Correlation between microdilution (MD), E-test (ET) and disk diffusion (DD) methods for antifungal susceptibility testing of posaconazole.

Sims C, Paetznick V, Rodriguez J, Chen E, Ostrosky-Zeichner L

Author address: 

Laboratory of Mycology Research, UT Health Science Ctr at Houston, Houston USA

Abstract: 

Background: Agar-based antifungal susceptibility testing with ET and DD are attractive alternatives to the MD method due to their relative ease and lack of need for specialized equipment. We examined the correlation between the MD, ET, and DD methods for determination of susceptibility to posaconazole in Candida spp. Methods: 270 bloodstream isolates of Candida spp. with a broad range of posaconazole MICs were tested. MD testing was performed following the NCCLS M27-2A method. ET and DD (using 5g disks by two manufacturers) testing was performed on Mueller-Hinton agar supplemented with 2% glucose and 0.5 μg methylene blue following the NCCLS M-44P method. MICs and inhibitory zone diameters (at the prominent growth reduction endpoint) were recorded at 24 and 48 hours. Results: Species distribution was as follows: Candida albicans (46.3%), C. parapsilosis (15.9%), C. tropicalis (15.2%), C. glabrata (13.3%), C. krusei (7.4%), C. lusitaniae (1.1%), and C. dubliniensis (0.8%). ET MIC’s (mode=0.25, 0.125; range=0.031-32, 0.031-32 at 24 and 48 hours, respectively) were slightly higher than those measured by MD (mode=0.031, 0.031; range=0.031-32, 0.031-32 at 24 and 48 hours). This difference may be related to the use of NCCLS M-44P recommended media for ET as opposed to glucose-supplemented RPMI agar. Nevertheless, overall concordance (% of isolates within 2 dilutions) between ET and MD was 64.8% and 82.6% at 24 and 48 hours, respectively. When considering an arbitrary breakpoint of
2005

abstract No: 

24

Full conference title: 

15th Annual Focus on Fungal Infections
    • FFI 15th (2005)