MICROM 442 ch 8-10 Flashcards
-broth microdilution
-disk diffusion
-gradient strips (Etests)
phenotypic testing methods
-PCR
-Sequencing
genotypic testing methods
-antibody-based detection (lateral low immunochromatographic assays)
-microscopy + machine learning
other testing methods
-“gold standard”
-double dilutions of antibiotics in each well + standard inoculum of bacteria into each well
-measure MIC e.g. 2µg/mL
broth dilution
-automated, high-output formats for clinical testing
-multiwell can fit many antibiotics
-colorimetric or fluorescent indicators to read bacterial growth
-instruments with automated readers»>
Antibiotic susceptibility testing (AST)/phenotypic -> broth microdilution
-bacteria lawn
-nitrocellulose strip with continuous gradient of bacteria
-measure MIC where ellipse of growth inhibition meets the strip
-interpret MIC according to same ranges as broth dilution
AST/phenotypic -> gradient strips (Etests)
-bacterial lawn
-paper disks with antibiotic placed on top
-antibiotics diffuse into agar
-standard single concentration used for each antibiotic
-does NOT give MIC
-does give S, I, R
AST/phenotypic -> disk diffusion
-for genes with good predictive value ie correlate with phenotypic
-look for presence/abscence of resistant gene
-vanA and vanB for VRE
-mecA for MRSA
-look for presence/absence of mutation associated with resistance e.g. rpoB for rifampin-resistant mycobacterium tuberculosis
AST/genotypic -> PCR
genotypic methods struggle more with predicting MIC which is
sometimes neeeded for theraputic dosing
sometimes genotype does not easily predict phenotypic resistance in particular
GN organisms may harbor multiple, complicated, resistance mechanisms including mutations involving membrane permeability
-to detect PBP2a from staphylococcus aureus
-mecA encodes PBP2a
-PBP2a positive = MRSA
-quick results directly from colony
antibody-based detection -> (lateral flow immunochromatographic assays)
-image bacteria challenged with antibiotic
-use machine learning to correlate growth patterns with susceptibility or resistance
digital microscopy
standardization for accurate AST determined by:
-FDA
-clinical & laboratory standards institute
-European committee on antimicrobial susceptibility testing
Reproducibility between labs and methods
-strict quality control standards
-guidelines for variable like media, drug concentration, incubation conditions (metabolism effects)
Ranges determined by many factors:
-pharmocokinetic/pharmacodynamic parameters
-site of infection (eliminated/spread differently)
wild-type MIC conditions
-clinical outcome studies (expected survival of patient at certain MIC)
-re-reviewed and revised every so often
site of infection
-some drugs [x] in urine
-some drugs inactivated by surfactants in the lungs
-some drugs are better/worse for penetrating the blood brain barrier
treatment considerations
-administration
-therapeutic drug monitoring informs dosing
-interxns with other drugs
-toxic side effects
-coverage for infections with multiple organisms
-site of infection
-allergies
administration
inhalation, topical, IV, oral
toxic side effects
-nephrotoxicity (kidneys)
-ototoxicity (deafness)
empiric therapy
broad-spectrum antibiotics
targeted therapy
narrow-spectrum antibiotics
meropenem is a
broad-spectrum antibiotic
ampicillin is a
narrow-spectrum antibiotics
local antibiograms can help
guide empiric treatment and are HOSPITAL SPECIFIC
