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Medical Microbiology > LAB Practical I > Flashcards

LAB Practical I Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What is selective media?

A

contains certain ingredients that enhance presence of desired organism

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2
Q

What media selects growth of Staphylococcus species?

A

mannitol salt agar

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3
Q

What is enrichment media?

A

contains specific nutrient additives to allow fastidious organisms to grow

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4
Q

What is an example of an enrichment media used?

A

chocolate agar plate

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5
Q

What are the C-agar lactose and glucose deeps used for?

A

determines the ability of an organism to utilize glucose/lactose

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6
Q

What is a “positive” result of C-agar lactose/glucose? What does this mean?

A

yellow color; demonstrates organism produced acid with/without gas

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7
Q

What is the pH indicator in the C-agar glucose/lactose deeps?

A

Phenol Red

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8
Q

What is the nitrate broth used for?

A

sees if organism can reduce NO3 (nitrate) into nitrite (NO2) or free nitrogen (N2) gas

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9
Q

What must be added into the nitrate broth tube in order to observe a color change?

A

sulfanilic acid (SA) and DMA

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10
Q

What is the Tryptone broth used for?

A

sees if the organism can breakdown tryptone into indole

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11
Q

What does the Tryptone broth test detect for?

A

tryptophanase

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12
Q

What reagent is added into the Tryptone broth to induce a color change and when do you add this reagent?

A

Kovac’s reagent; after incubation

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13
Q

What is a positive result in the tryptone broth test? What does this indicate?

A

red ring = indicates organism can break down tryptone into indole

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14
Q

What is the H2S agar plate?

A

contains thiosulfates and detects the production of H2S

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15
Q

What is a positive result on the H2S agar plate and what does this indicate?

A

colonies appear on plate with black centers; organism produces H2S gas

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16
Q

What is the Starch agar plate?

A

contains starch

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17
Q

What is the Starch agar plate used for?

A

detects presence of amylase

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18
Q

What must you add onto Starch agar plate (post incubation) to observe result?

A

Gram’s iodine

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19
Q

What is a positive result on the Starch agar plate and what does this indicate?

A

a clear zone/halo around colony represents organism produces amylase

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20
Q

What is the blood agar plate (BAP) what is it used for?

A

contains blood from animal (sheep); determines hemolytic reaction (pattern) of an organism

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21
Q

What was the dextrose tablet used for? What kind of test is this?

A

glucose sugar fermentation; rapid test

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22
Q

What was the indole tablet used for? What kind of test is this?

A

breakdown of tryptophan into indole; rapid test

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23
Q

What was the urease tablet used for? What kind of test is this?

A

determines ability of organism to hydrolyze urea; rapid test

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24
Q

What is the oxidase test?

A

tests for cytochrome oxidase

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25
Q

How was the oxidase test performed?

A

drop oxidase reagent on top of colonies

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26
Q

What is a positive result on the oxidase test? What does this indicate?

A

dark blue/purple color change on colonies within a few seconds; organism produces cytochrome c oxidase

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27
Q

What is the slide catalase test?

A

tests for catalase

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28
Q

How was the catalase test performed?

A

place drop of hydrogen peroxide on slide, scoop colony into it

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29
Q

What is a positive result on the oxidase test? What does it indicate?

A

formation of bubbles; indicates organism produces catalase

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30
Q

What must be added onto the nitrate broth if no color change is present after addition of Kovac’s reagent? What does a red color-change after this addition indicate? What does a non-red color-change indicate?

A

Zinc dust; if red = NO3 not reduced; if not red = nitrate reduced into something else

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31
Q

What does a gas bubble in the nitrate broth represent?

A

organism reduces nitrate to N2 gas

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32
Q

Why is there a clear halo as a positive result on the Starch agar plate?

A

organism produces amylase = breaks down starch; iodine sticks to starch

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33
Q

On an H2S plate, what does the black dot at a center of a colony indicate?

A

(positive result) H2S gas reacts with iron in media to form the black/brown precipitate

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34
Q

What is a beta hemolysis on a blood agar plate indicative of? How does it look like?

A

complete break down of red blood cell = clear zone of lysis

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35
Q

What is an alpha hemolysis on a blood agar plate indicative of? How does it look like?

A

partial breakdown of red blood cell = green/brown zone

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36
Q

What is a gamma hemolysis on a blood agar plate indicative of? How does it look like?

