Integrated post-genomic cell wall analysis reveals floating biofilm formation associated with high expression of flocculins in the pathogen Pichia kudriavzevii.

The pathogenic yeast Pichia kudriavzevii, previously known as Candida krusei, is more distantly related to Candida albicans than clinically relevant CTG-clade Candida species. Its cell wall, a dynamic organelle that is the first point of interaction between pathogen and host, is relatively understudied, and its wall proteome remains unidentified to date. Here, we present an integrated study of the cell wall in P. kudriavzevii. Our comparative genomic studies and experimental data indicate that the general structure of the cell wall in P. kudriavzevii is similar to Saccharomyces cerevisiae and C. albicans and is comprised of ß-1,3-glucan, ß-1,6-glucan, chitin, and mannoproteins. However, some pronounced differences with C. albicans walls were observed, for instance, higher mannan and protein levels and altered protein mannosylation patterns. Further, despite absence of proteins with high sequence similarity to Candida adhesins, protein structure modeling identified eleven proteins related to flocculins/adhesins in S. cerevisiae or C. albicans. To obtain a proteomic comparison of biofilm and planktonic cells, P. kudriavzevii cells were grown to exponential phase and in static 24-h cultures. Interestingly, the 24-h static cultures of P. kudriavzevii yielded formation of floating biofilm (flor) rather than adherence to polystyrene at the bottom. The proteomic analysis of both conditions identified a total of 33 cell wall proteins. In line with a possible role in flor formation, increased abundance of flocculins, in particular Flo110, was observed in the floating biofilm compared to exponential cells. This study is the first to provide a detailed description of the cell wall in P. kudriavzevii including its cell wall proteome, and paves the way for further investigations on the importance of flor formation and flocculins in the pathogenesis of P. kudriavzevii.

Chromosome-level assemblies from diverse clades reveal limited structural and gene content variation in the genome of Candida glabrata.

BACKGROUND: Candida glabrata is an opportunistic yeast pathogen thought to have a large genetic and phenotypic diversity and a highly plastic genome. However, the lack of chromosome-level genome assemblies representing this diversity limits our ability to accurately establish how chromosomal structure and gene content vary across strains. RESULTS: Here, we expanded publicly available assemblies by using long-read sequencing technologies in twelve diverse strains, obtaining a final set of twenty-one chromosome-level genomes spanning the known C. glabrata diversity. Using comparative approaches, we inferred variation in chromosome structure and determined the pan-genome, including an analysis of the adhesin gene repertoire. Our analysis uncovered four new adhesin orthogroups and inferred a rich ancestral adhesion repertoire, which was subsequently shaped through a still ongoing process of gene loss, gene duplication, and gene conversion. CONCLUSIONS: C. glabrata has a largely stable pan-genome except for a highly variable subset of genes encoding cell wall-associated functions. Adhesin repertoire was established for each strain and showed variability among clades.

Identification of Candida auris and related species by multiplex PCR based on unique GPI protein-encoding genes.

BACKGROUND: The pathogen Candida auris is rapidly gaining clinical importance because of its resistance to antifungal treatments and its persistence in hospital environments. Early and accurate diagnosis of C. auris infections is crucial, and however, the fungus has often been misidentified by commercial systems. OBJECTIVES: To develop conventional and real-time PCR methods for accurate and rapid identification of C. auris and its discrimination from closely related species by exploiting the uniqueness of certain glycosylphosphatidylinositol (GPI)-modified protein-encoding genes. METHODS: Species-specific primers for two unique putative GPI protein-encoding genes per species were designed for C. auris, C. haemulonii, C. pseudohaemulonii, C. duobushaemulonii, C. lusitaniae and C. albicans. Primers were blind tested for their specificity and efficiency in conventional and real-time multiplex PCR set-up. RESULTS: All primers combinations showed excellent species specificity. In multiplex mode, correct identification was aided by different-sized amplicons for each species. Efficiency of the C. auris primers was validated using a panel of 155 C. auris isolates, including all known genetically diverse clades. In real-time multiplex PCR, different melting points of the amplicons allowed the distinction of C. auris from four related species. C. auris limit of detection was 5 CFU/reaction with a threshold value of 32. The method was also able to detect C. auris in spiked blood and serum. CONCLUSIONS: PCR identification based on unique GPI protein-encoding genes allows for accurate and rapid species identification of C. auris and related species without need for expensive equipment when applied in conventional PCR set-up.

