The quorum sensing volatile molecule 2-amino acetophenon modulates host immune responses in a manner that promotes life with unwanted guests

Revealing the impact of Pseudomonas aeruginosa quorum sensing molecule 2'-aminoacetophenone on human bronchial-airway epithelium and pulmonary endothelium using a human airway-on-a-chip

Pseudomonas aeruginosa (PA) causes severe respiratory infections utilizing multiple virulence functions. Our previous findings on PA quorum sensing (QS)-regulated small molecule, 2'-aminoacetophenone (2-AA), secreted by the bacteria in infected tissues, revealed its effect on immune and metabolic functions favouring a long-term presence of PA in the host. However, studies on 2-AA's specific effects on bronchial-airway epithelium and pulmonary endothelium remain elusive. To evaluate 2AA's spatiotemporal changes in the human airway, considering endothelial cells as the first point of contact when the route of lung infection is hematogenic, we utilized the microfluidic airway-on-chip lined by polarized human bronchial-airway epithelium and pulmonary endothelium. Using this platform, we performed RNA-sequencing to analyse responses of 2-AA-treated primary human pulmonary microvascular endothelium (HPMEC) and adjacent primary normal human bronchial epithelial (NHBE) cells from healthy female donors and potential cross-talk between these cells. Analyses unveiled specific signaling and biosynthesis pathways to be differentially regulated by 2-AA in epithelial cells, including HIF-1 and pyrimidine signaling, glycosaminoglycan, and glycosphingolipid biosynthesis, while in endothelial cells were fatty acid metabolism, phosphatidylinositol and estrogen receptor signaling, and proinflammatory signaling pathways. Significant overlap in both cell types in response to 2-AA was found in genes implicated in immune response and cellular functions. In contrast, we found that genes related to barrier permeability, cholesterol metabolism, and oxidative phosphorylation were differentially regulated upon exposure to 2-AA in the cell types studied. Murine in-vivo and additional in vitro cell culture studies confirmed cholesterol accumulation in epithelial cells. Results also revealed specific biomarkers associated with cystic fibrosis and idiopathic pulmonary fibrosis to be modulated by 2-AA in both cell types, with the cystic fibrosis transmembrane regulator expression to be affected only in endothelial cells. The 2-AA-mediated effects on healthy epithelial and endothelial primary cells within a microphysiological dynamic environment mimicking the human lung airway enhance our understanding of this QS signaling molecule. This study provides novel insights into their functions and potential interactions, paving the way for innovative, cell-specific therapeutic strategies to combat PA lung infections.

The bacterial quorum sensing signal 2'-aminoacetophenone rewires immune cell bioenergetics through the Ppargc1a/Esrra axis to mediate tolerance to infection

How bacterial pathogens exploit host metabolism to promote immune tolerance and persist in infected hosts remains elusive. To achieve this, we show that Pseudomonas aeruginosa (PA), a recalcitrant pathogen, utilizes the quorum sensing (QS) signal 2'-aminoacetophenone (2-AA). Here, we unveil how 2-AA-driven immune tolerization causes distinct metabolic perturbations in murine macrophages' mitochondrial respiration and bioenergetics. We present evidence indicating that these effects stem from decreased pyruvate transport into mitochondria. This reduction is attributed to decreased expression of the mitochondrial pyruvate carrier (Mpc1), which is mediated by diminished expression and nuclear presence of its transcriptional regulator, estrogen-related nuclear receptor alpha (Esrra). Consequently, Esrra exhibits weakened binding to the Mpc1 promoter. This outcome arises from the impaired interaction between Esrra and the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Ppargc1a). Ultimately, this cascade results in diminished pyruvate influx into mitochondria and, consequently reduced ATP production in tolerized murine and human macrophages. Exogenously added ATP in infected macrophages restores the transcript levels of Mpc1 and Esrra and enhances cytokine production and intracellular bacterial clearance. Consistent with the in vitro findings, murine infection studies corroborate the 2-AA-mediated long-lasting decrease in ATP and acetyl-CoA and its association with PA persistence, further supporting this QS signaling molecule as the culprit of the host bioenergetic alterations and PA persistence. These findings unveil 2-AA as a modulator of cellular immunometabolism and reveal an unprecedented mechanism of host tolerance to infection involving the Ppargc1a/Esrra axis in its influence on Mpc1/OXPHOS-dependent energy production and PA clearance. These paradigmatic findings pave the way for developing treatments to bolster host resilience to pathogen-induced damage. Given that QS is a common characteristic of prokaryotes, it is likely that 2-AA-like molecules with similar functions may be present in other pathogens.

