Biology subjects

Zajac, C.

Publications and source records attributed to Zajac, C..

4 recordsLinked to original sources

bioRxiv2025

Aneuploidy, polyploidy, and loss of heterozygosity distinguish serial bloodstream isolates of Candida albicans

BackgroundThe opportunistic pathogen Candida albicans is the leading species causing invasive Candida infections worldwide. Genomic variation is widespread in clinical isolates and complicates identification of genetic variants underlying antifungal drug resistance and tolerance. Our understanding of genomic and phenotypic diversity during invasive infections is limited and studies of serial isolates from individual patients are uncommon. We performed comparative analyses of 101 C. albicans bloodstream isolates from 55 patients in the Minnesota Minneapolis-Saint Paul region, including serial isolates from 19 patients. We analyzed the phylogenetic relationships of these isolates relative to 199 globally-collected public C. albicans genomes. ResultsThis studys regional isolates span the phylogenetic diversity of C. albicans; 6 isolates represent novel outliers to known clades. Serial isolates from individual patients were separated by limited single nucleotide polymorphisms. Nevertheless, we identified extensive large-scale genomic variation between serial isolates including polyploidy, aneuploidy, copy number variation, loss of heterozygosity, and chromosomal rearrangements. We demonstrated how a heterozygous ERG251 loss of function variant drives azole tolerance in a clinical isolate from a patient with a history of recurrent infections. Using serial isolates, we demonstrated that polyploidy provides an adaptive advantage in the presence of fluconazole despite the absence of overt antifungal drug resistance. ConclusionsOur analysis of serial isolates reveals the genomic plasticity of C. albicans during invasive infections and identifies variation driving antifungal drug tolerance. Our findings reveal limitations in current antifungal susceptibility testing and highlight the need to account for genomic and phenotypic variation during invasive Candida infections.

microbiology↗

bioRxiv2025

Heterogeneity of Candida bloodstream isolates in an academic medical center and affiliated hospitals

Invasive Candida bloodstream infections (candidemia) are a deadly global health threat. Rare Candida species are increasingly important causes of candidemia and phenotypic data, including patterns of antifungal drug resistance, is limited. There is geographic variation in the distribution of Candida species and frequency of antifungal drug resistance, which means that collecting and reporting regional data can have significant clinical value. Here, we report the first survey of species distribution, frequency of antifungal drug resistance, and phenotypic variability of Candida bloodstream isolates from an academic medical center and 5 affiliated hospitals in the Minneapolis-Saint Paul region of Minnesota, collected during an 18-month period from 2019 to 2021. We collected 288 isolates spanning 11 species from 119 patients. C. albicans was the most frequently recovered species, followed by C. glabrata and C. parapsilosis, with 10% of cases representing additional, rare species. We performed antifungal drug susceptibility for the three major drug classes and, concerningly, we identified fluconazole, micafungin and multidrug resistance rates in C. glabrata that were [~] 2 times higher than that reported in other regions of the United States. We report some of the first phenotypic data in rare non-albicans Candida species. Through analysis of serial isolates from individual patients, we identified clinically relevant within-patient differences of MIC values in multiple drug classes. Our results provide valuable clinical data relevant to antifungal stewardship efforts and highlight important areas of future research, including within-patient dynamics of infection and the mechanisms of drug resistance in rare Candida species.

microbiology↗

bioRxiv2020

RNA-seq of Human T-Cells After Hematopoietic Stem Cell Transplantation Identifies Linc00402 as a Novel Regulator of T-Cell Alloimmunity

Mechanisms governing allogeneic T-cell responses after allogeneic hematopoietic stem cell (HSC) and solid organ transplantation are incompletely understood. Long non-coding RNAs (lncRNA) do not code for, but control gene expression with tissue specificity. However, their role in T-cell alloimmunity is unknown. We performed RNA-seq on donor T-cells from HSCT patients and found that increasing strength of allogeneic stimulation caused greater differential expression of lncRNAs. The differential expression was validated in an independent patient cohort, and also following ex vivo allogeneic stimulation of healthy human T-cells. Linc00402, a novel, conserved lncRNA, was identified as the most differentially expressed and was enriched 88 fold in human T-cells. Mechanistically, it was mainly located in the cytoplasm, and its expression was rapidly reduced following T-cell activation. Consistent with this, tacrolimus preserved the expression of Linc00402 following T-cell activation, and lower levels of Linc00402 were found in patients who subsequently went on to develop acute graft versus host disease (GVHD). The dysregulated expression of Linc00402 was also validated in murine T-cells, both in vitro and in vivo. Functional studies using multiple modalities to deplete Linc00402 in both mouse and human T-cells, demonstrated a critical role for Linc00402 in the T-cell proliferative response to an allogeneic stimulus but not a non-specific anti-CD3/CD28 stimulus. Thus, our studies identified Linc00402 as a novel, conserved regulator of allogeneic T-cell function. Because of its T-cell specific expression and its impact on allogeneic T-cell responses, targeting Linc00402 may improve outcomes after allogeneic HSC and solid organ transplantation. One sentence summaryLncRNAs are differentially expressed by allogeneic antigen-stimulated T-cells, and the novel lncRNA, Linc00402, is a specific regulator of mouse and human allogeneic T-cells.

immunology↗

bioRxiv2019

A Pipeline for Fecal Host DNA Analysis by Absolute Quantification of LINE-1 and Mitochondrial Genomic Elements Using ddPCR

Stool contains DNA shed from cells of the gastrointestinal (GI) tract and has great potential as a bio-specimen for non-invasive, nucleic acid-based detection of GI diseases. Whereas methods for studying faecal microbiome DNA are plentiful, there is a lack of well-characterised procedures for stabilisation, isolation, and quantitative analysis of faecal host DNA. We report an optimised pipeline for faecal host DNA analysis from the point-of-collection to droplet digital PCR (ddPCR) absolute quantification of host-specific gene targets. We evaluated multiple methods for preservation and isolation of host DNA from stool to identify the highest performing methods. To quantify host DNA even if present in partially degraded form, we developed sensitive, human-specific short-amplicon ddPCR assays targeting repetitive nuclear genomic elements (LINE-1) and mitochondrial genes. We validated the ability of these optimised methods to perform absolute quantification of host DNA in 200 stool DNA extracts from samples that were serially collected from three healthy individuals and three hospitalised patients. These specimens allowed assessment of host DNA day-to-day variability in stool specimens with widely varying physical characteristics (i.e., Bristol scores). We further extended this approach to mouse stool analysis, to enable faecal host DNA studies in animal disease models as well.

molecular biology↗