Identification of Candida dubliniensis in a prospective study of patients in the United States

Abstract

Although Candida albicans remains the fungal species most frequently isolated as an opportunistic oral pathogen, other yeast species are often identified in human immunodeficiency virus (HIV)-seropositive patients. Candida dubliniensis phenotypically resembles C. albicans in many respects, yet it can be identified and differentiated as a unique Candida species by its phenotypic and genetic profiles. The purpose of the present study was to prospectively test for the presence of C. dubliniensis among clinical isolates and to determine the clinical and demographic characteristics of patients harboring C. dubliniensis. Over a 90-day period, isolates from 724 patients that were presumptively identified as C. albicans were screened for C. dubliniensis by use of tests for germ tube and chlamydospore production, by detection of an inability to grow at 45 degrees C, by colony color on CHROMagar Candida medium, and by the results of a sugar assimilation test with the API 20C AUX yeast identification system. Among 699 isolates retrieved from those specimens evaluated, 5 from 25 HIV-seropositive patients and 1 isolate from a patient whose HIV status was unknown were shown to be consistent by phenotyping and by electrophoretic karyotyping with the European reference strain of C. dubliniensis. One of the C. dubliniensis isolates had dose-dependent susceptibility to fluconazole (MIC, 16 microg/ml). These results confirm the presence of this interesting species in the United States and support the need for further investigations into the prevalence and pathogenesis of C. dubliniensis.

FIG. 1

Identification of germ tube- and chlamydospore-positive yeast-like colonies after 48 h of incubation at 37°C. a, observed during initial growth and may wane upon subculturing; b, in the bioMerieux Vitek API 20C AUX database, there is no current assimilation profile which will identify C. dubliniensis.

FIG. 2

Phase-contrast micrographs showing chlamydospore production on TOC agar plates incubated at 25°C for 48 h. (A) Chlamydospores and pseudohyphae produced by C. albicans ATCC 18804; (b) typical production of abundant chlamydospores by the C. dubliniensis isolates in our study; the terminal pairs arrangement is shown. Magnifications, ×320.

FIG. 3

Electrophoretic karyotypes of Candida isolates. Lanes: 1, Succharomyces cerevisiae chromosomes, which were used as molecular mass standards (Bio-Rad); 2, C. dubliniensis CD-012-1; 3, C. dubliniensis CD-012-2; 4, C. dubliniensis CD-014; 5, C. dubliniensis CD-016; 6, C. dubliniensis CD-017; 7, C. dubliniensis CD-021; 8, C. dubliniensis CD-410; 9, C. albicans ATCC 18804; and 10, type strain C. dubliniensis CD36.