Neglected Pulmonary Infection Caused by Exophiala dermatitidis Misidentified as Rhodotorula spp.

Abstract

Exophiala dermatitidis is an emerging black fungus that causes pulmonary infections that may be underestimated by conventional culture methods. We encountered one case that initially appeared to be yeast and was misidentified as Rhodotorula spp. using a commercial identification kit. Thus, genetic identification and clinical background investigations were conducted on 46 strains of Rhodotorula spp. The sequences of the internal transcribed spacer and large-subunit RNA genes (D1/D2 regions) of 43 isolates, excluding two environmental isolates and one difficult-to-culture isolate, were determined and genetically identified. Notably, 22 isolates were identified as E. dermatitidis and misidentified as Rhodotorula spp. using the conventional method. Based on the exclusion criteria, the clinical information of 11 patients was retrospectively reviewed. Five cases (definite) had definite exacerbation of pulmonary infections due to E. dermatitidis, and six cases (possible) had undeniable infections. Of the 11 cases of pulmonary infection suggested to be caused by E. dermatitidis, comorbidities included two cases of chronic pulmonary aspergillosis (CPA), three cases of pulmonary non-tuberculous mycobacterial (NTM) infection and one case of pulmonary nocardiosis, suggesting a trend towards simultaneous detection of chronic pulmonary infections. Steroid and immunosuppressive drug use was observed in five cases, and β-D-glucan elevation was observed in three of five definite cases of pulmonary infections due to E. dermatitidis. The possibility of E. dermatitidis infection should be considered when Rhodotorula spp. are isolated from cultures of airway-derived specimens, and, in addition to CPA and NTM, identification of E. dermatitidis may be important in chronic pulmonary infections.