A

no breakdown of red blood cell = no zone of lysis

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37
Q

In the Dextrose (glucose) tablet rapid test, what is a positive result? What is it indicative of?

A

yellpwdsd

yellow color = organism ferments dextrose (glucose)

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38
Q

In the Indole tablet rapid test, what is a positive result? (or what must you add to observe a result?) What is it indicative of?

A

red ring after addition of Kovac’s reagent; breakdown of tryptophan into indole

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39
Q

In the Urease tablet rapid test, what is a positive result? What is it indicative of? What is a negative result, how does the media look like prior to inoculation?

A

positive = bright pink/magenta = organism hydrolyzes urea (via production of urease); negative = yellow; uninoculated = orange-ish

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40
Q

What is the motile nitrate agar deep used for?

A

determine if the organism is motile

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41
Q

What is a positive result on a motile nitrate agar deep?

A

bacteria spreads and fills tube thus turns media red in color

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42
Q

What is a negative result on a motile nitrate agar deep?

A

bacteria is non-motile and confined to place where it was originally inoculated

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43
Q

Which Staphylococcus species present an alpha hemolysis?

A

S. epidermidis

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44
Q

Which Staphylococcus species present a gamma hemolysis?

A

S. saprophyticus

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45
Q

Which Staphylococcus species present a beta hemolysis?

A

S. aureus

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46
Q

What kind of media is the Mannitol Salts Agar (MSA) plate?

A

selective and differential

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47
Q

What is the MSA plate used to identify? (staphylococcus)

A

S. aureus from other staphylococcus species

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48
Q

What does growth on the MSA plate indicate?

A

staphylococcus species

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49
Q

What is contained in the MSA plate?

A

NaCl, mannitol, and Phenol red

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50
Q

What is the purpose of each of the ingredients that make up the MSA plate?

A

NaCl = inhibits most organisms from growing except Staphylococcus species | Phenol Red = pH indicator | mannitol = differentiates S. aureus from other staphylococcus species

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51
Q

What does the red and yellow color changes on the MSA plate indicate?

A

red = pH 8.4 and yellow = pH 6.4

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52
Q

What is the coagulase test used for? Which of the three identifiable Staphylococcus species will it test positive for?

A

tests for bound coagulase on S. aureus only

53
Q

What is a positive result on the Coagulase Test? What does this indicate?

A

clumping of the organism

54
Q

How is the Coagulase test performed?

A

add drop of rabbit or human serum on glass slide and mix in organism

55
Q

What is the DNase Agar? What does it contain?

A

differential media used to detect and differentiate Staphylococcus

56
Q

What is a positive result on the DNase Agar plate and what does this indicate? What is a negative result?

A

red-purple color indicates organism hydrolyzed DNA via production of DNase | blue color = negative result (color change after 1min = false+)

57
Q

What is the DNase Agar plate used for?

A

tests ability of organism to produce DNase

58
Q

What is contained in the DNase Agar plate?

A

Tryptic soy agar supplemented with DNA

59
Q

What must be added on the DNase Agar plate after incubation to observe a result?

A

1% toluidine blue

60
Q

Which Staphylococcus organism tests positive for DNase Agar plate?

A

S. aureus

61
Q

Which Staphylococcus species is resistant to Novobiocin?

A

S. saprophyticus

62
Q

Are Streptococcus/Enterococcus species catalase positive or negative?

A

catalase negative

63
Q

Which Streptococcus Group performs a beta hemolysis on BAP?

A

Groups A and B

64
Q

Which Streptococcus Group performs an alpha hemolysis on BAP?

A

Group D

65
Q

Which Streptococcus Group performs a gamma hemolysis on BAP?

A

the “No Group” Group

66
Q

What is the Chocolate Agar Plate (CAP)?

A

lysed RBCs releases its growth factors contained within it = what some fastidious bacteria need to grow

67
Q

Which Streptococcus species is sensitive to Optochin?

A

S. pneumoniae

68
Q

What does the Optochin on the CAP test for? Which species does it differentiate?

A

sensitivity of alpha-hemolytic streptococcus; differentiates S. pneumoniae

69
Q

What does the Bacitracin on the BAP test for? Which species does it differentiate and why?

