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Comparison of the Vitek AST-YS01 card with CLSI broth microdilution reference method for testing fluconazole and voriconazole against C.neoformans

Abstract number: P1307

Aller A.I., Castro C., Romero A., González M.T., Claro R., Martín-Mazuelos E.

Objective: The purpose of this study was to compare the results obtained by the reference microdilution method (MDM) with those obtained with the comercial method AST-YS01card (YS01) for antifungal susceptibility testing of C. neoformans to fluconazole (FZ) and voriconazole (VZ)

Materials and Methods: We have studied retrospectively 89 clinical isolates of C. neoformans.

The susceptibility to two azoles was performed by the MDM according to the CLSI guidelines (M27-A2 document) modified by Ghannoum et al (J. Clin. Microbiol. 1992; 30:2881–86). The MICs were read at 48–72 h. of incubation. The YS01 was performed according to the manufacturer's instructions. The inoculum suspensions of C. neoformans isolates matched the turbidity of n°2 McFarland standard. The MICs were read at 24–48 h. of incubation.

The interpretative criteria for VZ were those published by the CLSI (Document M27-A3 and M27-S3). For FZ the isolates with MICgeqslant R: gt-or-equal, slanted16 mg/L were considered resistant and the isolates with MIC < 8 mg/L were considered susceptible, as suggested previously by Aller A.I. et al (Antimicrob Agents Chemother 2000; 44: 1544–48). C. krusei ATCC 6258, C. parapsilosis ATCC 22019, C. neoformans 90112 and C. neoformans 90113 were included as control strains.

Results: For FZ 23 isolates of C. neoformans (25.8%) failed to grow in the Vitek 2 system at 24 h. and they needed to be read after 24 h. of incubation (mean time of 28 h. with a range from 25 to 32 h.). The overall essential agreement (EA) between the two methods was of 97.7% to FZ. For VZ only 12 isolates grew well in the YS01 (13.5%), making it impossible to obtain results. The cathegorical agreement between both methods for FZ is summarised in table 1. YS01 was not able to identify the C. neoformans isolates resistant to FZ (2/4, 50%).

Conclusions:

1These data suggest the potential value of YS01for determining the MICs of FZ to susceptible C. neoformans isolates.

2YST01 failed to recognize the FZ resistant C. neoformans isolates.

3According to our study, YS01 is not a reliable method for susceptibility testing of C. neoformans to VZ.

4Further studies including a higher number of strains resistant to both antifungal agents are necessary.

Table 1

MIC (category), no. (%)CA (%)Errors, no. (%)
SR Very majorMajorMinor
Vitek: 86 (96.6)
CLSI: 85 (95.5)
Vitek: 3 (3.3)
CLSI: 4 (4.4)
96.62 (2.24)1 (1.12)

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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