A novel class of Candida glabrata cell wall proteins with ß-helix fold mediates adhesion in clinical isolates.

Candida glabrata is an opportunistic pathogenic yeast frequently causing infections in humans. Though it lacks typical virulence factors such as hyphal development, C. glabrata contains a remarkably large and diverse set of putative wall adhesins that is crucial for its success as pathogen. Here, we present an analysis of putative adhesins from the homology clusters V and VI. First, sequence similarity network analysis revealed relationships between cluster V and VI adhesins and S. cerevisiae haze protective factors (Hpf). Crystal structures of A-regions from cluster VI adhesins Awp1 and Awp3b reveal a parallel right-handed ß-helix domain that is linked to a C-terminal ß-sandwich. Structure solution of the A-region of Awp3b via single wavelength anomalous diffraction phasing revealed the largest known lanthanide cluster with 21 Gd3+ ions. Awp1-A and Awp3b-A show structural similarity to pectate lyases but binding to neither carbohydrates nor Ca2+ was observed. Phenotypic analysis of awp1Δ, awp3Δ, and awp1,3Δ double mutants did also not confirm their role as adhesins. In contrast, deletion mutants of the cluster V adhesin Awp2 in the hyperadhesive clinical isolate PEU382 demonstrated its importance for adhesion to polystyrene or glass, biofilm formation, cell aggregation and other cell surface-related phenotypes. Together with cluster III and VII adhesins our study shows that C. glabrata CBS138 can rely on a set of 42 Awp1-related adhesins with ß-helix/α-crystallin domain architecture for modifying the surface characteristics of its cell wall.

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.

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.

Optimizing Small World Initiative service learning by focusing on antibiotics-producing actinomycetes from soil.

Small World Initiative and Tiny Earth are popular citizen science programs that are implemented worldwide in response to the global antibiotic resistance crisis. When starting up the program in Albacete (Spain), we noted that rates of isolated antibiotic-producing bacteria are generally low. To make the activity more stimulating for participating students, we modified the protocol to obtain more positive results by focusing on isolation of actinomycetes, the main producers of most clinically used antibiotics. Adaptations involved redesigning culture media, incubation times and temperatures, and modification of the ESKAPE antibiosis experiment by employing an agar-transplantation step. Of 390 bacterial isolates tested, almost 6% tested positive in antibiosis experiments and DNA sequence analysis confirmed that all positives are actinomycetes, demonstrating that our protocol is efficient toward isolating antibiotic-producing actinomycetes from soil. Evaluation forms filled by participating students indicated that the program was received very positively and that our modifications contribute to make this educational program more stimulating and efficient.