Deletion of GLX3 in Candida albicans affects temperature tolerance, biofilm formation and virulence.

Candida albicans is a predominant cause of fungal infections in mucosal tissues as well as life-threatening bloodstream infections in immunocompromised patients. Within the human body, C. albicans is mostly embedded in biofilms, which provides increased resistance to antifungal drugs. The glyoxalase Glx3 is an abundant proteomic component of the biofilm extracellular matrix. Here, we document phenotypic studies of a glx3Δ null mutant concerning its role in biofilm formation, filamentation, antifungal drug resistance, cell wall integrity and virulence. First, consistent with its function as glyoxalase, the glx3 null mutant showed impaired growth on media containing glycerol as the carbon source and in the presence of low concentrations of hydrogen peroxide. Importantly, the glx3Δ mutant showed decreased fitness at 37°C and formed less biofilm as compared to wild type and a reintegrant strain. At the permissive temperature of 28°C, the glx3Δ mutant showed impaired filamentation as well as increased sensitivity to Calcofluor white, Congo red, sodium dodecyl sulfate and zymolyase, indicating subtle alterations in wall architecture even though gross quantitative compositional changes were not detected. Interestingly, and consistent with its impaired filamentation, biofilm formation and growth at 37°C, the glx3Δ mutant is avirulent. Our results underline the role of Glx3 in fungal pathogenesis and the involvement of the fungal wall in this process.

Molecular identification of Candida auris by PCR amplification of species-specific GPI protein-encoding genes.

The emerging multidrug-resistant pathogenic yeast Candida auris causes life-threatening invasive infections and shows a capacity for hospital transmission that is uncommon in other Candida species. Rapid and accurate diagnosis of C. auris infections is crucial; however, the fungus is frequently misidentified. Here, we present a rapid and easily applicable PCR assay for reliable identification of C. auris by designing primers from unique GPI protein-encoding genes. Specificity of the used primers for C. auris was verified with a panel of 19 different Candida species including the clinically most relevant and phylogenetically closely related species. Efficacy of the PCR approach was validated by correctly identifying 112 C. auris isolates from an outbreak in a Spanish hospital, 20% of which were not reliably identified by MALDI-TOF MS, and 27 genotypically diverse C. auris isolates originating from hospitals in various countries, in a test that included (blind) negative controls. By employing two GPI protein primer pairs in a single PCR, a double screening can be performed, which enhances the robustness of the PCR assay and avoids potential false negatives due to recent evolutionary events, as was observed for two isolates. Our PCR method, which is based on the uniqueness of selected GPI protein-encoding genes, is useful for easy, low-cost, and accurate identification of C. auris infections in a clinical setting.

Proteomic analysis of hyperadhesive Candida glabrata clinical isolates reveals a core wall proteome and differential incorporation of adhesins.

Attachment to human host tissues or abiotic medical devices is a key step in the development of infections by Candida glabrata. The genome of this pathogenic yeast codes for a large number of adhesins, but proteomic work using reference strains has shown incorporation of only few adhesins in the cell wall. By making inventories of the wall proteomes of hyperadhesive clinical isolates and reference strain CBS138 using mass spectrometry, we describe the cell wall proteome of C. glabrata and tested the hypothesis that hyperadhesive isolates display differential incorporation of adhesins. Two clinical strains (PEU382 and PEU427) were selected, which both were hyperadhesive to polystyrene and showed high surface hydrophobicity. Cell wall proteome analysis under biofilm-forming conditions identified a core proteome of about 20 proteins present in all C. glabrata strains. In addition, 12 adhesin-like wall proteins were identified in the hyperadherent strains, including six novel adhesins (Awp8-13) of which only Awp12 was also present in CBS138. We conclude that the hyperadhesive capacity of these two clinical C. glabrata isolates is correlated with increased and differential incorporation of cell wall adhesins. Future studies should elucidate the role of the identified proteins in the establishment of C. glabrata infections.

Evolution of pathogenicity and sexual reproduction in eight Candida genomes.

Candida species are the most common cause of opportunistic fungal infection worldwide. Here we report the genome sequences of six Candida species and compare these and related pathogens and non-pathogens. There are significant expansions of cell wall, secreted and transporter gene families in pathogenic species, suggesting adaptations associated with virulence. Large genomic tracts are homozygous in three diploid species, possibly resulting from recent recombination events. Surprisingly, key components of the mating and meiosis pathways are missing from several species. These include major differences at the mating-type loci (MTL); Lodderomyces elongisporus lacks MTL, and components of the a1/2 cell identity determinant were lost in other species, raising questions about how mating and cell types are controlled. Analysis of the CUG leucine-to-serine genetic-code change reveals that 99% of ancestral CUG codons were erased and new ones arose elsewhere. Lastly, we revise the Candida albicans gene catalogue, identifying many new genes.