The breath volatilome is shaped by the gut microbiota

The gut microbiota is widely implicated in host health and disease, inspiring translational efforts to implement our growing body of knowledge in clinical settings. However, the need to characterize gut microbiota by its genomic content limits the feasibility of rapid, point-of-care diagnostics. The microbiota produces a diverse array of xenobiotic metabolites that disseminate into tissues, including volatile organic compounds (VOCs) that may be excreted in breath. We hypothesize that breath contains gut microbe-derived VOCs that inform the composition and metabolic state of the microbiota. To explore this idea, we compared the breath volatilome and fecal gut microbiomes of 27 healthy children and found that breath VOC composition is correlated with gut microbiomes. To experimentally interrogate this finding, we devised a method for capturing exhaled breath from gnotobiotic mice. Breath volatiles are then profiled by gas-chromatography mass-spectrometry (GC-MS). Using this novel methodology, we found that the murine breath profile is markedly shaped by the composition of the gut microbiota. We also find that VOCs produced by gut microbes in pure culture can be identified in vivo in the breath of mice monocolonized with the same bacteria. Altogether, our studies identify microbe-derived VOCs excreted in breath and support a mechanism by which gut bacterial metabolism directly contributes to the mammalian breath VOC profiles.

LC-HRMS-based metabolomics and lipidomics analyses of a novel probiotic Akkermansia Muciniphila in response to different nutritional stimulations

The mucin-degrading gut commensal Akkermansia muciniphila (A. muciniphila) negatively correlates with various diseases, including metabolic disorders, neurodegenerative disorders, and cancers, through interacting with host receptors by diverse molecules. Still, their exact metabolic capability within the nutrient-rich environment (such as in the human gut) is not fully characterized. Therefore, in the present study, we investigated the comprehensive metabolome and lipidome of A. muciniphila after supplementation of four major gut microbial nutrients: mucin, inorganic salts, bile salts, and short-chain fatty acids (SCFAs). Our results showed that mucin is the predominant driver of the different lipidomic and metabolomic profiles of A. muciniphila, and it promotes the overall growth of this bacteria. While the addition of inorganic salts, bile salts, and SCFAs was found to inhibit the growth of A. muciniphila. Interestingly, inorganic salts affected the purine metabolism in A. muciniphila cultures, while adding bile salts significantly increased the production of other bile acids and N-acyl amides. Lastly, SCFAs were identified to alter the A. muciniphila energy utilization of triglycerides, fatty acyls, and phosphatidylethanolamines. To our knowledge, this is the first study to examine the comprehensive lipidome and metabolome of A. muciniphila, which highlights the importance of nutritional impacts on the lipidome and metabolome of A. muciniphila and hence providing foundational knowledge to unveil the potential effects of A. muciniphila on host health.

Skeletal muscle mitochondrial dysfunction mediated by Pseudomonas aeruginosa quorum-sensing transcription factor MvfR: reversing effects with anti-MvfR and mitochondrial-targeted compounds

Sepsis and chronic infections with Pseudomonas aeruginosa, a leading "ESKAPE" bacterial pathogen, are associated with increased morbidity and mortality and skeletal muscle atrophy. The actions of this pathogen on skeletal muscle remain poorly understood. In skeletal muscle, mitochondria serve as a crucial energy source, which may be perturbed by infection. Here, using the well-established backburn and infection model of murine P. aeruginosa infection, we deciphered the systemic impact of the quorum-sensing transcription factor MvfR (multiple virulence factor regulator) by interrogating, 5 days post-infection, its effect on mitochondrial-related functions in the gastrocnemius skeletal muscle and the outcome of the pharmacological inhibition of MvfR function and that of the mitochondrial-targeted peptide, Szeto-Schiller 31 (SS-31). Our findings show that the MvfR perturbs adenosine triphosphate generation, oxidative phosphorylation, and antioxidant response, elevates the production of reactive oxygen species, and promotes oxidative damage of mitochondrial DNA in the gastrocnemius muscle of infected mice. These impairments in mitochondrial-related functions were corroborated by the alteration of key mitochondrial proteins involved in electron transport, mitochondrial biogenesis, dynamics and quality control, and mitochondrial uncoupling. Pharmacological inhibition of MvfR using the potent anti-MvfR lead, D88, we developed, or the mitochondrial-targeted peptide SS-31 rescued the MvfR-mediated alterations observed in mice infected with the wild-type strain PA14. Our study provides insights into the actions of MvfR in orchestrating mitochondrial dysfunction in the skeletal murine muscle, and it presents novel therapeutic approaches for optimizing clinical outcomes in affected patients.

