Dysbiosis of a microbiota-immune metasystem in critical illness is associated with nosocomial infections

An Enteric Bacterial Infection Triggers Neuroinflammation and Neurobehavioral Impairment in 3xTg-AD Transgenic Mice

BACKGROUND

Klebsiella pneumoniae is infamous for hospital-acquired infections and sepsis, which have also been linked to Alzheimer disease (AD)-related neuroinflammatory and neurodegenerative impairment. However, its causative and mechanistic role in AD pathology remains unstudied.

METHODS

A preclinical model of K. pneumoniae enteric infection and colonization is developed in an AD model (3xTg-AD mice) to investigate whether and how K. pneumoniae pathogenesis exacerbates neuropathogenesis via the gut-blood-brain axis.

RESULTS

K. pneumoniae, particularly under antibiotic-induced dysbiosis, was able to translocate from the gut to the bloodstream by penetrating the gut epithelial barrier. Subsequently, K. pneumoniae infiltrated the brain by breaching the blood-brain barrier. Significant neuroinflammatory phenotype was observed in mice with K. pneumoniae brain infection. K. pneumoniae-infected mice also exhibited impaired neurobehavioral function and elevated total tau levels in the brain. Metagenomic analyses revealed an inverse correlation of K. pneumoniae with gut biome diversity and commensal bacteria, highlighting how antibiotic-induced dysbiosis triggers an enteroseptic "pathobiome" signature implicated in gut-brain perturbations.

CONCLUSIONS

The findings demonstrate how infectious agents following hospital-acquired infections and consequent antibiotic regimen may induce gut dysbiosis and pathobiome and increase the risk of sepsis, thereby increasing the predisposition to neuroinflammatory and neurobehavioral impairments via breaching the gut-blood-brain barrier.

Relationship between very early enteral nutrition and persistent inflammation, immunosuppression, and catabolism syndrome in cardiovascular surgery patients: a propensity score-matched study

BACKGROUND

Early enteral nutrition (EN) is recommended for patients with critical illness to maintain intestinal immunity. However, the optimal timing of the commencement of EN remains unclear, particularly after cardiovascular surgery.

OBJECTIVES

We herein focused on Persistent Inflammation, Immunosuppression, and Catabolism Syndrome (PICS) as a predisposing immunodeficiency and investigated its association with very early EN (VEEN) (<24 h) in patients who underwent cardiovascular surgery.

METHODS

In this retrospective study, we used an administrative claims database with laboratory examinations between 2008 and 2021 to identify adult patients admitted to the intensive care unit after cardiovascular surgery. Patients who received EN the day after surgery were assigned to the EN <24 h group, whereas those who received EN on day 2 or day 3 were assigned to the control group. The primary outcome was a composite of the incidence of PICS and mortality on day 14 after surgery. We defined PICS as patients who were hospitalized for >14 day and meeting ≥2 of the following conditions: a lymphocyte count <800/μL, albumin <3.0 g/dL, and C-reactive protein >2.0 mg/dL. We compared the 2 groups using propensity score analysis.

RESULTS

A propensity score matching generated 2082 pairs. The primary outcome was significantly lower in the EN <24 h group than in the control group on days 14 {risk difference [95% confidence interval (CI)]: -3.1% [-5.9%, -0.3%]} and 28 (risk difference [95% CI]: -2.1% [-3.7%, -0.4%]). Mortality did not significantly differ between the 2 groups. The length of hospital stay was significantly shorter in the EN <24 h group: the difference (95% CI) was -2.2 (-3.7, -0.7) d.

CONCLUSIONS

Among patients who underwent cardiovascular surgery, VEEN provided on the day after surgery was associated with a lower incidence of PICS and a shorter length of hospital stay than EN provided 2 day or 3 day after surgery.

