Antifungal susceptibility testing, reporting and antifungal resistance: current status

Appropriate early treatment is crucial for prognosis in invasive fungal infections (IFIs). Antimicrobial susceptibility has generally an important role for treatment options and clinical outcome. “The European Committee on Antimicrobial Susceptibility Testing (EUCAST)” and “The Clinical and Laboratory Standards Institute (CLSI)” defined standard procedures and recommendations on interpretations of minimum inhibitory concentrations (MICs). However, they do not include epidemiological cut-off values (ECOFFs) and/or clinical breakpoints (CBPs) for every fungi and antifungal agent, so only MIC values can be shared to guide clinicians. Microbiological resistance is determined by interpreting the in vitro MICs with comparison of CBPs. There are many mechanisms that lead to antifungal resistance (AFR). There are increasing trends in fluconazole and echinocandin resistance for yeasts and in triazole resistance for molds. Although clinical reflections of these high MICs are sometimes very obvious, there is insufficient data to show in every fungi. Clinical resistance is the event that an infection does not resolve for various reasons despite appropriate treatment, and can be attributed to many