Biology subjects

Schweizer, T. A.

Publications and source records attributed to Schweizer, T. A..

10 recordsLinked to original sources

bioRxiv2024

Screening clinical Candida albicans isolates for invasiveness by mimicking the human environment

ObjectivesCandida albicans colonizes a wide range of human body niches, but also causes severe invasive infections, such as candidemia. No screening method exists to predict which colonizer may lead to invasive infections. Invasiveness and virulence are associated with yeast filamentation, triggered by environmental factors encountered in the host. Here, we monitored the filamentation profile and colony appearance time of a C.albicans strain isolated from a patients abscess. Using eight additional C.albicans clinical isolates, we established an in vitro screening-framework of filamentation to assess the invasiveness potential of individual isolates. MethodsWe monitored the filamentation pattern of nine C.albicans clinical isolates over 14 days in 48 environmental conditions, including combinations of glucose/nitrogen concentrations, pH and temperature, to mimic host environment variations. Additionally, we tested invasiveness by growing isolates on modified filtration membranes, mimicking physical human body barriers usually colonized by Candida. An automated image analysis pipeline was developed to quantify filamentation. ResultsTwo types of colony filamentation morphology were differentiated, star and hazy. The total filamentation area depended on environmental factors. Based on their filamentation response to environmental changes, the isolates clustered in three distinct groups reflecting their site of isolation in the host. We moreover found that filamentation morphologies on modified filtration membranes could be predictors of invasiveness. ConclusionThis work lays the ground for screening assays, which could help assessing the potential of a colonizing Candida isolate to cause invasive disease, paving the way for tailored preventive therapy regimens in the future.

microbiology↗

bioRxiv2023

Alpha-toxin elicited CX3CL1-release via ADAM10 in Staphylococcus aureus pneumoniaimpairs bactericidal function of human monocytes

Staphylococcus aureus is an important human pathogen causing severe invasive infections. Pathogenesis is attributed to a wide array of virulence factors, including several potent exotoxins such as the pore-forming alpha-toxin. In this study, we found that patients with S. aureus respiratory tract infections had elevated CX3CL1 levels in airway fluid and plasma. Using humanized organotypic lung models, we observed that stimulation of lung epithelium with alpha-toxin induce an intensified CX3CL1 expression apically in the epithelium as well as the release of CX3CL1. Blocking alpha-toxin or ADAM10 activity in organotypic lung using an alpha-toxin-blocking antibody or a specific ADAM-10 inhibitor confirmed their role in modulating CX3CL1 cleavage and release. Analyses of CD14+ human monocytes in combination with a CX3CR1 inhibitor revealed that alpha-toxin-mediated CX3CL1 release induce CX3CL1-dependent chemotaxis. In line with these data, lung tissue from patients with S. aureus respiratory tract infection showed elevated CX3CL1 and CD14 staining as compared to tissue from patients with non-infectious lung diseases. Functional studies of monocytes showed that CX3CL1 released by lung models resulted in upregulated CD83 and downregulated CD86, as well as impaired killing of phagocytosed S. aureus. Furthermore, stimulation of monocytes with soluble CX3CL1 hampered their reactive-oxygen and nitric-oxide production. Taken together, our data show that S. aureus triggers the release of lung epithelial CX3CL1; a process found to be dependent on the alpha-toxins effect on ADAM10 mediating cytotoxicity and resulting in impaired monocyte phagocytic killing. Hence, we identify an immunomodulatory effect of alpha-toxin involving the CX3CL1-ADAM10 axis extending beyond the cytolysis function.

microbiology↗

bioRxiv2023

Group A Streptococcus strains causing meningitis without distinct invasive phenotype

Group A streptococcal (GAS, aka Streptococcus pyogenes) meningitis is a fulminant disease associated with high morbidity and mortality. To elucidate the mechanisms underlying the invasiveness of GAS in meningitis, we compared GAS isolates derived from five cases of meningitis, to otitis and colonizing isolates. We did not observe differences in adherence to and invasion of human brain microvascular endothelial cells, virulence factors activity or barrier disruption. Whole genome sequencing did not reveal particular invasiveness traits. Most patients previously suffered from otitis media suggesting that meningitis likely resulted from a continuous spread of the infection rather than being attributable to changes in pathogens virulence.

