WEEK 11: ANTIMICROBIAL SUSCEPTIBILITY TESTING

Question 1

reviewed the susceptibility testing
literature.

Answer 1

Kirby and Bauer

Question 2

standardized procedure for the disk diffusion
henceforth called the

Answer 2

Kirby-Bauer disk diffusion test.

Question 3

` is responsible for updating the original
procedure of Kirby Bauer disk diffusion through global
consensus process to ensure uniformity and reproducibility

Answer 3

CLSI

Question 4

A. Conventional Methods IN ANTIMICROBIAL SUSCEPTIBILITY

Answer 4

1. Broth dilution (gold standard)
2. Agar dilution
3. Disk diffusion

Question 5

COMMERCIAL SYSTEM IN ANTIMICROBIAL SUSCEPTIBILITY

Answer 5

Commercial Systems
1. Antibiotic gradient diffusion or E-test
2. Vitek 2

Question 6

 Doubling dilution is incorporated into agar
 Multiple isolates tested on each plate

Answer 6

AGAR DILUTION

Question 7

Visually examine for growth, determine MIC (minimum
inhibitory concentration)

Answer 7

AGAR DILUTION

Question 8

 Final amount of organism spotted IN AGAR DILUTION

Answer 8

 Final amount of organism spotted: 1 x 104 CFU

Question 9

 Agent is applied in gradient to a test strip
 Plate is seeded with organism as in K-B
 Agent diffuses away from strip to inhibit growth

Answer 9

Antibiotic Gradient Diffusion (E-Test)

Question 10

 Surface of agar plate seeded with lawn of test
organism
 Inoculum: swan from 0.5 McFarland
 Disk containing known concentration of agent placed
on surface of plate
 Measure if diameter of zone of inhibitioN

Answer 10

Disk-Diffusion (Kirby-Bauer)

Question 11

INOCULUM FOR Disk-Diffusion (Kirby-Bauer)

Answer 11

 Inoculum: swan from 0.5 McFarland

Question 12

ginal method of determining susceptibility to
antimicrobials was based on

Answer 12

broth dilution methods

Question 13

proposed a single disk method for
antimicrobial susceptibility testing.

Answer 13

University of Washington School of Medicine and the King
County Hospital

Question 14

form a committee in 1961 to lay the
groundwork for the development of a standardized
procedure for single antimicrobial disk susceptibility
testing.

Answer 14

WHO

Question 15

represents the standard for clinical
laboratories performing susceptibility testing today

Answer 15

Performance Standards for
Antimicrobial Disk Susceptibility Tests; Approved
Standard 9th Edition,

Question 16

determine the sensitivity or
resistance of pathogenic aerobic and facultative
anaerobic bacteria t

Answer 16

Kirby-Bauer disk diffusion

Question 17

viable alternative to broth
dilution methods for laboratories without the resources
to utilize the newer automated methods for broth
microdilution testing.

Answer 17

e disk diffusion method of Kirby and Bauer

Question 18

FILTER PAPER SIZE

Answer 18

6-mm filter paper disk impregnated with a
knownconcentration of an antimicrobial compound is
placed on a Mueller-Hinton (MH) agar plate,

Question 19

The rate of diffusion of the antimicrobial through the agar is dependent on

Answer 19

the diffusion and solubility properties
of the drug in MH agar and the molecular weight of the antimicrobial compound.

Question 20

r the inhibitory effects of the antimicrobial
compound. The estimated time of a bacterial
suspensionto reach critical mass is

Answer 20

4 to 10 hours

Question 21

The size of the zone of inhibition of growth is
influenced by the depth of the agar, since the

Answer 21

antimicrobial diffuses in three dimensions, thus a shallow layer of agar will produce a larger zone of inhibition thana deeper layeR

Question 22

The concentration of
antimicrobial compound at this margin is called the

Answer 22

critical concentration

Question 23

The current interpretation standards can be found in

Answer 23

the Clinical Laboratory Standards Institute
Performance Standards for Antimicrobial Disk
Susceptibility Tests: Approved Standards 9th Edition

Question 24

MH agar is considered the best medium to use for
routine susceptibility testing of non-fastidious
bacteria

Answer 24

MH AGAR

Question 25

Mueller-Hinton agar is stable for approximately

Answer 25

70 days

Question 26

f you prepare the MH agar plates from dehydrated media, the plates must be poured to a depth of

Answer 26

4 mm (approximately 25 ml of liquid agar for 100-mm plates and 60 ml of liquid agar for 150-mm plates, but in any case, to a measured depth of 4 mm).

Question 27

pH of the MH agar should fall

Answer 27

between 7.2 and 7.4 at
room temperature

Question 28

______________ can reverse the
inhibitory effects of sulfonamides and trimethoprim resulting in ___________

Answer 28

Excessive thymidine or thymine can reverse the
inhibitory effects of sulfonamides and trimethoprim
resulting in smaller and less distinct zones of inhibition,
or no zones at al

Question 29

incorrect concentration of divalent cations (calcium
and magnesium) will affect the

Answer 29

results of aminoglycoside
and tetracycline tests against Pseudomonas aeruginosa.

Question 30

Excess cation concentration will result in

Answer 30

reduced zone sizes and low concentration will increase zone size

Question 31

Excess calcium will increase the zone size of P.
aeruginosa against daptomycin. Excess zinc ions may

Answer 31

reduce the zone size of carbapenems against P. aeruginosa

Question 32

spring-loaded cartridges contain

Answer 32

25 or 50 disks

Question 33

ealed cartridges containing commercially prepared paper disks should be stored at room temperature

Answer 33

either 8°C or frozen at - 14°C in a non-self-defrosting freezer

Question 34

are suspensions of either
barium sulfate or latex particles that allow visual
comparison of bacterial density

Answer 34

mcFarland standards

Question 35

, which is a small card
containing parallelblack lines.

Answer 35

Wickerham card

nasa macfarland standard siya

Question 36

preparing mh agar

Answer 36

. Allow a MH agar plate (one for each organism to be
tested) to come to room temperature. It is preferable to
allow the plates to remain in the plastic sleeve while they
warm to minimize condensation.
2. If the surface of the agar has visible liquid present, set the
plate inverted, ajar on its lid to allow the excess liquid to
drain from the agar surface and evaporate. Plates may be
placed in a 35°C incubator or in a laminar flow hood at
room temperature until dry (usually 10 to 30 minutes).
3. Appropriately label each MH agar plate for each
organismto be tested

Question 37

preparation of incolum

Answer 37

1. Using a sterile inoculating loop or needle, touch four or
   five isolated colonies of the organism to be tested.
2. Suspend the organism in 2 ml of sterile saline.
3. Vortex the saline tube to create a smooth suspension.
4. Adjust the turbidity of this suspension to a 0.5 McFarland
   standard by adding more organism if the suspension is
   too light or diluting with sterile saline if the suspension is
   too heavy.
5. Use this suspension within 15 minutes of preparation.
   Antibiotic Susceptibility Disks
   Mcfarland Standard
   Protocol
   Preparation of Mueller-Hinton (MH) Plate
   P

Question 38

inc