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[3Y1S] MT 6320 > U2.1.2 AST > Flashcards

U2.1.2 AST Flashcards

1
Q

Performedonbacteriaisolatedfromclinical specimens that are clinically significant

A

AST

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2
Q

T/F The goal of AST is to provide STANDARDIZED in-vitro testing of a bacterial pathogen to a set of available antibiotics to determine its “antibiogram” in order to predict the in vivo effectiveness of a particular
antibiotic or antibiotic regimen

A

True

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3
Q

T/F In AST, the normal flora and the implicated/probable bacteria causing the infection should be tested.

A

False, Implicated/probable bacteria causing the infection should only be tested !

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4
Q

T/F All organisms are subject to AST

A

False

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5
Q

Odd One Out

Organisms that are not subject to AST
a. S. pyogenes
b. H. influenzae
c. N. meningitidis
d. L. monocytogenes

A

b. H. influenzae
- Testing occasionally required

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6
Q

Odd One Out

Organisms that are subject to AST
a. S. pyogenes
b. S. pneumoniae
c. Enterococci
d. P. aeruginosa

A

a. S. pyogenes
- not subject to AST

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7
Q

Odd One Out

Organisms that are subject to AST
a. N. gonorrhoeae
b. H. influenzae
c. N. meningitidis
d. M. cattarhalis

A

c. N. meningitidis
- not subject to AST

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8
Q

T/F

Standardization of AST is important to optimize bacterial growth conditions to ensure that the inhibition of growth can be attributed to the antimicrobial agent.

A

T

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9
Q

T/F

Standardization of AST is important to optimize conditions for maintaining antimicrobial integrity and activity, attributing the failure to inhibit bacterial growth to organism-associated resistance.

A

T

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10
Q

T/F

Standardization of AST is important to maintain reproducibility and consistency in the resistance profile of an organism, regardless of what laboratory performs the test.

A

T

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11
Q

T/F

Methods used in AST directly measure the activitv of only one antimicrobial agents

A

F; one or more

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12
Q

T/F

Methods of AST directly detect the absence of a specific resistance mechanism

A

F; directly detect the presence

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13
Q

T/F

Methods of AST use special methods that measure complex antimicrobial-organism interactions

A

T

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14
Q

Standardization of AST

Bacterial inoculum size

A

1.5x10^8 CFU/mL

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15
Q

Standardization of AST

Colonies

A

should not be > 1 day old

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16
Q

Standardization of AST

If colony is too thin, _____
If colony is too thick, ____

A

too thin = incubate
too thick = add broth, sterile NSS

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17
Q

Standardization of AST

Growth medium : pH

A

7.2-7.4

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18
Q

Standardization of AST

Growth medium : Cation concentration

A

Ca : 25 mg/L
Mg : 12.5 mg/L

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19
Q

Standardization of AST

Incubation atmosphere

A

humidified, ambient air; no CO2

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20
Q

Standardization of AST

Incubation temperature

A

35-37 C

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20
Q

Standardization of AST

Incubation duration

A

16-18 hrs

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21
Q

Standardization of AST

Antimicrobial concentrations

A

Short term : 2-8C
Long term : -70C

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22
Q

Standardization of AST

Plate Diameter
100 mm = # of disks

A

10 disks

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23
Q

Standardization of AST

Plate Diameter
150 mm = # of disks

A

12 disks

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24
Q

3 Methods that directly measure the activity of one or more antimicrobial agents

A
  1. Traditional AST Methods
  2. Commercially Available Methods
  3. Special Screens & Indicator Tests
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25
Q

Traditional AST Methods

Preparation of the Standardized Inoculum : Picking of #-# similar looking colonies from a non-inhibitory medium

A

4-5 similar looking colonies

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26
Q

Traditional AST Methods

Preparation of the Standardized Inoculum : Picked colonies are then transferred to a broth medium
and allowed to grow to ____ phase (___ hrs)

A

Log phase; 3-5 hrs

27
Q

Traditional AST Methods

Preparation of the Standardized Inoculum : Alternative Method for Fastidious Organisms

A
  1. Pick 4-5 colonies from a fresh
    (16-24hr) culture
  2. Suspend in broth or NSS diluted to
    proper density
28
Q

Traditional AST Methods

Preparation of Standardized Inoculum : Tubirdity of broth is standardized by comparing it with ______

A

0.5 MacFarland Standard

29
Q

Traditional AST Methods

Preparation of MacFarland Standard

A

0.5mL 1.175% Barium Chloride
99.5 mL 1.5% Sulfuric Acid

30
Q

Traditional AST Methods

Inoculum Standardization : Standardized Inoculum must be used within ____ minutes

