Microbes Bind Complement Inhibitor Factor H via a Common Site

To cause infections microbes need to evade host defense systems, one of these being the evolutionarily old and important arm of innate immunity, the alternative pathway of complement. It can attack all kinds of targets and is tightly controlled in plasma and on host cells by plasma complement regulator factor H (FH). FH binds simultaneously to host cell surface structures such as heparin or glycosaminoglycans via domain 20 and to the main complement opsonin C3b via domain 19. Many pathogenic microbes protect themselves from complement by recruiting host FH. We analyzed how and why different microbes bind FH via domains 19–20 (FH19-20). We used a selection of FH19-20 point mutants to reveal the binding sites of several microbial proteins and whole microbes (Haemophilus influenzae, Bordetella pertussis, Pseudomonas aeruginosa, Streptococcus pneumonia, Candida albicans, Borrelia burgdorferi, and Borrelia hermsii). We show that all studied microbes use the same binding region located on one side of domain 20. Binding of FH to the microbial proteins was inhibited with heparin showing that the common microbial binding site overlaps with the heparin site needed for efficient binding of FH to host cells. Surprisingly, the microbial proteins enhanced binding of FH19-20 to C3b and down-regulation of complement activation. We show that this is caused by formation of a tripartite complex between the microbial protein, FH, and C3b. In this study we reveal that seven microbes representing different phyla utilize a common binding site on the domain 20 of FH for complement evasion. Binding via this site not only mimics the glycosaminoglycans of the host cells, but also enhances function of FH on the microbial surfaces via the novel mechanism of tripartite complex formation. This is a unique example of convergent evolution resulting in enhanced immune evasion of important pathogens viautilization of a “superevasion site.

Population Genetic Analysis of Propionibacterium acnes Identifies a Subpopulation and Epidemic Clones Associated with Acne

The involvement of Propionibacterium acnes in the pathogenesis of acne is controversial, mainly owing to its dominance as an inhabitant of healthy skin. This study tested the hypothesis that specific evolutionary lineages of the species are associated with acne while others are compatible with health. Phylogenetic reconstruction based on nine housekeeping genes was performed on 210 isolates of P. acnes from well-characterized patients with acne, various opportunistic infections, and from healthy carriers. Although evidence of recombination was observed, the results showed a basically clonal population structure correlated with allelic variation in the virulence genes tly and camp5, with pulsed field gel electrophoresis (PFGE)- and biotype, and with expressed putative virulence factors. An unexpected geographically and temporal widespread dissemination of some clones was demonstrated. The population comprised three major divisions, one of which, including an epidemic clone, was strongly associated with moderate to severe acne while others were associated with health and opportunistic infections. This dichotomy correlated with previously observed differences in in vitro inflammation-inducing properties. Comparison of five genomes representing acne- and health-associated clones revealed multiple both cluster- and strain-specific genes that suggest major differences in ecological preferences and redefines the spectrum of disease-associated virulence factors. The results of the study indicate that particular clones of P. acnes play an etiologic role in acne while others are associated with health

Synergy of extreme drought and shrub invasion reduce ecosystem functioning and resilience in water-limited climates

Extreme drought events and plant invasions are major drivers of global change that can critically affect ecosystem functioning and alter ecosystem-atmosphere exchange. Invaders are expanding worldwide and extreme drought events are projected to increase in frequency and intensity. However, very little is known on how these drivers may interact to affect the functioning and resilience of ecosystems to extreme events. Using a manipulative shrub removal experiment and the co-occurrence of an extreme drought event (2011/2012) in a Mediterranean woodland, we show that native shrub invasion and extreme drought synergistically reduced ecosystem transpiration and the resilience of key-stone oak tree species. Ecosystem transpiration was dominated by the water use of the invasive shrub Cistus ladanifer, which further increased after the extreme drought event. Meanwhile, the transpiration of key-stone tree species decreased, indicating a competitive advantage in favour of the invader. Our results suggest that in Mediterranean-type climates the invasion of water spending species and projected recurrent extreme drought events may synergistically cause critical drought tolerance thresholds of key-stone tree species to be surpassed, corroborating observed higher tree mortality in the invaded ecosystems. Ultimately, this may shift seasonally water limited ecosystems into less desirable alternative states dominated by water spending invasive shrubs

Co-ordinated multidisciplinary intervention to reduce time to successful extubation for children on mechanical ventilation : the SANDWICH cluster stepped-wedge RCT

