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Broth microdilution, Etest and disk diffusion methods for Trichosporon asahii susceptibility testing against established and new antifungal agents

Abstract number: 1733_1468

Kanellopoulou M., Adamou D., Martsoukou M., Skarmoutsou N., Alexopoulos E., Milioni A., Arsenis G., Velegraki A., Papafrangas E.

The genus Trichosporon is a basidiomycetous yeast phylogenetically close to Cryptococcus. T. asahii is an emerging cause of disseminated trichosporonosis. Isolation of T. asahii from patient indwelling devices and biological secretions, without related dissemination, is hitherto of ambiguous clinical significance.

Objectives: (a) To monitor over 3 years (2002–2005) T. asahii susceptibility to antifungals isolated from urinary tract and bronchial secretions of patients without trichosporonosis; (b) to compare broth microdilution (BMD), Etest and disk diffusion (DD) methods for determining susceptibility to established antifungals and to posaconazole.

Methods: Seventeen urine specimen isolates from patients with indwelling catheter (n = 15) and from respiratory secretions with endotracheal catheter (n = 2) were tested against posaconazole (POS; Schering Plough Research Institute, New Jersey, USA), amphotericin (AB; Sigma, St. Louis, MO, USA), flucytosine (FC; Sigma), itraconazole (IT; Janssen, Beerse, Belgium) fluconazole and voriconazole (FLU and VOR; Pfizer, Sandwich, Kent, UK). Strains were tested by BMD (CLSI, M-27A2) and Etest (AB Biodisk, Solna, Sweden). FLU and POS were also tested by DD (CLSI, M-44A, 2004) using commercially prepared disks (OXOID, Basingstoke, UK). Incubations were performed at 35°C and read at 24, 48 and 72 hours. The QC isolates used were: Candidakrusei ATCC6258 and C. parapsilosis ATCC22019.

Results: MIC ranges (mg/mL) were AB: 0.5–16, FC: 2–64, IT: 0.25–2, FLU: 2–32, VO: 0.215–1 and POS: 0.125–0.5. No intrazonal growth was observed in the DD method. Inhibition zone diameters ranged from 5 to 35 mm (FLU) and 10 to 20 mm (POS). Interclass correlation coefficients (ICCs) and 95% confidence intervals for comparing the methods were calculated using log2 transformed data. ICC for BMD versus Etest ranged from 0.98 to 0.99 (P < 10-4) for all drugs. Pearson's correlation coefficient used as a measure of linear associations for FLU and POS BMD versus Etest, versus disk diffusion was 0.944 (P < 0.01).

Conclusion: High AB, FC, IT and FLU MICs warrant clinical alertness for breakthrough Trichosporon infections when used for prophylaxis. Pending clinical studies, the low VOR and POS MICs suggest that they may be a better alternative for prophylaxis in patients at risk. Disk diffusion is an option for rapidly testing T. asahii isolates, provided it is further evaluated. Standardised susceptibility testing can aid the selection of the most relevant antifungal therapy for the management of trichosporonosis.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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