microbiology↗

bioRxiv2022

Intervertebral disc cell chondroptosis elicits neutrophil response in Staphylococcus aureus spondylodiscitis

ObjectiveTo understand the pathophysiology of spondylodiscitis due to Staphylococcus aureus, an emerging infectious disease of the intervertebral disc (IVD) and vertebral body with a high complication rate, by combining clinical insights and experimental approaches. DesignClinical data and histological material of nine patients suffering from S. aureus spondylodiscitis were retrospectively collected at a single center. To mirror the clinical findings experimentally, we developed a novel porcine ex vivo model mimicking acute S. aureus spondylodiscitis and assessed the interaction between S. aureus and IVD cells within their native environment. In addition, the inflammatory features underlying this interaction were assessed in primary human IVD cells. Finally, mirroring the clinical findings, we assessed primary human neutrophils for their ability to respond to secreted inflammatory modulators of IVD cells upon S. aureus challenge. ResultsAcute S. aureus spondylodiscitis in patients was characterized by tissue necrosis and neutrophil infiltration. Additionally, the presence of empty IVD cells lacunae was observed. This was mirrored in the ex vivo porcine model, where S. aureus induced extensive IVD cell death, leading to empty lacunae. Concomitant engagement of the apoptotic and pyroptotic cell death pathways was observed in primary human IVD cells, resulting in cytokine release. Among the released cytokines, functionally intact neutrophil-priming as well as broad pro- and anti-inflammatory cytokines known for their involvement in IVD degeneration were found. ConclusionsIn patients as well as ex vivo in a novel porcine model, S. aureus spondylodiscitis infection caused IVD cell death, resulting in empty lacunae, which was accompanied by release of inflammation markers and recruitment of neutrophils. These findings offer valuable insights into the important role of inflammatory IVD cell death during the onset of spondylodiscitis and potential future therapeutic approaches.

immunology↗

bioRxiv2021

Limited adaptive evolution of Staphylococcus aureus during transition from colonization to invasive infection

Staphylococcus aureus carriage is a risk factor for invasive infections. Unique genetic elements favoring the transition from colonizing to invasive phenotype have not yet been identified and phenotypic traits are understudied. We therefore assessed pheno- and genotypic profiles of eleven S. aureus isolate pairs sampled from colonized patients simultaneously suffering from invasive S. aureus infections. Ten out of 11 isolate pairs presented the same spa and MLST suggesting colonization as origin for the invasive infection. Systematic analysis of colonizing and invasive isolate pairs showed similar adherence, hemolysis and reproductive fitness properties, minimal genetic differences, identical antibiotic tolerance and bacterial virulence in Galleria mellonella. Our results provide insights into the similar phenotype associated with limited adaptive genetic evolution between the colonizing and invasive isolates. Disruption of the physical barriers mucosa or skin were identified in the majority of patients further emphasizing colonization as a major risk factor for invasive disease. ImportanceS. aureus is a major pathogen of humans causing a wide range of disease. The failure to develop a vaccine and antibiotic warrant the exploration of novel treatment strategies. Asymptomatic colonization of the human nasal passages is a major risk factor for invasive disease and decolonization procedures have shown efficacy in preventing invasive infections. However, the transition of S. aureus from a benign colonizer of the nasal passages to a major pathogen is not well understood and host as well as bacterial properties have been discussed as being relevant for this behavioral change. We conducted a thorough investigation of patient-derived strain pairs reflecting colonizing and invasive isolates in a given patient. Although we identified limited genetic adaptation in certain strains as well as slight differences in adherence capacity of colonizing and invasive isolates, our work suggests that barrier breaches are a key event in the disease continuum of S. aureus.

microbiology↗

bioRxiv2021

Quantification of within patient Staphylococcus aureus phenotypic heterogeneity as a proxy for presence of persisters across clinical presentations

