Rapid Identification of Candida dubliniensis with Commercial Yeast Identification Systems

Abstract

Candida dubliniensis is a newly described species that is closely related phylogenetically to Candida albicans and that is commonly associated with oral candidiasis in human immunodeficiency virus-positive patients. Several recent studies have attempted to elucidate phenotypic and genotypic characteristics of use in separating the two species. However, results obtained with simple phenotypic tests were too variable and tests that provided more definitive data were too complex for routine use in the clinical laboratory setting. The objective of this study was to determine if reproducible identification of C. dubliniensis could be obtained with commercial identification kits. The substrate reactivity profiles of 80 C. dubliniensis isolates were obtained by using the API 20C AUX, ID 32 C, RapID Yeast Plus, VITEK YBC, and VITEK 2 ID-YST systems. The percentages of C. dubliniensisisolates capable of assimilating or hydrolyzing each substrate were compared with the percentages from the C. albicans profiles in each kit's database, and the results were expressed as percentC. dubliniensis and percent C. albicans. Any substrate that showed >50% difference in reactivity was considered useful in differentiating the species. In addition, assimilation of methyl-α-d-glucoside (MDG), d-trehalose (TRE), and d-xylose (XYL) by the same isolates was investigated by the traditional procedure of Wickerham and Burton (L. J. Wickerham and K. A. Burton, J. Bacteriol. 56:363–371, 1948). At 48 h (the time recommended by the manufacturer for its new database), we found that the assimilation of four carbohydrates in the API 20C AUX system could be used to distinguish the species, i.e., glycerol (GLY; 88 and 14%), XYL (0 and 88%), MDG (0 and 85%), and TRE (15 and 97%). Similarly, results with the ID 32 C system at 48 h showed that XYL (0 and 98%), MDG (0 and 98%), lactate (LAT; 0 and 96%), and TRE (30 and 96%) could be used to separate the two species. Phosphatase (PHS; 9 and 76%) and α-d-glucosidase (23 and 94%) proved to be the most useful for separation of the species in the RapID Yeast Plus system. While at 24 h the profiles obtained with the VITEK YBC system showed that MDG (10 and 95%), XYL (0 and 95%), and GLY (26 and 80%) could be used to separate the two species, at 48 h only XYL (6 and 95%) could be used to separate the two species. The most useful substrates in the VITEK 2 ID-YST system were TRE (1 and 89%), MDG (1 and 99%), LAT (4 and 98%), and PHS (83 and 1%). While the latter kit was not yet commercially available at the time of the study, it would appear to be the most valuable for the identification of C. dubliniensis. Although assimilation of MDG, TRE, and XYL proved to be the most useful for species differentiation by the majority of commercial systems, the results with these carbohydrates by the Wickerham and Burton procedure were essentially the same for both species, albeit following protracted incubation. Thus, it is the rapidity of the assimilation achieved with the commercial systems that allows the differentiation of C. dubliniensis from C. albicans.

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

“…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). Growth at 45°C has been considered to be a particularly useful test for the differentiation of C. dubliniensis (no growth) from C. albicans (growth) by Pinjon et al (1998).…”

“…Growth at 45°C has been considered to be a particularly useful test for the differentiation of C. dubliniensis (no growth) from C. albicans (growth) by Pinjon et al (1998). Although the C. dubliniensis isolates examined did not assimilate a-methyl-D D-glucoside, xylose and DL DL-lactate such non-assimilation is again regarded as a typical property of C. dubliniensis (Gales et al 1999;Pincus et al 1999;Giammanco et al 2000) and the biocode obtained (vide supra) is typical of C. dubliniensis (Giammanco et al 2000;Sullivan et al 1997). In some studies, C. dubliniensis has been differentiated on CHROMagar Candida based on the production of dark green colonies compared with the lighter green colonies of C. albicans (Kirkpatrick et al 1998).…”

“…The five isolates of C. dubliniensis studied were from HIV-positive andnegative patients from Dublin, Eire. The Irish isolates were originally identified on the basis of dark green colony colour on CHROMagar Candida medium on primary isolation , lack of growth at 45°C (Pinjon et al 1998), characteristic carbohydrate assimilation profiles with the API ID 32C yeast identification system (Pincus et al 1999) and polymerase chain reaction analysis with C. dubliniensis-specific primers (Donnelly et al 1999) as well as colonial morphology and chlamydospore production on Staib agar (Al Mosaid et al 2001).…”

Candida dubliniensis: Ten years on

“…More accurate discrimination between C. albicans and C. dubliniensis isolates has been achieved by the use of improved carbohydrate assimilation test databases [13] and the application of assays based on the colony morphology of each species when grown on media supplemented with particular plant extracts. For example, when grown on Staib agar (i.e.…”

Candida albicans or Candida dubliniensis?

“…to grow at 45°C and Kirkpatrick et al [25] reported an even higher percentage of C. albicans isolates (36%) that failed to grow at this temperature. Pincus et al [20] stated that these variable results may be explained by poor temperature control in incubators or differences in media composition.…”