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Clinical Bacteriology > LAB S19 > Flashcards

LAB S19 Flashcards

1
Q

gram staining of staphylococcus

A

positive

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2
Q

diameter of staphylococcus

A

0.5- 1.5 um

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3
Q

arrangement of staphylococci

A

grape-like clusters

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3
Q

arrangement of staphylococci

A

grape-like clusters

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4
Q

specimen obtained for pyogenic infections

A

pus

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5
Q

specimen obtained from septicemia

A

blood

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6
Q

specimen obtained from meningitis

A

CSF

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7
Q

specimen obtained from resporatory infections

A

sputum

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8
Q

specimen obtained from UTI

A

urine

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9
Q

specimen obtained from suspected carriers

A

nasal swab

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10
Q

direct smear is prepared from climical material such as

A

CSF or pus

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11
Q

the direct smears should aldo be examined for the presence of:

A

imflammatory cells

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12
Q

2 routine culture media for staphylococcus

A
  1. Blood Agar Medium

2. Mannitol Salt Agae

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13
Q

enriched medium that supports the growth of staphylococci and permits observation of the pattern of hemolysis of blood

A

blood agar medium

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14
Q

both a selective and differential medium for staphylococci

A

Mannitol Salt Agar

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15
Q

selective component of agar

A

7.5% NaCl

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16
Q

7.5% NaCl inhibits the growth of other organisms except halotolerant species like:

A

staphylococcus

enterococcus

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17
Q

the differential component of MSA

A

mannitol

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18
Q

mannitol fermentation results in acids which is indicated by

A

phenol red to yellow

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19
Q

approximate formula of per liter MSA

A 
Pancreatic digest of casein (5g)
peptic digest of animal tissue (5g)
beef extract (1g)
NaCl (75g)
D-mannitol (10g)
Phenol red (25mg)
Agar (15g)
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20
Q

incubation of MSA and BAM for colonial characterization

A

35-37C

24- 48 hrs

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21
Q

usual size of staphylococcal colonies

A

medium to large (1-2 mm)

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22
Q

usual color of staphylococcal colonies

A

off-white or gray

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23
Q

usual surface of staphylococcal colonies

A

smooth

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24
Q

usual elevation of staphylococcal colonies

A

slightly raised, low convex

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25
Q

usual density of staphylococcal colonies

A

opaque

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26
Q

usual comsistency of staphylococcal colonies

A

butyrous

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27
Q

usual size of S. aureus

A

large (4-6mm diameter)

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28
Q

color of some strains of S. aureus

A

creamy yellow or yellow-orange

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29
Q

golden yellow pigment produced by some strains of S. aureus

A

lipochrome

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30
Q

hemolytic property of S. aureus which is apparent after prolonged incubation

A

B- hemolysis

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31
Q

usual size of S. epidermidis

A

small to medium

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32
Q

usual density of S. epidermidis

A

opaque

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33
Q

usual color of S. epidermidis

A

gray-white

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34
Q

hemolytic property of S. epidermidis

A

non-hemolytic

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35
Q

staphylococcus which may have slimee producing strains that adhere to agar surface

A

S. epidermidis

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36
Q

usual size of S. saprophyticus

A

large

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37
Q

usual margin of S. saprophyticus

A

entire

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38
Q

usual surface of S. saprophyticus

A

very glossy, smooth

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39
Q

usual density of S. saprophyticus

A

opaque

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40
Q

usual consistency of S. saprophyticus

A

butyrous

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41
Q

usual elevation of S. saprophyticus

A

convex

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42
Q

color of S. saprophyticus colonies

A

usually white but can be yellow or orange

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43
Q

MSA with yellow discoloration and yellow colonies

A

S. aureus or S. saprophyticus

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44
Q

MSA with no color change and red colonies

A

S. epidermidis

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45
Q

Three identification tests of Staphylococcus

A
  1. catalase test
  2. coagulase test
  3. novobiocin test
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46
Q

test that distinguishes gram positive cocci: staphylococci and streptococci

A

catalase test

47
Q

staphylococcus is catalase:?

