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Pharm 232 > Antibiotic Sensitivity > Flashcards

Antibiotic Sensitivity Flashcards

1
Q

Beta lactams: penicillin/cephalosporins

A

inhibit cell well synthesis

  • inhibit connecting peptioglycan in cell wall ; binds to penicillin binding protein and prevent penicillin binding peptidase from connecting peptidoglycan

**impact gram + more

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2
Q

Chloramphenicol: antimicrobial mechanism

A

Anti-50S: prevent protein synthesis via stopping elongation of peptide chain during protein synthesis

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3
Q

Aminoglycosides + tetracyclines: MoA

A

Anti30S: stop protein synthesis directly by causing misreading of mRNA

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4
Q

Quinolines + fluoroquinolones MoA

A

prevent DNA synthesis via inhibiting gyrase and topoisomerase (can’t unfold); this blocks DNA replication

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5
Q

Rifampin MoA

A

prevent RNA synthesis via interacting with DNA dependent RNA poly

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6
Q

Polymyxin B

A

disrupts PM - increase permeability + changes its structure
— allows more shit to get in and kill bacteria

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7
Q

Sulfonamides + trimethoprim: MoA

A

inhibit FA synthesis (impact growth and DNA synthesis)

  • integrates into precursor for FA — prevents its synthesis
  • prevent FA synthesis
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8
Q

Isoniazid MoA

A

inhibits mycolic acid synthesis (only in mycobacteria cell wall)

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9
Q

MIC

A

minimum conc that inhibits bacteria growth (no colonies)

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10
Q

MBC

A

minimum bacteriocidial concentration - min conc needed to kill set bacteria

** confirm : when remove drug and plate — still no growth

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11
Q

What is standarization and what are the aspects of testing that must be standarized?

A

process to minimize env. factors that could impact antimicrobial

  • optimize growing conditions: ensure that any inhibition of growth is because of the antimicrobial
  • optimize antimicrobial: failure to inhibit growth is a result of R
  • reproducibility

** exact time (based on bacteria), concentration, total volume of dilution

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12
Q

Traits of Ideal Antimicrobial Agents

A

selective toxic
soluble in bodily fluid
non-allergenic
reasonable half life
long shelf life
inexpensive

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13
Q

What is selective toxicity

A

drug is harmful to a pathogen without being harmful to host
- relative not absolute though

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14
Q

Toxic SEs of Antibiotics

A

Drugs may be toxic to kidney, liver or nerves

  • disrupt normal microbiome
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15
Q

Broad spectrum

A

Work on a large range of bacteria
- more likely to have off target effects that disrupt microbiome

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16
Q

Narrow spectrum antibiotics

A

increased selection, reduced non-selective toxicity

17
Q

Bacteriocidal vs Bacteriostatic

A

Bacteriocidal - kills bacteria, can be bacteriostatic at low concentrations

Bacteriostatic: stops bacteria growth when present, bacteria growth continues once it is removed; requires the host immune system to kill the bacteria

18
Q

What are the convenient susceptibility tests for measuring antimicrobial activity

A

disk diffusion
broth dilution
agar dilution

19
Q

Limits of standardization

A

can’t reproduce in vivo environment - aka where antibiotic and bacteria actually interact

  • factors that may impact outcome that aren’t accounted for in testing: diffusion into tissue/host cell, serum protein binding, immune system status, and virulence
20
Q

What is broth dilution testing

A

Range of concentrations of antimicrobial are examines in series of doubling dilutions (log 2)

  • look at difference concentrations: determined based off the safest therapeutic concentration possible, level needed to detect R
  • can help get MIC: first clear tube seen
    —- MIC than translated to susceptible, intermediate, or resistant category based on past studies
21
Q

Macro vs micro dilution

A

macro - 2mL
micro - 100 uL (normally on 96 well plate; more efficient)

22
Q

Advantages and Disadvantages of broth dilution testing

A

Advantages: quantitative, simple, easy to reproduce, could automate

Negatives: time consuming, tedious, uses a lot of media, possibility for human error

23
Q

What is agar dilution testing

A

serial dilutions of antibiotic is added to melted media and solidified (plates with different concentrations)

  • fixed number of organisms are then plated onto each plates (as dots); incubate and examine for colony growth

MIC - first plate with no colony growth

24
Q

Advantages and Disadvantages of agar dilution testing

A

Advantage: more gradual changes

Disadvantages: labour intensive, expensive and takes a lot of space

25
Q

What is the disc diffusion method?

A
  • make bacterial lawn : spread bacteria evenly over whole plate
  • add antibiotic discs onto plate, incubate
  • look for inhibition of growth around the disc; measure to get zone of inhibition

** requires standardized bacteria suspension, concentration of discs, incubation time, temp, media

26
Q

Epsilometer test

A

like disc test but strip with varying conc of drug on it
— gives zone of inhibition that looks like an egg

  • MIC where no growth
27
Q

Advantages and Disadvantages of Disc Diffusion

A

Advantages: simple, flexible, easy to replication, easy to interpret (mm of inhibition), consistent

Disadvantages: need to interpret results (diameter to conc —- need to characterize), qualitative

28
Q

Advantages and Disadvantages of Etest

A

Advantages: easy, well controlled concentrations

Disadvantages:high costs, limited number of antibiotics

29
Q

Types of Automated Antimicrobial testing

A

Vitek, MicroScan, BD Phoenix

  • automatically generate growth curve based on readings (done at the same time as the bacteria grows etc)
30
Q

Automated Testing Advantages and Disadvantages

A

A: less tedious, more reproducible, fast, automated date output

D: limited antimicrobial, limited ability to detect some forms of R, expensive

31
Q

What are breakpoints

A

interpretative criteria used for all susceptibility testing methods that is used to interpret results and put them into categories

—basically take a shit ton of information and create reference ranges to help categorize stuff

correlates zones with MICs seen in agar and broth testing

32
Q

T or F: as MIC decreases, zone of inhibition decreases

A

F - as MIC increases, zone decreases

33
Q

What are the 3 categories

A

1) Susceptible: agent may be appropriate choice; R is absent or not significant

2) Intermediate: maybe good if concentrations are good enough

3) Resistant: isolates not inhibited by antimicrobial

34
Q

Antimicrobial battery

A

antimicrobial agents that are chosen for testing against a set bacteria

35
Q

What are 3 pieces of info needed for all antibiotic orders?

A

when to take them
how much to take
how many days to take them

Pharm 232 (7 decks)

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