BackgroundDifficult-to-treat infections caused by antibiotic susceptible strains have been linked with the occurrence of persisters. Persisters are a subpopulation of dormant bacteria that tolerate antibiotic exposure despite lacking genetic resistance. They can be identified phenotypically upon plating on nutrient agar because of their altered growth dynamics, resulting in colony size heterogeneity. The occurrence of within-patient bacterial phenotypic heterogeneity in various infections and clinical determinants of persister formation remain unknown. MethodsWe plated bacteria derived from 132 patient-samples of difficult-to-treat infections directly on nutrient-rich agar and monitored colony growth by time-lapse imaging. Of these, we retained 36 Staphylococcus aureus mono-cultures for further analysis. We investigated clinical factors potentially associated with increased colony growth-delay with regression analyses. Additionally, we corroborated the clinical findings using in vitro grown static biofilms, exposed to distinct antibiotics. ResultsThe extent of phenotypic heterogeneity of patient-derived S. aureus varied substantially between patients. Increased heterogeneity coincided with increased median growth-delay. Multivariable regression showed that rifampicin treatment was significantly associated with increased median growth-delay. S. aureus grown in biofilms and exposed to high concentrations of rifampicin or a combination of rifampicin with either clindamycin or levofloxacin exhibited prolonged growth-delay, correlating with a strain-dependent increase in antibiotic tolerance. ConclusionsUpon direct cultivation on nutrient-rich agar, S. aureus from difficult-to-treat infections commonly exhibited colony size heterogeneity. This was due to heterogeneous delays in growth resumption, with delays larger than two days in the most extreme cases. Since bacteria in a dormant state are tolerant to antibiotics, the observation of large growth-delays might have direct clinical implications. Future studies are needed to assess the potential of bacterial phenotypic heterogeneity quantification for staphylococcal infections prognosis.

microbiology↗

bioRxiv2021

Cerebello-cerebral Functional Connectivity Networks in Major Depressive Disorder: A CAN-BIND-1 Study Report

ObjectiveNeuroimaging studies have demonstrated aberrant structure and function of the "cognitive-affective cerebellum" in Major Depressive Disorder (MDD), although the specific role of the cerebello-cerebral circuitry in this population remains largely uninvestigated. The objective of this study was to delineate the role of cerebellar functional networks in depression. MethodsA total of 308 unmedicated participants completed resting-state functional magnetic resonance imaging scans, of which 247 (148 MDD; 99 Healthy Controls, HC) were suitable for this study. Seed-based resting-state functional connectivity (RsFc) analysis was performed using three cerebellar regions of interest (ROIs): ROI1 corresponded to default mode network (DMN) / inattentive processing; ROI2 corresponded to attentional networks including frontoparietal, dorsal attention, and ventral attention; ROI3 corresponded to motor processing. These ROIs were delineated based on prior functional gradient analyses of the cerebellum. A general linear model was used to perform within-group and between-group comparisons. ResultsIn comparison to HC, participants with MDD displayed increased RsFc within the cerebello-cerebral DMN (ROI1) and significantly elevated RsFc between the cerebellar ROI1 and bilateral angular gyrus at a voxel threshold (p < 0.001, two-tailed) and at a cluster level (p < 0.05, FDR-corrected). Group differences were non-significant for ROI2 and ROI3. ConclusionsThese results contribute to the development of a systems neuroscience approach to the diagnosis and treatment of MDD. Specifically, our findings confirm previously reported associations between MDD, DMN, and cerebellum, and highlight the promising role of these functional and anatomical locations for the development of novel imaging-based biomarkers and targets for neuromodulation therapies.

neuroscience↗

bioRxiv2021

Genomic surveillance of vancomycin-resistant Enterococcus faecium reveals spread of a linear plasmid conferring a nutrient utilization advantage

