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PHRM 865: Theraputics V > Susceptibility Testing > Flashcards

Susceptibility Testing Flashcards

1
Q

What types of susceptibility testing are there?

A
  • Disc Diffusion, Vitek 2, Etest, Agar Dilution, Broth Dilution
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2
Q

What is the importance about the Broth Dilution in Susceptibility Testing?

A
  • Two fold dilution of drug conc. liquid media [Broth] with no proteins
  • GOLD STANDARD
  • Looks at MIC and MBC
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3
Q

What is the difference between MIC and MBC?

A
  • Minimum Inhibitory Conc. [MIC]: lowest drug conc. that prevents visable growth
  • Minimum Bactericidal Conc. [MBC]: lowest drug conc. resulting in> 99.9% decreased in inoculum (not done often)
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4
Q

What is the importance of Agar Dilution in Susceptibility Testing?

A
  • Two fold dilution of antibiotics incorporated in molten agar, poured into petro dishes, and then allowed to solidify
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5
Q

What is important to know about Epsilometer Test [Etest] in Susceptibility Testing?

A
  • Plastic strips containing a continuous conc. gradient of drug where microorganism are streaked onto
  • More “Precise”
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6
Q

What is the importacne of Vitvek 2 in Susceptibility Testing?

A
  • Small plastic reagent cards containing 64 wall for testing
  • Looks at turbidity
  • Computerized
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7
Q

What are the two automated AST systems and what is important to know about them?

A
  • Mircoscan & BD Phoneix
  • ALGORITHM-DERIVED MIC
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8
Q

What is important to know about Disc Diffusion [Kirby Bauer] in Susceptibility Testing?

A
  • Fixed amount of antibiotics on disc creating zone of inhibition
  • Results are S, I, R; NO MIC
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9
Q

What is the definition of a breakpoint?

A
  • MIC or zone diameter used to categorize an organism into 1 of 5 criteria [Susceptible, Susceptible-dose Dependent, Intermiediate, Resistant, Nonsusceptible]
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10
Q

What is Susceptibile in Interpretice Criteria?

A
  • Isolates with MIC at or below or zone diameter at or great than susceptibility breakpoint are inhibited by normal dosing.
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11
Q

What is Susceptibile-Dose Dependent in Interpretive Criteria?

A
  • Susceptibility is dependent on the dosing regimen that is used
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12
Q

What is Intermediate in Interpretive Criteria?

A
  • Isolates with MICs approaches conc. and response rate maybe lower then for susceptible isolates UNLESS it is concentrated
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13
Q

What is Resistant in Interpretive Criteria?

A
  • Isolates with MIC at or above or zone diameter at or below the resistant breakpoint are not inhibited
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14
Q

What is Nonsusceptible in Interpretive Criteria?

A
  • Isolates for which only susceptable breakpoint is designated
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15
Q

How are Breakpoints/interpretive criteria established?

A
  • Pharmacology [PK/PD]
  • Outcomes [Clinical or Bacteriologic]
  • Phenotypes
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16
Q

What is selective and cascade reporting in Susceptibilty testing and what is there rationale?

A
  • Selective: Based on defined criteria unrelated to AST
  • Cascade: Based on AST
  • They want to encourage appropriate use of antimicrobial agents
17
Q

What is the Inoculum Effect within Susceptibility Testing?

A
  • Increased in MIC when higher inoculum is used will increase the activity
  • More common in b-lactams
18
Q

What is Tolerance in Susceptibility Testing?

A
  • MBC > 32 x MIC
  • Has poor outcomes because MBC is rarely found
19
Q

What are some of the important terms to know about when talking about MIC Statistics in Susceptibilty Testing?

MIC50, MIC90, Range, Mean, Mode??

A
  • MIC50: antibiotic that inhibits 50%
  • MIC90: antibiotic that inhibits 90%
  • Range: lowest MIC to highest MIC
  • Geometric Mean MIC: antilog of the mean of the log MIC [better measurement]
  • Modal Mean: most common MIC
20
Q

What are the 3 general definition to know about when discussing Synergy Testing?

A
  • Synergy, Antagonism, Additivity
21
Q

What is the definition of Synergy in Synergy Testing?

A
  • The activity of an antimicrobial combination is greater then that expected from the additive activity on the individual agents
22
Q

What is the definition of Antagonism in Synergy Testing?

A
  • The activitiy of an antimircobial combination is less than that expected from the additive activity of the individual agents
23
Q

What is the definition of Additivity in Synergy Testing?

A
  • Neither synergy or antagonism
24
Q

What is the Checkerboard method of synergy testing?

A
  • Measures inhibitory activity of the combination of cross dilution of 2 antibiotics [does not mean killing]
25
Q

What is the Time-Killing Curves of synergy testing?

A
  • Measures the rate and extent of the killing [basically how much bug is left and are you actaully killing it]
26
Q

What is Post-Antibiotic Effect [PAE]?

A
  • Persistant effect of the antibiotic on bacterial growth after exposure

PHRM 865: Theraputics V (7 decks)

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