Antifungal susceptibility of yeasts isolated from patients with fungaemia: comparison of the Etest on direct blood samples and CLSIM27A3

Abstract number: P838

Objectives: We prospectively performed antifungal susceptibility testing using the E-test (ETdir) on direct blood samples from 163 patients (225 strains), and on 63 strains artificially inoculated in BACTEC. ETdir MICs (24 h of incubation) of amphotericin B, fluconazole, voriconazole, posaconazole, isavuconazole, and caspofungin were compared with results using CLSI M27-A3.

Methods: Strains were from highly fluconazole-susceptible species (FLUCO-S: 93 C. albicans, 77 C. parapsilosis, 18 C. tropicalis, 6 C. dubliniensis, 1 C. neoformans, 1 C. kefyr), or less fluconazole-susceptible species (FLUCO R: 52 C. glabrata, 29 C. krusei, 8 C. guilliermondii, 2 R. mucilaginosa, 1 T. mucoides). Voriconazole breakpoints were used for posaconazole and isavuconazole (R 4 mg/mL). Strains were classified as susceptible (S) or resistant (R) following the CLSI procedure. The percentage of strains correctly classified by ETdir was calculated.

Results: Major discrepancies (M: R by ETdir and S by CLSI) were found mostly for C. glabrata, C. krusei and the triazoles. Very major discrepancies (VM: S by ETdir and R by CLSI) were found for fluconazole in C. krusei (n = 2), and for voriconazole in C. glabrata (n = 1) and T. mucoides (n = 1) (see table).

Conclusions: ETdir in yeast-positive blood cultures is rapid (24 h) and easy, and reliably determines the antifungal susceptibility to triazoles and caspofungin of yeasts (especially highly fluconazole-susceptible species) from fungemic patients.

J. Guinea (CA08/00384) and M. Torres-Narbona (CM08/00277) are contracted by FIS. This study received financial support from Basilea Pharmaceutica.

	Overall (correct/VM/M)	FLUCO-S (correct/VM/M)	FLUCO-R (correct/VM/M)	% of strains with MIC discrepancies ±2-fold dilutions
Fluconazole	90.9/0.7/8.4	100/0/0	71.7/2.2/26.1	78.8
Voriconazole	98.3/0.7/1	100/0/0	94.6/2.2/3.3	83.7
Posaconazole	88.5/0/11.5	100/0/0	64.1/0/35.9	63.5
Isavuconazole	96.5/0/3.5	99.5/0/0.5	90.2/0/9.8	71.9
Amphotericin B	31.7/66.5/1.8	25.3/73.7/1	45.5/51.1/3.4	62
Caspofungin	100/0/0	100/0/0	100/0/0	88.2