Adhesins in human fungal pathogens: glue with plenty of stick.

Understanding the pathogenesis of an infectious disease is critical for developing new methods to prevent infection and diagnose or cure disease. Adherence of microorganisms to host tissue is a prerequisite for tissue invasion and infection. Fungal cell wall adhesins involved in adherence to host tissue or abiotic medical devices are critical for colonization leading to invasion and damage of host tissue. Here, with a main focus on pathogenic Candida species, we summarize recent progress made in the field of adhesins in human fungal pathogens and underscore the importance of these proteins in establishment of fungal diseases.

Efficacy of the combination of amphotericin B and echinocandins against Candida auris in vitro and in the Caenorhabditis elegans host model.

IMPORTANCE: Multidrug resistance is a rising problem among non-Candida albicans species, such as Candida auris. This therapeutic problem has been very important during the COVID-19 pandemic. The World Health Organization has included C. auris in its global priority list of health-threatening fungi, to study this emerging multidrug-resistant species and to develop effective alternative therapies. In the present study, the synergistic effect of the combination of amphotericin B and echinocandins has been demonstrated against blood isolates of C. auris. Different susceptibility responses were also observed between aggregative and non-aggregative phenotypes. The antifungal activity of these drug combinations against C. auris was also demonstrated in the Caenorhabditis elegans host model of candidiasis, confirming the suitability and usefulness of this model in the search for solutions to antimicrobial resistance.

The plant defensin RsAFP2 induces cell wall stress, septin mislocalization and accumulation of ceramides in Candida albicans.

The antifungal plant defensin RsAFP2 isolated from radish interacts with fungal glucosylceramides and induces apoptosis in Candida albicans. To further unravel the mechanism of RsAFP2 antifungal action and tolerance mechanisms, we screened a library of 2868 heterozygous C. albicans deletion mutants and identified 30 RsAFP2-hypersensitive mutants. The most prominent group of RsAFP2 tolerance genes was involved in cell wall integrity and hyphal growth/septin ring formation. Consistent with these genetic data, we demonstrated that RsAFP2 interacts with the cell wall of C. albicans, which also contains glucosylceramides, and activates the cell wall integrity pathway. Moreover, we found that RsAFP2 induces mislocalization of septins and blocks the yeast-to-hypha transition in C. albicans. Increased ceramide levels have previously been shown to result in apoptosis and septin mislocalization. Therefore, ceramide levels in C. albicans membranes were analysed following RsAFP2 treatment and, as expected, increased accumulation of phytoC24-ceramides in membranes of RsAFP2-treated C. albicans cells was detected. This is the first report on the interaction of a plant defensin with glucosylceramides in the fungal cell wall, causing cell wall stress, and on the effects of a defensin on septin localization and ceramide accumulation.

Usefulness of Chromogenic Media with Fluconazole Supplementation for Presumptive Identification of Candida auris.

Introduction:Candida auris is a major threat to public health. Rapid detection is essential for early treatment and transmission control. The use of chromogenic media allows the presumptive identification of this new species. The aim of this study is to describe the morphological characteristics of C. auris colonies on three commercial chromogenic media. Methods: Nineteen C. auris isolates from different countries/clades and 18 isolates of other species were cultivated in CHROMagarTM Candida Plus, HiCromeTM Candida, CHROMagar-Candida, and fluconazole-supplemented (32 mg/L) CHROMagar-Candida media. Results: On CHROMagarTM Candida Plus and HiCromeTM Candida, C. auris isolates from Colombia, Venezuela, India, Korea, and Japan displayed blue-shaded colonies, while isolates from Spain and Germany exhibited light pink shades with a bluish halo. All isolates showed white to pink colonies on CHROMagar-Candida. On CHROMagar Candida supplemented with fluconazole, whilst C. auris, C. glabrata, or C. krusei showed a similar pink color at 48 h incubation, phenotypic differentiation was possible by the rough, paraffin-like texture or the intense purple color acquired by C. krusei and C. glabrata, respectively. Moreover, in this medium, the presence of C. auris in combination with other species of similar color was not limiting for its early identification, due to this medium selecting only strains resistant to this antifungal. Conclusions: The use of chromogenic media such as CHROMagarTM Candida Plus facilitates a presumptive identification of C. auris. However, this identification can be difficult in the presence of mixed cultures. In these cases, the use of CHROMagarTM Candida medium with 32 mg/L fluconazole offers better performance for the identification of C. auris by inhibiting fluconazole-susceptible strains and selecting rare or high fluconazole MIC (>32 mg/L) isolates.