Host immunomodulation strategies to combat pandemic-associated antimicrobial-resistant secondary bacterial infections

The incidence of secondary bacterial infections has increased in recent decades owing to various viral pandemics. These infections further increase the morbidity and mortality rates associated with viral infections and remain a significant challenge in clinical practice. Intensive antibiotic therapy has mitigated the threat of such infections; however, overuse and misuse of antibiotics have resulted in poor outcomes, such as inducing the emergence of bacterial populations with antimicrobial resistance (AMR) and reducing the therapeutic options for this crisis. Several antibiotic substitutes have been suggested and employed; however, they have certain limitations and novel alternatives are urgently required. This review highlights host immunomodulation as a promising strategy against secondary bacterial infections to overcome AMR. The definition and risk factors of secondary bacterial infections, features and limitations of currently available therapeutic strategies, host immune responses, and future perspectives for treating such infections are discussed.

MASS cohort: Multicenter, longitudinal, and prospective study of the role of microbiome in severe pneumonia and host susceptibility

The MASS cohort comprises 2000 ICU patients with severe pneumonia, covering community-acquired pneumonia, hospital-acquired pneumonia, and ventilator-associated pneumonia, sourced from 19 hospitals across 10 cities in three provinces. A wide array of samples including bronchoalveolar lavage fluid, sputum, feces, and whole blood are longitudinally collected throughout patients' ICU stays. The cohort study seeks to uncover the dynamics of lung and gut microbiomes and their associations with severe pneumonia and host susceptibility, integrating deep metagenomics and transcriptomics with detailed clinical data.

Doxycycline post-exposure prophylaxis for sexually transmitted infections impacts the gut antimicrobial resistome

Doxycycline post-exposure prophylaxis (doxy-PEP) reduces bacterial sexually transmitted infections (STIs) among men who have sex with men and transgender women. While poised for widespread clinical implementation, the impact of doxy-PEP on antimicrobial resistance remains a primary concern as its effects on the gut microbiome and resistome, or the antimicrobial resistance genes (ARGs) present in the gut microbiome, are unknown. To investigate these effects, we studied participants from a randomized clinical trial who either received doxy-PEP as a one-time doxycycline 200 mg taken after condomless sex (DP arm, n = 100) or standard of care treatment (SOC arm, n = 50). From self-collected rectal swabs at enrollment (day-0) and after 6 months (month-6), we performed metagenomic DNA sequencing (DNA-seq) or metatranscriptomic RNA sequencing (RNA-seq). DNA-seq data was analyzable from 127 samples derived from 89 participants, and RNA-seq data from 86 samples derived from 70 participants. We compared the bacterial microbiome and resistome between the two study arms and over time. Tetracycline ARGs were detected in all day-0 DNA-seq samples and 85% of day-0 RNA-seq samples. The proportional mass of tetracycline ARGs in the resistome increased between day-0 and month-6 in DP participants from 46-51% in the metagenome (p = 0.02) and 4-15% in the metatranscriptome (p < 0.01), but no changes in other ARG classes were observed. Exposure to a higher number of doxycycline doses correlated with proportional enrichment of tetracycline ARGs in the metagenome (Spearman's ρ = 0.23, p < 0.01) and metatranscriptome (Spearman's ρ = 0.55, p < 0.01). Bacterial microbiome alpha diversity, beta diversity, and total bacterial mass did not differ between day-0 and month-6 samples from DP participants when assessed by either DNA-seq or RNA-seq. In an abundance-based correlation analysis, we observed an increase over time in the strength of the correlation between tetracycline ARGs and specific bacterial taxa, including some common human pathogens. In sum, doxy-PEP use over a 6-month period was associated with an increase in the proportion of tetracycline ARGs comprising the gut resistome, and an increase in the expression of tetracycline ARGs. Notably, doxy-PEP did not significantly alter alpha diversity or taxonomic composition of the gut microbiome, and did not demonstrate significant increases in non-tetracycline ARG classes. Further studies and population level surveillance are needed to understand the implications of these findings as doxy-PEP is implemented as a public health strategy.

