Antimicrobial Suceptibility Testing

Question 1

These are compounds that kill or inhibit microorganisms.

Answer 1

Antimicrobials

Question 2

These are antimicrobials, usually of low molecular weight, produced by microorganisms that inhibit or kill other microorganisms.

Answer 2

Antibiotics

Question 3

It is performed on bacterial and fungal isolates to determine which antimicrobial agents might be effective in treating infections caused by these organisms.

Answer 3

Antibiotic Susceptibility Testing

Question 4

What is the primary goal of AST?

Answer 4

To determine whether the bacterial isolate is capable of expressing resistance to the antimicrobial agents selectied for treatment.

Question 5

Which method/s are used for AST?

Answer 5

Diffusion and Dilution

Question 6

The methods for AST are done to determine the _____.

Answer 6

Minimal Inhibitory Concentration (MIC)

Question 7

It is the lowest antimicrobial concentration that completely inhibits visible bacterial growth.

Answer 7

Minimal Inhibitory Concentration (MIC)

Question 8

What is Minimal Inhibitory Concentration (MIC)?

Answer 8

It is the lowest antimicrobial concentration that completely inhibits visible bacterial growth.

Question 9

Standards that describe the methods for AST are published and frequently updated by the _________.

Answer 9

Clincal and Laboratory Standards Institute (CLSI)

Question 10

CLSI is formerly known as _____.

Answer 10

National Committee for Clinical Laboratory Standards (NCCLS)

Question 11

Standardized components of AST

Answer 11

• Bacterial inoculum size
• Growth medium
• Incubation atmosphere
• Incubation temperature
• Incubation duration
• Antimicrobial concentrations

Question 12

Bacterial Inoculum size for Disk Diffusion

Answer 12

1.5 x 10^8 CFU/mL

Question 13

Bacterial Inoculum size for Broth Microdilution

Answer 13

5 x 10^5 CFU/mL

Question 14

Standard growth medium for AST

Answer 14

Mueller-Hinton Base

Question 15

Growth medium components for AST

Answer 15

• pH
• Cation concentration
• Blood and serum supplements
• Thymidine content

Question 16

Standard pH of growth medium for AST

Answer 16

7.2 - 7.4

Question 17

Standard cation concentration of growth medium for AST

Answer 17

• Ca: 25 mg/L
• Mg: 12.5 mg/L

Question 18

Incubation atmosphere for AST

Answer 18

Ambient air

Question 19

Incubation temperature for AST

Answer 19

35 C

Question 20

Incubation duration for AST (Disk Diffusion)

Answer 20

16 - 18 hours

Question 21

Incubation duration for AST (Broth Microdilution)

Answer 21

16 - 20 hours

Question 22

Antimicrobial concentrations for AST

Answer 22

Based on CLSI, but the goal is to get the lowest concentration

Question 23

Agar depth for AST (Disk Diffusion)

Answer 23

3 - 5 mm

Question 24

Factors to consider when determining whether testing is warranted

Answer 24

• Body site from which the bacterium was isolated
• Presence of other organisms and quality of the specimen
• Host’s status

Question 25

Long term storage of ATB discs

Answer 25

-20 C or below in a non-frost-free freezer

Question 26

A working supply of disks can be stored in a refrigerator at ______ for at least 1 week.

Answer 26

2 - 8 C

Question 27

A working supply of disks can be stored in a refrigerator at 2-8 C for at least _____.

Answer 27

1 week

Question 28

Disks should always be stored in a tightly sealed container with ______.

Answer 28

desiccant

Question 29

The container should be allowed to warm to room temperature before opening to prevent _______.

Answer 29

condensation

Question 30

The container should be allowed to warm to ________ before opening to prevent condensation.

Answer 30

room temperature

Question 31

Which tool is used to obtain ATBs from the ampule?

Answer 31

Forceps

Question 32

Desiccant is used to ______.

Answer 32

prevent moisture

Question 33

It is one of the most critical steps in susceptibility testing.

Answer 33

Inoculum preparation

Question 34

# **Inoculum Preparation** Prepared by adding cells from ____ of similar colony morphology.

Answer 34

four to five isolated colonies

Question 35

# **Inoculum Preparation** Isolated colonies added are allowed to grow to the ____ phase.

Answer 35

log

Question 36

This result is obtained when too few bacteria are tested.

Answer 36

False-susceptible

Question 37

This result is obtained when too many bacteria are tested.

Answer 37

False-resistant

Question 38

The ____ of the inoculum is compared to the McFarland Standard.

Answer 38

turbidity

Question 39

Components of McFarland Turbidity Standard

Answer 39

* 99.5 mL of 1% sulfuric acid * 0.5 mL of 1.175% barium chloride

Question 40

If the inoculum is not turbid enough to meet the McFarland Standard, what should be done?

Answer 40

Add more organism

Question 41

If the inoculum is too turbid to meet the McFarland Standard, what should be done?

Answer 41

Dilute by adding more broth

Question 42

Methods of Diffusion in AST

Answer 42

* Kirby-Bauer Diffusion Method * Agar Cup Diffusion Method * Agar Cylinder Diffusion Method * Epsilometer or Gradient Diffusion Method

Question 43

Methods of Dilution in AST

Answer 43

* Macrobroth Method or Tube Dilution Method * Microtube Dilution Method

Question 44

Volume of broth in Macrobroth Method

Answer 44

1 mL or greater

Question 45

Volume of broth in Microtube Dilution Method

Answer 45

0.05 mL to 0.1 mL

Question 46

The most common method of Diffusion

Answer 46

Kirby-Bauer Diffusion Method

Question 47

Kirby-Bauer Diffusion Method is also known as _______.