IMPORTANCE

Skeletal muscle, pivotal for many functions in the human body, including breathing and protecting internal organs, contains abundant mitochondria essential for maintaining cellular homeostasis during infection. The effect of Pseudomonas aeruginosa (PA) infections on skeletal muscle remains poorly understood. Our study delves into the role of a central quorum-sensing transcription factor, multiple virulence factor regulator (MvfR), that controls the expression of multiple acute and chronic virulence functions that contribute to the pathogenicity of PA. The significance of our study lies in the role of MvfR in the metabolic perturbances linked to mitochondrial functions in skeletal muscle and the effectiveness of the novel MvfR inhibitor and the mitochondrial-targeted peptide SS-31 in alleviating the mitochondrial disturbances caused by PA in skeletal muscle. Inhibiting MvfR or interfering with its effects can be a potential therapeutic strategy to curb PA virulence.

The Bacterial Quorum-Sensing Signal 2-Aminoacetophenone Rewires Immune Cell Bioenergetics through the PGC-1α/ERRα Axis to Mediate Tolerance to Infection

How bacterial pathogens exploit host metabolism to promote immune tolerance and persist in infected hosts remains elusive. To achieve this, we show that Pseudomonas aeruginosa (PA), a recalcitrant pathogen, utilizes the quorum sensing (QS) signal 2-aminoacetophenone (2-AA). Here, we unveil how 2-AA-driven immune tolerization causes distinct metabolic perturbations in macrophages mitochondrial respiration and bioenergetics. We present evidence indicating that these effects stem from decreased pyruvate transport into mitochondria. This reduction is attributed to decreased expression of the mitochondrial pyruvate carrier (MPC1), which is mediated by diminished expression and nuclear presence of its transcriptional regulator, estrogen-related nuclear receptor alpha (ERRα). Consequently, ERRα exhibits weakened binding to the MPC1 promoter. This outcome arises from the impaired interaction between ERRα and the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). Ultimately, this cascade results in diminished pyruvate influx into mitochondria and, consequently reduced ATP production in tolerized macrophages. Exogenously added ATP in infected macrophages restores the transcript levels of MPC1 and ERRα and enhances cytokine production and intracellular bacterial clearance. Consistent with the in vitro findings, murine infection studies corroborate the 2-AA-mediated long-lasting decrease in ATP and acetyl-CoA and its association with PA persistence, further supporting this QS signaling molecule as the culprit of the host bioenergetic alterations and PA persistence. These findings unveil 2-AA as a modulator of cellular immunometabolism and reveal an unprecedented mechanism of host tolerance to infection involving the PGC-1α/ERRα axis in its influence on MPC1/OXPHOS-dependent energy production and PA clearance. These paradigmatic findings pave the way for developing treatments to bolster host resilience to pathogen-induced damage. Given that QS is a common characteristic of prokaryotes, it is likely that 2-AA-like molecules with similar functions may be present in other pathogens.

