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Y3 Medical Micro > L10 Antibiotic sensitivity > Flashcards

L10 Antibiotic sensitivity Flashcards

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USMLE® Step 1 flashcards
1
Q

when did antibiotic development start

A

1930s

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2
Q

what are the problems with AMR development

A

resistance

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3
Q

what causes AMR

A

AB use in the food industry
AB overuse
AB misuse
resistance spread through the environment - used in animals

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4
Q

what is the development of AMR like

A

resistance increased

new AB decreased

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5
Q

what are AB

A

variety of substances derived from microorganisms that control the growth of or kill bacteria

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6
Q

what are synthetic AB

A

usually chemically related to natural AB, made to accomplish comparable tasks

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7
Q

what are AB for

A

infections

infectious diseases caused by bacteria

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8
Q

what was previously used forAB and where

A

Greece and Serbia - moudly bread to treat wounds and infections
Russia - warm soil

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9
Q

when was penicillin discovered

A

1928 alexander fleming

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10
Q

when was penicillin available and by who

A

early WW2 chain and florey developed penicillin

1943

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11
Q

what are the types of AB sensitivity testing

A

clinical
epidemiological
pharmaceutical

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12
Q

what is the clinical AB sensitivity tests used for

A

confirms organism is sensitive to AB being used to treat patient it suggests alternative AB

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13
Q

what is the epidemiological AB sensitivity testing used for

A

sensitivity data on common pathogens makes useful public health info, locally and nationally

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14
Q

what is the pharmaceutical AB sensitivity testing used for

A

Provides info on activity of new ABs against a range of pathogens

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15
Q

what is the cons of sensitivity tests

A

AB may be successful/fail even if organism lab report sensitive/resistant
sensitivity tests are crude estimates
can’t take into account many crucial aspects of infection

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16
Q

what is the clinical relevance of sensitivity tests for microorganisms

A

different phenotype in vivo
growth rate different in vivo
may adhere to devices

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17
Q

what is the clinical relevance of sensitivity tests for infection location

A 
intra/extracellular
body compartment
pus?
foreign body?
within a biofilm
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18
Q

what is the clinical relevance of sensitivity tests for host IM response

A

contributes to recovery from infection
influenced by disease
influenced by drugs

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19
Q

what is the clinical relevance of sensitivity tests for drug pharamcology

A

pharmacokinetic behaviour
distribution (intra/extracellular)
in vivo metabolism
infection site penetration

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20
Q

AB sensitivity test methods

A

agar diffusion assays
broth dilution assays
agar incorporation assays

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21
Q

how is an agar diffusion assay done

A

spread plate
place AB discs onto lawn
incubate overnight
examine for inhibition xones

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22
Q

how is the agar diffusion assay measured

A

quantitative - clearing is different depending on AB effect

zone of inhibition is related to minimum inhibitory concentration

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23
Q

what is the theory of agar diffusion assay

A

zone of inhibition radius determined by

  • AB diffusion rate
  • bacteria growth rate
  • sensitivity to AB
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24
Q

what is MIC

A

minimum inhibitory concentration

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25
Q

why are controls important for agar diffusion assays

A

zone size can be affected by number of other factors

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26
Q

what are the controls for agar diffusion assays

A

include control organism of known sensitivity

inoculate test organism and control organism on same ‘stokes plate’

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27
Q

what are the problems with agar diffusion assays

A

low solubility, ionic charge high molecular weight
growth rate of bacteria
AB conc in disc

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28
Q

what is the problem with low solubility, ionic charge high molecular weight problem in diffusion assays

A

poor diffusion

small zone of inhibition even if sensitive

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29
Q

what is the problem with growth rate of bacteria problem in diffusion assays

A

slow growing organisms give rise to large zones

30
Q

what is the problem with AB conc in disc problem in diffusion assays

A

commercially available discs have 67-150% tolerance, 30ug disc could have 2-45ug

31
Q

what is agar diffusion assay II

A

automated addition of AB disc

32
Q

what is the agar diffusion assay III E test

A

plastic strip with AB gradient and printed conc
incubation AB diffuses out and gradient made
E test meniscus - MIC = bacterial growth crosses numbered strip

33
Q

what is a broth dilution assay

A

grow large bacteria culture, split into several tubes
add different conc AB to each tube
incubate
see growth = MIC, AB required
can be spread on plate after to check for bactericidal

