Candida inconspicua and Candida norvegensis: New Insights into Identification in Relation to Sexual Reproduction and Genome Organization

Abstract

Candida inconspicua and Candida (Pichia) norvegensis are two emerging pathogenic species that exhibit reduced susceptibility to azole derivatives. Conventional (biochemical) approaches do not readily differentiate between the two species. The first aim of this work was to analyze the performance of biochemical, proteomic (matrix-assisted laser desorption ionization-time of flight [MALDI-TOF]), and molecular approaches in the precise identification of these species. These results then led us to sequence 3 genomic loci, i.e., the internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA), the D1/D2 domain of the 28S rDNA, and the elongation factor 1␣ (EF-1␣) gene, either directly or following cloning, of 13 clinical isolates and 9 reference strains belonging to the 5 species included in the Pichia cactophila clade, namely, Pichia cactophila, Pichia insulana, C. inconspicua, C. norvegensis, and P. pseudocactophila. Finally, isolates of C. inconspicua were challenged for sexual reproduction on the appropriate medium. Our results show that EF-1␣ sequencing and proteic profiling by MALDI-TOF are the two most efficient approaches to distinguish between C. norvegensis and C. inconspicua. As a characteristic of the P. cactophila clade, we found multiple alleles of the rDNA regions in certain strains belonging to the tested species, making ITS or D1/D2 sequencing not appropriate for identification. Whatever the method of identification, including MALDI-TOF and EF-1␣ sequencing, none could differentiate C. inconspicua from P. cactophila. The results of phylogenetic analysis and the generation of asci from pure cultures of all C. inconspicua strains both support the identification of P. cactophila as the teleomorph of C. inconspicua. Candida spp. remain the predominant cause of invasive fungal infections (1). The incidence of candidemia, the main clinical form of invasive candidiasis, significantly increased in the 1980s (2). Concomitantly, non-C. albicans species have emerged among the causative agents of candidiasis (3). The reasons for this emergence remain unclear, but selective pressure due to a larger use of azole derivatives has been suggested (4). Indeed, in addition to C. glabrata and C. krusei, the two main fluconazole-resistant species isolated from patients with candidemia, a number of fluconazoleresistant species are now regularly isolated from deep-seated infections. Together, these "rare" species may account for as much as 10% of the etiologic agents in some medical centers (5).Candida inconspicua and Candida norvegensis (teleomorph [tel.]: Pichia norvegensis) are among those fluconazole-resistant emerging species that are more frequently isolated from invasive infections (6). In addition to this increasing concern, these two species are known to be difficult to differentiate from each other using routine techniques such as biochemical panels. Indeed, auxanograms such as ID32C differentiate the two species only according to the hydrolysis of esculin, a phenotypic trait whose variability is well know...

Population genomics shows no distinction between pathogenic Candida krusei and environmental Pichia kudriavzevii: One species, four names

“…Clinical infections with P . norvegensis have been reported [ 34 ]. We used Illumina sequencing to sequence the genomes of the type strain of P .…”

“…norvegensis and other P . cactophila clade species [ 28 , 34 ] and therefore seems to be a trait of the whole genus Pichia . C .…”

“…Apart from C . krusei , the only other known pathogens in family Pichiaceae are the rare species Pichia norvegensis (also called Candida norvegensis ) and Pichia cactophila (also called Candida inconspicua ) [ 34 ].…”

Oral Candida administration in a Clostridium difficile mouse model worsens disease severity but is attenuated by Bifidobacterium

“…Mouse gut fungi are undetectable by conventional mouse feces culture [8, 11, 13] but are easily identified in human [10, 31]. Antibiotic effects upon gut levels of Ascomycota ( Candida , Aspergillus and Pichia [32, 33]), Basidiomycota ( Tricosporon [34]), and Ochroconis and Aphanomyces , a dematiaceous fungus and a water mold [35, 36], respectively, have been observed. Pichia , a group with some species re-classified as Candida [33, 37], were detectable after antibiotic administration despite being undetectable in normal controls.…”

Evaluation of the ePlex Blood Culture Identification Panels for Detection of Pathogens in Bloodstream Infections

“…The small number ( n = 7) of fungemia detections in our study prevents us from drawing conclusions about the performance of the BCID-FP panel for the detection of fungal pathogens associated with sepsis. However, one Candida inconspicua isolate identified by MALDI-TOF MS (21), a fluconazole-resistant yeast as an emerging agent of invasive infection (22), was not targeted by the FP panel (23). However, there are other Candida species of clinical importance, such as C.…”