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MICR 262 > (Lab 2) Biochemical Tests > Flashcards

(Lab 2) Biochemical Tests Flashcards

1
Q

What biochemical test is shown?

A

Mannitol Salt Agar (MSA)

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2
Q

What is the purpose of MSA?

A
  • detect if an organism is halotolerant
  • detect if an organism can ferment mannitol
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3
Q

What are the ingredients in MSA?

A

Selective ingredients: 7.5% salt concentration (inhibits non-halotolerant organisms)

Differential ingredients: mannitol (for fermentation)

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4
Q

Does MSA use a reagent or a pH indicator? Describe it

A

Phenol Red pH indicator:
- yellow (acidic)
- red/orange (neutral)
- pink (alkaline)

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5
Q

What are the possible results in a MSA plate?

A

No growth: non-halotolerant

Growth: halotolerant

yellow growth: ferment mannitol

pink growth: use of proteins instead of mannitol

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6
Q

What biochemical test is shown?

A

Eosin Methylene Blue Agar (EMB)

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7
Q

What is the purpose of an EMB plate?

A
  • Selects for G- species
  • differentiates organisms that can ferment lactose
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8
Q

What ingredients are in an EMB plate?

A

Selective ingredients: Eosin and Methylene blue (inhibit G+ growth)

Differential ingredients: Lactose [differentiate coliforms (G-lactose fermenters) from non-coliforms]
Eosin (pH indicator. combines with color of methylene blue to produce results)

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9
Q

Does EMB use a reagent or pH indicator? Describe it.

A

pH indicator: Eosin:
- metallic green: very acidic (coliforms)
- dark purple: acidic
- pink: neutral/alkaline

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10
Q

What are the possible results in an EMB plate?

A
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11
Q

What biochemical test is shown?

A

Phenylethanol Agar (PEA)

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12
Q

What is the purpose of PEA?

A

Selects for G+ bacteria

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13
Q

What ingredients are in a PEA plate?

A

selective ingredients: phenylethanol

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14
Q

Does PEA use a pH indicator or a reagent? Describe it.

A

Neither. Indication is based on growth

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15
Q

What are the possible results for a PEA test?

A

Strong growth: Probably G+

Weak growth: Probably G-

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16
Q

What bacteria is PEA good for identifying?

A

G+ Staphylococcus and Streptococcus

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17
Q

What biochemical test is pictured?

A

Fluid Thioglycolate Broth

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18
Q

What is the purpose of FTB?

A

Determine the specific O2 requirements of different bacterial species

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19
Q

What ingredients are in FTB? Describe them.

A

Thioglycolate: bind O2

Resazurin: O2 indicator
- pink: O2 present
- clear - O2 absent

Gelatin: slows diffusion of O2 into media

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20
Q

What are obligate aerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage?

A
  • Use aerobic respiration only
  • contain both Superoxide dismutase and catalase
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21
Q

What are facultative anaerobes? What is their appearance in Thioglycolate broth? What enzymes do they have against oxidative damage? Provide an example.

A
  • use aerobic respiration if O2 available and anaerobic pathways if not
  • contain both Superoxide dismutase and catalase
  • majority of bacteria
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22
Q

What are aerotolerant anaerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage?

A
  • do not use O2 but can survive if present
  • contains only Superoxide dismutase
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23
Q

What are microaerophiles? How do they appear in Thioglycolate broth? What enzymes do they have against oxidative damage? Provide an example.

A
  • use aerobic respiration, but require low O2 concentration, ~ 1%
  • contains both Superoxide dismutase and catalase at low concentration
  • Neisseria gonorrhoeae
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24
Q

What are obligate anaerobes? What is their appearance in Thioglycolate broth? What enzymes do they have against oxidative damage? Provide an example.

A
  • do not use aerobic respiration. O2 is toxic
  • contains no enzyme against oxidative stress
  • Clostridium difficil
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25
Q

What biochemical test is pictured?

