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Clinical Bacteriology > (F) Lesson 11.2: Diagnostic Tests for Gram-Negative Bacilli > Flashcards

(F) Lesson 11.2: Diagnostic Tests for Gram-Negative Bacilli Flashcards

1
Q
  • Purpose: This test is used to differentiate gram-negative bacilli based on decarboxylation or deamination of lysine and the formation of hydrogen sulfide (H2S).
A

Lysine Iron Agar (LIA)

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2
Q

LIA

Lysine contains what?

Clue: Five answers

A
  • Lysine
  • Peptones
  • A small amount of glucose
  • Ferric ammonium citrate
  • Sodium thiosulfate
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3
Q

LIA

T or F: The medium has an anaerobic slant and an aerobic butt.

A

F (reverse: aerobic slant and anaerobic butt)

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4
Q

LIA

  • When glucose is fermented, the butt of the medium becomes acidic. What color does it turn to?
A

Yellow

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5
Q

LIA

This neutralizes the organic acids formed by glucose fermentation, and the butt of the medium reverts to the alkaline state (purple).

A

Cadaverine

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6
Q

LIA

T or F: If the decarboxylase is not produced, the butt remains acidic.

A

T

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7
Q

LIA

If oxidative deamination of lysine occurs, this compound is formed that, in the presence of ferric ammonium citrate and a coenzyme which forms a burgundy color on the slant.

A

Flavin mononucleotide

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8
Q

LIA

If deamination does not occur, the LIA slant remains what color?

A

Purple

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9
Q

LIA

Familiarize yourself with the media inclusions.

A
  • Enzymatic digest of gelatin (5 g)
  • Yeast extract (3 g)
  • Dextrose (1 g)
  • L-lysine (10 g)
  • Ferric ammonium citrate (0.5 g)
  • Sodium thiosulfate (0.04 g)
  • Bromocresol purple (0.02 g)
  • Agar (13.5 g) per 1000 mL
  • pH 6.7
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10
Q

LIA

Alkaline slant/alkaline butt (K/K) has a reaction of?

A

Lysine decarboxylation and no fermentation of glucose

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11
Q

LIA

Alkaline slant/acid butt (K/A) has a reaction of?

A

Glucose fermentation

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12
Q

LIA

Red slant/acid butt (R/A) has a reaction of?

A

Lysine deamination and glucose fermentation

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13
Q

LIA

T or F: Proteus spp. that produce hydrogen sulfide will not blacken the medium.

A

T

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14
Q

LIA

Alkaline slant and butt, H2S Positive Quality Control?

A
  • Citrobacter freundii
  • Salmonella typhimurium
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15
Q

LIA

Alkaline slant and butt Quality Control?

A

Escherichia coli

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16
Q

LIA

Red slant, acid butt Quality Control?

A

Proteus mirabilis

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17
Q
  • The combination test methyl red (MR) and Voges-Proskauer (VP) differentiates members of the Enterobacteriaceae family.

Iiyak ako pag di niyo pa nahulaan sagot.

A

Methyl Red and Voges-Proskauer Tests

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18
Q

This test is used to determine the ability of an organism:
* to produce and maintain stable acid end products from glucose fermentation
* to overcome the buffering capacity of the system
* to determine the ability of some organisms to produce
neutral end products from glucose fermentation

A

Methyl Red and Voges-Proskauer Tests

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19
Q

MR and VP Tests

This detects mixed acid fermentation that lowers the pH of the broth.

A

Methyl Red

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20
Q

MR and VP Tests

T or F: The methyl red indicator is added before the incubation.

A

F (after)

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21
Q

MR and VP Tests

This detects the organism’s ability to convert the acid products to
acetoin and 2,3-butanediol.

A

Voges-Proskauer

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22
Q

MR and VP Tests

Familiarize yourself with the media inclusions.

A
  • Peptic digest of animal tissue (3.5 g)
  • Pancreatic digest of casein (3.5 g)
  • Dextrose (5 g)
  • KPO4 (5 g) per 1000 mL
  • pH 6.9
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23
Q

Methyl Red Test

Positive Result?

A

Red-orange color

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24
Q

Methyl Red Result

Negative Result?

A

Yellow

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25
Q

Voges-Proskauer Test

Positive Result?

A

Red color (indicative of acetoin production)

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26
Q

Voges-Proskauer Test

Negative Result?

A

Yellow

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27
Q

MR and VP Tests

T or F: The MR test should not be read before 48 hours.

A

T

Some organisms will not have produced enough products from the fermentation of glucose.

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28
Q

T or F: MRVP testing should be used in conjunction with other confirmatory tests to differentiate organisms among the Enterobacteriaceae.

A

T

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29
Q

MR and VP Tests

MR Positive/VP Negative Quality Control?

A

Escherichia coli

30
Q

MR and VP Tests

MR Negative/VP Positive Quality Control?

A

Enterobacter aerogenes

31
Q
  • Purpose: This test is used to differentiate gram-positive, catalase-positive cocci (micrococci from staphylococci).
A

Microdase Test (Modified Oxidase)

32
Q
  • A rapid method to differentiate Staphylococcus from Micrococcus spp. by detection of the enzyme oxidase.
A

Microdase Test (Modified Oxidase)

33
Q
  • In the presence of atmospheric oxygen, the
    oxidase enzyme reacts with the oxidase reagent and cytochrome
    C to form the colored compound called?
A

Indophenol

34
Q

Microdase Test (Modified Oxidase)

Positive Result?

A

Development of blue to purple-blue color

35
Q

Microdase Test (Modified Oxidase)

Negative Result?

A

No color change

36
Q

Microdase Test (Modified Oxidase)

Staphylococci should yield a negative color change, except for?

