Development of a rezafungin isolate verification panel and comparison of reference method to ThermoFisher Sensititre YeastOne panel MIC results

Rezafungin is indicated for the treatment of adults with limited or no alternative treatment options for candidemia and invasive candidiasis. The development of a rezafungin isolate verification panel is described. A total of 35 Candida species isolates were chosen for initial testing and 30 isolates were selected for additional testing including C. albicans (n = 11), C. glabrata (n = 8), C. tropicalis (n = 7) and C. parapsilosis (n = 4). Modal MIC, range of results and categorical agreement results (based on an acceptable ±2 dilution from the modal MIC) were calculated. Both FDA STIC and CLSI breakpoints were applied to calculated categorical agreement. The replicate reference BMD (rBMD) MIC results spanned an average of 2.4-dilution range and were within ±1 dilution of the modal rBMD for 26/30 (86.7 %) isolates and within ±2 dilutions for all isolates (100 %). The final panel of isolates was used to compare rBMD MIC values with those generated using the Sensititre™ YeastOne™ panel. The correlation of YeastOne results to modal rBMD results was particularly good; 26 out of 30 isolates (86.7 %) were within ±1 dilution of the modal rBMD and 100 % were within ±2 dilutions. When categorical agreement was calculated using CLSI and FDA breakpoints, CLSI criteria performed better than FDA, albeit this was associated with a limited number of isolates with MIC results near the breakpoints. The availability of a curated verification panel with rezafungin modal MIC values will be a valuable resource for laboratories as they incorporate testing devices containing rezafungin into their yeast susceptibility testing paradigm.