Skeletal Muscle Mitochondrial Dysfunction Mediated by Pseudomonas aeruginosa Quorum Sensing Transcription Factor MvfR: Reversing Effects with Anti-MvfR and Mitochondrial-Targeted Compounds

Sepsis and chronic infections with Pseudomonas aeruginosa, a leading "ESKAPE" bacterial pathogen, are associated with increased morbidity and mortality and skeletal muscle atrophy. The actions of this pathogen on skeletal muscle remain poorly understood. In skeletal muscle, mitochondria serve as a crucial energy source, which may be perturbed by infection. Here, using the well-established backburn and infection model of murine P. aeruginosa infection, we deciphered the systemic impact of the quorum sensing (QS) transcription factor MvfR by interrogating five days post-infection its effect on mitochondrial-related functions in the gastrocnemius skeletal muscle and the outcome of the pharmacological inhibition of MvfR function and that of the mitochondrial-targeted peptide, Szeto-Schiller 31 (SS-31). Our findings show that the MvfR perturbs ATP generation, oxidative phosphorylation (OXPHOS), and antioxidant response, elevates the production of reactive oxygen species, and promotes oxidative damage of mitochondrial DNA in the gastrocnemius muscle of infected mice. These impairments in mitochondrial-related functions were corroborated by the alteration of key mitochondrial proteins involved in electron transport, mitochondrial biogenesis, dynamics and quality control, and mitochondrial uncoupling. Pharmacological inhibition of MvfR using the potent anti-MvfR lead, D88, we developed, or the mitochondrial-targeted peptide SS-31 rescued the MvfR- mediated alterations observed in mice infected with the wild-type strain PA14. Our study provides insights into the actions of MvfR in orchestrating mitochondrial dysfunction in the skeletal murine muscle, and it presents novel therapeutic approaches for optimizing clinical outcomes in affected patients.

Quorum-Sensing Signaling Molecule 2-Aminoacetophenone Mediates the Persistence of Pseudomonas aeruginosa in Macrophages by Interference with Autophagy through Epigenetic Regulation of Lipid Biosynthesis

Macrophages are crucial components of the host's defense against pathogens. Recent studies indicate that macrophage functions are influenced by lipid metabolism. However, knowledge of how bacterial pathogens exploit macrophage lipid metabolism for their benefit remains rudimentary. We have shown that the Pseudomonas aeruginosa MvfR-regulated quorum-sensing (QS) signaling molecule 2-aminoacetophenone (2-AA) mediates epigenetic and metabolic changes associated with this pathogen's persistence in vivo. We provide evidence that 2-AA counteracts the ability of macrophages to clear the intracellular P. aeruginosa, leading to persistence. The intracellular action of 2-AA in macrophages is linked to reduced autophagic functions and the impaired expression of a central lipogenic gene, stearoyl-CoA desaturase 1 (Scd1), which catalyzes the biosynthesis of monounsaturated fatty acids. 2-AA also reduces the expression of the autophagic genes Unc-51-like autophagy activating kinase 1 (ULK1) and Beclin1 and the levels of the autophagosomal membrane protein microtubule-associated protein 1, light chain 3 isoform B (LC3B) and p62. Reduced autophagy is accompanied by the reduced expression of the lipogenic gene Scd1, preventing bacterial clearance. Adding the SCD1 substrates palmitoyl-CoA and stearoyl-CoA increases P. aeruginosa clearance by macrophages. The impact of 2-AA on lipogenic gene expression and autophagic machinery is histone deacetylase 1 (HDAC1) mediated, implicating the HDAC1 epigenetic marks at the promoter sites of Scd1 and Beclin1 genes. This work provides novel insights into the complex metabolic alterations and epigenetic regulation promoted by QS and uncovers additional 2-AA actions supporting P. aeruginosa sustainment in macrophages. These findings may aid in designing host-directed therapeutics and protective interventions against P. aeruginosa persistence. IMPORTANCE This work sheds new light on how P. aeruginosa limits bacterial clearance in macrophages through 2-aminoacetophenone (2-AA), a secreted signaling molecule by this pathogen that is regulated by the quorum-sensing transcription factor MvfR. The action of 2-AA on the lipid biosynthesis gene Scd1 and the autophagic genes ULK1 and Beclin1 appears to secure the reduced intracellular clearance of P. aeruginosa by macrophages. In support of the 2-AA effect on lipid biosynthesis, the ability of macrophages to reduce the intracellular P. aeruginosa burden is reinstated following the supplementation of palmitoyl-CoA and stearoyl-CoA. The 2-AA-mediated reduction of Scd1 and Beclin1 expression is linked to chromatin modifications, implicating the enzyme histone deacetylase 1 (HDAC1), thus opening new avenues for future strategies against this pathogen's persistence. Overall, the knowledge obtained from this work provides for developing new therapeutics against P. aeruginosa.

