red color at top = + (organism produces indole and therefore tryptophan was fermented or respired)
Green at top = - (organism does not produce indole)

34
Q

What do the MRVP experiments test for?

A

What pathway does the organism use to ferment glucose

35
Q

What are the two pathways the MRVP tests for?

A

Mixed acid fermentation pathway

2,3 butanediol fermentation pathway

36
Q

Which pathway does MR test for?

A

Mixed acid fermentation pathway

37
Q

Which pathway does VP test for?

A

2,3 butanediol fermentation pathway

38
Q

What is the waste product in the MR test?

A

Lots of acid producing a huge pH drop

39
Q

What is the waste product in the VP test?

A

Acetoin

40
Q

What is the key ingredient of the MRVP test?

A

Glucose

41
Q

What are the reagents for the MR test?

A

3 drops of methyl red

42
Q

What is the interpretation of the MR test?

A

Red test tube = + mixed acid fermentation

Yellow test tube = - mixed acid fermentation

43
Q

What are the reagents for the VP test?

A

15 drops of alpha naphthol

5 drops of potassium hydroxide (KOH)

44
Q

What is the interpretation of the VP test?

A

Upper phase red = + 2,3 butanediol pathway

Upper phase brown = - 2,3 butanediol pathway

45
Q

What does the citrate experiment test for?

A

Can the organism use citrate as its sole source of carbon

46
Q

What will the organism do if it can use citrate as its sole source of carbon?

A

It will use the only source of nitrogen in the medium (ammonium ion NH4) to grow

47
Q

What happens to the media if the organism uses the sole source of N?

A

The organism will convert ammonium (NH4) to ammonia (NH3) and the pH of the media will increase

48
Q

What are the three ingredient of the citrate test?

A 
Citrate (only carbon source)
Ammonium ion (NH4) (only nitrogen source)
pH indicator (bromothymol blue)
49
Q

What is the interpretation of the citrate test?

A

Tube changes to blue = rise in pH = organism can utilize citrate
Tube stays green = organism cannot utilize citrate

50
Q

What transport protein allows the organism to utilize citrate as its only carbon source?

A

Citrate permease

51
Q

What is happening if the tube turns blue?

A

The pH increased which means that ammonia was produced from an ammonium ion, which means that the organism must be growing, which means that the organism must be using the only carbon source, citrate!

From Flashcardlet (133 decks)

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