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Microbiology - Portage Learning > Test 4 > Flashcards

Test 4 Flashcards

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1
Q

True or False: Differential media is best suited for distinguishing between two similar species of bacteria.

A

True

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2
Q

A researcher is asked to determine which of two vials contains E coli and which contains salmonella. Knowing both are Gram-negative while only one of them is capable of fermenting lactose, which type of media would be best suited?

A

differential media

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3
Q

What are the requirements of a fastidious microbe?

A

Organism with complex growth requirements, if absent organism will not grow. Enriched media contain specific and essential nutrients for the growth of particular subset of microorganisms

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4
Q

True or False: LB agar is classified as a selective, non-differential media. Why?

A

False, LB agar is the most basic type of agar and supports growth of virtually all microbes without restriction. It contains universal nutrients (non-differential) and restrictive factors are absent (non-selective)

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5
Q

What is agar used for in microbiology?

A

Used to create a solid, smooth surface on which microbes can grow

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6
Q

Blood agar is which type of medium? Select all that apply.

A

Differential + enriched

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7
Q

What is blood agar used for?

A

Differentiate between species based on hemolytic activity

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8
Q

Describe activity of Alpha hemolysis

A

greenish-brown color

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9
Q

Describe activity of beta hemolysis

A

distinct zone of clearing

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10
Q

Describe activity of gamma hemolysis

A

no change

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11
Q

Columbia CNA agar is used to isolate:

A

CNA agar restricts Gram-Negative microbes therefore only Gram- Positive microbes will grow.

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12
Q

True or False: Chocolate (cocoa) is not a component of Chocolate agar plates. Why?

A

Name is derived simply based on color and actually comes from presence of ‘cooked’ (lysed) red blood cells in the media

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13
Q

An unknown microbe is streaked onto a MacConkey agar plate. After an overnight incubation at 37°C, growth is observed. Would a Gram stain be necessary? Why or why not?

A

No, gram stain is not necessary since only gram-negative microbes will grow on macConkey agar

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14
Q

In an attempt to detect the presence of the pathogenic strain of E. coli O157:H7, a researcher spread a culture onto a MacConkey agar with failed results. What type of agar should they (correctly) try next? Why?

A

Microbe should be plated on SMAC since it is specifically formulated to detect O157:H7 (pathogenic e. coli).

Pathogenic E. coli cannot ferment sorbitol while non-pathogenic e. coli can ferment both sorbitol and lactose.

Colonies that ferment can be differentiated from non-fermenters.

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15
Q

What is a colony that ferments?

A

acidic conditions, non-pathogenic

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16
Q

What is a non-fermenting colony?

A

neutral to basic conditions, pathogenic

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17
Q

In Eosin Methylene Blue (EMB) agar, what color indicates the presence of E. coli?

A

Metallic green

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18
Q

Mannitol salt agar will turn what color in the presence of the pathogenic strain Staphylococcus aureus?

A

Yellow, pathogenic staph aureus will turn the agar from red to yellow

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19
Q

What is the process of spreading a bacterial culture onto a petri dish called?

A

Plating

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20
Q

Describe the primary advantage of using a petri dish over growing a liquid culture?

A

Primary advantage is cells are held into place. When grown in liquid culture, bacterial cells can multiply but free to move around. When grown on agar within petri dish and fixed with ability to form colonies.

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21
Q

True or False: The visualization of colonies on a petri dish represents bacterial cells that have often multiplied a million times over.

A

True, visualization of bacterial colony means it must have multiplied by a number greater than a million

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22
Q

True or False. The purpose of a quadrant streak is to expand a bacterial population. Why?

A

False, purpose of the quadrant streak is to generate individual colonies such that a single (pure) bacterial sample can be isolated.

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23
Q

To be considered a pure culture, the sample (1) can be traced back to a single cell and (2)__________ ?

A

The sample must not contain external contaminants. Pure samples would never contain multiple bacterial species, i.e. strep and staph

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24
Q

A dilution gradient is formed when carrying out what generalize plating strategy?

A

Quadrant streak (Phase dilution)

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25
Q

In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4? Why?

A

P4, phases rank P1 (highest)>P2>P3>P4(lowest)

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26
Q

True or False. When performing a dilution streak a new (or sterilized) loop is not required for each phase as long as the bacterial culture is pure. Why?

A

False, a new or sterilized loop is absolutely required for each phase. By failing to do so would prevent the establishment of a dilution gradient, since same bacterial concentration would be spread across both phase regions, whether or not the culture is pure

27
Q

In order to encourage growth of a slow growing microbe what might a researcher do during a phase dilution streak?

A

Research can 1) perform only a 3-phase dilution streak or 2) pass the loop through the previous phase multiple times (as opposed to only once)

28
Q

True or False. To restrict the growth of a pathogenic microbe a researcher might decrease an incubator from 37°C to 25°C. Why?

A

True, Pathogenic strains of bacteria tend to grow faster than non- pathogenic strains at 37°C, so researchers may set incubators at 25°C to restrict its growth.