Dietary carbohydrates regulate intestinal colonization and dissemination of Klebsiella pneumoniae

Bacterial translocation from the gut microbiota is a source of sepsis in susceptible patients. Previous work suggests that overgrowth of gut pathobionts, including Klebsiella pneumoniae, increases the risk of disseminated infection. Our data from a human dietary intervention study found that, in the absence of fiber, K. pneumoniae bloomed during microbiota recovery from antibiotic treatment. We thus hypothesized that dietary nutrients directly support or suppress colonization of this gut pathobiont in the microbiota. Consistent with our study in humans, complex carbohydrates in dietary fiber suppressed the colonization of K. pneumoniae and allowed for recovery of competing commensals in mouse models. In contrast, through ex vivo and in vivo modeling, we identified simple carbohydrates as a limiting resource for K. pneumoniae in the gut. As proof of principle, supplementation with lactulose, a nonabsorbed simple carbohydrate and an FDA-approved therapy, increased colonization of K. pneumoniae. Disruption of the intestinal epithelium led to dissemination of K. pneumoniae into the bloodstream and liver, which was prevented by dietary fiber. Our results show that dietary simple and complex carbohydrates were critical not only in the regulation of pathobiont colonization but also disseminated infection, suggesting that targeted dietary interventions may offer a preventative strategy in high-risk patients.

An Enterobacteriaceae bloom in aging animals is restrained by the gut microbiome

The gut microbiome plays important roles in host function and health. Core microbiomes have been described for different species, and imbalances in their composition, known as dysbiosis, are associated with pathology. Changes in the gut microbiome and dysbiosis are common in aging, possibly due to multi-tissue deterioration, which includes metabolic shifts, dysregulated immunity, and disrupted epithelial barriers. However, the characteristics of these changes, as reported in different studies, are varied and sometimes conflicting. Using clonal populations of Caenorhabditis elegans to highlight trends shared among individuals, we employed 16s rRNA gene sequencing, CFU counts and fluorescent imaging, identifying an Enterobacteriaceae bloom as a common denominator in aging animals. Experiments using Enterobacter hormaechei, a representative commensal, suggested that the Enterobacteriaceae bloom was facilitated by a decline in Sma/BMP immune signaling in aging animals and demonstrated its potential for exacerbating infection susceptibility. However, such detrimental effects were context-dependent, mitigated by competition with commensal communities, highlighting the latter as determinants of healthy versus unhealthy aging, depending on their ability to restrain opportunistic pathobionts.

Claudin-2 upregulation enhances intestinal permeability, immune activation, dysbiosis, and mortality in sepsis

Intestinal epithelial expression of the tight junction protein claudin-2, which forms paracellular cation and water channels, is precisely regulated during development and in disease. Here, we show that small intestinal epithelial claudin-2 expression is selectively upregulated in septic patients. Similar changes occurred in septic mice, where claudin-2 upregulation coincided with increased flux across the paracellular pore pathway. In order to define the significance of these changes, sepsis was induced in claudin-2 knockout (KO) and wild-type (WT) mice. Sepsis-induced increases in pore pathway permeability were prevented by claudin-2 KO. Moreover, claudin-2 deletion reduced interleukin-17 production and T cell activation and limited intestinal damage. These effects were associated with reduced numbers of neutrophils, macrophages, dendritic cells, and bacteria within the peritoneal fluid of septic claudin-2 KO mice. Most strikingly, claudin-2 deletion dramatically enhanced survival in sepsis. Finally, the microbial changes induced by sepsis were less pathogenic in claudin-2 KO mice as survival of healthy WT mice injected with cecal slurry collected from WT mice 24 h after sepsis was far worse than that of healthy WT mice injected with cecal slurry collected from claudin-2 KO mice 24 h after sepsis. Claudin-2 upregulation and increased pore pathway permeability are, therefore, key intermediates that contribute to development of dysbiosis, intestinal damage, inflammation, ineffective pathogen control, and increased mortality in sepsis. The striking impact of claudin-2 deletion on progression of the lethal cascade activated during sepsis suggests that claudin-2 may be an attractive therapeutic target in septic patients.