48
Q

streptococcus is catalase?

49
Q

principle of catalase test

A

ability of staphylococcus to produce catalase enzyme, whoch decomposes hydrogen peroxid into water and oxygen

50
Q

the evolution of oxygen in the catalase test resulting into rapid bubble formation is referred to as:

A

effervescence

51
Q

it is better to use staphylococci from this agar medium for catalase test

52
Q

procedure for slide catalase test

A

add 1 drop of 3% hydrogen peroxide

53
Q

procedure for tube catalase test

A

add 2-3 ml of 3% hydrogen peroxide to 18-24 hr culture slant

54
Q

how long to wait before observing catalase test result

A

20-30 secs

55
Q

single most reliable characteristic for identifying S. aureus

A

coagulase test

56
Q

principle of coagulase test

A

S. aureus produces coagulase, which bind plasma fibrinogen causing plasma to clot

57
Q

the culture for coagulase test should be taken from this medium

58
Q

medium for both sliide and tube coagulase

A

commercially produced lyophilized rabbit plasma with EDTA

59
Q

why rabbit plasma

A

high amlunts of coagulase reacting factor

60
Q

why not human plasma

A

contains variable amounts of CRF and contain staphylococcal antibodies

61
Q

why not citrated plasma

A

some bacteria like enterococci can utiloze citrate and yield positive result

62
Q

screening test for S. aureus

A

slide coagulase test

63
Q

principle of slide coagulase test

A

bound coagulase in cell wall of most S. aureus or clumping factors convert fibrinogen into fibrin

64
Q

bound coagulase causes:

A

rapid cell agglutination

65
Q

human coagulase negative species that can be slide coagulase positive

A

S. lugdunensis

S. schleiferi

66
Q

procedure of slide coagulase test

A

emulsify colony in 2 saline circles
drop plasma in one and water in the other
rock slide 5-10 secs

67
Q

positive result of slide coagulase test

A

white precipitates or clumping within 10-15 seconds of mixing

68
Q

positive for slide coagulase =

69
Q

negative for slide coagulase test:

A

confirm with tube coagulase test

70
Q

confirmatory test for S. aureus

A

tube coagulase test

71
Q

principle of tube coagulase test

A

free coagulase secreted extracellularly by all strains of S. aureus react with CRF, which react with fibrinogen to form fibrin

72
Q

positive result of tube coagulase test:

A

clotting of plasma

73
Q

positive for tube coagulase test

74
Q

negative for tube coagulase test

A

S. epidermidis or S. saprophyticus

proceed to novobiocin test

75
Q

procedure for tube coagulase test

A

pipet 0.5 ml plasma to test tube
transfer colony and emulsify until milky
incubate for 4 hrs in water bath

76
Q

if tube coagulase test is negative after 4 hours of incubation?

A

read again after 18-24 hours at room temperature

77
Q

why should tube coagulase negative result be read again after putting in room temperature?

A

some strains produce staphylokinase on prolonged incubation causing dissolution of the clot

78
Q

one of the methods to distinguish between coagulase negative staphylococci: S. epidermidis and S. saprophyticus

A

novobiocin test

79
Q

significant staphylococcus in urinary tract infections

A

S. saprophyticus

80
Q

important agent involved in several infectious processes

A

S. epidermidis

81
Q

concentration of novobiocin disc

82
Q

less than 12 mm ZOI in novobiocin

A

resistant = S. saprophyticus

83
Q

greater than 16 mm ZOI

A

susceptible- S. epidermidis

84
Q

5 additional culture media for isolation of staphylococcus species

A
  1. Columbia CNA agar
  2. Phenylethyl Alcohol (PEA) agar
  3. Vogel-Johnson (VJ) agar
  4. Chapman stone agar
  5. Baird-Parker agar
85
Q