Comparative genomics of the fungal pathogens Candida dubliniensis and Candida albicans.

Candida dubliniensis is the closest known relative of Candida albicans, the most pathogenic yeast species in humans. However, despite both species sharing many phenotypic characteristics, including the ability to form true hyphae, C. dubliniensis is a significantly less virulent and less versatile pathogen. Therefore, to identify C. albicans-specific genes that may be responsible for an increased capacity to cause disease, we have sequenced the C. dubliniensis genome and compared it with the known C. albicans genome sequence. Although the two genome sequences are highly similar and synteny is conserved throughout, 168 species-specific genes are identified, including some encoding known hyphal-specific virulence factors, such as the aspartyl proteinases Sap4 and Sap5 and the proposed invasin Als3. Among the 115 pseudogenes confirmed in C. dubliniensis are orthologs of several filamentous growth regulator (FGR) genes that also have suspected roles in pathogenesis. However, the principal differences in genomic repertoire concern expansion of the TLO gene family of putative transcription factors and the IFA family of putative transmembrane proteins in C. albicans, which represent novel candidate virulence-associated factors. The results suggest that the recent evolutionary histories of C. albicans and C. dubliniensis are quite different. While gene families instrumental in pathogenesis have been elaborated in C. albicans, C. dubliniensis has lost genomic capacity and key pathogenic functions. This could explain why C. albicans is a more potent pathogen in humans than C. dubliniensis.

ProFASTA: a pipeline web server for fungal protein scanning with integration of cell surface prediction software.

Surface proteins, such as those located in the cell wall of fungi, play an important role in the interaction with the surrounding environment. For instance, they mediate primary host-pathogen interactions and are crucial to the establishment of biofilms and fungal infections. Surface localization of proteins is determined by specific sequence features and can be predicted by combining different freely available web servers. However, user-friendly tools that allow rapid analysis of large datasets (whole proteomes or larger) in subsequent analyses were not yet available. Here, we present the web tool ProFASTA, which integrates multiple tools for rapid scanning of protein sequence properties in large datasets and returns sequences in FASTA format. ProFASTA also allows for pipeline filtering of proteins with cell surface characteristics by analysis of the output created with SignalP, TMHMM and big-PI. In addition, it provides keyword, iso-electric point, composition and pattern scanning. Furthermore, ProFASTA contains all fungal protein sequences present in the NCBI Protein database. As the full fungal NCBI Taxonomy is included, sequence subsets can be selected by supplying a taxon name. The usefulness of ProFASTA is demonstrated here with a few examples; in the recent past, ProFASTA has already been applied successfully to the annotation of covalently-bound fungal wall proteins as part of community-wide genome annotation programs. ProFASTA is available at: http://www.bioinformatics.nl/tools/profasta/.

Pga13 in Candida albicans is localized in the cell wall and influences cell surface properties, morphogenesis and virulence.

The fungal cell wall is an essential organelle required for maintaining cell integrity and also plays an important role in the primary interactions between pathogenic fungi and their hosts. PGA13 encodes a GPI protein in the human pathogen Candida albicans, which is highly up-regulated during cell wall regeneration in protoplasts. The Pga13 protein contains a unique tandem repeat, which is present five times and is characterized by conserved spacing between the four cysteine residues. Furthermore, the mature protein contains 38% serine and threonine residues, and therefore probably is a highly glycosylated cell wall protein. Consistent with this, a chimeric Pga13-V5 protein could be localized to the cell wall, but only after deglycosylation was performed. Disruption of PGA13 led to increased sensitivity to Congo red, Calcofluor white, and zymolyase, and to a diminished ability of protoplasts to recover their cell wall. In addition, pga13Δ mutants exhibited delayed filamentation, a higher surface hydrophobicity, and increased adherence and flocculation (cell-cell interactions). Furthermore, transcript profiling showed that expression of four members of the ALS family (adhesin-encoding genes) is up-regulated in the pga13Δ null mutant. Altogether, these results indicate that Pga13 is a wall-localized protein that contributes to cell wall synthesis and is important for acquiring normal surface properties. The contribution of Pga13 to surface hydrophilicity may be important for cell dispersal during development of invasive infections, and possibly for morphological development. This is consistent with the observed reduced virulence of pga13Δ mutants in a mouse model of disseminated candidiasis.