Skin dysbiosis and loss of microbiome site specificity in critically ill patients

An increasing amount of evidence has linked critical illness with dysbiotic microbiome signatures in different body sites. The disturbance of the indigenous microbiota structures has been further associated with disease severity and outcome and has been suggested to pose an additional risk for complications in intensive care units (ICUs), including hospital-acquired infections. A better understanding of the microbial dysbiosis in critical illness might thus help to develop strategies for the prevention of such complications. While most of the studies addressing microbiome changes in ICU patients have focused on the gut, the lung, or the oral cavity, little is known about the microbial communities on the skin of ICU patients. Since the skin is the outermost organ and the first immune barrier against pathogens, its microbiome might play an important role in the risk management for critically ill patients. This observational study characterizes the skin microbiome in ICU patients covering five different body sites at the time of admission. Our results show a profound dysbiosis on the skin of critically ill patients, which is characterized by a loss of site specificity and an overrepresentation of gut bacteria on all skin sites when compared to a healthy group. This study opens a new avenue for further investigations on the effect of skin dysbiosis in the ICU setting and points out the need of strategies for the management of dysbiosis in critically ill patients.IMPORTANCEUnbalanced gut microbiota in critically ill patients has been associated with poor outcome and complications during the intensive care unit (ICU) stay. Whether the disturbance of the microbial communities in these patients is extensive for other body sites, such as the skin, is largely unknown. The skin not only is the largest organ of the body but also serves as the first immune barrier against potential pathogens. This study characterized the skin microbiota on five different body sites in ICU patients at the time of admission. The observed disturbance of the bacterial communities might help to develop new strategies in the risk management of critically ill patients.

Defining sepsis in small animals

OBJECTIVE

To discuss the definitions of sepsis in human and veterinary medicine.

DESIGN

International, multicenter position statement on the need for consensus definitions of sepsis in veterinary medicine.

SETTING

Veterinary private practice and university teaching hospitals.

ANIMALS

Dogs and cats.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Sepsis is a life-threatening condition associated with the body's response to an infection. In human medicine, sepsis has been defined by consensus on 3 occasions, most recently in 2016. In veterinary medicine, there is little uniformity in how sepsis is defined and no consensus on how to identify it clinically. Most publications rely on modified criteria derived from the 1991 and 2001 human consensus definitions. There is a divergence between the human and veterinary descriptions of sepsis and no consensus on how to diagnose the syndrome. This impedes research, hampers the translation of pathophysiology insights to the clinic, and limits our abilities to optimize patient care. It may be time to formally define sepsis in veterinary medicine to help the field move forward. In this narrative review, we present a synopsis of prior attempts to define sepsis in human and veterinary medicine, discuss developments in our understanding, and highlight some criticisms and shortcomings of existing schemes.

CONCLUSIONS

This review is intended to serve as the foundation of current efforts to establish a consensus definition for sepsis in small animals and ultimately generate evidence-based criteria for its recognition in veterinary clinical practice.

Microbiome Dynamics: A Paradigm Shift in Combatting Infectious Diseases

Infectious diseases have long posed a significant threat to global health and require constant innovation in treatment approaches. However, recent groundbreaking research has shed light on a previously overlooked player in the pathogenesis of disease-the human microbiome. This review article addresses the intricate relationship between the microbiome and infectious diseases and unravels its role as a crucial mediator of host-pathogen interactions. We explore the remarkable potential of harnessing this dynamic ecosystem to develop innovative treatment strategies that could revolutionize the management of infectious diseases. By exploring the latest advances and emerging trends, this review aims to provide a new perspective on combating infectious diseases by targeting the microbiome.

