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BACTERIOLOGY > Disk Diffusion Test > Flashcards

Disk Diffusion Test Flashcards

1
Q

Test for S. pneumoniae’s penicillin resistance

A

Oxacillin disk screen

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2
Q

Medium for Oxacillin disk screen

A

MHA with 5% sheep blood and 1 µg oxacillin

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3
Q

Incubation for Oxacillin disk screen

A

35°C, 5-7% CO2, 20-24 hours

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4
Q

Result interpretation for Oxacillin disk screen

A

≤21 mm = Resistant, intermediate, or susceptible (requires MIC testing)

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5
Q

Test for MRSA to penicillinase-resistant penicillins

A

Oxacillin screen agar

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6
Q

Medium for Oxacillin screen agar

A

MHA with 6 µg oxacillin and 4% NaCl

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7
Q

Incubation for Oxacillin screen agar

A

30-35°C, 24 hours

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8
Q

Positive result for Oxacillin screen agar

A

Growth = Resistance

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9
Q

Negative result for Oxacillin screen agar

A

No growth = Susceptible

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10
Q

Test to detect mecA-mediated oxacillin resistance

A

Cefoxitin disk diffusion

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11
Q

Medium for Cefoxitin disk diffusion

A

MHA with 30 µg cefoxitin

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12
Q

Incubation for S. aureus and S. lugdunensis

A

33-35°C, 16-18 hours

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13
Q

Incubation for CoNS

A

35°C, 24 hours

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14
Q

Result for S. aureus and S. lugdunensis

A

≤21 mm = mecA positive; ≥22 mm = mecA negative

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15
Q

Result for CoNS

A

≤24 mm = mecA positive; ≥25 mm = mecA negative

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16
Q

Test for Vancomycin resistance in VRE and VRSA

A

Vancomycin screen agar

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17
Q

Medium for Vancomycin screen agar

A

BHI with 6 µg vancomycin/mL

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18
Q

Incubation for Vancomycin screen agar

A

35°C, 24 hours

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19
Q

Positive result for Vancomycin screen agar

A

Growth = Resistance

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20
Q

Negative result for Vancomycin screen agar

A

No growth = Susceptible

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21
Q

Purpose of β-lactamase detection

A

Detects β-lactamase production, resistance to Ampicillin, Penicillin, and derivatives (-cillin)

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22
Q

Organisms tested for β-lactamase production

A

Enterococcus, N. gonorrhoeae, H. influenzae, Bacteroides

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23
Q

Method for Chromogenic Cephalosporin test

A

Nitrocefin disk + saline + bacterial loop

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24
Q

Incubation for Chromogenic Cephalosporin test

A

22-25°C, 10 minutes (Staph. 60 minutes)

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25
Positive result for Chromogenic Cephalosporin test
Red/Pink = β-lactamase producer
26
Method for Acidimetric β-lactamase detection
Penicillin + phenol red indicator + bacteria
27
Incubation for Acidimetric β-lactamase detection
22-25°C, 10-15 minutes (Staph. 60 minutes)
28
Positive result for Acidimetric β-lactamase detection
Yellow = β-lactamase producer
29
Method for Iodometric β-lactamase detection
Penicillin + iodine-starch complex + bacteria
30
Incubation for Iodometric β-lactamase detection
22-25°C, 10 minutes (Staph. 60 minutes)
31
Positive result for Iodometric β-lactamase detection
Colorless/White = β-lactamase producer
32
Purpose of ESBL detection
Detects resistance to Penicillin, Monobactams, and Cephalosporins
33
Organisms tested for ESBL
Klebsiella, E. coli
34
Method for ESBL detection
Disk diffusion with Cefotaxime (CTX), Ceftazidime (CAZ), and Clavulanic acid (CLA)
35
Incubation for ESBL detection
35°C, 24 hours
36
Positive result for ESBL detection
Larger ZOI with CTX/CAZ + CLA compared to CTX or CAZ alone
37
Purpose of Aminoglycoside screen
Detect high-level resistance to Aminoglycosides in Enterococci
38
Medium for Aminoglycoside screen
BHI broth with Gentamicin and Streptomycin
39
Incubation for Aminoglycoside screen
35°C, 24 hours
40
Positive result for Aminoglycoside screen
Growth = Resistance
41
Negative result for Aminoglycoside screen
No growth = Susceptible
42
Purpose of ICR test
Detects inducible clindamycin resistance
43
Organisms tested for ICR
S. aureus, S. lugdunensis, S. pneumoniae, beta-hemolytic Streptococci
44
Media for ICR test
5% Sheep BAP or MHA with 15 µg Erythromycin (E) and 2 µg Clindamycin (Cd)
45
Incubation for ICR test
35°C, 16-18 hours (for S. aureus, S. lugdunensis), or 35°C, 20-24 hours with 5% CO2 (for S. pneumoniae, beta-hemolytic Streptococci)
46
Positive result for ICR test
Flattening of CD zone (D-zone) = Clindamycin resistant
47
Purpose of Modified Hodge test
Detects carbapenemase production in Enterobacterales
48
Media for Modified Hodge test
MHA
49
Disk for Modified Hodge test
10 µg Meropenem or Ertapenem
50
Incubation for Modified Hodge test
35°C, 16-18 hours
51
Positive result for Modified Hodge test
Clover-leaf like appearance, indented or enhanced growth
52
Purpose of CNP test
Confirmatory test for carbapenemase production
53
Reagents for CNP test
Imipenem, Phenol red indicator
54
Incubation for CNP test
35°C, 2 hours
55
Positive result for CNP test
Tube A = Red/Orange, Tube B = Yellow
56
Determines MIC of 1 antimicrobial against 1 bacteria
Gradient diffusion testing
57
1 gradient of antibiotic concentration in a plastic strip
E-test/Epsilometer
58
1 gradient of antibiotic concentration in a paper strip
Liofilchem
59
Concentration causing 99.9% reduction in CFU/mL after broth dilution and subculture
Minimum bactericidal concentration (MBC)
60
Antibiotic inhibits but does not kill bacteria, linked to beta-lactam resistance
Tolerance
61
Serum bactericidal test using patient’s own serum
Schlichter test
62
Highest drug concentration in the serum
Peak specimen
63
Lowest drug concentration in the serum
Trough specimen
64
Drug peak concentration collection: IV 30–60 mins, IM 60 mins, Oral 90 mins after admin
Timing of specimen collection
65
Bacteria inoculated in antimicrobial concentrations, incubated, and colony counts measured over time
Time-kill assay
66
Effectiveness of multiple antimicrobials on a single bacterial strain
Synergy test
67
Normal flora of the human microbiome
Colonizer
68
Bacteria that multiply on the host
Resident
69
Bacteria that do not multiply on the host
Transient

BACTERIOLOGY (49 decks)

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