Comparison of RapID Yeast Plus System with API 20C System for Identification of Common, New, and Emerging Yeast Pathogens

Abstract

The ability to identify yeast isolates by the new enzymatic RapID Yeast Plus System was compared to the ability to identify yeast isolates by the API 20C system. A total of 447 yeast isolates representing Blastoschizomyces capitatus, 17Candida spp., 5 Cryptococcus spp.,Geotrichum spp., 2 Hanseniaspora spp.,Hansenula anomala, Hansenula wingei, 3Rhodotorula spp., Saccharomyces cerevisiae,Sporobolomyces salmonicolor, Trichosporon beigelii, and 2 Prototheca spp. were evaluated. Also, five quality control strains (Candida spp. andCryptococcus laurentii) with well-documented reactivities by the RapID Yeast Plus System were used. Each isolate was evaluated by both methods with a 48-h culture grown at 30°C on Sabouraud dextrose agar (Emmons modification) by following the recommendations of the manufacturers. The RapID Yeast Plus System enzymatic reactions were read after 4 h of incubation, and the API 20C carbohydrate assimilation identification profiles were obtained after 72 h of incubation. There was good (95.7%) agreement between the identifications obtained by the two methods with the eight commonCandida spp. and with Cryptococcus neoformans. The agreement was lower when the emerging Candida spp. and other yeast-like pathogens were tested (79.1 and 75.2%, respectively). These preliminary data suggest the potential utility of the RapID Yeast Plus System for use in the clinical laboratory for the rapid identification of common yeast pathogens as well as certain new and emerging species.

Identification of clinically relevant yeast species by DNA sequence analysis of the D2 variable region of the 25–28S rRNA gene

“…15,16,26,44,45 Even up-to-date methods based on phenotype analysis occasionally generate misidentification. [8][9][10][11]15,16 Application of the genetic concept of ÔspeciesÕ is impractical in yeast because of the difficulty in obtaining matings and assessing their outcome. 46 DNA sequence data provide a readily accessible source of genetic relatedness, and the utility of the D1 and D2 regions of the 25-28S rRNA gene to differentiate yeast sibling species has been investigated.…”

“…One strain (260U) was consistently identified as C. guilliermondii by preliminary tests, API 20C AUX and D2-based phylogeny, while the RapID failed in identification, consistent with the previously reported poor reliability of this system in C. guilliermondii detection. 9 Notably, neither C. guillermondii nor D. capitatus reference sequence have yet been included in the commercial MicroSeq ID Fungal gene library (Applied Biosystems, version 2.0), indicating that D2 sequencing and interrogation of free-access databases are advisable for identification of these species. An interesting observation was for strains 695Ea and 695Eb, both isolated from the same primary plate, in which D2 sequence-based taxonomy provided evidence of mixed C. norvegensis-C. krusei co-infection.…”

“…These observations confirm the validity of the API 20C AUX for phenotypic identification, 8,11 and pose the problem of whether the limited repertoire of carbon sources and ⁄ or the short time available for substrate reaction and ⁄ or subjective reading can occasionally result in misidentification of some Candida species by the RapID system, as previously documented for C. parapsilosis 8,50 and other yeast species. 9,26 The estimated cost of in-house D2 sequence-based identification, from yeast thermolysis to data reporting, calculated on five samples per day using the official price lists for ingredients and supplies, was approximately twice the RapID system, but less than half of the MicroSeq D2 LSU rDNA fungal identification system (Applied Biosystems), and could further be lowered if more samples are processed. The execution time is c. 6 h, slightly longer than rapid biochemical identification tests (4.5 h), but fully affordable in one working day.…”

Phenotypic methods and commercial systems for the discrimination between C. albicans and C. dubliniensis

“…Particularly, D-xylose may be helpful for the identification of C. dubliniensis (Gales et al, 1999;Ellepola et al, 2003;Fotedar and Al-Hedaithy, 2003). Various commercially available yeast identification systems depending primarily on adaptations of carbohydrate assimilation procedures have been developed for C. albicans identification (Espinel-Ingroff et al, 1998;Gales et al, 1999;Pincus et al, 1999;Xu et al, 2002). The carbohydrate assimilation is examined either visually for changes in turbidity or color of pH indicators, or read automatically by using a photometer (Sandven, 1990).…”

Comparison of Three Commercial Systems for Identification of Yeasts Commonly Isolated in the Clinical Microbiology Laboratory

“…Since traditional methods are tedious and time-consuming to perform in the routine laboratory, numerous commercial systems that can identify these pathogens within 4 to 72 h, depending on the system, have been developed (4,6,7,9,10). The RapID Yeast Plus System is a micromethod that identifies yeasts in 4 h and has been studied by a number of investigators (3,9). These studies, however, compared the system only against conventional methods or the API 20C Aux assimilation assay.…”