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
- ICAAC 54th (2014)