A

15 minutes

31
Q

Traditional AST Methods

Comparison is done ____. Methods done for precision are ___

A

comparison : visually
methods : nephelometric or spectrophotometric

32
Q

Traditional AST Methods

Commercially available and widely used standard

A

0.5 McFarland Standard

33
Q

Traditional AST Methods

QC : McFarland Standard should be checked _____. At _____nm

A

checked montly; 625nm

34
Q

Traditional AST Methods: Choice of Antimicrobials

Selection of Test Batteries/ Panel depends on :

A
  • Protocol of hospital
  • ID of organism
  • any known resistance patterns
  • method of AST
  • availability of antimicrobial agents
35
Q

Traditional AST Methods

Other name for disk diffusion Method

A

Kirby Bauer

36
Q

Traditional AST Methods

Commonly used in vitro tests in the laboratory

A

Disk Diffusion Method

37
Q

Traditional AST Methods

Agar used in Kirby Bauer

A

Mueller Hinton Agar

38
Q

Traditional AST Methods

Measured in Kirby Bauer

A

Diameters of zones of inhibitions

39
Q

Traditional AST Methods

Findings in Kirby Bauer is reported as

A

SIR
Susceptible, Intermediate, Resistant

40
Q

T/F Kirby Bauer Method : As the agent diffuses farther, the concentration increases until it reaches a point when the bacterial growth is not anymore inhibited.

A

F, concentration decreases

41
Q

Traditional AST Methods

Based on the inverse linear relationship between the zone of inhibition diameter and the logarithm of the minimum inhibitory concentration (MIC)

A

Kirby Bauer Method

42
Q

Kirby Bauer Method

Incubation

A

35C for 16-18 hours at ambient atmosphere

43
Q

Kirby Bauer Method

For Fastidious Organisms

A

5-10% CO2

44
Q

Kirby Bauer Method

Characteristic of reading plates

A

should be confluent, no individual colonies should be present

45
Q

Kirby Bauer Method

Factors ignored during reading (3)

A
  1. Proteus : hazy/swarming growth within the zone
  2. Sulfonamides & TMP : hazing
  3. Beta-hemolytic bacteria : hemolysis produced
46
Q

Traditional AST Methods

Determine Minimum
Inhibitory Concentration (MIC)

A

Dilution Susceptibility Testing

47
Q

Traditional AST Methods

  • Use of serial 2-fold dilutions
    of the antimicrobial agent (expressed as ug or mcg/ml)
  • Once MIC is determined, ti is interpreted as S, I, R
A

Dilution Susceptibility Testing

48
Q

Dilution Susceptibility Testing

2 Types of Broth Dilution

A

Macrodilution & Microdilution

49
Q

Dilution Susceptibility Testing : Broth Dilution

Use of test tubes, Volume: 1-2 ml

A

Macrodilution

50
Q

Dilution Susceptibility Testing : Broth Dilution

Use of wells, Volume: 0.05-0.1mL

A

Microdilution

51
Q

Broth Dilution

Report the MIC and is translated into the 3 general interpretative categories :

A

SIR
Susceptible, Intermediate, Resistant

52
Q

Broth Dilution

NB: Recently added categories include

A
  1. Susceptible Dose Dependent
  2. Non susceptible
53
Q

Broth Dilution

specific concentrations that separate or define the different
categories

A

Breakpoints

54
Q

Dilution Susceptibility Testing

Antimicrobial Concentrations and organisms to be tested are placed together on an agar medium

A

Spot Inoculation

55
Q

Dilution Susceptibility Testing

Series of dilutions, with one dilution per plate

A

Agar Dilution

56
Q

Dilution Susceptibility Testing

Standard Inoculum for Agar Dilution

A

1x10^4 CFU/spot

57
Q

Dilution Susceptibility Testing

lowest concentration of an antimicrobial agent ni agar that completely inhibits visible growth

A

MIC

58
Q

Dilution Susceptibility Testing

Advantage: Anaerobic OrganismsUseful for determining the MIC of N. gonorrhoeae

A

Agar Plate Dilution

59
Q

Commercially Available Methods (2)

A
  1. Diffusion in Agar Derivation
  2. E-test
60
Q

Commercially Available Methods

also known as Gradient Diffusion Susceptibility Test

A

E-test

61
Q

Commercially Available Methods

Principle: Establishment of an antimicrobial density gradient

A

E-test

62
Q

E-test

Uses _____________ placed in a radial fashion on an inoculated plate.

A

thin plastic strips (with gradations)

63
Q

E-test

Interpretation : MIC is read wherein the ____________-

A

growth ellipse intersects the Etest strip

64
Q

E-test

used for ____ organisms

A

fastidious organisms

[3Y1S] MT 6320 (8 decks)

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