The human gut microbiome in critical illness: disruptions, consequences, and therapeutic frontiers

With approximately 39 trillion cells and over 20 million genes, the human gut microbiome plays an integral role in both health and disease. Modern living has brought a widespread use of processed food and beverages, antimicrobial and immunomodulatory drugs, and invasive procedures, all of which profoundly disrupt the delicate homeostasis between the host and its microbiome. Of particular interest is the human gut microbiome, which is progressively being recognized as an important contributing factor in many aspects of critical illness, from predisposition to recovery. Herein, we describe the current understanding of the adverse impacts of standard intensive care interventions on the human gut microbiome and delve into how these microbial alterations can influence patient outcomes. Additionally, we explore the potential association between the gut microbiome and post-intensive care syndrome, shedding light on a previously underappreciated avenue that may enhance patient recuperation following critical illness. There is an impending need for future epidemiological studies to encompass detailed phenotypic analyses of gut microbiome perturbations. Interventions aimed at restoring the gut microbiome represent a promising therapeutic frontier in the quest to prevent and treat critical illnesses.

Microbiota Implications in Endocrine-Related Diseases: From Development to Novel Therapeutic Approaches

This comprehensive review article delves into the critical role of the human microbiota in the development and management of endocrine-related diseases. We explore the complex interactions between the microbiota and the endocrine system, emphasizing the implications of microbiota dysbiosis for the onset and progression of various endocrine disorders. The review aims to synthesize current knowledge, highlighting recent advancements and the potential of novel therapeutic approaches targeting microbiota-endocrine interactions. Key topics include the impact of microbiota on hormone regulation, its role in endocrine pathologies, and the promising avenues of microbiota modulation through diet, probiotics, prebiotics, and fecal microbiota transplantation. We underscore the importance of this research in advancing personalized medicine, offering insights for more tailored and effective treatments for endocrine-related diseases.

A novel Sagittaria sagittifolia L. polysaccharides mitigate DSS-induced colitis via modulation of gut microbiota and MAPK/NF-κB signaling pathways

Sagittaria sagittifolia L. polysaccharides possess anti-inflammatory, antioxidant, and immune-modulatory properties. In this study, we identified a novel S. sagittifolia L. polysaccharide, named PSSP-1, and evaluated its potential in alleviating dextran sulfate sodium (DSS)-induced colitis in a mouse model. The results demonstrated that administration of PSSP-1 at doses of 100, 200, and 400 mg/kg·bw significantly reduced the disease activity index (DAI) and suppressed the expression of inflammatory cytokines in UC mice. Furthermore, PSSP-1 treatment upregulated the expression levels of claudin-1, occludin, and ZO-1, and promoted the diversity and abundance of beneficial gut microbiota, including Lactobacillus and Candidatus_Saccharimonas, while reducing the levels of Bacteroidetes and Verrucomicrobiota. Particularly, the Lactobacillus_johnsonii species may play a potentially significant role in modulating colitis. Subsequently, there was a significant increase in the levels of short-chain fatty acids (SCFAs). Additionally, the correlation analyses revealed positive associations between PSSP-1 supplementation and Nitrosospira and Dialister, which are implicated in gut inflammation. Mechanistically, PSSP-1 intervention inhibited the protein phosphorylation of key molecules in the MAPK and NF-κB signaling pathways. Collectively, these findings suggest that PSSP-1 mitigates colitis symptoms by repairing the intestinal barrier, promoting microbial metabolism, and regulating the gut microbiota-MAPK/NF-κB signaling pathways.

Pathogenesis and therapeutic opportunities of gut microbiome dysbiosis in critical illness

For many years, it has been hypothesized that pathological changes to the gut microbiome in critical illness is a driver of infections, organ dysfunction, and other adverse outcomes in the intensive care unit (ICU). The advent of contemporary microbiome methodologies and multi-omics tools have allowed researchers to test this hypothesis by dissecting host-microbe interactions in the gut to better define its contribution to critical illness pathogenesis. Observational studies of patients in ICUs have revealed that gut microbial communities are profoundly altered in critical illness, characterized by markedly reduced alpha diversity, loss of commensal taxa, and expansion of potential pathogens. These key features of ICU gut dysbiosis have been associated with adverse outcomes including life-threatening hospital-acquired (nosocomial) infections. Current research strives to define cellular and molecular mechanisms connecting gut dysbiosis with infections and other outcomes, and to identify opportunities for therapeutic modulation of host-microbe interactions. This review synthesizes evidence from studies of critically ill patients that have informed our understanding of intestinal dysbiosis in the ICU, mechanisms linking dysbiosis to infections and other adverse outcomes, as well as clinical trials of microbiota-modifying therapies. Additionally, we discuss novel avenues for precision microbial therapeutics to combat nosocomial infections and other life-threatening complications of critical illness.

