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LQB462 > Staphylococci and streptococci > Flashcards

Staphylococci and streptococci Flashcards

1
Q

Staphylococcus spp. have what Gram reaction?

A

Positive

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2
Q

What is the most common arrangement of Staphylococcus spp.?

A

Grape-like clusters

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3
Q

What is a facultative anaerobe?

A

An organism that can grow in the presence or absence of oxygen; facultative anaerobes are capable of aerobic respiration or fermentation if oxygen is not present.

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4
Q

Are Staphylococcus spp. aerobes, anaerobes, or facultative?

A

Facultative anaerobes

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5
Q

List three regions where S. aureus is NRF.

A
  • Skin
  • Nasopharynx
  • Mucosa
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6
Q

List two regions where S. epidermidis is NRF.

A
  • Skin

- Mucosa

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7
Q

List three regions where S. saprophyticus is NRF.

A
  • Skin
  • Genitourinary tract
  • Mucosa
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8
Q

Staphylococcus aureus, epidermidis, and saprophyticus are examples of ____ pathogens.

A

Opportunistic

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9
Q

How do Staphylococcus aureus, epidermidis, and saprophyticus cause infection?

A

Breaks in the skin/mucosal surface and/or change in the immune system.

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10
Q

List four conditions associated with Staphyloccus aureus, epidermidis, or saprophyticus infection.

A
  • Bacteraemia
  • Toxic shock
  • Wound infections
  • UTI
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11
Q

Staphylococci are organisms from which phylum?

A

Firmicutes

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12
Q

Staphylococci are organisms from which phylogenetic class?

A

Bacilli

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13
Q

Staphylococci are organisms from which phylogenetic order?

A

Bacillales

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14
Q

Staphylococci are organisms from which phylogenetic family?

A

Staphylococcaceae

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15
Q

Staphylococci are organisms from which phylogenetic genus?

A

Staphylococcus

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16
Q

What is empirical treatment?

A

Treatment based on pt presentation and knowledge of infections common to that site.

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17
Q

What does MCS stand for?

A

Microscopy, culture and sensitivity.

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18
Q

What is the first step of specimen processing?

A

Microscopy - performing a Gram stain.

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19
Q

List three things you would expect to see in microscopy of a wound exudate specimen.

A
  • NRF
  • Potential pathogen
  • PMNs (neutrophils)
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20
Q

What non-selective media is always used to 16-streak a possible bacterial aetiological agent?

A

HBA

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21
Q

What selective media is used to 16-streak a possible bacterial aetiological agent from a skin swab?

A

MSA

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22
Q

What makes HBA a differential media?

A

Haemolysis

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23
Q

What is gamma haemolysis (gammaH)?

A

No haemolysis, only nutrient use.

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24
Q

What is alpha haemolysis (alphaH)?

A

Incomplete haemolysis, showing a greenish tint.

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25
Q

Why does alphaH have a greenish tint?

A

Green bacteria produce H2O2, reducing haemoglobin to green oxidised methemoglobin.

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26
Q

Production of H2O2 which reduces haemoglobin to green oxidised methemoglobin produces what kind of haemolysis reaction on HBA?

A

AlphaH

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27
Q

What is beta haemolysis (betaH)?

A

Complete haemolysis, showing a clear zone.

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28
Q

What makes MSA a selective media?

A

The high salt concentration (7.5% NaCl, 10X more than most media) which supports Staphylococci and inhibits most other bacteria.

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29
Q

What makes MSA a differential media?

A

The mannitol which differentiates between organisms that can and cannot ferment it.

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30
Q

What colour are mannitol fermenting (MF) organisms grown on MSA?

A

Yellow

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31
Q

What colour are non-mannitol fermenting (NMF) organisms grown on MSA?

A

Pink

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32
Q

What organisms grow well on MSA?

A

Staphylococcus and halotolerant species.

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33
Q

How does S. aureus appear on MSA?

A

Yellow colonies, yellow zone.

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34
Q

How does S. epidermidis appear on MSA?

A

Clear pink colonies, pink agar.

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35
Q

How does S. saprophyticus appear on MSA?

A

Usually pink colonies and agar but 10% of strains ferment mannitol (yellow).

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36
Q

S. aureus is ____ haemolytic.

A

BetaH

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37
Q

Is S. aureus MF or NMF?

38
Q

S. epidermidis is ____ haemolytic or ____ haemolytic depending on the strain.

A

betaH, gammaH.

39
Q

Is S. epidermidis MF or NMF?

40
Q

Is S. aureus catalase POS or NEG?

41
Q

Is S. epidermidis catalase POS or NEG?

42
Q

Is S. aureus motile or non-motile?

A

Non-motile

43
Q

Is S. epidermidis motile or non-motile?

A

Non-motile

44
Q

S. saprophyticus is ____ haemolytic.

45
Q

Is S. saprophyticus MF or NMF?

A

Generally NMF but 10% of strains are MF.

46
Q

S. saprophyticus usually causes what kind of infections?

47
Q

Is S. saprophyticus catalase POS or NEG?

48
Q

Is S. saprophyticus motile or non-motile?