Proteolytic cleavage of covalently linked cell wall proteins by Candida albicans Sap9 and Sap10.

The cell wall of the human-pathogenic fungus Candida albicans is a robust but also dynamic structure which mediates adaptation to changing environmental conditions during infection. Sap9 and Sap10 are cell surface-associated proteases which function in C. albicans cell wall integrity and interaction with human epithelial cells and neutrophils. In this study, we have analyzed the enzymatic properties of Sap9 and Sap10 and investigated whether these proteases cleave proteins on the fungal cell surface. We show that Sap9 and Sap10, in contrast to other aspartic proteases, exhibit a near-neutral pH optimum of proteolytic activity and prefer the processing of peptides containing basic or dibasic residues. However, both proteases also cleaved at nonbasic sites, and not all tested peptides with dibasic residues were processed. By digesting isolated cell walls with Sap9 or Sap10, we identified the covalently linked cell wall proteins (CWPs) Cht2, Ywp1, Als2, Rhd3, Rbt5, Ecm33, and Pga4 as in vitro protease substrates. Proteolytic cleavage of the chitinase Cht2 and the glucan-cross-linking protein Pir1 by Sap9 was verified using hemagglutinin (HA) epitope-tagged versions of both proteins. Deletion of the SAP9 and SAP10 genes resulted in a reduction of cell-associated chitinase activity similar to that upon deletion of CHT2, suggesting a direct influence of Sap9 and Sap10 on Cht2 function. In contrast, cell surface changes elicited by SAP9 and SAP10 deletion had no major impact on the phagocytosis and killing of C. albicans by human macrophages. We propose that Sap9 and Sap10 influence distinct cell wall functions by proteolytic cleavage of covalently linked cell wall proteins.

Mass spectrometric quantification of the adaptations in the wall proteome of Candida albicans in response to ambient pH.

The mucosal layers colonized by the pathogenic fungus Candida albicans differ widely in ambient pH. Because the properties and functions of wall proteins are probably pH dependent, we hypothesized that C. albicans adapts its wall proteome to the external pH. We developed an in vitro system that mimics colonization of mucosal surfaces by growing biomats at pH 7 and 4 on semi-solid agarose containing mucin as the sole nitrogen source. The biomats expanded radially for at least 8 days at a rate of ~30 µm h(-1). At pH 7, hyphal growth predominated and growth was invasive, whereas at pH 4 only yeast and pseudohyphal cells were present and growth was noninvasive. Both qualitative mass spectrometric analysis of the wall proteome by tandem mass spectrometry and relative quantification of individual wall proteins (pH 7/pH 4), using Fourier transform mass spectrometry (FT-MS) and a reference mixture of (15)N-labelled yeast and hyphal walls, identified similar sets of >20 covalently linked wall proteins. The adhesion proteins Als1 and Als3, Hyr1, the transglucosidase Phr1, the detoxification enzyme Sod5 and the mammalian transglutaminase substrate Hwp1 (immunological detection) were only present at pH 7, whereas at pH 4 the level of the transglucosidase Phr2 was >35-fold higher than at pH 7. Sixteen out of the 22 proteins identified by FT-MS showed a greater than twofold change. These results demonstrate that ambient pH strongly affects the wall proteome of C. albicans, show that our quantitative approach can give detailed insights into the dynamics of the wall proteome, and point to potential vaccine targets.

Pga26 mediates filamentation and biofilm formation and is required for virulence in Candida albicans.

The Candida albicans gene PGA26 encodes a small cell wall protein and is upregulated during de novo wall synthesis in protoplasts. Disruption of PGA26 caused hypersensitivity to cell wall-perturbing compounds (Calcofluor white and Congo red) and to zymolyase, which degrades the cell wall ß-1,3-glucan network. However, susceptibility to caspofungin, an inhibitor of ß-1,3-glucan synthesis, was decreased. In addition, pga26Δ mutants show increased susceptibility to antifungals (fluconazol, posaconazol or amphotericin B) that target the plasma membrane and have altered sensitivities to environmental (heat, osmotic and oxidative) stresses. Except for a threefold increase in ß-1,6-glucan and a slightly widened outer mannoprotein layer, the cell wall composition and structure was largely unaltered. Therefore, Pga26 is important for proper cell wall integrity, but does not seem to be directly involved in the synthesis of cell wall components. Deletion of PGA26 further leads to hyperfilamentation, increased biofilm formation and reduced virulence in a mouse model of disseminated candidiasis. We propose that deletion of PGA26 may cause an imbalance in the morphological switching ability of Candida, leading to attenuated dissemination and infection.