Recovering intestinal redox homeostasis to resolve systemic inflammation for preventing remote myocardial injury by oral fullerenes

The unbalanced immune state is the dominant feature of myocardial injury. However, the complicated pathology of cardiovascular diseases and the unique structure of cardiac tissue lead to challenges for effective immunoregulation therapy. Here, we exploited oral fullerene nanoscavenger (OFNS) to maintain intestinal redox homeostasis to resolve systemic inflammation for effectively preventing distal myocardial injury through bidirectional communication along the heart-gut immune axis. Observably, OFNS regulated redox microenvironment to repair cellular injury and reduce inflammation in vitro. Subsequently, OFNS prevented myocardial injury by regulating intestinal redox homeostasis and recovering epithelium barrier integrity in vivo. Based on the profiles of transcriptomics and proteomics, we demonstrated that OFNS balanced intestinal and systemic immune homeostasis for remote cardioprotection. Of note, we applied this principle to intervene myocardial infarction in mice and mini-pigs. These findings highlight that locally addressing intestinal redox to inhibit systemic inflammation could be a potent strategy for resolving remote tissue injury.

Microbiota-Accessible Boron-Containing Compounds in Complex Regional Pain Syndrome

The microbiota-gut-brain axis has garnered increasing attention in recent years for its role in various health conditions, including neuroinflammatory disorders like complex regional pain syndrome (CRPS). CRPS is a debilitating condition characterized by chronic neuropathic pain, and its etiology and pathophysiology remain elusive. Emerging research suggests that alterations in the gut microbiota composition and function could play a significant role in CRPS development and progression. Our paper explores the implications of microbiota in CRPS and the potential therapeutic role of boron (B). Studies have demonstrated that individuals with CRPS often exhibit dysbiosis, with imbalances in beneficial and pathogenic gut bacteria. Dysbiosis can lead to increased gut permeability and systemic inflammation, contributing to the chronic pain experienced in CRPS. B, an essential trace element, has shown promise in modulating the gut microbiome positively and exerting anti-inflammatory effects. Recent preclinical and clinical studies suggest that B supplementation may alleviate neuropathic pain and improve CRPS symptoms by restoring microbiota balance and reducing inflammation. Our review highlights the complex interplay between microbiota, inflammation, and neuropathic pain in CRPS and underscores the potential of B as a novel therapeutic approach to target the microbiota-gut-brain axis, offering hope for improved management of this challenging condition.

Rationally-defined microbial consortia suppress multidrug-resistant proinflammatory Enterobacteriaceae via ecological control

Persistent colonization and outgrowth of pathogenic organisms in the intestine may occur due to long-term antibiotic usage or inflammatory conditions, which perpetuate dysregulated immunity and tissue damage1,2. Gram-negative Enterobacteriaceae gut pathobionts are particularly recalcitrant to conventional antibiotic treatment3,4, though an emerging body of evidence suggests that manipulation of the commensal microbiota may be a practical alternative therapeutic strategy5-7. In this study, we rationally isolated and down-selected commensal bacterial consortia from healthy human stool samples capable of strongly and specifically suppressing intestinal Enterobacteriaceae. One of the elaborated consortia, consisting of 18 commensal strains, effectively controlled ecological niches by regulating gluconate availability, thereby reestablishing colonization resistance and alleviating antibiotic-resistant Klebsiella-driven intestinal inflammation in mice. Harnessing these microbial activities in the form of live bacterial therapeutics may represent a promising solution to combat the growing threat of proinflammatory, antimicrobial-resistant bacterial infection.