A

Non-motile

49
Q

You have performed a Gram stain and noted GPC in grape-like clusters. What PID should you now perform?

A

Catalase test

50
Q

A catalase test should only be performed on Gram ____ organisms.

51
Q

A catalase test is usually performed to differentiate between which two genera?

A

Staphylococcus and Streptococcus

52
Q

What is catalase?

A

An enzyme produced by microbes living in oxygenated environments to neutralise toxic forms of oxygen metabolites (e.g. H2O2).

53
Q

Why is catalase production a virulence factor?

A

The host response to various organisms is to produce H2O2 (hydrogen peroxide); neutralising this response helps the organism survive.

54
Q

Blood agar gives what rapid catalase test result?

55
Q

What catalase test should be performed if only blood agar is available?

A

Modified rapid catalase (M.R. catalase).

56
Q

A GPC in grape-like clusters that is catalase POS is most likely what genus?

A

Staphylococcus spp.

57
Q

A GPC in grape-like clusters that is catalase NEG is most likely what genus?

A

Streptococcus spp.

58
Q

A GPC in grape-like clusters that is pseudo-catalase POS (actually NEG) is most likely what genus?

A

Enterococcus spp.

59
Q

A catalase test that shows a delayed reaction (≥ 10 sec) with minor effervescence is what kind of reaction?

A

Pseudo-POS, recorded as NEG.

60
Q

What genus of organisms produces a delayed reaction (≥ 10 sec) with minor effervescence to a catalase test?

A

Enterococcus spp.

61
Q

What catalase reaction do Enterococcus spp. return?

A

Pseudo-catalase POS (delayed reaction [≥ 10 sec] with minor effervescence), actually catalase NEG.

62
Q

What is coagulase?

A

An enzyme that coagulates (clots) blood plasma.

63
Q

How does coagulase clot blood plasma?

A

Coagulase catalyses conversion of soluble fibrinogen to insoluble fibrin, resulting in a clot.

64
Q

How does producing coagulase protect bacteria?

A

Coagulase causes clotting around the wound, preventing the immune system entering the region to clear the infection.

65
Q

The tube coagulase test is performed on organisms that test catalase ____.

66
Q

The tube coagulase test is performed on organisms that test ____ POS.

67
Q

Is the tube coagualse test a PID or CID?

68
Q

What does the tube coagulase test differentiate between?

A

S. aureus and other Staphylococcus spp.

69
Q

Is S. aureus coagulase POS or NEG?

70
Q

Is S. epidermidis coagulase POS or NEG?

A

NEG (CoNS)

71
Q

Is S. saprophyticus coagulase POS or NEG?

A

NEG (CoNS)

72
Q

What is meant by ‘CoNS’?

A

Coagulase NEG Staphylococcus spp.

73
Q

What is detected by a slide coagulase test?

A

Bound coagulase/clumping factor

74
Q

A NEG slide coagulase test should be confirmed with what test?

A

Tube coagulase test

75
Q

Is Staphylococcus latex agglutination a PID or CID test?

76
Q

What test should be performed if a GPC returns a catalase POS then a coagulase NEG result?

A

Novobiocin susceptibility

77
Q

What two organisms would you suspect if a GPC returned a catalase POS then a coagulase NEG result?

A

S. epidermidis or S. saprophyticus

78
Q

From what type of agar are colonies taken for a Novobiocin susceptibility test?

A

Blood agar

79
Q

Is a Novobiocin test a PID or CID?

80
Q

What two Staphylococcus organisms are SENS to Novobiocin?

A

S. aureus and S. epidermidis

81
Q

Which Staphylococcus organism is RES to Novobiocin?

A

S. saprophyticus

82
Q

What organism would you ID if a GPC returned a catalase POS, coagulase NEG, then Novobiocin SENS?

A

S. epidermidis

83
Q

What organism would you ID if a GPC returned a catalase POS, coagulase NEG, then Novobiocin RES?

A

S. saprophyticus

84
Q

How wide does the zone of clearance have to be for an organism to be RES to Novobiocin?

A

≤12mm diameter

85
Q

Is an organism with ≤12 mm diameter zone of clearance in a Novobiocin test SUSC or RES?

86
Q

Is an organism with >12 mm diameter zone of clearance in a Novobiocin test SUSC or RES?

87
Q

An organism that is coagulase NEG and has a >12 mm diameter zone of clearance in a Novobiocin test is likely to be what genus and species?

A

Staphylococcus epidermidis

88
Q

An organism with a ≤12 mm diameter zone of clearance in a Novobiocin test is likely to be what genus and species?

A

Staphylococcus saprophyticus

89
Q

What is used as a substitute for methicillin when testing S. aureus for SUSC or RES?

90
Q

A GPC that returned a catalase POS, coagulase POS, and cefoxitin SUSC result would be reported as ____.

91
Q

A GPC that returned a catalase POS, coagulase POS, and cefoxitin RES result would be reported as ____.

92
Q

An organism RES to cefoxitin is assumed to be RES to ____.

A

Methicillin

LQB462 (4 decks)

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