contains sheep blood, colistin, and nalidixic acid

A

Columbia CNA agar

86
Q

purpose of sheep blood in Columbia CNA agar

A

supports fastidious bacteria

allows hemolytic reactions

87
Q

purpose of colistin and nalidixic acid in Columbia CNA agar

A

selective for G+ and inhibits G-

88
Q

formula per liter of Columbia CNA agar

A 
pancreatic digest of casein (12g)
peptic digest of animal tissue (5g)
yeast extract (3g)
beef extract (3g)
corn starch (1g)
NaCl (5g)
Agar (13.5g)
colistin (10mg)
nalidixic acid (10mg)
89
Q

contains sheep blood but cannot be used for determining hemolytic reactions

A

phenylethyl alcohol (PEA) agar

90
Q

components of PEA agar that inhibits G- bacteria

A

B-phenylethyl alcohol

91
Q

formula per liter of PEA agar

A 
pancreatic digest of casein (15g)
papic digest of soybean meal (5g)
NaCl (5g)
B-PEA (2.5 g)
Agar (15 g)
92
Q

agar which inhibits all nonstaphylococcal organisms

A

Vogel Johnson agar

93
Q

selectivity of VJ agar is due to these three components

A

potassium tellurite
lithium chloride
glycine

94
Q

principle of VJ agar

A

tellurite is reduced by S. aureus into metallic tellurium = black or gray colonies
mannitol degraded to acid = phenol red turned to yellow

95
Q

approximate per liter formula of VJ agar

A 
tryptone (10g)
yeast extract (5g)
mannitol (10g)
dipotassium phosphate (5g)
lithium chloride (5g)
glycine (10g)
agar (15g)
phenol red (25mg)
96
Q

agar containing high salt content, gelatin, ammonium sulfate, mannitol and bromcresol purple

A

Chapman stone agar

97
Q

selective component of chapman stone agar

A

5.5% salt content

98
Q

allows detection of hydrolysis in chapman stone agar, characterized by clear zone around colonies

A

ammonium sulfate

99
Q

differential component of chapamn stone agar

A

mannitol and bromcresol purple

100
Q

yellow colonies surrounded by clear halo in chapman stone agar

101
Q

nonpigmented colonies with or without colonies

A

S. epidermidis

102
Q

approximate per liter formula of chapman stone agar

A 
yeast extract (2.5g)
pancreatic digest of casein (10g)
gelatin (30g)
D-mannitol (10g)
NaCl (55 g)
Ammonium sulfate (75g)
dipotassium phosphate (5g)
agar (15g)
103
Q

Also has inhibitory action for nonstaphylococcal organisms but incorporates sodium pyruvate and egg yolk

A

Baird Parker Agar

104
Q

3 selective components of Baird Parker agar

A

tellurite, lithium chloride, glycine

105
Q

stimulates growth of S. aureus im Baird Parker Agar without destroying selectivity

A

Sodium pyruvate

106
Q

function of egg yolk in Baird-Parker agar

A

demonstrate:
proteolysis by lecithinase
lipolysis by lipase

through clear zones in the agar

107
Q

colonial characteristic of S. aureus in Baird parker agar

A

black, shiny, convex, 1-5 mm with narrow white edge

108
Q

colonial characteristic of S. epidermidis in Baird Parker Agar

A

black, shiny, irregular shape with opaque zone around colonies after 24 hrs

109
Q

2 additional identification tests for S. aureus

A

DNase test

thermostable endonucelase test

110
Q

principle of DNase test

A

detects DNase which depolymerizes DNA into nucleotides

111
Q

method of DNase test

A

inoculate DNA agar plate (streak or spot)
incubate 35 C for 24-48 hrs
flood with 1N HCl (precipitates DNA)

112
Q

positive DNase reaction

A

clear area surrounding growth

113
Q

positive for DNase test

114
Q

eliminates the need for 1N HCl

A

methyl green or toluidine blue

115
Q

method for thermostable nuclease test

A

3mm holes are cut into DNase test agar by cork borer
wells are filled with 24 hr broth culture boiled in water bath for 15 minutes
plate incubated overnight at 35C

116
Q

positive thermostable nuclease test

A

pink zone = S. aureus

Clinical Bacteriology (12 decks)

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