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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
Q

Positive result for Chromogenic Cephalosporin test

A

Red/Pink = β-lactamase producer

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26
Q

Method for Acidimetric β-lactamase detection

A

Penicillin + phenol red indicator + bacteria

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27
Q

Incubation for Acidimetric β-lactamase detection

A

22-25°C, 10-15 minutes (Staph. 60 minutes)

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28
Q

Positive result for Acidimetric β-lactamase detection

A

Yellow = β-lactamase producer

29
Q

Method for Iodometric β-lactamase detection

A

Penicillin + iodine-starch complex + bacteria

30
Q

Incubation for Iodometric β-lactamase detection

A

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

31
Q

Positive result for Iodometric β-lactamase detection

A

Colorless/White = β-lactamase producer

32
Q

Purpose of ESBL detection

A

Detects resistance to Penicillin, Monobactams, and Cephalosporins

33
Q

Organisms tested for ESBL

A

Klebsiella, E. coli

34
Q

Method for ESBL detection

A

Disk diffusion with Cefotaxime (CTX), Ceftazidime (CAZ), and Clavulanic acid (CLA)

35
Q

Incubation for ESBL detection

A

35°C, 24 hours

36
Q

Positive result for ESBL detection

A

Larger ZOI with CTX/CAZ + CLA compared to CTX or CAZ alone

37
Q

Purpose of Aminoglycoside screen

A

Detect high-level resistance to Aminoglycosides in Enterococci

38
Q

Medium for Aminoglycoside screen

A

BHI broth with Gentamicin and Streptomycin

39
Q

Incubation for Aminoglycoside screen

A

35°C, 24 hours

40
Q

Positive result for Aminoglycoside screen

A

Growth = Resistance

41
Q

Negative result for Aminoglycoside screen

A

No growth = Susceptible

42
Q

Purpose of ICR test

A

Detects inducible clindamycin resistance

43
Q

Organisms tested for ICR

A

S. aureus, S. lugdunensis, S. pneumoniae, beta-hemolytic Streptococci

44
Q

Media for ICR test

A

5% Sheep BAP or MHA with 15 µg Erythromycin (E) and 2 µg Clindamycin (Cd)

45
Q

Incubation for ICR test

A

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
Q

Positive result for ICR test

A

Flattening of CD zone (D-zone) = Clindamycin resistant

47
Q

Purpose of Modified Hodge test

A

Detects carbapenemase production in Enterobacterales

48
Q

Media for Modified Hodge test

49
Q

Disk for Modified Hodge test

A

10 µg Meropenem or Ertapenem

50
Q

Incubation for Modified Hodge test

A

35°C, 16-18 hours

51
Q

Positive result for Modified Hodge test

A

Clover-leaf like appearance, indented or enhanced growth

52
Q

Purpose of CNP test

A

Confirmatory test for carbapenemase production

53
Q

Reagents for CNP test

A

Imipenem, Phenol red indicator

54
Q

Incubation for CNP test

A

35°C, 2 hours

55
Q

Positive result for CNP test

A

Tube A = Red/Orange, Tube B = Yellow

56
Q

Determines MIC of 1 antimicrobial against 1 bacteria

A

Gradient diffusion testing

57
Q

1 gradient of antibiotic concentration in a plastic strip

A

E-test/Epsilometer

58
Q

1 gradient of antibiotic concentration in a paper strip

A

Liofilchem

59
Q

Concentration causing 99.9% reduction in CFU/mL after broth dilution and subculture

A

Minimum bactericidal concentration (MBC)

60
Q

Antibiotic inhibits but does not kill bacteria, linked to beta-lactam resistance

61
Q

Serum bactericidal test using patient’s own serum

A

Schlichter test

62
Q

Highest drug concentration in the serum

A

Peak specimen

63
Q

Lowest drug concentration in the serum

A

Trough specimen

64
Q

Drug peak concentration collection: IV 30–60 mins, IM 60 mins, Oral 90 mins after admin

A

Timing of specimen collection

65
Q

Bacteria inoculated in antimicrobial concentrations, incubated, and colony counts measured over time

A

Time-kill assay

66
Q

Effectiveness of multiple antimicrobials on a single bacterial strain

A

Synergy test

67
Q

Normal flora of the human microbiome

68
Q

Bacteria that multiply on the host

69
Q

Bacteria that do not multiply on the host

BACTERIOLOGY (49 decks)

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