A

sensitivity of beta-hemolytic streptococcus to bacitracin | S. pyogenes because they are highly sensitive to bacitracin

70
Q

What does the 6.5% NaCl broth contain? Which species does it select for?

A

high concentrations of NaCl inhibit growth of most Streptococcus species | selects for E. faecalis

71
Q

What is the positive result on the 6.5% NaCl broth? What does it indicate?

A

turbidity = positive = indicates growth of organism in high salt concentrations

72
Q

What is the Bile Esculin Test? Which species does it select for?

A

contains bile = inhibits growth of most Streptococcus | selects for Enterococcus species (grows in presence of 40% bile)

73
Q

What is the positive result on the Bile Esculin Test? What is the reaction indicator?

A

ferric citrate

74
Q

What does a positive result on the Bile Esculin Test indicate?

A

organism hydrolyzes esculin to esculatin = forms complex iron in media = turns dark brown/black

75
Q

What is the Sodium Hippurate test?

A

hippurate and sodium

76
Q

What is the Sodium Hippurate test used to distinguish between?

A

Group A beta-hemolytic vs. Group B beta-hemolytic | Group B is able to hydrolyze hippurate to benzoic acid

77
Q

What is the positive result on the Sodium Hippurate test? What does it indicate?

A

permanent precipitate after 10 minutes of adding ferric chloride = indicates presence of benzoic acid –» organism hydrolyzed hippurate to benzoic acid

78
Q

What must be added into the Sodium Hippurate test after incubation to observe a result?

A

ferric chloride

79
Q

What is the Bile Solubility test? Which species does it test for?

A

bile activates enzymes that lead to rapid autolysis of S. pneumoniae

80
Q

What is the positive result on a Bile Solubility test? What does this indicate?

A

if the colony disappears due to the addition of the bile salts = indicates organism was led to rapid autolysis due to activation of autolytic enzymes

81
Q

How was the Bile Solubility test performed?

A

dropped 10% of bile salts on colonies of an alpha-hemolytic streptococcus on CAP or BAP plates

82
Q

What species does the StrepQuick Test identify?

A

Enterococcus and Group A streptococcus

83
Q

What are the 3 tests on the StrepQuick Test? What do they stand for?

A

PYR (pyroglutamic aminopeptidase), LAP (leucine aminopeptidase), and ESC (esculin hydrolysis)

84
Q

What is the Lancefield Test?

A

grouping based on the polysaccharide antigens on cell wall

85
Q

What indicates a positive result on a Lancefield test?

A

agglutination in the circle = indicates which streptococcus species you have

86
Q

What is inulin? Which test was it used for and what did it determine?

A

Inulin is a type of fiber (= carbohydrate) used as a C-agar to observe utilization of inulin as a carbon source in order to ferment it

87
Q

What is Sporulating agar? What is it used for?

A

nutrient slant agar containing Mn and Ca | provides conditions to enhance spore formation = stresses bacteria into sporulating

88
Q

What is the difference between C-agar and KL-agar?

A

KL-agar contains additional ingredients top enhance growth of bacillus

89
Q

What is KL-agar used for?

A

determine sugar fermentation pattern of bacillus, Corynebacteria and other strict anaerobes

90
Q

Which KL-agars were used and what are positive results?

A

salicin and glucose; yellow = acid fermentation w/ or w.o gas

91
Q

How will bacillus grow on BAP plates?

A

unique white fuzzy colonies

92
Q

What is the Nutrient Gelatin deep?

A

contains gelatin that solidified at 30ºC or below

93
Q

What does the Nutrient Gelatin deep test for?

A

presence of gelatinase

94
Q

What is a positive result on the Nutrient Gelatin deep? What does this indicate?

A

the media does not solidify after placed in freezer (almost liquidy) | organism produces gelatinase that hydrolyzes gelatin

95
Q

What is the Lowenstein-Jensen Agar?

A

contains inhibitors to prevent normal flora growth allowing slow-growing mycobacteria to multiply = selective media

96
Q

What is the Middlebrook-Cohn 7H10 agar?

A

contains inhibitors to prevent contaminants from growing

97
Q

What is the positive result on the Middlebrook-Cohn 7H10 agar? What does it indicate?

A

growth = organism is not susceptible to antimicrobials present

98
Q

What is the purpose of the Middlebrook-Cohn 7H10 agar? Which species does it select for?