34
Q

what is MBC

A

minimum bactericidal conc

35
Q

what is bacteriostatic

A

plated from the broth dilution tubes - see when stopped growth in tube
but when plated onto agar that conc still grows = didnt kill bacteria

36
Q

what is a control for broth dilution assays

A

control organism of known sensitivity included in parallel

37
Q

what is an agar incorporation assay

A

inoculate plate containing AB with test cultures, controls using multipoint indicator

38
Q

what is the benefit pf agar incorporation assays

A

can test multiple organisms at once

39
Q

what is the agar incorporation breakpoint method

A

using appropriate series of selected AB (break point) conc MICs can be estimated

40
Q

what factors affect sensitivity tests

A

slow growing organisms
inoculum size must be standardised
culture medium composition

41
Q

affect of too much carbohydrate in culture medium

A

acid pH affects amino glycoside activity

42
Q

affect of thymine in culture medium

A

interferes with sulphonamide detection

43
Q

affect of divalent cations in culture medium

A

affect amino glycosides

44
Q

agar diffusion pros

A

low technology
quick set up
cheap
flexible

45
Q

agar diffusion cons

A

slow assay

46
Q

what is the affect for slow growing bacteria in sensitivity tests

A

mtb can take up to 4 weeks to grow

47
Q

how is mtb test sped up

A

measure production of co2 from labelled substrate

1-2 weeks

48
Q

what are the pros of broth dilution

A

accurate MIC

easy automation

49
Q

what are the pros of agar incorporation

A

20 + strains on one plate

easy to automate

50
Q

what are cons of agar incorporation

A

AB stability in agar

AB conc critical

51
Q

what is the agar diffusion assay

A

antibiotic diffuses from an impregnated paper disc into an agar medium on which the test organism is growing

52
Q

what is the broth dilution assay

A

serial dilutions of the antibiotic in growth medium are inoculated with the test organism

53
Q

what is the agar incorporation assay

A

antibiotic dilutions are incorporated in an agar medium and spot inoculated with a number of test organisms

54
Q

what is combination therapy indifference

A

actions of neither drug affected by presence of other

55
Q

what is combination therapy antagonism

A

one drug prevents full effect of another

56
Q

what is combination therapy synergism

A

two drugs work better together than sum of their individual activities

57
Q

when should combination therapy be used

A

treating severe infect when mo single agent sufficient
preventing emergence of resistant organisms
treating polymicrobial infections e.g. intra abdominal abscesses

58
Q

what may the beneficial interaction of AB in synergy do

A

potentiate activity of other at biochemical level
assist other to penetrate bacterial cell
protect from inactivation
overcome spontaneous mutation to resistance

59
Q

example of synergy that potentiate activity of other at biochemical level

A

trimethoprim and sulphonamides target sequential steps in folate synthesis in bacteria

60
Q

example of synergy that assist other to penetrate bacterial cell

A

penicillin and amino glycoside against enterococci due to increased uptake of latter

61
Q

example of synergy protect from inactivation

A

beta lactamase enzyme inhibitor protects beta lactam

62
Q

example of synergy spontaneous mutation to resistance

A

combination therapy of three drugs for TB treatment

63
Q

how can AB antagonism interfere with AB

A

antagonism of bactericidal activity
inducible resistance
chemical interactions

64
Q

examples of antagosims of bactericidal activity

A

bacteriostatic agents inhibit the activity of bactericidal agents like beta-lactams that rely on bacterial growth for killing activity
one AB with bateriostatic one with bactericidal = only stops growth doesnt kill - remove AB can recover

65
Q

example of antagonism inducible resistance

A

chromosomal beta-lactamases by potent inducers like cefoxitin, may cause resistance to poor inducers like cefotaxime

66
Q

example of antagonism chemical interactions

A

high conc beta lactam ring of some beta lactams can interact chemically with amino groups of amino glycosides = inactivate both

67
Q

alternative to AB sensitivity testing detecting phenotype

A

detect resistance gene itself

detect the protein product of resistance gene

68
Q

where is the mecA gene

A

SCCmec element

69
Q

how is SCCmec detected

A

PCR primer pairs

70
Q

how is MRSA detected

A

mecA protein product detected - resistance gene in MRSA
oxoid PBP2’ latex agglutination test
if RMSA present =clump

Y3 Medical Micro (16 decks)

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