Answer 47

* Agar Diffusion Method * Disk Diffusion Method

Question 48

Step-by-Step Procedure for AST

Answer 48

1. Preparation of pure inoculum 2. Standardize pure inoculum 3. Streak the pure inoculum 4. Appy antibiotic discs 5. Incubate 6. Measure ZOI

Question 49

Which media can be used for AST?

Answer 49

* Mueller-Hinton Broth * Trypticase Soy Agar * Sterilized Distilled Water * Natural Saline Solution * Brain Heart Infusion Broth

Question 50

Which tool is used to streak the pure inoculum into the medium for AST?

Answer 50

Sterile cotton swab

Question 51

What motion/pattern is used in streaking the pure inoculum on the agar in AST?

Answer 51

Zigzag

Question 52

The spaces between each antibiotic must be ____ away from each other.

Answer 52

15 mm

Question 53

Instrument/s used for measuring ZOI

Answer 53

* Ruler * Microcaliper * Vernier caliper

Question 54

Unit of measurement for measuring ZOI

Answer 54

mm

Question 55

# **Identify the test being described.** It measures the amount of antimicrobial agent in serum or body fluid.

Answer 55

Antimicrobial Concentration Test (Assay)

Question 56

# **Identify the test being described.** It measures the lowest concentration of antimicrobial agent that kills a bacterial isolate.

Answer 56

Minimum Bactericidal Concentration Test

Question 57

# **Identify the test being described.** It measures the highest dilution or titer of a patient's serum that is inhibitory to the patient's own infecting bacterium and highest dilution or titer that is bactericidal.

Answer 57

Serum Bactericidal Test

Question 58

# **Identify the test being described.** It measures the susceptibility of a bacterial isolate to a combination of two or more antimicrobial agents.

Answer 58

Synergy Test

Question 59

# **Identify the test being described.** It measures the rate of killing of bacteria by an antimicrobial agent.

Answer 59

Time-kill Assay

Question 60

Antibiotics affecting gram (+) organisms only

Answer 60

* Vancomycin * Bacitracin

Question 61

Antibiotics affecting *Mycobacterium tuberculosis*

Answer 61

Isoniazid

Question 62

Antibiotics affecting gram (+) and (-) organisms

Answer 62

* Penicillin * Fluoroquinolones * Rifamycins * Tetracyclines * Streptomycin * Chloramphenicol * Sulfa drugs

Question 63

ATBs targeting the cell wall

Answer 63

* Penicillin * Vancomycin * Bacitracin * Isoniazid

Question 64

ATBs targeting the DNA

Answer 64

Fluoroquinolones

Question 65

ATBs targeting the RNA

Answer 65

Rifamycin

Question 66

ATBs targeting protein synthesis

Answer 66

* Tetracyclines * Streptomycin * Chloramphenicol

Question 67

# **Abbreviate the ATB** Penicillin

Answer 67

PCN

Question 68

# **Abbreviate the ATB** Vancomycin

Answer 68

VAN

Question 69

# **Abbreviate the ATB** Bacitracin

Answer 69

BAC

Question 70

# **Abbreviate the ATB** Isoniazid

Answer 70

INH

Question 71

# **Abbreviate the ATB** Fluoroquinolones

Answer 71

FQ

Question 72

# **Abbreviate the ATB** Rifamycins

Answer 72

RIF

Question 73

# **Abbreviate the ATB** Tetracyclines

Answer 73

TET

Question 74

# **Abbreviate the ATB** Streptomycin

Answer 74

STR

Question 75

# **Abbreviate the ATB** Chloramphenicol

Answer 75

CHL

Question 76

# **Abbreviate the ATB** Meropenem

Answer 76

MPM

Question 77

# **Abbreviate the ATB** Imipenem

Answer 77

IPM

Question 78

# **Abbreviate the ATB** Levofloxacin

Answer 78

LEV

Question 79

# **Abbreviate the ATB** Ciprofloxacin

Answer 79

CIP

Question 80

# **Abbreviate the ATB** Erythromycin

Answer 80

ERY

Question 81

# **Abbreviate the ATB** Amoxicillin

Answer 81

AMX

Question 82

# **Abbreviate the ATB** Gentamycin

Answer 82

GEN

Question 83

# **Abbreviate the ATB** Aztreonam

Answer 83

ATM

Question 84

# **Abbreviate the ATB** Ceftriaxone

Answer 84

CRO

Question 85

# **Abbreviate the ATB** Polymixin B

Answer 85

PB

Question 86

# **Abbreviate the ATB** Azithromycin

Answer 86

AZM

Question 87

Concentration of Meropenem

Answer 87

10 ug

Question 88

Concentration of Imipenem

Answer 88

10 ug

Question 89

Concentration of Levofloxacin

Answer 89

5 ug

Question 90

Concentration of Ciprofloxacin

Answer 90

5 ug

Question 91

Concentration of Erythromycin

Answer 91

15 ug

Question 92

Concentration of Amoxicillin

Answer 92

30 ug