Candida guilliermondii and Other Species of Candida Misidentified as Candida famata: Assessment by Vitek 2, DNA Sequencing Analysis, and Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry in Two Global Antifungal Surveillance Programs

Abstract

bCandida famata (teleomorph Debaryomyces hansenii) has been described as a medically relevant yeast, and this species has been included in many commercial identification systems that are currently used in clinical laboratories. Among 53 strains collected during the SENTRY and ARTEMIS surveillance programs and previously identified as C. famata (includes all submitted strains with this identification) by a variety of commercial methods (Vitek, MicroScan, API, and AuxaColor), DNA sequencing methods demonstrated that 19 strains were C. guilliermondii, 14 were C. parapsilosis, 5 were C. lusitaniae, 4 were C. albicans, and 3 were C. tropicalis, and five isolates belonged to other Candida species (two C. fermentati and one each C. intermedia, C. pelliculosa, and Pichia fabianni). Additionally, three misidentified C. famata strains were correctly identified as Kodomaea ohmeri, Debaryomyces nepalensis, and Debaryomyces fabryi using intergenic transcribed spacer (ITS) and/or intergenic spacer (IGS) sequencing. The Vitek 2 system identified three isolates with high confidence to be C. famata and another 15 with low confidence between C. famata and C. guilliermondii or C. parapsilosis, displaying only 56.6% agreement with DNA sequencing results. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) results displayed 81.1% agreement with DNA sequencing. One strain each of C. metapsilosis, C. fermentati, and C. intermedia demonstrated a low score for identification (<2.0) in the MALDI Biotyper. K. ohmeri, D. nepalensis, and D. fabryi identified by DNA sequencing in this study were not in the current database for the MALDI Biotyper. These results suggest that the occurrence of C. famata in fungal infections is much lower than previously appreciated and that commercial systems do not produce accurate identifications except for the newly introduced MALDI-TOF instruments.

Development of Two Molecular Approaches for Differentiation of Clinically Relevant Yeast Species Closely Related to Candida guilliermondii and Candida famata

“…Accurate identification of clinical isolates closely related to C. guilliermondii or C. famata has clinical importance because of the remarkably diverse susceptibility profiles of these species (22)(23)(24). Because these genetically related species are difficult to identify by conventional methods, molecular techniques are more suitable for their differentiation (24,30).…”

“…Candida fermentati (the anamorph of Pichia caribbica), an emerging species that is very closely related to C. guilliermondii, has often been misidentified as C. guilliermondii using routine identification methods (22)(23)(24)(25)(26). Because of lower susceptibility to triazoles, Candida palmioleophila, which is often misidentified as Candida famata (the anamorph of Debaryomyces hansenii) or C. guilliermondii, has been emphasized in recent studies (24,25,27).…”

“…The above-mentioned yeast species are likely to be confused with one another by conventional identification methods. In particular, isolates confused with C. famata were frequently misidentified, and C. famata was, in fact, very rare in clinical specimens (22,24,25,27).…”

“…The above-mentioned yeast species are likely to be confused with one another by conventional identification methods. In particular, isolates confused with C. famata were frequently misidentified, and C. famata was, in fact, very rare in clinical specimens (22,24,25,27).Currently, limited tools are available for molecular differentiation of these closely related yeast species. Molecular methods such as PCR-restriction fragment length polymorphism (RFLP), real-time PCR, Luminex techniques, electrophoretic karyotyping, and PCR with type-specific primers have been developed to distinguish some of these species, but other species were not involved in those studies (30-33).…”

“…Because of lower susceptibility to triazoles, Candida palmioleophila, which is often misidentified as Candida famata (the anamorph of Debaryomyces hansenii) or C. guilliermondii, has been emphasized in recent studies (24,25,27). Additionally, Debaryomyces nepalensis and Debaryomyces fabryi, two species that are closely related to C. famata, have been isolated from clinical samples, including blood (22,28,29), and also are potential pathogens. The above-mentioned yeast species are likely to be confused with one another by conventional identification methods.…”