A

determines antimicrobial susceptibility | selects for mycobacteria

99
Q

What does the Middlebrook 7H9 broth test for?

A

tellurite reduction test

100
Q

What must you add to the Middlebrook 7H9 broth to observe a positive result?

A

0.2% potassium tellurite

101
Q

What is a positive result on the Middlebrook 7H9 broth? What does this indicate?

A

jet black precipitate = organism could reduce tellurite

102
Q

What is the Arylsulfatase test broth? What must you add in order to observe a result?

A

contains tripotassium phenolphthalein sulfate | must add 0.3mL of 1M of sodium carbonate

103
Q

What is the purpose of the Arylsulfatase test?

A

detect arylsulfatase activity

104
Q

What is a positive result on the Arylsulfatase test? What does it indicate?

A

red/pink color = organism can produce arylsulfatase = can split phenolphthalein from tripotassium phenolphthalein sulfate

105
Q

What is the Tween 80 hydrolysis broth? What does it test for?

A

contains Tween 80 and neutral red = forms an amber color | tests for the presence of lipase that can hydrolyze Tween 80

106
Q

What is the positive result on the Tween 80 hydrolysis broth test? What does this indicate?

A

red color = no Tween 80 | indicates organism produced lipase and hydrolyzed Tween 80 thus no amber color observed

107
Q

What does the Christensen’s urea slant test for?

A

production of urease

108
Q

What is the positive result on Christensen’s urea slant test? What does this indicate?

A

red color = organism can produce urease that led to the hydrolysis of urea

109
Q

What is the MacConkey Agar plate? What does it differentiate or select for?

A

a selective/differential media that is not specific to mycobacteria but selects for gram– bacilli and coliforms

110
Q

What is a positive result on the MacConkey Agar plate? What does this indicate?

A

pink colonies indicate organism can ferment lactose = coliform; growth indicates gram– bacilli and other enterics such as Salmonella and Shigekka

111
Q

What is the Hektoen-enteric agar plate (HE)? What does it select for? Which species does it differentiate?

A

selects for gram– bacteria; differentiates between coliforms and Shigella/Salmonella species

112
Q

What do salmon-orange colored colonies indicate on an HE plate?

A

coliforms as they ferment sugar

113
Q

What do bluish-green colonies indicate on an HE plate?

A

Shigella/Salmonella since they don’t ferment sugars

114
Q

What do colonies with a black center indicate on an HE plate?

A

H2S production is detected = formation of an iron sulfide precipitate

115
Q

What is an ornithine decarboxylase plate (ODC)?

A

contains a phenol red pH indicator = detects production of ornithine decarboxylase

116
Q

What is a positive result on a ODC plate?

A

media will turn from yellowish-orange to red due to the production of the enzyme that caused the media pH to go from 5.6 to 7

117
Q

What is the Kliger’s Iron Agar slant (KIA) used for?

A

differentiates between certain members of the Enterobacteriaceae via hydrogen sulfide production and fermentation of glucose and lactose

118
Q

What does yellow butt indicate on the KIA slant?

A

glucose fermentation

119
Q

What does a complete yellow color change indicate on the KIA slant?

A

glucose and lactose fermentation throughout

120
Q

What does a black color change indicate on the KIA slant?

A

H2S production

121
Q

What does a no-color change indicate on the KIA slant?

A

no glucose or lactose fermentation or H2S production

122
Q

What is the purpose of the Lysine Iron Agar (LIA) slant?

A

detects the production of lysine decarboxylase (LDC) or lysine deaminase (LDA) and H2S production

123
Q

What does a purple butt indicate on the LIA slant?

A

Lysine decarboxylase positive

124
Q

What does a yellow butt indicate on the LIA slant?

A

lysine decarboxylase negative; glucose fermentation occurred

125
Q

What does a red slant (top part) indicate on the LIA slant?

A

lysine deaminase positive

126
Q

What does a black color change on the LIA slant indicate?

A

H2S production

127
Q

What is the Simmon’s Citrate Agar slant?

A

contains citrate

128
Q

What does the Simmon’s Citrate Agar slant test for?

A

use of citrate as the only source of carbon

129
Q

What is a positive result on the Simmon’s Citrate Agar slant? What does this indicate?

A

color change from green to blue = organism utilized citrate to produce NH3

Medical Microbiology (20 decks)

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