TABLE 2.
Widely used methodologies for antifungal susceptibility testing
| Methodology or system | Strengths | Weaknesses |
|---|---|---|
| Broth microdilution | Gold standard Can be used for both yeasts and filamentous fungi Methodologies are standardized and available for both yeasts and filamentous fungi Plates can be produced in the laboratory | Subjective interpretation by CLSI methodology, alleviated using EUCAST (spectrophotometer) |
| Labor-intensive to make plates and expensive to buy them commercially prepared | ||
| Technical training requirement is high | ||
| Can be used for any new antifungal that is discovered | ||
| Disk diffusion | A methodology has been standardized Inexpensive Disks can be produced in the laboratory | Very few interpretive criteria are available |
| Disk diameters are categorical only and do not directly correlate with MIC values | ||
| Good for resource-limited settings | Commercially available for only a few antifungals | |
| Gradient diffusion | Inexpensive compared to broth microdilution | Interpretation is somewhat subjective |
| Can be used for both yeasts and filamentous fungi | Must be purchased commercially | |
| Good for resource-limited settings | Not available for antifungals in development | |
| Provides an MIC value | ||
| Improved discrimination between amphotericin B-susceptible and -resistant isolates | ||
| Improved discrimination between true resistance and trailing growth phenomenon | ||
| YeastOne | Interpretation is less subjective than standard broth microdilution | Interpretation of trailing growth in azoles can be problematic Cannot be used for filamentous fungi Must be purchased commercially Even though it is broth microdilution, it does not follow CLSI or EUCAST guidelines for interpretation |
| Easier to train new technicians than standard broth microdilution | ||
| Long shelf life of dried trays | ||
| Does not require freezer storage | ||
| VITEK 2 | No subjectivity to interpretation | Expensive for both initial startup costs and for cartridges |
| Very easy to set up and perform | Cannot be used for filamentous fungi | |
| Dual use for laboratories that already use VITEK 2 for identification | Available for only a limited number of antifungals Overcalls resistance for some species (like Candida auris) | |
| Agar screening for Aspergillus | Easy to perform | It is only a screening test |
| Easy to interpret | Needs to be backed up with broth microdilution | |
| Inexpensive |