L10 Antibiotic sensitivity Flashcards
when did antibiotic development start
1930s
what are the problems with AMR development
resistance
what causes AMR
AB use in the food industry
AB overuse
AB misuse
resistance spread through the environment - used in animals
what is the development of AMR like
resistance increased
new AB decreased
what are AB
variety of substances derived from microorganisms that control the growth of or kill bacteria
what are synthetic AB
usually chemically related to natural AB, made to accomplish comparable tasks
what are AB for
infections
infectious diseases caused by bacteria
what was previously used forAB and where
Greece and Serbia - moudly bread to treat wounds and infections
Russia - warm soil
when was penicillin discovered
1928 alexander fleming
when was penicillin available and by who
early WW2 chain and florey developed penicillin
1943
what are the types of AB sensitivity testing
clinical
epidemiological
pharmaceutical
what is the clinical AB sensitivity tests used for
confirms organism is sensitive to AB being used to treat patient it suggests alternative AB
what is the epidemiological AB sensitivity testing used for
sensitivity data on common pathogens makes useful public health info, locally and nationally
what is the pharmaceutical AB sensitivity testing used for
Provides info on activity of new ABs against a range of pathogens
what is the cons of sensitivity tests
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
what is the clinical relevance of sensitivity tests for microorganisms
different phenotype in vivo
growth rate different in vivo
may adhere to devices
what is the clinical relevance of sensitivity tests for infection location
intra/extracellular body compartment pus? foreign body? within a biofilm
what is the clinical relevance of sensitivity tests for host IM response
contributes to recovery from infection
influenced by disease
influenced by drugs
what is the clinical relevance of sensitivity tests for drug pharamcology
pharmacokinetic behaviour
distribution (intra/extracellular)
in vivo metabolism
infection site penetration
AB sensitivity test methods
agar diffusion assays
broth dilution assays
agar incorporation assays
how is an agar diffusion assay done
spread plate
place AB discs onto lawn
incubate overnight
examine for inhibition xones
how is the agar diffusion assay measured
quantitative - clearing is different depending on AB effect
zone of inhibition is related to minimum inhibitory concentration
what is the theory of agar diffusion assay
zone of inhibition radius determined by
- AB diffusion rate
- bacteria growth rate
- sensitivity to AB
what is MIC
minimum inhibitory concentration
why are controls important for agar diffusion assays
zone size can be affected by number of other factors
what are the controls for agar diffusion assays
include control organism of known sensitivity
inoculate test organism and control organism on same ‘stokes plate’
what are the problems with agar diffusion assays
low solubility, ionic charge high molecular weight
growth rate of bacteria
AB conc in disc
what is the problem with low solubility, ionic charge high molecular weight problem in diffusion assays
poor diffusion
small zone of inhibition even if sensitive
what is the problem with growth rate of bacteria problem in diffusion assays
slow growing organisms give rise to large zones
what is the problem with AB conc in disc problem in diffusion assays
commercially available discs have 67-150% tolerance, 30ug disc could have 2-45ug
what is agar diffusion assay II
automated addition of AB disc
what is the agar diffusion assay III E test
plastic strip with AB gradient and printed conc
incubation AB diffuses out and gradient made
E test meniscus - MIC = bacterial growth crosses numbered strip
what is a broth dilution assay
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
what is MBC
minimum bactericidal conc
what is bacteriostatic
plated from the broth dilution tubes - see when stopped growth in tube
but when plated onto agar that conc still grows = didnt kill bacteria
what is a control for broth dilution assays
control organism of known sensitivity included in parallel
what is an agar incorporation assay
inoculate plate containing AB with test cultures, controls using multipoint indicator
what is the benefit pf agar incorporation assays
can test multiple organisms at once
what is the agar incorporation breakpoint method
using appropriate series of selected AB (break point) conc MICs can be estimated
what factors affect sensitivity tests
slow growing organisms
inoculum size must be standardised
culture medium composition
affect of too much carbohydrate in culture medium
acid pH affects amino glycoside activity
affect of thymine in culture medium
interferes with sulphonamide detection
affect of divalent cations in culture medium
affect amino glycosides
agar diffusion pros
low technology
quick set up
cheap
flexible
agar diffusion cons
slow assay
what is the affect for slow growing bacteria in sensitivity tests
mtb can take up to 4 weeks to grow
how is mtb test sped up
measure production of co2 from labelled substrate
1-2 weeks
what are the pros of broth dilution
accurate MIC
easy automation
what are the pros of agar incorporation
20 + strains on one plate
easy to automate
what are cons of agar incorporation
AB stability in agar
AB conc critical
what is the agar diffusion assay
antibiotic diffuses from an impregnated paper disc into an agar medium on which the test organism is growing
what is the broth dilution assay
serial dilutions of the antibiotic in growth medium are inoculated with the test organism
what is the agar incorporation assay
antibiotic dilutions are incorporated in an agar medium and spot inoculated with a number of test organisms
what is combination therapy indifference
actions of neither drug affected by presence of other
what is combination therapy antagonism
one drug prevents full effect of another
what is combination therapy synergism
two drugs work better together than sum of their individual activities
when should combination therapy be used
treating severe infect when mo single agent sufficient
preventing emergence of resistant organisms
treating polymicrobial infections e.g. intra abdominal abscesses
what may the beneficial interaction of AB in synergy do
potentiate activity of other at biochemical level
assist other to penetrate bacterial cell
protect from inactivation
overcome spontaneous mutation to resistance
example of synergy that potentiate activity of other at biochemical level
trimethoprim and sulphonamides target sequential steps in folate synthesis in bacteria
example of synergy that assist other to penetrate bacterial cell
penicillin and amino glycoside against enterococci due to increased uptake of latter
example of synergy protect from inactivation
beta lactamase enzyme inhibitor protects beta lactam
example of synergy spontaneous mutation to resistance
combination therapy of three drugs for TB treatment
how can AB antagonism interfere with AB
antagonism of bactericidal activity
inducible resistance
chemical interactions
examples of antagosims of bactericidal activity
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
example of antagonism inducible resistance
chromosomal beta-lactamases by potent inducers like cefoxitin, may cause resistance to poor inducers like cefotaxime
example of antagonism chemical interactions
high conc beta lactam ring of some beta lactams can interact chemically with amino groups of amino glycosides = inactivate both
alternative to AB sensitivity testing detecting phenotype
detect resistance gene itself
detect the protein product of resistance gene
where is the mecA gene
SCCmec element
how is SCCmec detected
PCR primer pairs
how is MRSA detected
mecA protein product detected - resistance gene in MRSA
oxoid PBP2’ latex agglutination test
if RMSA present =clump
