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[8] LABORATORY DIAGNOSIS > Staphylococcus species > Flashcards

Staphylococcus species Flashcards

1
Q

Specimens for LABORATORY DIAGNOSIS of Staphylococcus species

A
  • Pus from wound and other pyogenic infections
  • Blood from septicemia
  • CSF from meningitis
  • Sputum from respiratory infections
  • Urine from UTI
  • Nasal swab from suspected carriers
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2
Q

G+ cocci, 0.5-1.5 µm in diameter, and [?]

A

grape-like clusters

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3
Q

G+ cocci arranged as [?]

A

single cells, pairs, tetrads, and short chains

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4
Q

The direct smears should also be examined for the presence of

A

inflammatory cells

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5
Q

These cells, background tissue debris and proteinaceous material generally stain

A

pink to red

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6
Q

Enriched medium that supports the growth of staphylococci

A

Blood agar medium (BAM)

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7
Q

permits observation of the pattern of hemolysis of blood

A

Blood agar medium (BAM)

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8
Q

both a selective and differential medium for staphylococci

A

Mannitol salt agar (MSA)

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9
Q

Uninoculated MSA appears

A

light to medium rose red in color.

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10
Q

inhibits the growth of other organisms (except for enterococci)

A

high salt (7.5% NaCl) concentration

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11
Q

selectively allows the growth of halotolerant styaphylococci

A

high salt (7.5% NaCl) concentration

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12
Q

Mannitol fermentation results in acids indicated by a change in the

A

phenol red indicator to yellow

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13
Q

aids in the differentiation of staphylococcal species

A

Mannitol fermentation

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14
Q

Interpretation of colonial morphologies is usually performed after

A

24 to 48 hours of incubation at 35-37 oC

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15
Q

medium to large (1-2 mm in diameter)

off-white or gray, smooth, entire, slightly raised, low convex, opaque, and butyrous in consistency

A

Staphylococcal colonies On BAM

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16
Q

usually large (4-6 mm in diameter)

produce golden yellow pigments “lipochrome”

may have a distinct or hazy zone of β-hemolysis around the colonies (apparent after prolonged incubation)

A

Staphylococcal colonies On BAM

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17
Q

produce small to medium, opaque, gray-white colonies;

most colonies nonhemolytic;

slime-producing strains are extremely sticky and adhere to the agar surface

A

S. epidermidis On BAM

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18
Q

colonies are large, entire, very glossy, smooth, opaque, butyrous, convex; usually white but colonies can be yellow or orange.

A

S. saprophyticus On BAM

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19
Q

produce growth of yellow colonies with yellow discoloration of the medium

A

Mannitol-fermenting staphylococci

  • S. aureus
  • S. saprophyticus
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20
Q

produce small red colonies with no color change to the medium

A

Non-mannitol fermentation

  • S. epidermidis
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21
Q

distinguishes staphylococci which are strongly catalase-positive from streptococci (catalase-negative)

A

Catalase test

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22
Q

Catalase test

Based on the ability of the bacteria to produce catalase enzyme decomposes hydrogen peroxide into [?]

The evolution of oxygen results in [?]

A

water and oxygen

effervescence

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23
Q

single most reliable characteristic for identifying S. aureus; slide or
tube procedures

A

Coagulase test

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24
Q

Coagulase test is done on

A

catalase-(+)

gram-(+) cocci

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25
Q

Coagulase test

The coagulase enzyme produced by S. aureus binds [?]and activates a cascade of reactions causing plasma to clot.

A

plasma fibrinogen

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26
Q

The medium for both slide coagulase and tube coagulase procedures is [?], which is commercially available in lyophilized form.

A

rabbit plasma with EDTA

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27
Q

Rabbit plasma has high amounts of [?]

A

coagulase-reacting factor (CRF)

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28
Q

is the preferred anticoagulant.

A

EDTA

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29
Q

must not be used because it contains variable amounts of CRF and may contain anti-staphylococcal antibodies.

A

Human plasma

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30
Q

should not be used as some bacteria are able to utilize citrate (such as enterococci) will yield positive results if they are mistaken for staphylococci; always perform a catalase test first.

A

Citrated plasma

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31
Q

screening test for S. aureus

A

Slide coagulase test

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32
Q

Strains that are negative with the slide coagulase test must be confirmed with a

A

tube coagulase test

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33
Q

Slide coagulase test

Based on the presence of bound coagulase or [?] on the surface of the cell wall of most strains of S. aureus. This factor reacts directly with and converts fibrinogen in plasma into fibrin, causing rapid cell agglutination

A

“clumping factor”

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34
Q

Some human [?] produce clumping factor and may be slide coagulase-positive.

