Two-Laboratory Comparison of Flow Cytometry Susceptibility Testing of Pathogenic Yeasts.

R. RAMANI1, C. PINA-VAZ 2, S. COSTA-DE-OLIVERIA 2, A. G. RODRIGUES 2, V. CHATURVEDI 1;

Author address: 

1Wadsworth Ctr., NYS DOH, Albany, NY, 2Univ. of Porto, Porto, Portugal.

Abstract: 

Background: Flow cytometry is being increasingly used for antifungal susceptibility testing (FCST). However, there are no reports on inter-laboratory comparisons. A collaborative FCST evaluation was done by laboratories in US (C1) and Portugal (C2) for amphotericin B (AB), fluconazole (FL), and voriconazole (VZ). Methods: Ten clinical isolates - C. albicans (2), C.glabrata (2), C. krusei (2), C. parapsilosis (2), & C. tropicalis (2) were tested. MICs of AB, FL and VZ were determined using CLSI/NCCLS M27-A2 protocol (C1). FCST MICs with fluorescent probe propidium iodide (PI, 1 µg/ml) and FUN-1, 0.5 µM) were determined using FACSCalibur flow cytometer (C1) and Beckman Coulter XL-MCL flow cytometer (C2). The FCST MIC was defined either as the lowest drug concentration that produced 50% increase in mean channel fluorescence as compared to growth control (PI) or the lowest concentration of drug that resulted in staining index (ratio between median intensity of fluorescence of treated & non-treated cells) of 1.0 (FUN-1). The MICs from the two laboratories were compared using t-Test. Results: AB MIC ranges were 0.12 - 0.5 µg/ml (C1) and 0.25 - 2.0 µg/ml (C2) when PI was used; they were 0.25 - 0.5 µg/ml (C1) and 0.25 - 2.0 µg/ml (C2) when FUN-1 was used. FL MIC ranges were using PI 0.25 - 64.0 µg/ml (C1) and 0.25 - 32.0 µg/ml (C2) and using FUN-1 were 0.12 - 64.0 µg/ml (C1) and 0.25 - 32.0 µg/ml (C2). VZ MIC ranges using PI were 0.03 - 0.5 µg/ml (C1) and 0.015 - 1.0 µg/ml (C2), and using FUN-1 were 0.10). However, comparison of VZ MICs revealed significant differences with both probes (p
2006

abstract No: 

M-1579

Full conference title: 

46th Interscience Conference on Antimicrobial Agents and Chemotherapy
    • ICAAC 46th