Amphotericin B, itraconazole, posaconazole, and isavuconazole MICs against clinical Mucorales isolates obtained by visual inspection and spectrophotometric reading according to the EUCAST 9.4 procedure

We compared the antifungal susceptibility of 92 Mucorales isolates obtained by visual inspection and spectrophotometric readings following EUCAST (European Committee on Antimicrobial Susceptibility Testing) testing. Amphotericin B minimum inhibitory concentrations (MICs) were up to 1 mg/l against most isolates and variable among species, except for Cunninghamella bertholletiae. Posaconazole MICs against most isolates were up to 1 mg/l and high against Mucor circinelloides, some Rhizopus arrhizus, and Rhizopus microsporus. Isavuconazole MICs ranged between 1 and 8 mg/l but were invariably >8 mg/l against M. circinelloides and C. bertholletiae. The agreement between MICs obtained by visual endpoint or spectrophotometric readings was moderate and higher when using the >= 90% fungal growth inhibition endpoint. The agreement between minimum inhibitory concentration (MIC) values obtained by visual inspection or spectrophotometric readings was moderate and higher when the >= 90% fungal growth inhibition endpoint was chosen. Isavuconazole presented higher MICs than posaconazole, regardless of the inhibition endpoint used.

Automated summary

We compared antifungal susceptibility of 92 Mucorales isolates using visual inspection and spectrophotometric readings following EUCAST testing. Most isolates had Amphotericin B MICs up to 1 mg/l, varying among species except for C. bertholletiae. Posaconazole MICs were up to 1 mg/l against most isolates, but high against M. circinelloides, some R. arrhizus, and R. microsporus. Isavuconazole MICs ranged from 1 to 8 mg/l, but were always >8 mg/l against M. circinelloides and C. bertholletiae. Agreement between MICs obtained by visual inspection or spectrophotometric readings was moderate, but higher when using the >= 90% fungal growth inhibition endpoint. Isavuconazole had higher MICs than posaconazole, regardless of the inhibition endpoint used.