Comparative parameter analysis of CLSI and EUCAST broth microdilution for yeasts and filamentous fungi

Abstract

Invasive fungal infections caused by opportunistic fungi such as Candida spp., Aspergillus spp., and Cryptococcus spp. continue to be major causes of morbidity and mortality in spite of advancements in diagnostic tools and antifungal treatments. Despite the tendency to broaden the therapeutic options in invasive fungal infections, the misuse of these antifungals has led to the emergence of antifungal resistance. In this context, antifungal susceptibility testing (AFST) plays a vital role in guiding treatment decisions, predicting clinical outcomes, detecting resistance, and mapping epidemiological trends. Broth microdilution is the gold standard method for AFST, and both the Clinical Laboratory Standards Institute (CLSI) and the European Committee on Antibiotic Susceptibility Testing (EUCAST) have standardized this technique. Although the two organizations share several key practices, such as the use of RPMI-1640 broth medium and standardized incubation conditions, they also have critical differences in inoculum density, glucose concentration, and MIC determination methods. These differences can influence the results, making reproducibility and consistency in testing essential. AFST also plays a critical role in the development of new antifungal agents by assessing their activity against various fungal strains. Given the growing concern of antifungal resistance, accurate and standardized susceptibility testing remains crucial for effective treatment and the development of new therapies.