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VET 413: Infectious Disease/Immunology > Antimicrobial Resistance & Susceptibility > Flashcards

Antimicrobial Resistance & Susceptibility Flashcards

1
Q

antimicrobial resistance

A

the ability of a bacterium to survive and/or multiply when faced with a drug used to inhibit its growth and/or kill it

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2
Q

what are the outcomes of antimicrobial resistance

A
  • drug is no longer effective
  • increased animal disease and spread
  • drug eliminates good pathogens but not the targeted pathogen
  • use in animals can lead to resistance in humans
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3
Q

selective pressure

A

driving cause of antimicrobial resistance

antimicrobial kills off the bacteria that are susceptible and leave behind the ones that are resistant –> resistant population survives and grows

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4
Q

what are 4 mechanisms of bacteria use to become resistant

A
  1. pumping drug out of the bacteria
  2. preventing the entry of the drug into the bacteria
  3. inactivating the drug once inside
  4. changing the target site for the drug
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5
Q

intrinsic resistance

A

drug resistance that is naturally present in the microorganism

drug never has and never will work against the pathogen type

can NOT change this resistance - does not develop over time

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6
Q

acquired resistance

A

ability of a microorganism to survive and multiply in the presence of an antimicrobial that would normally inhibit/kill that organism

drug used to work but no longer does - develops over time

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7
Q

what are two methods of acquired resistance

A
  1. mutation
  2. acquisition
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8
Q

mutation

A

bacteria mutates its genetic code

rate of mutation increases with stress

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9
Q

acquisition

A

most common method

horizontal transfer of genes encoding resistance
- conjugation of plasmid
- transduction via bacteriophages
- transformation by up taking naked DNA

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10
Q

can acquisition of resistance occur between bacterial species

A

yes

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11
Q

how many resistant organisms does a normal population of bacteria have

A

very few - carrying around extra DNA is heavy

antimicrobial treatment will eliminate the susceptible bacteria and leave behind the resistant ones that will then proliferate to form a resistant population

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12
Q

antimicrobial susceptibility testing

A

method for determining if a bacterial isolate is susceptible to a range of antimicrobials that may be used to treat an infection with this bacteria

only a PREDICTION - not a guarantee

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13
Q

contraindications for susceptibility testing

A
  1. strain is predictably susceptible to certain antimicrobials
  2. infection type has high level of efficacy for empiric therapy (ex. first time UTIs)
  3. infection is highly mixed (will not provide useful information)
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14
Q

considerations for susceptibility testing

A
  • location of infection
  • breakpoints
  • MIC
  • zone of inhibition
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15
Q

how does location of infection impact susceptibility test result interpretation

A

test will predict if a particular drug will reach the tissue in concentrations high enough to inhibit bacteria

requires PK data to establish breakpoints specific for that location

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16
Q

breakpoints

A

cutoff values that determine the interpretation of MIC/zone of inhibition values as either susceptible, intermediate, or resistant

drug, host, and bacteria specific values

17
Q

do all species have established breakpoints

A

no - must extrapolate from other species or body sites

not always appropriate/accurate

18
Q

what drug concentration are breakpoints based off of

A

the concentration in the SERUM

19
Q

MIC

A

minimum inhibitory concentration

lowest concentration of antimicrobial drug that inhibits growth of a bacterium (ug/mL)

20
Q

zone of inhibition

A

diameter of bacterial growth that is inhibited around an antimicrobial disk

21
Q

what are the three methods of AST

A
  1. broth micro dilution
  2. E-test
  3. disk diffusion
22
Q

broth micro dilution

A

measures MIC

culture gets isolated and inoculated into broth –> placed into wells –> variable concentration of different drugs added to wells (drugs based off of panel type) –> check for growth

23
Q

broth micro dilution results

A
  1. no growth achieved at a specific concentration –> compare to breakpoint to determine if S, I, or R
    - MIC = lowest concentration that achieved no growth
  2. growth achieved at all concentrations –> resistant
    - MIC > highest concentration
  3. no growth achieved at any concentration –> susceptible
    - MIC < lowest concentration
24
Q

what does NA, NI, or NN mean on a susceptibility report

A

no information provided to categorize as S, I or R

25
Q

what are the pros of broth microdilution

A
  • gets an MIC
  • has standardized breakpoints
  • works for some slow growing or fastidious organisms
26
Q

what are the cons of broth microdilution

A
  • more expensive
  • need special equipment
27
Q

e-test

A

antimicrobial strip testing

measures MIC

28
Q

disk diffusion

A

measures zone of inhibition

standardized lawn of bacteria spread over plate –> filter paper disks with antimicrobial applied to lawn –> incubate –> check for zone diameter of inhibition

29
Q

disk diffusion result interpretations

A

S, I, or R depending on zone size, drug, and host species

30
Q

pros of disk diffusion

A
  • easy
  • inexpensive
  • no special equipment
  • more flexibility with drugs used
31
Q

cons of disk diffusion

A
  • no MIC measured
  • doesn’t work for slow growing/fastidious organisms
32
Q

AST interpretation

A

categorization based on breakpoints established for host, drug, and organism based on the MIC or zone diameter

used to determine whether a drug can be used to treat an infection

33
Q

susceptible

A

bacterial isolate is inhibited by usually attainable concentration of drug for infection site

MIC </= susceptibility breakpoint

34
Q

intermediate

A

MIC approaches the usually attainable concentration levels for susceptible isolates

clinical efficacy might be achieved in body sites where the drug concentrates

MIC = intermediate breakpoint

35
Q

resistant

A

bacterial isolate is not inhibited by the usually achievable concentrations of antimicrobial

MIC >/= resistant breakpoint

36
Q

effect of susceptibility report on drugs that reach greater concentration at the target site than in serum

A

susceptibility test will UNDERESTIMATE true susceptibility

ex. topical administration for skin infections or UTIs

37
Q

effect of susceptibility report on drugs that reach lower concentration at the target site than in serum

A

susceptibility test will OVERESTIMATE true susceptibility

ex. intracellular bacteria, eye, prostate

38
Q

does “no interpretation” mean that drug will not be effective

A

NO - only means that efficacy can’t be predicted

39
Q

is an interpretation of resistance or susceptibility more likely to be correct

A

resistance

R is more likely to correctly predict failure of the drug to work than S is likely to predict success of the drug

VET 413: Infectious Disease/Immunology (38 decks)

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