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40 Cards in this Set
- Front
- Back
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3 types of antimicrobial therapy
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empiric
directed prophylactic |
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empiric amtimicrobial therapy
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based on diagnosis and probability of susceptibility; 70% of prescriptions are empiric, correct most of te time
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directed antimicrobial therapy
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following susceptibility testing; makes use of the report. only 12% so what are we working for? confirms the efficacy of empiric usually
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prophylactic antimicrobial therapy
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preventative/protective
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why do a susceptibility test?
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-epidemiologic studies, to build up antibiograms - database of organisms in each hospital
-organism i.d. |
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when antimicrobial susceptibiity testing is not necessary:
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-when organism is routinely suscept. or resistant to certain antibioitcs.
eg., GNB against PENICILLIN.. duh -when orgn is NORMAL FLORA! |
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factors that affect performance of antimicrobial test
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-inoculum size
-media -incubation time,temp, atm -antibiotic stability -delays |
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how does inoculm size affect antimic testing
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must be standardized with mcfarland standard
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how would incubating the organism for too short of time affect the test results?
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it would look susceptible because didnt have time to grow
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what type of media to use
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mueller hinton agar; neutral pH, ca/mg concentration, specific depth for disk diffusion
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how would an expired antibiotic affect test results?
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organism would look more resistant because antibiotic wasn't working as well.
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how would a delay between prep of standard and actual testing affect results?
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organism continues to grow and so looks more resistant than it is
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advantages of kirby-bauer
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simple, qquick, flexible in which antibiotic to use
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limitations:
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qualitative, not quantitative.
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disk diffusion method is aka
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kirby-bauer
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principle of agar dilution method
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make serial dilutions of the antibiotic; add bacteria; find the MIC
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MIC
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minimal inhibitory concentration - the lowest concetnration of antibiotic necessary to inhibit the bacteria - no visible growth.
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advantages of agar dilution method
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-QUALITATIVE AND QUANTITATIVE
-reproducible -can test many organisms at same time |
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principle of schlicter test
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tests the serum of patient to see MIC and MBC of the actual serum, not just standardized concentrations
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what do antimicrobial synergy and antagonism test?
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the additive or interfering effects of combinations of antibiotics.
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why a patient would need more than one antibioitc
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mixed infections
use lower doses of 2 antib so that higher, toxic doses arent necessary |
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3 types of automated susceptibility testing
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-photometry/nephelometry
-fluorometry -flow cytometry |
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what does a b-lactamase test test for?
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the presence of b-lactamase; that's an enzyme that breaks down the b-lactam ring in penicillin or cephalosporins
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3 b-lactamase testing methods
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-iodometric
-acidometric -chromogenic cephalosporin disk |
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how does iodometric method work
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add iodine to incubated inoculation.
if acid, iodine will break down. indicator is starch, and if breakdown, it is white. if dark brown, iodine is intact. |
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how does acidometric method work?
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a pH indicator shows that acid is produced if the b-lactam ring of penicillin or cephalosporins is broken down
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how does the chromogenic ceph disk test work?
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if b-lactam ring of nitrocefin is broken down, there's a color change.
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diff btwn antimicrobial and antibiotic
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antimicrobial is designed to interfere with microbe growth in a host; can be synthetic or even ofor fungi (never virsues tho)
antibiotic is a drug made from antoher organism, designed to kill the bacteria. |
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quorum sensing
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signalling by bacteria setting up an infection; mimicked in antibiotics to interfere and clear bugs via immune system
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aminoglycosides - specific toxicity
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oto (mid ear) and renal
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how hepatic function alters microbial action
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inability to metabolize antibiotic leads to toxicity
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factor to consider in admin antibacterials to diabetes mellitus patients
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absorb antibiotics poorly at intramuscular sites
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how renal function alters microbial use
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renal distress, can't handle antibiotics excreted by kidney; it builds up in tubules.
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bacterium tests susceptible; patient doesn't respond:
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1. buildup of pus - acid; erythromycin and aminoglycos can't handle.
2. Hi Ca+ in bones inhibits antibiotics 3. multiple orgs at one site; confer 4. CNS infectn/abcess/osteomyelitis - drug can't penetrate. 5. vasc. occlusion - cant penetrate. 6. undetected B-lactamase produced 7. Need bactericidal, gave static. 8. Organism set up intracell. houskeeping; can't penetrate. 9. # cells at inoculum site too much for inoculum size to handle. |
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why patient responds when shouldnt
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-acid ph activates tetracycline
-kidney concentrates antibiotic, kills UTI bacteria -host defense removes bacteria w/out antibiotic |
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advantages/limitations of kirby bauer
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adv: quick, simjple, flexible in which antibiotic is used- economical
limit: qualitative, not quantitative; only tells if susc. or resist, not HOW susc or resist; not as reproducible; agar depth easy to mess up |
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name of instrument that delivers bug to dilution plates in agar dilution
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steer's replicator
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MIC
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the lowest concentration of antibiotic necessary to inhibit the bacteria so that there is no visible growth
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MBC
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minimal concentration that results in a 99.9# reduction in the colony-forming-units per ml of drug.
minimum conc. of drug necessary to kill the bacteria, not just inhibit it. |
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advantages/limitations of e-test
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adv: QUantitative, esp good for fastidious organism tests cuz can grow on enriched media;
limit: depth is crucial; dropping strip wrong onto plate alters diffusion of drug into media. |
