(Part 1) 1.21 Antimicrobial susceptibility Testing

Question 1

The goal of AST:

Determine whether the bacterial etiology of concern is capable of
expressing SUSCEPTIBILITY to the antimicrobial agents that are potential choices of therapy

T or F

Answer 1

F

RESISTANCE

Question 2

Lowest concentration of antimicrobial that completely inhibits visible growth

Answer 2

Minimum inhibitory concentration (MIC)

Question 3

Antimicrobial agent in question has ossible effectivenes against the isolate, but possible less

Answer 3

Intermediate

Question 4

Antimicrobial agent in question may be an appropriate choice for treating the infection

Answer 4

Susceptible

Question 5

Antimicrobial agent in question may not be an appropriate choice for treatment

Answer 5

Resistant

Question 6

Altering dosing results in higher drug exposure

Answer 6

Susceptible dose dependent SDD

Question 7

The antimicrobial agent with MICs above a susceptible breakpoint

Answer 7

Nonsusceptible

Question 8

Standard medium for any type of susceptibility test

Answer 8

Mueller Hinton agar

Question 9

What are the 2 important req for Inoculum prep?

Answer 9

Use of pure culture
Use of a standard sized inoculum

Question 10

Incubation for inoculum prep?

Answer 10

3-5 hrs at 35-37C

Question 11

Compare the turbidity of bacterial suspension with ?

Answer 11

0.5 McFarland standard

Question 12

Components of 0.5 McFarland standard

Answer 12

1% Sulfuric acid
1.175% barium chloride

Question 13

Matching the turbidity with 0.5 McFarland standard provides an optical density comparable to the density of a bacterial suspension of ______________

Answer 13

1.5x10^8 CFU/mL

Question 14

Methods used in AST:

Testing involves challenging the organisms of interest with antimicrobial agents in a liquid environment

Answer 14

Borth dilution: tube or microplate

Question 15

Methods used in AST:

Antimicrobials and organisms to be tested are brought together on an agar-based medium

Answer 15

Agar dilution

Question 16

In broth dilution, each antimicrobial agent is tested using a range of concentrations expressed as _______ of broth

Answer 16

mg/mL

Question 17

Methods used in AST:

Uses antibiotic diks placed on the surface of an agar plate seeded with a lawn of the bacterial isolate

Answer 17

Disk Diffusion (Kirby Bauer)

Question 18

The Zone of inhibition is directly proportional to the MIC

T or F

Answer 18

F

Inversely proportional

Question 19

How many mm of agar should be used in kirby bauer?

Answer 19

150 mm

Question 20

How many disks should be used in kirby bauer?

Answer 20

12

Question 21

How thick should the agar be in Kirby bauer?

Answer 21

4mm

Question 22

Incubation for kirby bauer

Answer 22

35C for 18-24 hrs

Question 23

As Ca2+ and Mg2+ increases ____________ becomes more resistant to aminoglycosides

Answer 23

P. aeruginosa

Question 24

What is the result for sulfonamides (Susceptible)

Answer 24

2 concentric rings around the disk

Question 25

Inoculum is too light

Very dry agar surface

<4mm agar depth

Higher disk concentration

> 15 mins delay after disk is applied and before incubation

Answer 25

False sensitive

Question 26

Inoculum is too heavy

Too much moisture on the agar

Agar depth >4mm

Deteriorating antibiotic disks

> 15 mins delay after seeding the plate and before antibiotic disks are applied

Answer 26

False resistant

Question 27

In E-Test, “E” stands for?

Answer 27

Elliptical

Question 28

This test uses strips with varying concentrations of antibiotic along its length

Answer 28

E test

Question 29

How is MIC is taken in E test?

Answer 29

Growth inhibition edge intersects

Question 30

Principle of VITEK system?

Answer 30

Turbidimetry

Question 31

What is the substrate used in Beta lactamase Production

Answer 31

Cephalosporin

Question 32

Involves continuation of conventional broth dilution testing

Answer 32

MBC

Question 33

Refers to the concentration resulting to a 99.9% reduction in CFU per milliliter

Answer 33

MBC

Question 34

Involves exposing a bacterial isolate to a concentration of antibiotic n a broth medium and measuring the rate of killing over a specified time period.

Answer 34

Time-kill studies

Question 35

Analogous to the MIC-MBC test except that the test medium used is the patient’s serum containing the therapeutic antimicrobial agents the patient has been receiving

Answer 35

Serum bactericidal test (Schlicter Test)

Question 36

In Schlicter test:

This specimen is collected after the antimicrobial agent is given

Answer 36

Peak specimen

Question 37

In Schlicter test

This specimen is collected just before the patient is to receive the next antimicrobial dose

Answer 37

Trough specimen

Question 38

The highed dilution the inhibits visibly detectable growth is the

Answer 38

serum-static titer

Question 39

Serum dilution resulting in a 99.9% reduction in the CFU/mL is recorded as

Answer 39

Serum-cidal titer