Molecular typing and antifungal susceptibility of Exophiala species isolates from patients with cystic fibrosis

The black yeast Exophiala dermatitidis is a frequent agent of colonization of the lungs in patients with cystic fibrosis (CF). A total of 71 clinical isolates of Exophiala species from 13 patients were identified at the species level by sequencing the internal transcribed spacer (ITS) regions 1 and 2 of ribosomal DNA (rDNA) genes, and typed by random amplification of polymorphic DNA (RAPD), using two different primers, BG-2 and ERIC-1. Likewise, in vitro susceptibility of these isolates to some systemic antifungal drugs was investigated using the CLSI method. Almost all the isolates were identified as E. dermatitidis, but long term colonization with the closely related species E. phaeomuri-formis was observed in one patient. No clustering was found according to the geographic origin of the isolates, the isolation date, or antifungal susceptibility. Variations were seen in susceptibility of studied isolates to antifungals, but most of them exhibited low susceptibility to amphotericin B. Nevertheless, although some patients were successively colonized by two distinct genotypes, most of the isolates were distributed in patient-specific clusters. This phenomenon may be due to genomic variations of E. dermatitidis in the lung environment of CF patients. These results are consistent with colonization of the airways of the patients by a poorly distributed environmental fungus, with particular reservoirs which need to be defined