Comparison of the Sensititre YeastOne and Fungitest methods with the NCCLS M27-A2 reference method for antifungal susceptibility testing of yeasts

Abstract

Background: The recent introduction of Sensititre YeastOne, a colorimetric microdilution method that includes new antifungal agents has opened the field to MIC’s determination by an easy-to-perform method. The aim of this study was to compare this test with the NCCLS M27-A protocol and with Fungitest, a current routine method for yeasts susceptibility testing. Methods: Sensititre YeastOne method (Trek diagnostic), and the NCCLS M27-A2 were performed on 300 yeasts clinical isolates distributed as follow: 125 C. albicans, 273 non-albicans species. Four antifungal agents were tested by the reference method: amphotericine B (AmB), fluconazole (FZ), itraconazole (ITZ), and voriconazole (VOR). The reading of the Sensititre and NCCLS results was visually performed after 24 and 48 h respectively. The Fungitest (Biorad) method was applied on 121 among the 300 isolates and the reading was made after 24 to 48 h incubation time according to the positive control growth. Results: By the NCCLS method, the MICs50/MICs90 (µg/ml) were as follows: 1/2 (AmB); 16/64 (FZ); 0.25/4 (ITZ) and 0.125/2 (VOR). Sensititre vs. NCCLS: The overall agreement within 2 dilutions for AmB, FZ, ITZ and VOR was respectively 54, 82, 80 and 78%. The MICs50/MICs90 were in absolute concordance for VOR by both techniques. Very major errors (%) were recorded as follows: 0.01/0 (AmB with a MIC ≥ 4/8µg/ml for resistant strains respectively), 1.6 (FZ), 3.6 (ITZ) and 2.3 (VOR with a MIC ≥ 8µg/ml for resistant strains). Fungitest vs. NCCLS: The agreement between both methods including minor discrepancies was 98% (AmB), 88% (FZ) and 98% (ITZ). Following the breakpoints given by the manufacturer, very major errors were 6.3% for FZ, 0.03% for ITZ and none for AmB. Conclusions: Sensititre is a convenient alternative to the NCCLS method for yeast susceptibility testing. Fungitest in spite of good correlations must change the breakpoints and include new antifungal agents to be competitive