Healthcare-associated outbreaks of vancomycin-resistant Enterococcus faecium (VREfm) are a worldwide problem with increasing prevalence. The genomic plasticity of this hospital-adapted pathogen contributes to its efficient spread despite infection control measures. Here, we aimed to identify the genomic and phenotypic determinants of healthcare-associated transmission of VREfm. We assessed the VREfm transmission networks at the tertiary-care University Hospital of Zurich (USZ) between October 2014 and February 2018 and investigated microevolutionary dynamics of this pathogen. We performed whole-genome sequencing for the 69 VREfm isolates collected during this timeframe and assessed the population structure and variability of the vancomycin resistance transposon. Phylogenomic analysis allowed us to reconstruct transmission networks and to unveil external or indirect transmission networks, not detectable by traditional surveillance. Notably, it unveiled a persistent clone, sampled 31 times over a 29-month period. Exploring the evolutionary dynamics of this clone and characterizing the phenotypic consequences revealed the spread of a variant with decreased daptomycin susceptibility and the acquired ability to utilize N-acetyl-galactosamine (GalNAc), one of the primary constituents of the human gut mucins. This nutrient utilization advantage was conferred by a novel plasmid, termed pELF_USZ, which exhibited a linear topology. This plasmid, which was harbored by two distinct clones, was transferable by conjugation. Overall, this work provides an example of the potential of the integration of epidemiological, functional genomic and evolutionary perspectives to understand adaptation strategies contributing to the successful spread of VREfm. Significance statementSequencing microbial pathogens causing outbreaks has become a common practice to characterize transmission networks. In addition to the signal provided by vertical evolution, bacterial genomes harbor mobile genetic elements, shared horizontally between clones. While macroevolutionary studies have revealed an important role of plasmids and genes encoding carbohydrate utilization systems in the adaptation of Enterococcus faecium to the hospital environment, mechanisms of dissemination and the specific function of many of these genetic determinants remain to be elucidated. Here, we characterize a plasmid providing a nutrient utilization advantage and show evidence for its clonal and horizontal spread at a local scale. Further studies integrating epidemiological, functional genomics and evolutionary perspectives will be critical to identify changes shaping the success of this pathogen.

microbiology↗

bioRxiv2021

Blunted Fas signaling favors RIPK1-driven neutrophil necroptosis in critically ill COVID-19 patients

Critically ill COVID-19 patients are characterized by a severely dysregulated cytokine profile and elevated neutrophil counts, which are thought to contribute to disease severity. However, to date it remains unclear how neutrophils contribute to pathophysiology during COVID-19. Here, we assessed the impact of the dysregulated cytokine profile on the tightly regulated cell death program of neutrophils. We show that in a subpopulation of neutrophils, canonical apoptosis was skewed towards rapidly occurring necroptosis. This phenotype was characterized by abrogated caspase-8 activity and increased RIPK1 levels, favoring execution of necroptosis via the RIPK1-RIPK3-MLKL axis, as further confirmed in COVID-19 biopsies. Moreover, reduction of sFas-L levels in COVID-19 patients and hence decreased signaling to Fas directly increased RIPK1 levels and correlated with disease severity. Our results suggest an important role for Fas signaling in the regulation of cell death program ambiguity via the ripoptosome in neutrophils during COVID-19 and a potential therapeutic target to curb inflammation and thus influence disease severity and outcome.

immunology↗

bioRxiv2020

Neutrophil and monocyte dysfunctional effector response towards bacterial challenge in critically-ill COVID-19 patients

COVID-19 displays diverse disease severities and symptoms. Elevated inflammation mediated by hypercytokinemia induces a detrimental dysregulation of immune cells. However, there is limited understanding of how SARS-CoV-2 pathogenesis impedes innate immune signaling and function against secondary bacterial infections. We assessed the influence of COVID-19 hypercytokinemia on the functional responses of neutrophils and monocytes upon bacterial challenges from acute and corresponding recovery COVID-19 ICU patients. We show that severe hypercytokinemia in COVID-19 patients correlated with bacterial superinfections. Neutrophils and monocytes from acute COVID-19 patients showed severely impaired microbicidal capacity, reflected by abrogated ROS and MPO production as well as reduced NETs upon bacterial challenges. We observed a distinct pattern of cell surface receptor expression on both neutrophils and monocytes leading to a suppressive autocrine and paracrine signaling during bacterial challenges. Our data provide insights into the innate immune status of COVID-19 patients mediated by their hypercytokinemia and its transient effect on immune dysregulation upon subsequent bacterial infections

immunology↗