Antifungal Susceptibility Testing in Clinical Mycology

Antifungal susceptibility testing (AFST) has become indispensable in clinical mycology, guiding timely and effective treatment of invasive fungal infections. Traditional reference methods, such as broth microdilution and agar dilution, establish minimum inhibitory concentrations (MICs) that inform clinical breakpoints and epidemiological cut-off values (ECVs). Commercial systems—gradient diffusion strips, automated microdilution panels and colourimetric assays—offer greater convenience but require rigorous validation against reference standards. Emerging technologies, including fluorescence-based probes, flow cytometry, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF MS) and molecular detection of resistance mutations, promise to shorten turnaround times and improve detection of non-wild-type isolates. Despite advances, challenges persist in standardising interpretive criteria for moulds, neonatal and neutropenic populations, and rare or emerging species. Harmonisation of Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines remains a priority to ensure global comparability. Ultimately, robust AFST underpins antifungal stewardship, mitigates the impact of resistance, and supports precision medicine in the face of a diversifying pathogen landscape.

Research from Nature Portfolio

Recent work has demonstrated the potential of MALDI-ToF MS for rapid detection of antifungal resistance in Candida glabrata. By analysing proteomic fingerprints after brief exposure to echinocandins and azoles, this approach can distinguish susceptible and resistant phenotypes in under three hours. Although initial assays struggled to detect certain FKS2-associated echinocandin resistance, integration of growth-kinetic data and refined spectral algorithms has enhanced sensitivity. These studies underscore the feasibility of proteomic-based AFST as a complement to conventional MIC determination and point towards automated workflows for clinical laboratories.

Antifungal Susceptibility Testing in Clinical Mycology publication trend

The graph below shows the total number of articles in antifungal susceptibility testing in clinical mycology across all publications each year (not limited to Nature Index journals).

Technical terms

Minimal inhibitory concentration (MIC): lowest concentration of an antifungal that prevents visible growth of a fungus in vitro.

Epidemiological cut-off value (ECV): MIC threshold distinguishing wild-type strains from those bearing acquired resistance mechanisms.

MALDI-ToF mass spectrometry: analytical technique that profiles microbial proteins for rapid identification and susceptibility assessment.

Broth microdilution (BMD): reference method for determining MICs by exposing fungi to serial dilutions of antifungal agents in liquid medium.

Clinical breakpoints: interpretive MIC thresholds used to categorise isolates as susceptible, intermediate or resistant.

References

1. Role and Interpretation of Antifungal Susceptibility Testing for the Management of Invasive Fungal Infections. Journal of Fungi (2020).
2. Potential Use of MALDI-ToF Mass Spectrometry for Rapid Detection of Antifungal Resistance in the Human Pathogen Candida glabrata. Scientific Reports (2017).
3. Evolutionary trends in antifungal resistance: a meta-analysis. Microbiology Spectrum (2024).
4. Commercial Methods for Antifungal Susceptibility Testing of Saprophytic Molds: Can They Be Used to Detect Resistance?. Journal of Fungi (2024).