A
  • S. sciuri
  • S. lentus
  • S. vitulus
37
Q

Microdase Test (Modified Oxidase)

Positive Quality Control?

A

Micrococcus luteus

38
Q

Microdase Test (Modified Oxidase)

Negative Quality Control?

A

Staphylococcus aureus

39
Q
  • Purpose: This test is used to presumptively identify various genera of Enterobacteriaceae and verotoxin-producing Escherichia coli.
A

4-Methylumbelliferyl-b-d-Glucuronide (MUG) Test

40
Q
  • E. coli and other Enterobacteriaceae produce this enzyme to which hydrolyzes b-d-glucopyranosid-uronic derivatives to aglycons and d-glucuronic acid
A

B-d-glucuronidase

41
Q

MUG Test

The substrate 4-methylumbelliferyl-b-d-glucuronide is impregnated into the disk and is hydrolyzed by the enzyme to yield the?

A

4-methylumbelliferyl moiety

42
Q

MUG Test

T or F: Verotoxin-producing strains of E. coli do not produce MUG.

43
Q

MUG Test

Positive Results?

A

Electric blue fluorescence

44
Q

MUG Test

Negative Result?

A

Lack of fluorescence

45
Q

MUG Test

T or F: Only test on oxidase-positive organisms, because some oxidase-negative organisms naturally fluoresce.

46
Q

MUG Test

Positive Quality Control?

A

Escherichia coli

47
Q

MUG Test

Negative Quality Control?

A

Klebsiella pneumoniae

48
Q
  • Purpose: This test is used to determine the ability of an organism to reduce nitrate to nitrite. All members of the Enterobacteriaceae family reduce nitrate, but some members further metabolize nitrite to other compounds.
A

Nitrate Reduction

49
Q

Nitrate Reduction

This requires an electron acceptor other than
atmospheric oxygen (O2).

A

Anaerobic metabolism

50
Q

Nitrtate Reduction

The organisms produce this enzyme which converts the nitrate (NO3) to nitrite (NO2).

A

Nitrate reductase

51
Q

Nitrate Reduction

The reduction of nitrate to nitrite is determined by adding what two components?

A
  • Alpha-naphthylamine
  • Sulfanillic acid
52
Q

Nitrate Reduction

Sulfanillic acid + nitrite?

A

Diazonium salt

53
Q

Nitrate Reduction

The diazonium salt couples with alpha-naphthylamine to produce?

A

A red, water-soluble azo dye

54
Q

Nitrate Reduction

If no color change occurs, then?

A

The organism did not reduce nitrate or reduced it further to NH3, NO, or N2O.

55
Q

Nitrate Reduction

if nitrate remains after adding zinc, the zinc will reduce the compound to nitrite and the reaction will turn ____, indicating a negative test result for nitrate reduction by the organism.

56
Q

Nitrate Reduction

If no color change occurs after the addition of zinc, this indicates that the organism ____ nitrate to one of the other nitrogen compounds previously described.

57
Q

Nitrate Reduction

This is placed in the broth for two reasons:
* To detect deterioration of the broth before inoculation, as evidenced by gas formation in the tube
* To identify denitrification by organisms that produce gas by alternate pathways

A

Durham tube

58
Q

Nitrate Reduction

Familiarize yourself with the media inclusions.

A
  • Pancreatic digest of gelatin (20 g)
  • KNO3 (2 g) per 1000 mL
59
Q
  • This is read for the presence or absence of three metabolic products: gas, nitrate (NO3), and nitrite (NO2).
A

Nitrate Reduction

60
Q

Nitrate Reduction

I’m begging you, please read the table. Don’t make me turn them into cards </3

A

Please go </3

61
Q

Nitrate Reduction

T or F: Nitrate reduction is a supportive test for identification of Enterobacteriaceae to the genus level.

62
Q

Nitrate Reduction

Positive: NO3 + no gas Quality Control

A

Escherichia coli

63
Q

Nitrate Reduction

Positive: NO3 + gas Quality Control

A

Pseudomonas aeruginosa

64
Q

Nitrate Reduction

Negative Quality Control?

A

Acinetobacter baumannii

65
Q
  • Purpose: This test is used to determine whether an organism can reduce nitrites to gaseous nitrogen or to other compounds containing nitrogen.
A

Nitrite Reduction

66
Q

Nitrite Reduction

T or F: Microorganisms capable of reducing nitrite to nitrogen do not turn color and do produce gas in the nitrate reduction test.

67
Q

Nitrite Reduction

Familiarize yourself with the media inclusions.

A
  • Brain-heart infusion broth (2 g)
  • Pancreatic digest of casein (10 g)
  • Peptic digest of animal tissue (5 g), yeast extract (3 g)
  • NaCl (5 g)
  • NaNO2 (0.1 g) per 1000 mL
  • pH 6.9
68
Q

Nitrite Reduction

Positive Result?

A
  • No color change to red 2 minutes after the addition of the reagents
  • Gas production observed in the Durham tube
69
Q

Nitrite Reduction

Negative Result?

A
  • The broth becomes red after the addition of the reagents
  • No gas production is observed
70
Q

Nitrite Reduction

If the broth does not become red and no gas production is
observed, ____ is added to determine whether the nitrite has not been oxidized to nitrate (thus invalidating the test).

A

Zinc dust

If oxidation has occurred, the mixture turns red after the addition of zinc.

71
Q

Nitrite Reduction

Positive Quality Control?

A

Proteus mirabilis

Colorless with gas production

72
Q

Nitrite Reduction

Negative Quality Control?

A

Acinetobacter baumannii

Red with no gas production

Clinical Bacteriology (33 decks)

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