Tackling recalcitrant Pseudomonas aeruginosa infections in critical illness via anti-virulence monotherapy

Intestinal barrier derangement allows intestinal bacteria and their products to translocate to the systemic circulation. Pseudomonas aeruginosa (PA) superimposed infection in critically ill patients increases gut permeability and leads to gut-driven sepsis. PA infections are challenging due to multi-drug resistance (MDR), biofilms, and/or antibiotic tolerance. Inhibition of the quorum-sensing transcriptional regulator MvfR(PqsR) is a desirable anti-PA anti-virulence strategy as MvfR controls multiple acute and chronic virulence functions. Here we show that MvfR promotes intestinal permeability and report potent anti-MvfR compounds, the N-Aryl Malonamides (NAMs), resulting from extensive structure-activity-relationship studies and thorough assessment of the inhibition of MvfR-controlled virulence functions. This class of anti-virulence non-native ligand-based agents has a half-maximal inhibitory concentration in the nanomolar range and strong target engagement. Using a NAM lead in monotherapy protects murine intestinal barrier function, abolishes MvfR-regulated small molecules, ameliorates bacterial dissemination, and lowers inflammatory cytokines. This study demonstrates the importance of MvfR in PA-driven intestinal permeability. It underscores the utility of anti-MvfR agents in maintaining gut mucosal integrity, which should be part of any successful strategy to prevent/treat PA infections and associated gut-derived sepsis in critical illness settings. NAMs provide for the development of crucial preventive/therapeutic monotherapy options against untreatable MDR PA infections.

An Organ System-Based Synopsis of Pseudomonas aeruginosa Virulence

Driven in part by its metabolic versatility, high intrinsic antibiotic resistance, and a large repertoire of virulence factors, Pseudomonas aeruginosa is expertly adapted to thrive in a wide variety of environments, and in the process, making it a notorious opportunistic pathogen. Apart from the extensively studied chronic infection in the lungs of people with cystic fibrosis (CF), P. aeruginosa also causes multiple serious infections encompassing essentially all organs of the human body, among others, lung infection in patients with chronic obstructive pulmonary disease, primary ciliary dyskinesia and ventilator-associated pneumonia; bacteremia and sepsis; soft tissue infection in burns, open wounds and postsurgery patients; urinary tract infection; diabetic foot ulcers; chronic suppurative otitis media and otitis externa; and keratitis associated with extended contact lens use. Although well characterized in the context of CF, pathogenic processes mediated by various P. aeruginosa virulence factors in other organ systems remain poorly understood. In this review, we use an organ system-based approach to provide a synopsis of disease mechanisms exerted by P. aeruginosa virulence determinants that contribute to its success as a versatile pathogen.

A Europium-Organic Framework Sensing Material for 2-Aminoacetophenone, a Bacterial Biomarker in Water

2-Aminoacetophenone (2-AA) is a metabolite produced in large quantities by the pathogenic bacteria Pseudomonas aeruginosa (PA), which is a biomarker for PA in water. State-of-the-art analytical techniques to detect PA usually require expensive instruments and a long analysis time which are not suitable for real-time water quality monitoring, especially for high-quality drinking water. Herein, we reported the application of a europium metal-organic framework (Eu-MOF) as a luminescent sensing material, which provides a facile, environmentally friendly and low-cost way for the fast detection of PA in water. Eu-MOF shows a high sensitivity toward 2-AA with a K_SV value of 3.563 × 10⁴ M^-1, rapid luminescence response in 12 s and high-selectivity and anti-interference ability with the existence of common detection indexes in drinking water owing to the good match of the energy levels of Eu-MOF and 2-AA. A systematical optimization of the sensing conditions to enhance the sensing function of Eu-MOF for 2-AA was discussed in detail, to give fundamentals for the rational design of MOF-based sensing materials.

