Antifungal Susceptibility Testing of Dematiaceous Fungi Using Etest

Ko, Woo Tae; Suh, Moo Kyu; Ha, Gyoung Yim

Abstract

BACKGROUND
Despite the increase of infections caused by dematiaceous fungi, the antifungal susceptibility of these fungi has been the little study. It is necessary to perform antifungal susceptibility testing of dematiaceous fungi. Etest (AB Biodisk, Sweden) is a rapid, easy-to-perform in-vitro antifungal susceptibility test.
OBJECTIVE
The purpose of the study was to investigate the minimal inhibitory concentration (MICs) of dematiaous fungi isolated from skin lesion using Etest.
METHODS
The dematiaceous fungal strains studied were nine clinical isolates of chromoblastomycosis and phaeohyphomycosis agents (3 strains of Exophiala dermatitidis, 4 strains of Fonsecaea pedrosoi, 2 strains of Exophiala jeanselmei) and two standard strains (Aspergillus flavus KCTC 6905, Aspergillus fumigatus KCTC 6145). MIC endpoints of Etest for amphotericin B (AMB) and itraconazole (ITZ) susceptibility were read after 72, 96, and 120 hours incubation for each isolates on RPMI 1640 agar.
RESULTS
MIC of AMB was 0.125~1.0 microgram/mL on E. dermatitidis & F. pedrosoi, and 0.19~0.25 microgram/mL on E. jeanselmei. MIC of ITZ was 0.38~1.5 microgram/mL on E. dermatitidis, 0.016~0.125 microgram/mL on F. pedrosoi, and 0.064~0.25 microgram/mL on E. jeanselmei. Two strains of E. dermatitidis isolated from Korean patients with phaeohyphomycosis showed ITZ-resistant.
CONCLUSION
This study showed that Etest represented a simple and efficacious method for antifungal susceptibility testing of dematiaceous fungi.