JAC Advance Access originally published online on November 22, 2007
Journal of Antimicrobial Chemotherapy 2008 61(1):135-138; doi:10.1093/jac/dkm442
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Original research |
Comparison of disc diffusion assay with the CLSI reference method (M27-A2) for testing in vitro posaconazole activity against common and uncommon yeasts
1 Unidad de Microbiología Experimental, Centro de Investigación, Hospital Universitario La Fe, Valencia, Spain 2 Servicio de Microbiología, Hospital Universitario La Fe, Valencia, Spain 3 Division of Infectious Diseases, VCU Medical Center, Richmond, VA, USA 4 Servicio de Microbiología Hospital Universitario Valme, Sevilla, Spain 5 Department of Microbiology, ACIA, Barcelona, Spain 6 Departamento Microbiología, Facultad de Farmacia, Universidad de Valencia, Spain
Received 19 July 2007; returned 8 October 2007; revised 25 September 2007; accepted 20 October 2007
* Corresponding author. Tel: +34-96-1973111; Fax: +34-96-3868718; E-mail: canton_emi{at}gva.es
Objectives: To evaluate the suitability of disc diffusion (DD) assay for testing posaconazole activity and to corroborate its activity against recently isolated yeasts by the CLSI reference microdilution M27-A2 method.
Methods: A total of 224 yeast isolates (7 species with 52 to 11 isolates each, and 15 species with 1 to 6 isolates) were evaluated, 125 were recent bloodstream isolates, 30 isolates from other sources and six ATCC isolates that included amphotericin B-resistant Candida albicans ATCC 200955, Candida lusitaniae (ATCC 200950, 200951, 200952 and 200953) and amphotericin B- and itraconazole-resistant Candida tropicalis ATCC 200956. MICs were determined at 24 and 48 h by following the CLSI guidelines, document M27-A2. DD testing was performed by following CLSI M44-A document with 5 µg posaconazole discs. Inhibition zone diameters were measured at the transition point at which growth decreased at both 24 and 48 h.
Results: DD showed very good reproducibility, with coefficient of variability median value 4.56. Posaconazole demonstrated good in vitro activity against all clinical isolates, including the emerging species and amphotericin B-resistant ATCC isolates except for C. tropicalis ATCC 200956 (posaconazole MIC 
16 mg/L). Only 1.5% and 4.1% of isolates were inhibited by >2 mg/L posaconazole at 24 and 48 h. Good correlation was obtained between methods (R = 0.763 at 24 h and 0.602 at 48 h). DD detected posaconazole-resistant isolates (MIC > 2 mg/L).
Conclusions: DD could be an alternative to the microdilution reference method, as no major discrepancies were detected.
Keywords: susceptibility , M44-A , azoles