Evaluation of a customised Sensititre YeastOne plate containing isavuconazole for antifungal susceptibility testing in Singapore.

Abstract

This study evaluated the performance of a customised Sensititre YeastOne (SYO) plate including isavuconazole (YIT) against existing practice (comprising SYO YO10 plate and isavuconazole gradient strip) in order to streamline the workflow for antifungal susceptibility testing in a tertiary hospital in Singapore. A total of 101 (51 yeasts and 50 moulds) clinical isolates were included for analysis. Isolates included in the study were recovered from a variety of body sites and reflected the case mix encountered in daily practice. Antifungal susceptibility testing was performed using three methods: YO10, YIT and gradient diffusion strip (for isavuconazole only). Reproducibility, essential agreement (EA) and categorical agreement (CA) were calculated. When YO10 and YIT plates were compared, the reproducibility was 100% for eight common antifungals. The CA was >97% for all antifungals except for amphotericin B (89.4%), but this was attributed to seven isolates with minimum inhibitory concentrations bordering the wild-type (WT) cut-off. The EA obtained when testing isavuconazole using YIT versus gradient diffusion was 77.2% overall, 90.2% for yeasts and 64% for moulds. In conclusion, the YIT plate is suitable for antifungal susceptibility testing of yeasts in our laboratory. Its use for mould isolates needs to be monitored further.