High rate of Exophiala dermatitidis recovery in the airways of patients with cystic fibrosis is associated with pancreatic insufficiency

Abstract

The black-pigmented fungus Exophiala dermatitidis is considered to be a harmless colonizer of the airways of cystic fibrosis (CF) patients. The aim of this study was to establish the recovery rate of E. dermatitidis in respiratory specimens from CF patients, transplant recipients, and subjects with other respiratory disorders in Sweden. Second, we wished to determine if particular clinical traits were associated with E. dermatitidis colonization of the airways and the antifungal susceptibility profiles of Exophiala strains. Sputum and bronchoalveolar lavage samples (n = 492) derived from 275 patients were investigated. E. dermatitidis was isolated in respiratory specimens from 19% (18/97) of the CF patients but in none of the other patient categories. All isolates were recovered after 6 to 25 days of incubation on erythritol-chloramphenicol agar (ECA) medium. Morphological and genetic analyses confirmed species identity. Pancreatic insufficiency was positively associated with the presence of E. dermatitidis in sputum samples (P = 0.0198). Antifungal susceptibility tests demonstrated that voriconazole and posaconazole had the lowest MICs against E. dermatitidis. In conclusion, E. dermatitidis is a frequent colonizer of the respiratory tract in CF patients in Sweden and appears to be associated with more advanced disease. Whether E. dermatitidis is pathogenic remains to be elucidated.

Fig. 1.

Recovery of E. dermatitidis from sputa of CF patients cultivated on ECA and Sabouraud agar (SAB), respectively, following various incubation times.

Fig. 2.

Direct microscopy examination of CF patient sputum samples that were culture positive for E. dermatitidis. Sputum was stained with the fluorescent dye blankophore and examined by fluorescence microscopy (magnification, ×400). Chains of yeast-like structures (a) and/or fungal hyphae (b) are seen.

Fig. 3.

Dendrogram of sequence similarities between the rRNA operon combined ITS1 and ITS2 regions of strains of E. dermatitidis derived from an unrooted UPGMA cluster analysis. Strains isolated from samples from patients at Sahlgrenska University Hospital, Gothenburg, Sweden, are numbered 274 to 3305. Sequences from reference strains of E. dermatitidis, representing each known sequence type, are included in the analysis. Strain designations: BMU, Research Center for Medical Microbiology, Beijing University, Beijing, China; CBS, Centralbureau voor Schimmelcultures, Utrecht, Netherlands; EM, Medical Microbiology, Athens Medical School, Athens, Greece; IFM, Research Institute for Pathogenic Fungi, Chiba, Japan; UTHSC, University of Texas Health Science Center, San Antonio, TX. The scale bar indicates sequence dissimilarities.

Fig. 4.

Multivariate analysis of OPLS was used to relate score vectors (microbial agents isolated from the CF sputum samples, e.g., S. aureus, Haemophilus influenzae, P. aeruginosa, Stenotrophomonas spp., A. fumigatus, and Burkholderia spp.) to the chosen Y variable (E. dermatitidis isolated from CF sputum samples). Loading plots with jackknifed confidence intervals are indicated by boxes. Positive plots indicate that variables are positively associated with E. dermatitidis. Negative plots are variables that are associated negatively with E. dermatitidis.

Fig. 5.

MICs of fluconazole, itraconazole, voriconazole, posaconazole, caspofungin, amphotericin B, and flucytosine according to Etests performed on 51 E. dermatitidis strains isolated from sputa of CF patients. The concentration of each antifungal agent necessary to inhibit 50% and 90% of the isolates, respectively, are indicated as MIC₅₀ and MIC₉₀. GM, geometric mean (μg/ml).