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Updated: Dec 9, 2025
Broth Microdilution In Vitro Screening: An Easy and Fast Method to Detect New Antifungal Compounds
Published on: February 14, 2018
How to: perform antifungal susceptibility testing of microconidia-forming dermatophytes following the new reference
Maiken C Arendrup1, Gunnar Kahlmeter2, Jesus Guinea3
1Unit of Mycology, Department of Microbiological Surveillance and Research, Statens Serum Institut, Copenhagen, Denmark; Department of Clinical Microbiology, University Hospital Rigshospitalet, Copenhagen, Denmark; Department of Clinical Medicine, University of Copenhagen, Denmark.
Background:
Antifungal drug resistance in dermatophytes was first reported shortly after the turn of the millennium and has today been reported in Trichophyton and occasionally in Microsporum, but not in Epidermophyton species. Although drug resistance in dermatophytes is not routinely investigated, resistance in Trichophyton spp. is increasingly reported worldwide. The highest rates are observed in India (36% and 68% for terbinafine (MIC ≥4 mg/L) and fluconazole (MICs ≥16 mg/L), respectively), and apparently involve the spread of a unique clade related to the Trichophyton mentagrophytes/Trichophyton interdigitale complex.
Objectives:
The European Committee on Antimicrobial Susceptibility Testing Subcommittee on Antifungal Susceptibility Testing (EUCAST-AFST) has released a new method (E.Def 11.0) for antifungal susceptibility testing against microconidia-forming dermatophytes including tentative MIC ranges for quality control strains and tentative breakpoints against Trichophyton rubrum and T. interdigitale. Here, the details of the new procedure E.Def 11.0 are described.
Sources:
This technical note is based on the multicentre validation of the EUCAST dermatophyte antifungal susceptibility testing method, the mould testing method (E.Def 9.3.2) and the updated quality control tables for antifungal susceptibility testing document, v 5.0 (available on the EUCAST website).
Contents:
The method is based on the EUCAST microdilution method for moulds but significant differences include: (a) an altered test medium selective for dermatophytes; (b) an altered incubation time and temperature; and (c) a different end-point criterion (spectrophotometric determination) of fungal growth. It can easily be implemented in laboratories already performing EUCAST microdilution methods and has been validated for terbinafine, voriconazole, itraconazole and amorolfine against T. rubrum and T. interdigitale.
Implications:
This standardized procedure with automated end-point reading will allow broader implementation of susceptibility testing of dermatophytes and so facilitate earlier appropriate therapy. This is important, as resistance is rapidly emerging and largely underdiagnosed.