A Perspective Of Intestinal Immune-Microbiome Interactions In Alcohol-Associated Liver Disease

Uncovering the intricacies of the gut microbiome and how it interacts with the host immune system has opened up pathways in the search for the treatment of disease conditions. Alcohol-associated liver disease is a major cause of death worldwide. Research has shed light on the breakdown of the protective gut barriers, translocation of gut microbes to the liver and inflammatory immune response to microbes all contributing to alcohol-associated liver disease. This knowledge has opened up avenues for alternative therapies to alleviate alcohol-associated liver disease based on the interaction of the commensal gut microbiome as a key player in the regulation of the immune response. This review describes the relevance of the intestinal immune system, the gut microbiota, and specialized and non-specialized intestinal cells in the regulation of intestinal homeostasis. It also reflects how these components are altered during alcohol-associated liver disease and discusses new approaches for potential future therapies in alcohol-associated liver disease.

Host and Pathogen Communication in the Respiratory Tract: Mechanisms and Models of a Complex Signaling Microenvironment

Chronic lung diseases are a leading cause of morbidity and mortality across the globe, encompassing a diverse range of conditions from infections with pathogenic microorganisms to underlying genetic disorders. The respiratory tract represents an active interface with the external environment having the primary immune function of resisting pathogen intrusion and maintaining homeostasis in response to the myriad of stimuli encountered within its microenvironment. To perform these vital functions and prevent lung disorders, a chemical and biological cross-talk occurs in the complex milieu of the lung that mediates and regulates the numerous cellular processes contributing to lung health. In this review, we will focus on the role of cross-talk in chronic lung infections, and discuss how different cell types and signaling pathways contribute to the chronicity of infection(s) and prevent effective immune clearance of pathogens. In the lung microenvironment, pathogens have developed the capacity to evade mucosal immunity using different mechanisms or virulence factors, leading to colonization and infection of the host; such mechanisms include the release of soluble and volatile factors, as well as contact dependent (juxtracrine) interactions. We explore the diverse modes of communication between the host and pathogen in the lung tissue milieu in the context of chronic lung infections. Lastly, we review current methods and approaches used to model and study these host-pathogen interactions in vitro, and the role of these technological platforms in advancing our knowledge about chronic lung diseases.

Role of luxS in immune evasion and pathogenicity of piscine Streptococcus agalactiae is not dependent on autoinducer-2

luxS-mediated autoinducer 2 (AI-2)-dependent quorum sensing (QS) has been demonstrated to affect many bacterial phenotypes, including virulence. Streptococcus agalactiae harbors a functional luxS gene required for the biosynthesis of AI-2. In this study, we investigated the regulation effect and mechanism of the luxS/AI-2 QS system in the pathogenicity of the piscine S. agalactiae strain GD201008-001. We found that inactivation of luxS caused a marked decrease in biofilm formation, hemolytic activity, antiphagocytosis and intracellular survival of S. agalactiae. Except for hemolytic activity, the altered phenotypes due to the luxS deletion were AI-2-independent. Further investigation indicated that high levels of the proinflammatory cytokines IL-1β and IL-6 could be induced in macrophages co-incubated with the luxS deletion mutant and synthetic AI-2, single or combined. Also, the results of tilapia infection showed that inactivation of luxS significantly decreased the virulence of S. agalactiae but upregulated the expression of cytokines in spleens and brains. Increased proinflammatory effects of the luxS mutant were restored in the luxS complemented strain but could not be restored by AI-2 addition. All the findings suggest that luxS is involved in virulence-associated phenotypes and immunological evasion of S. agalactiae, and furthermore, this involvement is mostly AI-2-independent. This study will provide valuable insights into our understanding of the role of the LuxS/AI-2 QS system in the pathogenesis of S. agalactiae.

Pseudomonas aeruginosa Quorum Sensing Molecule Alters Skeletal Muscle Protein Homeostasis by Perturbing the Antioxidant Defense System