A

coagulase-negative species

  • S. lugdunensis
  • S. schleiferi subsp schleiferi
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35
Q

Slide coagulase test

The test can be performed with growth from [?]

But should not be performed from media having a [?] (MSA) since the high salt causes some strains of S. aureus to autoagglutinate

A

blood agar (or nonselective medium)

high salt content

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36
Q

This is a confirmatory test for S. aureus since free coagulase is secreted by virtually all strains of S. aureus.

A

Tube coagulase test

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37
Q

Tube coagulase test

Based on the detection of free coagulase which is secreted extracellularly by S. aureus. The free coagulase reacts with a substance in the plasma called coagulase-reacting factor (CRF), which in turn reacts with fibrinogen in plasma to form

A

fibrin (clot formation).

38
Q

Some animal isolates [?] may be tube coagulase- positive.

Other phenotypic tests distinguish them form S. aureus.

A 
S. intermedius
S. hyicus
S. delphini
S. schleiferi subsp. coagulans 
strain of S. schleiferi subsp. schleiferi
39
Q

When observing for any degree of clot formation (partial or complete) after incubation, [?]; do NOT agitate as a small clot formed may be dislodged and will not reform anymore.

A

gently tilt the tube

40
Q

Tube coagulase tests that are negative after [?] should be held at room temperature and read again after 18 to 24 hours, because some strains will produce [?] on prolonged incubation at 35°C, causing dissolution of the clot during the incubation period.

A

4 hours incubation at 35°C

fibrinolysin (staphylokinase)

41
Q

one of the methods to distinguish between coagulase-negative staph, s. epidermidis and s. aureus

A

Novobiocin test

42
Q

Novobiocin test is performed as a disk susceptibility test using a

A

novobiocin disk (NB,5 µg)

43
Q

Other than S. saprophyticus, some human staphylococcal species [?] are resistant to novobiocin.

A

S. cohnii subspecies
S. hominis subsp. novobiosepticus
S. xylosus
S. pseudolugdunensis

44
Q

Sheep blood supports the growth of fastidious bacteria and allows detection of hemolytic reactions.

A

Columbia CNA Agar

45
Q

Antimicrobial agents, colistin and nalidixic acid, render the medium selective for G+ bacteria by inhibiting G- bacteria.

A

Columbia CNA Agar

46
Q

Sheep blood supports the growth of fastidious bacteria particularly G+ cocci.

A

Phenylethyl Alcohol (PEA) Agar

47
Q

The medium should not be used for determination of hemolytic reactions since atypical reactions may be observed.

A

Phenylethyl Alcohol (PEA) Agar

48
Q

PEA inhibits

A

G- bacteria

49
Q

Selectivity of the medium is achieved by potassium tellurite, lithium chloride and glycine which inhibit nonstaphylococcal organisms, both G+ and G- bacteria

A

Vogel-Johnson (VJ) Agar

50
Q

Vogel-Johnson (VJ) Agar

is reduced to metallic tellurium by S. aureus producing colonies that are black or gray-black in color

A

Tellurite

51
Q

Vogel-Johnson (VJ) Agar

is degraded into acid which is indicated by phenol red, which changes the color of the medium to yellow

A

mannitol

52
Q

It is selective due to relatively high salt content, although it is reduced to 5.5%

A

Chapman Stone Agar

53
Q

serves as a substrate for gelatinase activity

A

Gelatin

54
Q

allows detection of gelatin hydrolysis which is characterized by clear zone around the colonies

A

ammonium sulfate

55
Q

Chapman Stone Agar is differential due to

A

mannitol fermentation

56
Q

Yellow colonies surrounded by clear halo presumptively identifies

A

S.

aureus.

57
Q

White nonpigmented colonies with or without clear zone probably is

A

S.

epidermidis.

58
Q

Baird-Parker Agar

have inhibitory action for organisms other than staphylococci.

A

Tellurite, lithium chloride and glycine

59
Q

Baird-Parker Agar

is incorporated in order to stimulate the growth of S. aureus without destroying the selectivity.

A

Sodium pyruvate

60
Q

Reduction of tellurite to tellurium produces a

A

black coloration

61
Q

Addition of egg yolk is used to demonstrate proteolysis and lipolysis by [?] and [?] respectively producing clear zones around the colonies.

A

lecithinase and lipase

62
Q

Black, shiny, convex colonies 1-5 mm in diameter with a narrow, white edge.

