Comparison of the Mics Obtained by Clsi and Eucast Methods for Isavuconazole, Posaconazole, Voriconazole and Amphotericin B Against Mucorales

A. Alastruey-Izquierdo, A. Santerre-Henriksen, M. Jones, M. Cuenca-Estrella


Background:CLSI and EUCAST are the current approved standards for antifungal susceptibility 
testing (AFST). Isavuconazole (ISAV) is a new triazole antifungal agent that was granted approval by 
the U.S. Food and Drug Administration on March 6, 2015 for the treatment of invasive aspergillosis 
and mucormycosis. The aim of this study was to compare the Minimum Inhibitory Concentrations 
(MICs) of 3 triazoles (including ISAV) and amphotericin B (AMB) to mucorales by CLSI and EUCAST. 

Methods: 82 mucorales strains were tested for AFST following EUCAST and CLSI. All strains were 
identified to species level by sequencing the ITS region. The AFST was performed following EUCAST 
reference method 9.1 and CLSI M38-A2. The antifungals used were: AMB, ISAV, voriconazole (VCZ) 
and posaconazole (PCZ). A flavus ATCC 204304 and A. fumigatus ATCC 204305 were used as 
quality control strains. MICs were read at 24 and 48 h. 

Results: Both EUCAST and CLSI recommend reading at 24 h for mucorales. However in CLSI 
methodology over 23 % of the strains did not grow at this incubation time in contrast with EUCAST 
that showed good growth at 24h for all mucorales strains. Table 1 shows geometric mean (GM), 
MIC50 (MIC causing inhibition of 50% of the isolates tested), MIC90 (MIC causing inhibition of 90% of 
the isolates tested) and range for all the strains tested at 24 and 48 h by EUCAST and CLSI. Strains 
that showed no growth at 24h for CLSI were not taken into account for the calculations in table 1. 

Conclusions: CLSI showed poor growth at 24h. EUCAST showed higher MICs than CLSI for all 
antifungals at the same incubation time. Comparable results are found between EUCAST 24h and 
CLSI 48h.



abstract No: 

    • ICAAC 54th (2014)