Virulence of Candida auris from different clinical origins in Caenorhabditis elegans and Galleria mellonella host models.

Candida auris is an emerging multidrug-resistant fungal pathogen responsible for nosocomial outbreaks of invasive candidiasis. Although several studies on the pathogenicity of this species have been reported, the knowledge on C. auris virulence is still limited. This study aims to analyze the pathogenicity of C. auris, using one aggregating isolate and eleven non-aggregating isolates from different clinical origins (blood, urine and oropharyngeal specimens) in two alternative host models of candidiasis: Caenorhabditis elegans and Galleria mellonella. Furthermore, possible associations between virulence, aggregation, biofilm-forming capacity, and clinical origin were assessed. The aggregating phenotype isolate was less virulent in both in vivo invertebrate infection models than non-aggregating isolates but showed higher capacity to form biofilms. Blood isolates were significantly more virulent than those isolated from urine and respiratory specimens in the G. mellonella model of candidiasis. We conclude that both models of candidiasis present pros and cons but prove useful to evaluate the virulence of C. auris in vivo. Both models also evidence the heterogeneity in virulence that this species can develop, which may be influenced by the aggregative phenotype and clinical origin.

Characterization of Awp14, A Novel Cluster III Adhesin Identified in a High Biofilm-Forming Candida glabrata Isolate.

Candida glabrata is among the most prevalent causes of candidiasis. Unlike Candida albicans, it is not capable of changing morphology between yeast and hyphal forms but instead has developed other virulence factors. An important feature is its unprecedented large repertoire of predicted cell wall adhesins, which are thought to enable adherence to a variety of surfaces under different conditions. Here, we analyzed the wall proteome of PEU1221, a high biofilm-forming clinical strain isolated from an infected central venous catheter, under biofilm-forming conditions. This isolate shows increased incorporation of putative adhesins, including eight proteins that were not detected in walls of reference strain ATCC 2001, and of which Epa22, Awp14, and Awp2e were identified for the first time. The proteomics data suggest that cluster III adhesin Awp14 is relatively abundant in PEU1221. Phenotypic studies with awp14Δ deletion mutants showed that Awp14 is not responsible for the high biofilm formation of PEU1221 onto polystyrene. However, awp14Δ mutant cells in PEU1221 background showed a slightly diminished binding to chitin and seemed to sediment slightly slower than the parental strain suggesting implication in fungal cell-cell interactions. By structural modeling, we further demonstrate similarity between the ligand-binding domains of cluster III adhesin Awp14 and those of cluster V and VI adhesins. In conclusion, our work confirms the increased incorporation of putative adhesins, such as Awp14, in high biofilm-forming isolates, and contributes to decipher the precise role of these proteins in the establishment of C. glabrata infections.

Candida parapsilosis Colony Morphotype Forecasts Biofilm Formation of Clinical Isolates.

Candida parapsilosis is a frequent cause of fungal bloodstream infections, especially in critically ill neonates or immunocompromised patients. Due to the formation of biofilms, the use of indwelling catheters and other medical devices increases the risk of infection and complicates treatment, as cells embedded in biofilms display reduced drug susceptibility. Therefore, biofilm formation may be a significant clinical parameter, guiding downstream therapeutic choices. Here, we phenotypically characterized 120 selected isolates out of a prospective collection of 215 clinical C. parapsilosis isolates, determining biofilm formation, major emerging colony morphotype, and antifungal drug susceptibility of the isolates and their biofilms. In our isolate set, increased biofilm formation capacity was independent of body site of isolation and not predictable using standard or modified European Committee on Antimicrobial Susceptibility Testing (EUCAST) drug susceptibility testing protocols. In contrast, biofilm formation was strongly correlated with the appearance of non-smooth colony morphotypes and invasiveness into agar plates. Our data suggest that the observation of non-smooth colony morphotypes in cultures of C. parapsilosis may help as an indicator to consider the initiation of anti-biofilm-active therapy, such as the switch from azole- to echinocandin- or polyene-based strategies, especially in case of infections by potent biofilm-forming strains.