When Should Clinical Mycology Laboratories Perform Antifungal Susceptibility Testing? Revisiting Practice Through the Lens of Intrinsic Resistance

Mycopathologia. 2025 Dec 21;191(1):11. doi: 10.1007/s11046-025-01033-6.

Abstract

Background: Antifungal susceptibility testing (AFST) guides therapy for invasive and refractory fungal infections, but routine testing of species with predictable, species-level (intrinsic) resistance can waste laboratory resources.

Methods: Narrative synthesis of guideline documents and recent literature to define intrinsic resistance, summarize major fungal examples, and propose a selective AFST framework.

Results: Key taxa show intrinsic non-susceptibility (e.g., Pichia kudriavzevii to fluconazole; Mucorales to short-tailed azoles; Cryptococcus spp. to echinocandins). Terminology differences between EUCAST and CLSI are noted. Recommended AFST is targeted to invasive/rare pathogens, treatment failure, surveillance, outbreak investigation, and evaluation of novel agents.

Conclusion: A selective AFST strategy, reserving routine testing for species with variable or emergent resistance, enhances laboratory efficiency and antifungal stewardship while ensuring appropriate clinical therapy.

Keywords: Acquired resistance; Fungi; Intrinsic resistance; Natural resistance; Resistance.

Publication types

  • Review

MeSH terms

  • Antifungal Agents* / pharmacology
  • Drug Resistance, Fungal*
  • Fungi* / drug effects
  • Humans
  • Laboratories, Clinical*
  • Microbial Sensitivity Tests / methods
  • Microbial Sensitivity Tests / standards
  • Mycology* / methods
  • Mycoses* / drug therapy
  • Mycoses* / microbiology

Substances

  • Antifungal Agents