ANTIMICROBIAL SUSCEPTIBILITY TESTING Flashcards

memorization

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1
Q

It is the least amount of antibiotic (highest dilution) that prevents visible growth.

A

Minimal Inhibitory Concentration (MIC)

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2
Q

Concentration of antibiotic that results in 99.9% decrease in CFU per mL

A

Minimal Bactericidal Concentration (MBC)

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3
Q

Kirby-Bauer disk diffusion test:

Principle: There is a/an ________ relationship the diameter of the zone of inhibited growth around the antibiotic disk and the logarithm of the ____________ of the antibiotic

A

There is an INVERSE LINEAR relationship;
the logarithm of the MINIMAL INHIBITORY CONCENTRATION

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4
Q

The lower the MIC, the ____ potency, and the ________ zone of inhibition

A

The lower the MIC, the higher potency, and the larger the zone of inhibition

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5
Q

Plate size used in Kirby-Bauer disk diffusion test:

A

150 x 15 mm plate

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6
Q

Agar used in KB disk diffusion test:

A

Mueller-Hinton Agar

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7
Q

pH of the medium should be:

A

7.2 to 7.4 pH

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8
Q

Agar depth should be held constant at:

A

4 mm (if in range: 4-6 mm)

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9
Q

The density of the inoculum should be adjusted to:

A

0.5 McFarland Standard

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10
Q

Equivalence of McFarland standard into CFU/mL

A

1.5 x 10^8 CFU/mL

if in range: 1-2 x 10^8 CFU/mL (Recall)

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11
Q

Preparation of McFarland Standard:

A

0.5 mL of 1.175% BaCl2 and
99.5 mL of 1% H2SO4

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12
Q

Too heavy inoculum results in:

A

Smaller zones/ False resistant

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13
Q

Too light inoculum results in:

A

Larger zones/ False susceptible

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14
Q

Only overnight colonies less than ____ hours should be test.

A

24 hours

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15
Q

Let inoculum dry at least ______ but not more than ______ before adding the disks.

A

at least 5 minutes but not more than 30 minutes

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16
Q

Too much moisture on the surface of agar results in:

A

Confluent growth, smaller zone, FR (false resistant)

17
Q

Very dry agar surface results in:

A

Gives poor growth, larger zone, FS (false susceptible)

18
Q

Place no more than ____ disks per 150-mm plate (___ disks in outer ring, ___ in center)

A

Place no more than 12 disks per 150 mm plate (8 disks in outer ring, 4 in center)

19
Q

Distance between the disk is:

A

24 mm

20
Q

Antibiotics that are best indicators of poor storage, as they are the first to deteriorate

A
  1. Penicillin
  2. methicillin
21
Q

Incubate plate at:

A

35C for 16-18 hours

If in range: 35 +/- 2C (Recall)

22
Q

Incubation of MRSA may require:

A

24 hours

23
Q

Incubate the plate in an _______ position

A

UPSIDE DOWN

24
Q

Why are plates incubated in an Upside-down position?

A

To avoid accumulation of moisture

25
Q

Quality control:

Test QC strains of ______, ______, _______, _______ for _______ days.

A

Test QC strains of:
E. coli
S. aureus
P. aeruginosa
Enterococcus faecalis

for 20-30 consecutive days.

26
Q

If QC results are acceptable, frequency can be reduced to ______ basis.

A

weekly

27
Q

Three (3) types of B-lactamase direct tests:

A
  1. Acidometric
  2. Iodometric
  3. Chromogenic
28
Q

Most sensitive, most specific, and easiest B-lactamase test to use:

A

Chromogenic

29
Q

What is the positive color of the chromogenic B-lactamase test?

A

RED

30
Q

Plastic strip containing antibiotic concentration gradient placed on inoculum lawn on Mueller-Hinton plate & incubated overnight. It is used to determine MIC:

A

E test

31
Q

A test used to detect inducible clindamycin resistance MRSA isolates that are resistant to erythromycin & susceptible to clindamycin on initial testing.

A

D test