Antifungal susceptibility testing in Aspergillus spp. according to EUCAST methodology

Area of Science:

• Mycology
• Clinical Microbiology
• Antimicrobial Resistance

Background:

• Increasing availability of novel antifungal agents necessitates robust in vitro antifungal susceptibility testing (AFST) for Aspergillus species.
• Existing reference methods require updates to meet current clinical and research demands for Aspergillus AFST.
• The European Committee on Antimicrobial Susceptibility Testing (EUCAST) Antifungal Susceptibility Testing Subcommittee (AFST-EUCAST) is developing new guidelines.

Purpose of the Study:

• To present modified guidelines for standardized in vitro susceptibility testing of Aspergillus species against antifungal agents.
• To establish a reliable, economic, and reproducible method for AFST of Aspergillus.
• To facilitate accurate identification of antifungal resistance in Aspergillus and improve inter-laboratory agreement.

Main Methods:

• Modification of the reference broth dilution method (M38-A) for filamentous fungi.
• Utilized RPMI 1640 supplemented with 2% glucose (RPMI 2%G) as the assay medium.
• Standardized inoculum preparation using conidium counting (2x10^5-5x10^5 CFU/ml) and a 48-hour incubation at 35°C, with visual Minimum Inhibitory Concentration (MIC) determination.

Main Results:

• The modified method provides a standardized approach for AFST of Aspergillus species.
• Visual determination of MIC as a no-growth endpoint is employed.
• The protocol aims for a high degree of conformity and agreement in susceptibility measurements.

Conclusions:

• The described standard method offers a valid and economical approach for AFST of Aspergillus.
• This standardized testing is essential for identifying antifungal resistance and guiding clinical treatment.
• The guidelines aim to enhance consistency and reliability in antifungal susceptibility testing across laboratories.