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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
# Voges-Proskauer Test Positive Result?
Red color (indicative of **acetoin production**)
26
# Voges-Proskauer Test Negative Result?
Yellow
27
# MR and VP Tests T or F: The MR test should not be read before 48 hours.
T ## Footnote Some organisms will not have produced enough products from the fermentation of glucose.
28
T or F: MRVP testing should be used in conjunction with other confirmatory tests to differentiate organisms among the Enterobacteriaceae.
T
29
# MR and VP Tests **MR Positive/VP Negative** Quality Control?
Escherichia coli
30
# MR and VP Tests **MR Negative/VP Positive** Quality Control?
Enterobacter aerogenes
31
* **Purpose:** This test is used to **differentiate gram-positive, catalase-positive cocci** (micrococci from staphylococci).
Microdase Test (Modified Oxidase)
32
* A rapid method to differentiate Staphylococcus from Micrococcus spp. by detection of the enzyme oxidase.
Microdase Test (Modified Oxidase)
33
* In the presence of atmospheric oxygen, the oxidase enzyme reacts with the oxidase reagent and cytochrome C to form the colored compound called?
Indophenol
34
# Microdase Test (Modified Oxidase) Positive Result?
Development of blue to purple-blue color
35
# Microdase Test (Modified Oxidase) Negative Result?
No color change
36
# Microdase Test (Modified Oxidase) Staphylococci should yield a negative color change, except for?
* S. sciuri * S. lentus * S. vitulus
37
# Microdase Test (Modified Oxidase) Positive Quality Control?
Micrococcus luteus
38
# Microdase Test (Modified Oxidase) Negative Quality Control?
Staphylococcus aureus
39
* **Purpose:** This test is used to **presumptively identify** various genera of Enterobacteriaceae and verotoxin-producing Escherichia coli.
4-Methylumbelliferyl-b-d-Glucuronide (MUG) Test
40
* E. coli and other Enterobacteriaceae produce this enzyme to which hydrolyzes b-d-glucopyranosid-uronic derivatives to aglycons and d-glucuronic acid
B-d-glucuronidase
41
# MUG Test The substrate 4-methylumbelliferyl-b-d-glucuronide is impregnated into the disk and is hydrolyzed by the enzyme to yield the?
4-methylumbelliferyl moiety
42
# MUG Test T or F: Verotoxin-producing strains of E. coli do not produce MUG.
T
43
# MUG Test Positive Results?
Electric blue fluorescence
44
# MUG Test Negative Result?
Lack of fluorescence
45
# MUG Test T or F: Only test on oxidase-positive organisms, because some oxidase-negative organisms naturally fluoresce.
T
46
# MUG Test Positive Quality Control?
Escherichia coli
47
# MUG Test Negative Quality Control?
Klebsiella pneumoniae
48
* **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.
Nitrate Reduction
49
# Nitrate Reduction This requires an electron acceptor other than atmospheric oxygen (O2).
Anaerobic metabolism
50
# Nitrtate Reduction The organisms produce this enzyme which converts the nitrate (NO3) to nitrite (NO2).
Nitrate reductase
51
# Nitrate Reduction The reduction of nitrate to nitrite is determined by adding what two components?
* Alpha-naphthylamine * Sulfanillic acid
52
# Nitrate Reduction Sulfanillic acid + nitrite?
Diazonium salt
53
# Nitrate Reduction The diazonium salt couples with alpha-naphthylamine to produce?
A red, water-soluble azo dye
54
# Nitrate Reduction If no color change occurs, then?
The organism did not reduce nitrate or reduced it further to NH3, NO, or N2O.
55
# 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.
Positive
56
# 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.
Reduced
57
# 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
Durham tube
58
# Nitrate Reduction Familiarize yourself with the media inclusions.
* Pancreatic digest of gelatin (20 g) * KNO3 (2 g) per 1000 mL
59
* This is read for the presence or absence of three metabolic products: gas, nitrate (NO3), and nitrite (NO2).
Nitrate Reduction
60
# Nitrate Reduction I'm begging you, please read the table. Don't make me turn them into cards
Please go
61
# Nitrate Reduction T or F: Nitrate reduction is a supportive test for identification of Enterobacteriaceae to the genus level.
T
62
# Nitrate Reduction **Positive: NO3 + no gas** Quality Control
Escherichia coli
63
# Nitrate Reduction **Positive: NO3 + gas** Quality Control
Pseudomonas aeruginosa
64
# Nitrate Reduction Negative Quality Control?
Acinetobacter baumannii
65
* **Purpose:** This test is used to determine whether an organism **can reduce nitrites to gaseous nitrogen** or to other compounds containing nitrogen.
Nitrite Reduction
66
# 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.
T
67
# Nitrite Reduction Familiarize yourself with the media inclusions.
* 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
# Nitrite Reduction Positive Result?
* No color change to red 2 minutes after the addition of the reagents * Gas production observed in the Durham tube
69
# Nitrite Reduction Negative Result?
* The broth becomes red after the addition of the reagents * No gas production is observed
70
# 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).
Zinc dust ## Footnote If oxidation has occurred, the mixture turns red after the addition of zinc.
71
# Nitrite Reduction Positive Quality Control?
Proteus mirabilis | Colorless with gas production
72
# Nitrite Reduction Negative Quality Control?
Acinetobacter baumannii | Red with no gas production

Clinical Bacteriology (33 decks)

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