Evaluation of Phenotypic Markers for Selection and Identification of Candida dubliniensis

Abstract

Candida dubliniensis is often associated with C. albicans in cultures. Easy-to-perform selective isolation procedures for these closely related species do not exist. Therefore, we evaluated previously described discriminatory phenotypic markers forC. dubliniensis. A total of 150 oral rinses from human immunodeficiency virus (HIV)-infected patients were cultured on CHROMagar Candida. Dark green colonies described as being indicative ofC. dubliniensis and other green colonies, 170 in total, were isolated. Chlamydospore formation, intracellular β-d-glucosidase activity, ability to grow at 42°C, carbohydrate assimilation pattern obtained by the API ID 32C, and Fourier transform infrared (FT-IR) spectroscopy were used for phenotypic characterization. Sequencing of the 5′ end of the nuclear large-subunit (26S) ribosomal DNA gene was used for definitive species identification for C. dubliniensis. C. dubliniensis was found in 34% of yeast-colonized HIV-infected patients. The color of the colonies on CHROMagar Candida proved to be insufficient for selecting C. dubliniensis, since only 30 of 53 provenC. dubliniensis isolates showed a dark green color in primary cultures. The described typical chlamydospore formation can give only some indication of C. dubliniensis. The assimilation pattern proved to be insufficient to discriminate C. dubliniensis from C. albicans. All C. dubliniensis strains showed no or highly restricted growth at 42°C and a lack of β-d-glucosidase activity. Unfortunately, atypical C. albicans strains can also exhibit these phenotypic traits. FT-IR spectroscopy combined with hierarchical clustering proved to be as reliable as genotyping for discriminating the two species.

Comparison of Candida dubliniensis and C. albicans based on polar lipid composition

“…For example, C. dubliniensis produces abundant chlamydospores that are frequently arranged in triplets, contiguous pairs or clusters on the tips of short pseudohyphal elements (Sullivan et al 1995;Staib and Morschhauser 1999;Tintelnot et al 2000). On the other hand, chlamydospores of C. albicans occur mostly singly on elongated pseudomycelia (Tintelnot et al 2000). The present findings for growth at 45°C, substrate assimilation profile analysis and production of chlamydospores agree with previous findings for C. dubliniensis reported by Sullivan et al (1997), Pinjon et al (1998), Staib and Morschhauser (1999), Pincus et al (1999) and Giammanco et al (2000).…”

“…A number of differences between C. dubliniensis and C. albicans have been described. For example, C. dubliniensis produces abundant chlamydospores that are frequently arranged in triplets, contiguous pairs or clusters on the tips of short pseudohyphal elements (Sullivan et al 1995;Staib and Morschhauser 1999;Tintelnot et al 2000). On the other hand, chlamydospores of C. albicans occur mostly singly on elongated pseudomycelia (Tintelnot et al 2000).…”

“…More recently it has been recovered from the oral cavities of HIV-negative individuals and from other anatomical locations in both HIV-infected and HIV-negative individuals. These locations have included skin, nail, faeces, blood, urine, wounds and vaginal flora (Pinjon et al 1998;Odds et al 1998;Sullivan and Coleman 1998;Meis et al 1999;Brandt et al 2000;Giammanco et al 2000;Tintelnot et al 2000;Marriott et al 2001;Gee et al 2002). Candida dubliniensis is genetically and phenotypically closely related to C. albicans, with which it shares many characteristics, including the ability to produce germ tubes and chlamydospores .…”

Phagocytosis, oxidative burst, and killing of Candida dubliniensis and Candida albicans by human neutrophils

“…Furthermore, eight clinical isolates of C. albicans originating from the diagnostic laboratory in Aachen were included in the study (four from sputum, three from urine, and one from blood). C. dubliniensis strains (n = 10) tested comprised three reference strains (NCPF 3108, CBS 7988, CBS 7987 T ), six strains cultured from the oral cavity of HIV-infected patients attending an outpatient clinic for infectious diseases at the Humboldt University in Berlin [16], and one strain cultured from the sputum of a non-HIV-infected patient.…”

“…With the exception of C. albicans reference strains, all strains tested were genotypically assigned to the respective species by sequence analysis of 500 base pairs of the 5P end of the large ribosomal subunit (LSU) rRNA gene using the recently designed primers [17]. Details of this procedure have been previously published [16,18].…”