cWe compared EUCAST and CLSI antifungal susceptibility testing (AFST) methods for triazoles and amphotericin B against 124 clinical Mucorales isolates. The EUCAST method yielded MIC values 1-to 3-fold dilutions higher than those of the CLSI method for amphotericin B. The essential agreements between the two methods for triazoles were high, i.e., 99.1% (voriconazole), 98.3% (isavuconazole), and 87% (posaconazole), whereas it was significantly lower for amphotericin B (66.1%). Strategies for harmonization of the two methods for Mucorales AFST are warranted.
Mucormycosis is a life-threatening fungal infection caused by fungi belonging to the subphylum Mucoromycotina and order Mucorales (1). The etiologic agents of mucormycosis include the genera Rhizopus, Mucor, Lichtheimia, Cunninghamella, Rhizomucor, and Apophysomyces among others (2, 3). The disease is the second most common mold infection in hematologic malignancies and organ transplantation and is increasingly reported in patients with uncontrolled diabetes or ketoacidosis (1, 2). Notably, diagnosis is very difficult (4), and outbreaks of mucormycosis in hospitals (5), among victims of natural disasters such as the Joplin tornado (6), and among soldiers following combat-related injuries (7), as well as food-borne outbreaks in healthy individuals due to Mucor circinelloides (8), highlight the potential of Mucorales to cause severe infections. Despite aggressive antifungal therapy and, in selected cases, extensive surgical debridement, the overall mortality due to mucormycosis remains unacceptably high (9). Primary antifungal therapies for mucormycosis are amphotericin B (AMB) lipid formulations, whereas open-label salvage studies suggest posaconazole (POS) as an option for patients who are refractory to or intolerant of polyenes (10, 11). Furthermore, recent data also demonstrated the activity of isavuconazole (ISAV), which was approved by the U.S. Food and Drug Administration on 6 March 2015 for the primary treatment of invasive aspergillosis and mucormycosis, against Mucorales in vitro and in vivo, adding a second triazole antifungal for the therapy of patients with mucormycosis (12)(13)(14). Different species of Mucorales show differences in their in vitro susceptibilities to AMB, POS, and voriconazole (VRC) (15-17). So far, reported in vitro antifungal susceptibility testing (AFST) of Mucorales is mainly based on the Clinical and Laboratory Standards Institute broth microdilution method (CLSI BMD) (18), and recently, a multicentric study based on CLSI susceptibility data proposed epidemiologic cutoff values (ECV) for the detection of AMB, POS, and itraconazole resistance among the 4 most commonly encountered and clinically relevant species of Mucorales (19). In addition to the CLSI BMD method, the other international standard method for AFST and surveillance of antifungal resistance is the European Committee on Antimicrobial Susceptibility Testing (EUCAST) method (20). Limited EUCAST AFST data and a lack of data comparing the two reference BMD methods for M...