ANTIMICROBIAL SUSCEPTIBILITY TESTING

Question 1

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

Answer 1

Minimal Inhibitory Concentration (MIC)

Question 2

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

Answer 2

Minimal Bactericidal Concentration (MBC)

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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

Question 5

Plate size used in Kirby-Bauer disk diffusion test:

Answer 5

150 x 15 mm plate

Question 6

Agar used in KB disk diffusion test:

Answer 6

Mueller-Hinton Agar

Question 7

pH of the medium should be:

Answer 7

7.2 to 7.4 pH

Question 8

Agar depth should be held constant at:

Answer 8

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

Question 9

The density of the inoculum should be adjusted to:

Answer 9

0.5 McFarland Standard

Question 10

Equivalence of McFarland standard into CFU/mL

Answer 10

1.5 x 10^8 CFU/mL

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

Question 11

Preparation of McFarland Standard:

Answer 11

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

Question 12

Too heavy inoculum results in:

Answer 12

Smaller zones/ False resistant

Question 13

Too light inoculum results in:

Answer 13

Larger zones/ False susceptible

Question 14

Only overnight colonies less than ____ hours should be test.

Answer 14

24 hours

Question 15

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

Answer 15

at least 5 minutes but not more than 30 minutes

Question 16

Too much moisture on the surface of agar results in:

Answer 16

Confluent growth, smaller zone, FR (false resistant)

Question 17

Very dry agar surface results in:

Answer 17

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

Question 18

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

Answer 18

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

Question 19

Distance between the disk is:

Answer 19

24 mm

Question 20

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

Answer 20

1. Penicillin
2. methicillin

Question 21

Incubate plate at:

Answer 21

35C for 16-18 hours

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

Question 22

Incubation of MRSA may require:

Answer 22

24 hours

Question 23

Incubate the plate in an _______ position

Answer 23

UPSIDE DOWN

Question 24

Why are plates incubated in an Upside-down position?

Answer 24

To avoid accumulation of moisture

Question 25

Quality control for MIC: Test QC strains of ______, ______, _______, _______ for _______ days.

Answer 25

Test QC strains of: E. coli S. aureus P. aeruginosa Enterococcus faecalis for 20-30 consecutive days.

Question 26

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

Answer 26

weekly

Question 27

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

Answer 27

1. Acidometric 2. Iodometric 3. Chromogenic

Question 28

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

Answer 28

Chromogenic

Question 29

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

Answer 29

RED

Question 30

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

Answer 30

E test

Question 31

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

Answer 31

D test