The clinical value of anal swabs for microbial detection in allogeneic haematopoietic stem cell transplantation

The intestinal microbiota plays critical roles in allogeneic hematopoietic stem cell transplantation (allo-HSCT). Rapid and effective microbial detection methods have important guiding value for the selection of intervention strategies for allo-HSCT recipients. We evaluated the application of the anal swab test before transplantation in allo-HSCT recipients. A total of 120 patients who underwent anal swab testing before allo-HSCT were retrospectively analyzed and divided into 3 groups: sterile (aseptic growth-negative), G+ (gram-positive bacterial colonization), and G- (gram-negative bacterial colonization). On 16S rRNA sequencing, gram-negative bacteria predominated in the G- group before and after transplantation. Compared with the sterile group, the percentage of natural killer cells was higher and the percentage of T cells was lower after transplantation in the G- group at 1 month after transplantation. The percentage of CD4+ and CD4+CD8+ T cells was lower and the percentage of regulatory T cells was higher in the G- group. The plasma levels of proinflammatory cytokines (TNF-α, IFN-γ, IL-6, and IL-17A) at 2 weeks post-transplantation were lower in the G- group than in the sterile group, as was the cumulative incidence of grade III-IV acute graft-versus-host disease (GVHD). Gram-negative bacterial colonization before allo-HSCT was associated with low rates of bloodstream infections within 100 days post-transplantation and cytomegalovirus reactivation at 100 days to 2 years post-transplantation. Moreover, patients in the G- group had a higher rate of 2-year GVHD-free, relapse-free survival compared with patients in the sterile group. The detection results using anal swabs were consistent with the gram-negative or gram-positive bacteria abundance of 16S rRNA sequencing results and associated with immune homeostasis and clinical outcomes after allo-HSCT. Anal swab testing may have potential advantages as a simple and effective method for microbial detection in allo-HSCT.

The gut microbiota composition is linked to subsequent occurrence of ventilator-associated pneumonia in critically ill patients

Ventilator-associated pneumonia (VAP) is the most frequent nosocomial infection in critically ill-ventilated patients. Oropharyngeal and lung microbiota have been demonstrated to be associated with VAP occurrence, but the involvement of gut microbiota has not been investigated so far. Therefore, the aim of this study is to compare the composition of the gut microbiota between patients who subsequently develop VAP and those who do not. A rectal swab was performed at admission of every consecutive patient into the intensive care unit (ICU) from October 2019 to March 2020. After DNA extraction, V3-V4 and internal transcribed spacer 2 regions deep-sequencing was performed on MiSeq sequencer (Illumina) and data were analyzed using Divisive Amplicon Denoising Algorithm 2 (DADA2) pipeline. Among 255 patients screened, 42 (16%) patients with invasive mechanical ventilation for more than 48 h were included, 18 (43%) with definite VAP and 24 without (57%). Patients who later developed VAP had similar gut bacteriobiota and mycobiota α-diversities compared to those who did not develop VAP. However, gut mycobiota was dissimilar (β-diversity) between these two groups. The presence of Megasphaera massiliensis was associated with the absence of VAP occurrence, whereas the presence of the fungal genus Alternaria sp. was associated with the occurrence of VAP. The composition of the gut microbiota, but not α-diversity, differs between critically ill patients who subsequently develop VAP and those who do not. This study encourages large multicenter cohort studies investigating the role of gut-lung axis and oropharyngeal colonization in the development of VAP in ICU patients. Trial registration number: NCT04131569, date of registration: 18 October 2019. IMPORTANCE The composition of the gut microbiota, but not α-diversity, differs between critically ill patients who subsequently develop ventilator-associated pneumonia (VAP) and those who do not. Investigating gut microbiota composition could help to tailor probiotics to provide protection against VAP.

