ANTIFUNGAL SUSCEPTIBILITY TEST (AFST) Flashcards
- A measure of potency of an agent to
inhibit growth in-vitro of an organism
A. Susceptibility Test
methods of susceptibility test
Methods:
- Disk Diffusion
- Gradient Diffusion (MIC)
- Broth Dilution (MIC)
- Macrobroth Dilution
- Microbroth Dilution
- Automated (MIC)
- Molecular
- For establishing antibiograms
for pathogenic isolate collections obtained
within the institution
Antifungal Susceptibility Test (AFST)
- Routine testing is not recommended
Antifungal Susceptibility Test (AFST)
To help manage refractory
Candida spp. infections in patients who appear to
be experiencing therapeutic failure with
standard doses
Antifungal Susceptibility Test (AFST)
- To manage invasive Candida
spp. infections when the utility of the azoles or
other classes are uncertain (e.g., due to nonCandida albicans isolate or resistance pattern
change
Antifungal Susceptibility Test (AFST)
- Performance Standards for
Antifungal Susceptibility Testing of Yeasts 3rd
Edition
- CLSI M27M44 ED3:2022
Performance Standards for
Antifungal Susceptibility Testing of Filamentous
Fungi 3rd Edition
- Includes updated minimal inhibitory
concentration (micro/microbroth dilution), zone
diameter, and quality control tables - Interpretation of Results
- Clinical breakpoints for
echinocandins, voriconazole and fluconazole
against several Candida spp.
- CLSI M38M51 ED3:2022
have been endorsed for
Aspergillus spp. which may be used in clinical
reports.
ECVS
In the absence of clinical
breakpoints, ___________________
have been developed and endorsed for many
species including Cryptococcus spp.
Epidemiological Cutoff Values (ECV)
Clinical Breakpoint for Fungi (Candida
spp., Cryptococcus spp., and Aspergillus spp.)
European Committee on Antimicrobial
Susceptibility Test (EUCAST)
- Colorimetric Broth Microdilution
- Robust & Reproducible
- Easy to set-up
- Clear and visible endpoints
- Long shelf-life
- Also works with Aspergillus spp
- Sensititre ® Yeastone ™ Test Panel
- Agar Dilution Method
- Uses a strip with a predefined gradient
of the antimicrobial agent - Determines MIC
- Difficulties:
- Selection of medium to be used
(i.e., RPMI-1640 agar with 0.2% glucose)
ETEST
- Yeast ID and AFST results in 14-18 hours
- 7 Antifungals tested; however only
fluconazole, caspofungin and voriconazole are
USFDA approved - 88-98% reproducibility and accuracy
- Limitations:
- Lowest caspofungin
concentration is higher than the Candida
glabrata CLSI Breakpoint → Misclassification as
“susceptible”
- VITEK ® 2 Automated System
- Isolate growth phase & inoculum size
- We should take note the slow
grower extends to 24 hours - Incubation time and temperature
- Media type (glucose concentration)
Factors Affecting Antifungal Susceptibility
Test
- Isolates are inhibited by the usually
achievable concentration of antimicrobial when
the dosage recommended to treat the site of
infection is used, resulting in likely clinical
efficac
Susceptible
Implies clinical safety when higher than
normal dose is used, and maximal blood level is
achieved (used with azoles)
- Dosing regimen: i.e., higher doses,
more frequent doses, or both
- Susceptible-Dose Dependent (SDD)
- Isolates are not inhibited by the usually
achievable concentrations of the agent with
normal dosage schedules
Resistant (R)
- There is not enough data to make
interpretation
Intermediate (I)
Organism naturally susceptible
becomes resistant
- Associated with drug exposure
- Only sometimes predictable
- Stable, transient
- Example:
- Many of the Candida spp. but
especially Candida glabrata: azoles
- Candida spp.(esp. C. glabrata):
echinocandrins
- Aspergillus fumigatus:
Itraconazole
Acquired