A

Starch agar (non-selective)

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26
Q

What is the purpose of a starch agar plate?

A

Determine if a bacteria has the enzyme amylase to digest carbohydrates

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27
Q

Does starch agar use a pH indicator or a reagent?

A

Reagent: Iodine

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28
Q

What are the possible results with a starch agar?

A

Black: Iodine + starch

clear: iodine + glucose

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29
Q

What biochemical test is pictured?

A

Skim milk agar

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30
Q

What is the purpose of the skim milk agar?

A

Determine if an organism contains contains casease to digest casein protein into amino acids

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31
Q

What are the possible results for skim milk agar?

A

Clear halo: has casease
no halo: no casease

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32
Q

What biochemical test is pictured?

A

gelatin deep

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33
Q

What is the purpose of a gelatin deep?

A

determine if an organism produces the exoenzyme gelatinase

34
Q

What are the possible results for gelatin deep?

A

Solid: negative
liquid: positive

35
Q

What biochemical test is pictured?

A

Oxidase test

36
Q

What is the purpose of the oxidase test?

A

detect a specific cytochrome oxidase found in the electron transport chain of some bacteria

37
Q

What is significant info for Enterobacteriaceae and oxidase test?

A

They are all oxidase negative

38
Q

Does the oxidase test use a reagent or a pH indicator? Describe it

A

Reagent: Oxidase reagent by cytochrome oxidase

39
Q

What precautions are taken to prevent a false positive in the oxidase test?

A
  1. do not use metal
  2. look at results within 30 seconds
  3. do not pick up agar
40
Q

What are the possible results you could see for the oxidase test?

A

Positive: purple/blue
negative: no color

41
Q

What biochemical test is pictured?

A

catalase test

42
Q

What is the purpose of the catalase test?

A

Looking for the presence of catalase in certain bacteria

43
Q

What category of bacteria contain catalase?

A

Most aerobic and facultative anaerobic bacteria

44
Q

What are the possible results you can see in the catalase test?

A

gas bubbles: positive
no bubbles: negative

45
Q

What is the catalase test able to distinguish best?

A

Distinguish between hemolytic G+ Enterococcus (neg), Streptococcus (neg), and Staphylococcus (pos)

46
Q

What biochemical test is pictured?

A

Carbohydrate fermentation test

47
Q

What is the purpose of a carbohydrate fermentation test?

A

determine if a microbe can ferment a specific sugar

48
Q

What are the ingredients are in the carbohydrate fermentation test?

A
  • 1 sugar (glucose, lactose, or mannitol)
  • Phenol red pH indicator
  • durham tube for gas collection
49
Q

Does the carbohydrate fermentation tube use a pH indicator or reagent?

A

pH indicator: Phenol red
- yellow: pH~6
- red/orange: pH~7
- pink: pH~8

50
Q

What are the possible results you can see with the carbohydrate fermentation tube?

A

Yellow: positive (+A/+AG)
- sugar fermentation with or without gas

Orange/red: negative (-)
- no sugar fermentation

pink: negative (-alk)
- no sugar fermentation
- protein digestion

51
Q

What biochemical test is pictured? What is its purpose?

A

IMViC: Indole test
- to determine whether bacteria can break down tryptophan. Produces indole as a by-product

52
Q

Does indole use a pH indicator or a reagent?

A

No pH because ammonia and pyruvate neutralize.
Reagent: Kovac’s reagent

  • Kovac’s reagent=yellow
  • Kovac’s reagent + indole=red
53
Q

What are the possible results with indole?

A

Red: positive
Yellow: negative

54
Q

Why is IMViC an important ID procedure after Gram stain?

A

Differentiates between members of Enterobacteriaceae

55
Q

What biochemical test is pictured? What is its purpose?

A

Methyl Red, Vogues-Proskauer (MRVP)

determine whether bacteria ferment glucose into mixed acids (MR) or acetoin (VP) (mutually exclusive)

56
Q

Does MR use a pH indicator or a reagent?