An Enterobacteriaceae bloom in aging animals is restrained by the gut microbiome

The gut microbiome plays important roles in host function and health. Core microbiomes have been described for different species, and imbalances in their composition, known as dysbiosis, are associated with pathology. Changes in the gut microbiome and dysbiosis are common in aging, possibly due to multi-tissue deterioration, which includes metabolic shifts, dysregulated immunity, and disrupted epithelial barriers. However, the characteristics of these changes, as reported in different studies, are varied and sometimes conflicting. Using clonal populations of C. elegans to highlight trends shared among individuals, and employing NextGen sequencing, CFU counts and fluorescent imaging to characterize age-dependent changes in worms raised in different microbial environments, we identified an Enterobacteriaceae bloom as a common denominator in aging animals. Experiments using Enterobacter hormachei, a representative commensal, suggested that the Enterobacteriaceae bloom was facilitated by a decline in Sma/BMP immune signaling in aging animals and demonstrated its detrimental potential for increasing susceptibility to infection. However, such detrimental effects were context-dependent, mitigated by competition with commensal communities, highlighting the latter as determinants of healthy versus unhealthy aging, depending on their ability to restrain opportunistic pathobionts.

Vascular traffic control of neutrophil recruitment to the liver by microbiota-endothelium crosstalk

During bloodstream infections, neutrophils home to the liver as part of an intravascular immune response to eradicate blood-borne pathogens, but the mechanisms regulating this crucial response are unknown. Using in vivo imaging of neutrophil trafficking in germ-free and gnotobiotic mice, we demonstrate that the intestinal microbiota guides neutrophil homing to the liver in response to infection mediated by the microbial metabolite D-lactate. Commensal-derived D-lactate augments neutrophil adhesion in the liver independent of granulopoiesis in bone marrow or neutrophil maturation and activation in blood. Instead, gut-to-liver D-lactate signaling primes liver endothelial cells to upregulate adhesion molecule expression in response to infection and promote neutrophil adherence. Targeted correction of microbiota D-lactate production in a model of antibiotic-induced dysbiosis restores neutrophil homing to the liver and reduces bacteremia in a model of Staphylococcus aureus infection. These findings reveal long-distance traffic control of neutrophil recruitment to the liver by microbiota-endothelium crosstalk.

Antimicrobial Resistance in the Global Health Network: Known Unknowns and Challenges for Efficient Responses in the 21st Century

Antimicrobial resistance (AMR) is one of the Global Health challenges of the 21st century. The inclusion of AMR on the global map parallels the scientific, technological, and organizational progress of the healthcare system and the socioeconomic changes of the last 100 years. Available knowledge about AMR has mostly come from large healthcare institutions in high-income countries and is scattered in studies across various fields, focused on patient safety (infectious diseases), transmission pathways and pathogen reservoirs (molecular epidemiology), the extent of the problem at a population level (public health), their management and cost (health economics), cultural issues (community psychology), and events associated with historical periods (history of science). However, there is little dialogue between the aspects that facilitate the development, spread, and evolution of AMR and various stakeholders (patients, clinicians, public health professionals, scientists, economic sectors, and funding agencies). This study consists of four complementary sections. The first reviews the socioeconomic factors that have contributed to building the current Global Healthcare system, the scientific framework in which AMR has traditionally been approached in such a system, and the novel scientific and organizational challenges of approaching AMR in the fourth globalization scenario. The second discusses the need to reframe AMR in the current public health and global health contexts. Given that the implementation of policies and guidelines are greatly influenced by AMR information from surveillance systems, in the third section, we review the unit of analysis ("the what" and "the who") and the indicators (the "operational units of surveillance") used in AMR and discuss the factors that affect the validity, reliability, and comparability of the information to be applied in various healthcare (primary, secondary, and tertiary), demographic, and economic contexts (local, regional, global, and inter-sectorial levels). Finally, we discuss the disparities and similarities between distinct stakeholders' objectives and the gaps and challenges of combatting AMR at various levels. In summary, this is a comprehensive but not exhaustive revision of the known unknowns about how to analyze the heterogeneities of hosts, microbes, and hospital patches, the role of surrounding ecosystems, and the challenges they represent for surveillance, antimicrobial stewardship, and infection control programs, which are the traditional cornerstones for controlling AMR in human health.