Characterization of a New Clinical Yeast Species, Candida tunisiensis sp. nov., Isolated from a Strain Collection from Tunisian Hospitals

Abstract

dFrom a collection of yeast isolates isolated from patients in Tunisian hospitals between September 2006 and July 2010, the yeast strain JEY63 (CBS 12513), isolated from a 50-year-old male that suffered from oral thrush, could not be identified to the species level using conventional methods used in clinical laboratories. These methods include matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), germ tube formation, and the use of CHROMagar Candida and metabolic galleries. Sequence analysis of the nuclear rRNA (18S rRNA, 5.8S rRNA, and 26S rRNA) and internal transcribed spacer regions (ITS1 and ITS2) indicated that the ribosomal DNA sequences of this species were not yet reported. Multiple gene phylogenic analyses suggested that this isolate clustered at the base of the Dipodascaceae (Saccharomycetales, Saccharomycetes, and Ascomycota). JEY63 was named Candida tunisiensis sp. nov. according to several phenotypic criteria and its geographical origin. C. tunisiensis was able to grow at 42°C and does not form chlamydospores and hyphae but could grow as yeast and pseudohyphal forms. C. tunisiensis exhibited most probably a haploid genome with an estimated size of 10 Mb on at least three chromosomes. Using European Committee for Antimicrobial Susceptibility Testing (EUCAST) and Clinical and Laboratory Standards Institute (CLSI) Candida albicans susceptibility breakpoints as a reference, C. tunisiensis was resistant to fluconazole (MIC ‫؍‬ 8 g/ml), voriconazole (MIC ‫؍‬ 0.5 g/ml), itraconazole (MIC ‫؍‬ 16 g/ml), and amphotericin B (MIC ‫؍‬ 4 g/ml) but still susceptible to posaconazole (MIC ‫؍‬ 0.008 g/ml) and caspofungin (MIC ‫؍‬ 0.5 g/ml). In conclusion, MALDI-TOF MS permitted the early selection of an unusual isolate, which was still unreported in molecular databases but could not be unambiguously classified based on phylogenetic approaches.

<p>Distribution of Pathogenic Yeasts in Different Clinical Samples: Their Identification, Antifungal Susceptibility Pattern, and Cell Invasion Assays</p>

“…As observed by others and in our study many new types of yeast are reported as probable human pathogens which should be included in diagnostic protocols. 54 In the present study, a total of six species viz., Cy. fabianii, T. asahii, C. africana, K. marxianus, Lodderomyces sp., Ko.…”

Metabolic profiling of Candida clinical isolates of different species and infection sources

“…In recent years, methods for the rapid identification of microorganisms have been developed, which have enabled the detection of new species and characterization of their components and/or metabolites. These methods have been based on proteomic profiles, using MALDI-TOF MS, and metabolome profiles, by 1 H-NMR and hyphenated mass spectrometry 8 , 12 – 15 .…”

“…Different Candida species may have very different antifungal susceptibility profiles. In this context, it is important to obtain accurate taxonomic identification to apply appropriate treatments 8 , 9 . Traditionally, fungi are identified by phenotypic traits including morphology, colony appearance and pigmentation in chromogenic culture medium 8 , 10 , 11 .…”

“…In this context, it is important to obtain accurate taxonomic identification to apply appropriate treatments 8 , 9 . Traditionally, fungi are identified by phenotypic traits including morphology, colony appearance and pigmentation in chromogenic culture medium 8 , 10 , 11 . Recently, alternative methods for rapid identification of microorganisms have been studied, such as proteomics, using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and metabolomics by nuclear magnetic resonance (NMR) 8 , 12 – 15 .…”

“…Traditionally, fungi are identified by phenotypic traits including morphology, colony appearance and pigmentation in chromogenic culture medium 8 , 10 , 11 . Recently, alternative methods for rapid identification of microorganisms have been studied, such as proteomics, using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and metabolomics by nuclear magnetic resonance (NMR) 8 , 12 – 15 . MALDI-TOF MS has short analysis time, low error rate and high precision for microorganism identification because it can discriminate between closely related and critical species, making it suitable for implementation in the field of clinical routine 12 , 16 , 17 .…”