A

S. aureus

63
Q

Black, shiny, irregular shape. Opaque zone develop around the colonies after 24 hours.

A

S. epidermidis

64
Q

Other tests for S. aureus correlate highly with [?]

A

coagulase production

65
Q

S. aureus produces both [?] and a [?] having endo- and exonucleolytic activities.

A

deoxyribonuclease (DNase) and a thermostable nuclease

66
Q

DNase test detects bacterial deoxyribonuclease which is an [?] that depolymerizes (breaks down) DNA into subunits composed of nucleotides.

A

extracellular enzyme

67
Q

Inoculate, either by [?] or [?] , a DNase test agar plate (containing deoxy-ribonucleic acid), and incubate at [?]; after incubation, flood with [?] which will precipitate DNA.

A

streak inoculation or spot inoculation

35 oC for 24-48 h

N hydrochloric acid

68
Q

A [?] surrounding the growth after addition of 1N HCL indicates a positive reaction for DNase activity.

A negative reaction is indicated by no [?] around the colonies

A

clear area

clearing and a cloudy precipitate

69
Q

Alternative method:

The test may also be carried out in agar plates with dye, such as [?] and [?]. This eliminates the need to add 1N HCl.

A

methyl green toluidine blue

70
Q

The same DNase test agar is used;

[?] holes are cut into the agar with a sterile cork borer

wells are filled with a [?]

boiled in a water bath for [?].

plate is incubated overnight at [?]

A

3 mm

24-hour broth culture

15 minutes

35°C

71
Q

S. aureus which is thermostable endonucleasepositive will show a [?] surrounding the well containing the boiled suspension.

Negative test is when the [?] in the medium remains

A

pink zone

blue color

72
Q

determines whether bacteria can utilize glucose in the presence or absence of oxygen

A

Oxidation-Fermentation (O-F) test

73
Q

Oxidation-Fermentation (O-F) test

sole carbohydrate

pH indicator is used

A

glucose

bromthymol blue

74
Q

Oxidation-Fermentation (O-F) test

Two tubes are inoculated by stabbing; one tube

(“[?] tube”) sterile mineral oil which shields it from oxygen in air

(“[?] tube”) is exposed to oxygen

A

closed

open

75
Q

Micrococci are [?] because they are aerobic bacteria;

produce acids from [?] only in the presence of oxygen

Medium in the [?] turns yellow

A

oxidative

glucose

open tube

76
Q

Staphylococi are [?]

glucose = produce acids in the presence and absence oxygen

This is evidenced C. bound coagulase by yellow color change of the medium in both open and closed tubes.

A

fermentative; facultative anaerobes

77
Q

performed as an agar disk susceptibility procedure using commercially available disks

A

Susceptibility to Bacitracin, 0.04 U and Furazolidone, 100 µg

78
Q

Micrococci are

?; zones of inhibition: 9mm

A

bacitracin - susceptible

furazolidone - resistant

79
Q

endopeptidase enzyme that can lyze the cell wall of staphylococci but not micrococci.

A

Lysostaphin test

80
Q

Lysostaphin solution is added to a bacterial suspension and incubated at

A

35-37 oC for 2 hour

81
Q

Micrococci are lysostaphin-resistant — bacterial suspension remains

A

turbid; it does not clear

82
Q

Staphylococci are lysostaphin-susceptible — there is

A

clearing of the bacterial suspension

83
Q

is also known as the microdase test; it is recommended for gram-positive, catalase-positive cocci only

A

Modified oxidase test

84
Q

Modified oxidase test uses filter paper disks impregnated with [?] in dimethyl sulfoxide (DMSO).

A colony from the growth medium is removed with an applicator stick and rubbed onto the disk

A

tetramethyl-pphenylenediamine dihydrochloride

85
Q

Micrococcus species are modified oxidase-[?]; the test is indicated by development of a [?].

A

modified oxidase-positive

blue-purple color within 30 seconds

86
Q

Staphylococcus species are generally modified oxidase-[?]

A

modified oxidase-negative

no change in color

87
Q

Production of acids from glycerol in the presence of erythromycin uses a medium containing

A

glycerol (1%) and erythromycin (0.4 µg/mL)

88
Q

It is prepared with an [?] containing [?] indicator and poured into Petri plates.

A

enriched agar base

bromcresol purple

89
Q

Micrococci will not produce acids from glycerol, so the medium will remain [?] in color.

A

purple

90
Q

Staphylococci will produce acids from glycerol causing a [?] color
change in the medium.

A

yellow

[8] LABORATORY DIAGNOSIS (5 decks)

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