29
Q

When given an unknown bacterial sample the first step is to expand the current bacterial population. Which form of media best suites this need? Why?

  1. MSA agar
  2. LB media
  3. MacConkey agar
  4. Columbia CNA agar
A

LB Media, since all other options are forms of selective media, meaning they may inhibit growth of unknown sample. Culture should first be expanded and then place onto selective/differential agar plates

30
Q

What type of media are MSA agar, MacConkey agar and Columbia CNA agar?

A

Selective media

31
Q

What is plating? What can you use?

A

Process of spreading a bacterial culture onto a petri dish filled with agar

sterile loop, sterile swab or sterilized wire loop in a back and forth motion

32
Q

What is a quadrant streak? What is it used for?

A

A phase-dilution approach used to generate an individual colony so that a single/pure bacterial sample can be picked from the plate

Used to isolate a microbe on an agar plate

33
Q

What is another name for a liquid growth media, and what are the basic components?

A

Alternate Name: Nutrient broth

Basic Components: sugars, amino acids, vitamins

34
Q

What does a nutrient broth provide?

A

Provides microbe with source of carbon/energy, encouraging expansion

35
Q

What is selective media?

A

Allows for only the growth of certain microbes while restricting the growth of all others

36
Q

What is differential media?

A

Used to distinguish between two (or more) related microbes

37
Q

What is agar?

A

In its simplest form agar is liquid growth media that has had a hardening agent added to it.

38
Q

How is agar created?

A

When a polysaccharide derived from seaweed (algae) extract is added to growth media.

39
Q

What is agar used for?

A

Used to create a solid, smooth surface for microbes to grow

40
Q

What is beta hemolysis?

A

Classified as the capacity of a microbe to completely lyse red blood cells.

Zone clearing

41
Q

What is gamma hemolysis?

A

Designates the absence or lack of hemolytic activity and resulting colonies are white or tan growing on red background color unaffected blood agar

42
Q

Why are alpha hemolysis colonies greenish-brown?

A

Present greenish-brown due to incomplete lysis of red blood cells

43
Q

What is the primary purpose of Columbia CNA agar?

A

Suppresses growth of gram-negative bacteria and used to isolate gram-positive microbes

44
Q

Name the type of plate derived from BAP that contains lysed red blood cells.

A

Primary component in formulation of chocolate agar

45
Q

Define the selective and differential abilities of a MacConkey agar plate.

A

MacConkey agar is both selective and differential

Selective Abilities: gram negative microbes will grow on agar - gram-positive do not.

Differential: Distinguishes between microbes capable of fermenting lactose (red colonies) and non-fermenters (white/tan colonies)

46
Q

What colors would you expect to see on an EMB plate containing E. coli?

A

The plate is red in color when E. coli ps present, but new colonies will become a metallic green shade.

47
Q

In a three-phase dilution gradient, which phase most likely contains individual colonies: phase 1 (P1) or phase 3 (P3)?

A

More likely to appear in Phase 3.

48
Q

Is it possible to see individual colonies in P2?

A

Only if small portion of P1 was carried over into P2

49
Q

A researcher is asked to determine if a sample contains Neisseria meningitides. Knowing Neisseria meningitides is slow growing and other foreign microbes may also be present in the culture, which type of media would be best suited?

A

Selective

50
Q

The polysaccharide-based hardening agent added to LB media to produce LB agar is derived from what

A

seaweed extract

51
Q

Columbia CNA agar is used to isolate

A

gram positive

52
Q

Columbia CNA agar is most closely related to which media

A

blood agar

53
Q

An unknown microbe is streaked onto a MacConkey agar plate. After an overnight incubation at 37 C growth is observed. Would a Gram stain be necessary? Why or why not ?

A

No, only gram negative microbes will grow on a MacConkey agar

54
Q

In Eosin Methylene Blue agar, what color indicates the presence of E. coli?

A

metallic green

55
Q

Mannitol salt agar will turn what color in the presence of the pathogenic strain staphylococcus aureus?

A

yellow

56
Q

Which type of agar media is best suited to support the growth of Staphylococcus

A

mannitol salt agar

57
Q

In order to visual individual colonies of bacteria would you culture your sample in a liquid media or a solid agar media?

A

solid agar media, because cells are held into place

58
Q

T/F: The purpose of a quadrant streak is to produce individual colonies of a bacterial population

A

True

59
Q

To be considered a pure culture, the sample (1) can be traced back to a single cell and (2)

A

free of contaminants

60
Q

When performing a quadrant streak, the sample is spread across the plate in such a way to form what?

A

dilution gradient

61
Q

When performing a dilution streak a new (or sterilized) loop is not required for each phase as long as the bacterial culture is pure

A

False

62
Q

The number of phases (3 vs. 4) and/or the number of times a loop passes through a previous phase (once vs. multiple times) is acceptable provided what happens

A

Growth of individual colonies is present within the resulting gradient, if that is not provided the experiment must be repeated

63
Q

Pathogenic strains of bacteria tend to grow slower than normal nonpathogenic bacterial strains

A

False

Microbiology - Portage Learning (7 decks)

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