A

pH indicator: Methyl red

57
Q

What results can you expect with an MR test?

A

Red (pH ≤ 4) - MR+
No color (pH > 4) - MR-

58
Q

Does VP use a pH indicator or a reagent?

A

Reagent: Barritt’s reagent A & B

59
Q

What results can you expect with a VP test?

A

Reagents alone produce copper color

Reagents turn red in the presence of acetoin

60
Q

How long does MRVP broth need to incubate? Why?

A

48 hours because acetoin is produced within that time for non-acidic fermentation. Less than that, it can give a false negative since acids will be produced first

61
Q

What biochemical test is pictured? What is its purpose?

A

Citrate test: Determine if bacteria can use citrate as a sole carbon source. Organisms won’t grow if they can’t use citrate.

If organism grows it uses protein in media to produce alkaline substances

62
Q

Does the citrate test use a pH indicator or a reagent?

A

pH indicator: Bromothymol Blue

63
Q

What results can you expect with a citrate test?

A

Blue tube (alkaline pH) OR any growth: positive

Green tube and no growth (neutral pH): negative

64
Q

What biochemical test is pictured? What is its purpose?

A

Hydrogen sulfide test - test if an organism can produce H2S from cysteine (sulfur-containing amino acid)

Cysteine desulfurase

65
Q

What media is used for the H2S test? What are its ingredients?

A

Peptone iron deep
- peptone: Source of cysteine
- iron: Binds to H2S to visualize results

66
Q

Why is a deep used for H2S test?

A

To simulate anaerobic conditions

67
Q

Does H2S test use a reagent or a pH indicator? Why?

A

Reagent: iron

Pyruvate (acidic) and NH3 (basic) produced from the breakdown of cysteine neutralize each other

68
Q

What biochemical test is pictured? What is its purpose?

A

Urease test: determine if bacteria can hydrolyze urea (urease)

69
Q

What media is used for Urease test? What are the ingredients?

A

Urea slant
- urea as substrate
- phenol red as a pH indicator

70
Q

Does the urease test use a pH indicator or reagent? Why?

A

pH indicator: phenol red
CO2 acidic and NH3 basic

71
Q

What results can we expect with the urease test?

A

yellow-acidic: negative
red/orange-neutral: negative
pink-alkaline: Positive

72
Q

How might urease activity be a virulence factor?

A

Urease activity for H. pylori neutralizes stomach acids which can cause ulcers. In P. vulgaris, it allows the bacteria to grow in the presence of urine and can cause diaper rash NH3 burn

73
Q

What is the purpose of nitrate reduction test?

A

determine if bacteria can reduce nitrate.

74
Q

Does nitrate reduction use pH indicator or reagent?

A

Reagent A+B and Zinc

75
Q

What possible results can you have with nitrate reduction test?

A

NO3- present: negative (red)
NO2- present: pos (red)
N2 or NH3 present: pos (yellow)

76
Q

What biochemical test is shown? What is its purpose?

A

Lysine Decarboxylase test: determine if bacteria can decarboxylase lysine

77
Q

What is the media used for Lysine Decarboxylase test? What are the ingredients?

A

Lysine broth
- Lysine -> alkaline products
- glucose -> acidic products
- Bromcresol purple: pH indicator

78
Q

What are the expected results of Lysine Decarboxylase test?

A
79
Q

What biochemical test is shown? What is its purpose?

A

Phenylalanine deaminase test: determine if bacteria can deaminate phenylalanine

80
Q

Does Phenylalanine deaminase test use a pH indicator or reagent?

A

reagent: Ferric Chloride (FeCl3)

81
Q

What are the expected results of Phenylalanine deaminase test?

A
82
Q

Which tests can be used to differentiate species of Enterobacteriaceae?

A

Lactose fermentation
IMViC
Hydrogen Sulfide

MICR 262 (30 decks)

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