Background Daily assessment of patient readiness for liberation from invasive mechanical ventilation can reduce the duration of ventilation. However, there is uncertainty about the effectiveness of this in a paediatric population. Objectives To determine the effect of a ventilation liberation intervention in critically ill children who are anticipated to have a prolonged duration of mechanical ventilation (primary objective) and in all children (secondary objective). Design A pragmatic, stepped-wedge, cluster randomised trial with economic and process evaluations. Setting Paediatric intensive care units in the UK. Participants Invasively mechanically ventilated children (aged < 16 years). Interventions The intervention incorporated co-ordinated multidisciplinary care, patient-relevant sedation plans linked to sedation assessment, assessment of ventilation parameters with a higher than usual trigger for undertaking an extubation readiness test and a spontaneous breathing trial on low levels of respiratory support to test extubation readiness. The comparator was usual care. Hospital sites were randomised sequentially to transition from control to intervention and were non-blinded. Main outcome measures The primary outcome measure was the duration of invasive mechanical ventilation until the first successful extubation. The secondary outcome measures were successful extubation, unplanned extubation and reintubation, post-extubation use of non-invasive ventilation, tracheostomy, post-extubation stridor, adverse events, length of intensive care and hospital stay, mortality and cost per respiratory complication avoided at 28 days. Results The trial included 10,495 patient admissions from 18 paediatric intensive care units from 5 February 2018 to 14 October 2019. In children with anticipated prolonged ventilation (n = 8843 admissions: control, n = 4155; intervention, n = 4688), the intervention resulted in a significantly shorter time to successful extubation [cluster and time-adjusted median difference –6.1 hours (interquartile range –8.2 to –5.3 hours); adjusted hazard ratio 1.11, 95% confidence interval 1.02 to 1.20; p = 0.02] and a higher incidence of successful extubation (adjusted relative risk 1.01, 95% confidence interval 1.00 to 1.02; p = 0.03) and unplanned extubation (adjusted relative risk 1.62, 95% confidence interval 1.05 to 2.51; p = 0.03), but not reintubation (adjusted relative risk 1.10, 95% confidence interval 0.89 to 1.36; p = 0.38). In the intervention period, the use of post-extubation non-invasive ventilation was significantly higher (adjusted relative risk 1.22, 95% confidence interval 1.01 to 1.49; p = 0.04), with no evidence of a difference in intensive care length of stay or other harms, but hospital length of stay was longer (adjusted hazard ratio 0.89, 95% confidence interval 0.81 to 0.97; p = 0.01). Findings for all children were broadly similar. The control period was associated with lower, but not statistically significantly lower, total costs (cost difference, mean £929.05, 95% confidence interval –£516.54 to £2374.64) and significantly fewer respiratory complications avoided (mean difference –0.10, 95% confidence interval –0.16 to –0.03). Limitations The unblinded intervention assignment may have resulted in performance or detection bias. It was not possible to determine which components were primarily responsible for the observed effect. Treatment effect in a more homogeneous group remains to be determined. Conclusions The intervention resulted in a statistically significant small reduction in time to first successful extubation; thus, the clinical importance of the effect size is uncertain. Future work Future work should explore intervention sustainability and effects of the intervention in other paediatric populations. Trial registration This trial is registered as ISRCTN16998143. Funding This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 18. See the NIHR Journals Library website for further project information

Atrial Heterogeneity Generates Re-entrant Substrate during Atrial Fibrillation and Anti-arrhythmic Drug Action: Mechanistic Insights from Canine Atrial Models

Anti-arrhythmic drug therapy is a frontline treatment for atrial fibrillation (AF), but its success rates are highly variable. This is due to incomplete understanding of the mechanisms of action of specific drugs on the atrial substrate at different stages of AF progression. We aimed to elucidate the role of cellular, tissue and organ level atrial heterogeneities in the generation of a re-entrant substrate during AF progression, and their modulation by the acute action of selected anti-arrhythmic drugs. To explore the complex cell-to-organ mechanisms, a detailed biophysical models of the entire 3D canine atria was developed. The model incorporated atrial geometry and fibre orientation from high-resolution micro-computed tomography, region-specific atrial cell electrophysiology and the effects of progressive AF-induced remodelling. The actions of multi-channel class III anti-arrhythmic agents vernakalant and amiodarone were introduced in the model by inhibiting appropriate ionic channel currents according to experimentally reported concentration-response relationships. AF was initiated by applied ectopic pacing in the pulmonary veins, which led to the generation of localized sustained re-entrant waves (rotors), followed by progressive wave breakdown and rotor multiplication in both atria. The simulated AF scenarios were in agreement with observations in canine models and patients. The 3D atrial simulations revealed that a re-entrant substrate was typically provided by tissue regions of high heterogeneity of action potential duration (APD). Amiodarone increased atrial APD and reduced APD heterogeneity and was more effective in terminating AF than vernakalant, which increased both APD and APD dispersion. In summary, the initiation and sustenance of rotors in AF is linked to atrial APD heterogeneity and APD reduction due to progressive remodelling. Our results suggest that anti-arrhythmic strategies that increase atrial APD without increasing its dispersion are effective in terminating AF

Identification and Structural Characterization of a New Three-Finger Toxin Hemachatoxin from Hemachatus haemachatus Venom

10.1371/journal.pone.0048112PLoS ONE710