[An update on antifungal susceptibility testing]

Area of Science:

• Mycology
• Clinical Microbiology
• Antimicrobial Resistance

Context:

• Increasing incidence of invasive fungal infections.
• Emergence of antifungal drug-resistant fungal strains.
• Need for reliable antifungal susceptibility testing (AST).

Purpose:

• To review standardized methods for antifungal susceptibility testing (AST).
• To compare guidelines from Clinical Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST).
• To discuss the utility and limitations of commercial AST methods.

Summary:

• CLSI and EUCAST provide equivalent broth microdilution guidelines (M27-A2, E. Dis. 7.1) for yeasts, with some methodological and interpretative differences.
• CLSI also offers M38-A for filamentous fungi and M44-A for disk diffusion; EUCAST is developing guidelines for Aspergillus spp.
• Commercial methods like E-test, Sensititre, and Vitek2 correlate well with reference methods, but MIC determination and clinical outcome correlation can be challenging.
• Careful interpretation of AST results is necessary due to complexities in fungal MIC determination, host factors, and variable correlation with clinical outcomes.

Impact:

• Highlights the importance of standardized AST in managing fungal infections.
• Provides an overview of available reference and commercial AST methods.
• Emphasizes the need for expert interpretation and suggests utilizing reference laboratories for complex cases.