Skeletal muscle function is compromised in many illnesses, including chronic infections. The Pseudomonas aeruginosa quorum sensing (QS) signal, 2-amino acetophenone (2-AA), is produced during acute and chronic infections and excreted in human tissues, including the lungs of cystic fibrosis patients. We have shown that 2-AA facilitates pathogen persistence, likely via its ability to promote the formation of bacterial persister cells, and that it acts as an interkingdom immunomodulatory signal that epigenetically reprograms innate immune functions. Moreover, 2-AA compromises muscle contractility and impacts the expression of genes involved in reactive oxygen species (ROS) homeostasis in skeletal muscle and in mitochondrial functions. Here, we elucidate the molecular mechanisms of 2-AA's impairment of skeletal muscle function and ROS homeostasis. Murine in vivo and differentiated C2C12 myotube cell studies showed that 2-AA promotes ROS generation in skeletal muscle via the modulation of xanthine oxidase (XO) activity, NAD(P)H oxidase2 (NOX2) protein level, and the activity of antioxidant enzymes. ROS accumulation triggers the activity of AMP-activated protein kinase (AMPK), likely upstream of the observed locations of induction of ubiquitin ligases Muscle RING Finger 1 (MuRF1) and Muscle Atrophy F-box (MAFbx), and induces autophagy-related proteins. The protein-level perturbation in skeletal muscle of silent mating type information regulation 2 homolog 1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1), and uncoupling protein 3 (UCP3) is rescued by the antioxidant N-acetyl-l-cysteine (NAC). Together, these results unveil a novel form of action of a QS bacterial molecule and provide molecular insights into the 2-AA-mediated skeletal muscle dysfunction caused by P. aeruginosa IMPORTANCE Pseudomonas aeruginosa, a bacterium that is resistant to treatment, causes serious acute, persistent, and relapsing infections in humans. There is increasing evidence that bacterial excreted small molecules play a critical role during infection. We have shown that a quorum sensing (QS)-regulated excreted small molecule, 2-AA, which is abundantly produced by P. aeruginosa, promotes persistent infections, dampens host inflammation, and triggers mitochondrial dysfunction in skeletal muscle. QS is a cell-to-cell communication system utilized by bacteria to promote collective behaviors. The significance of our study in identifying a mechanism that leads to skeletal muscle dysfunction, via the action of a QS molecule, is that it may open new avenues in the control of muscle loss as a result of infection and sepsis. Given that QS is a common characteristic of prokaryotes, it is possible that 2-AA-like molecules promoting similar effects may exist in other pathogens.

Growth Regulation in Amphibian Pathogenic Chytrid Fungi by the Quorum Sensing Metabolite Tryptophol

Amphibians face many threats leading to declines and extinctions, but the chytrid fungal skin pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) have been identified as the causative factors leading to one of the greatest disease-driven losses of amphibian biodiversity worldwide. Infection may lead to different clinical outcomes, and lethal infections are commonly associated with unrestricted, exponential fungal growth in the amphibian epidermis. Mechanisms underpinning Bd and Bsal growth in the amphibian host are poorly understood. Here, we describe a quorum sensing mechanism that allows cell-to-cell communication by Bd and Bsal in order to regulate fungal densities and infection strategies. Addition of chytrid culture supernatant to chytrid cultures resulted in a concentration-dependent growth reduction and using dialysis, small metabolites were shown to be the causative factor. U-HPLC-MS/MS and in vitro growth tests identified the aromatic alcohol tryptophol as a key metabolite in regulating fungal growth. We determined tryptophol kinetics in both Bd and Bsal and confirmed the autostimulatory mode of action of this quorum sensing metabolite. Finally, we linked expression of genes that might be involved in tryptophol production, with in vitro and in vivo chytrid growth. Our results show that Bd and Bsal fungi use tryptophol to act as multicellular entities in order to regulate their growth.

From Acetoin to ( Z)-3-Hexen-1-ol: The Diversity of Volatile Organic Compounds that Induce Plant Responses

Evidence that plants can respond to volatile organic compounds (VOCs) was first presented 35 years ago. Since then, over 40 VOCs have been found to induce plant responses. These include VOCs that are produced not only by plants but also by microbes and insects. Here, we summarize what is known about how these VOCs are produced and how plants detect and respond to them. In doing so, we highlight notable observations we believe are worth greater consideration. For example, the VOCs that induce plant responses appear to have little in common. They are derived from many different biosynthetic pathways and have few distinguishing chemical or structural features. Likewise, plants appear to use several mechanisms to detect VOCs rather than a single dedicated "olfactory" system. Considering these observations, we advocate for more discovery-oriented experiments and propose that future research take a fresh look at the ways plants detect and respond to VOCs.

A bacterial biosensor encoding a genetically modified LuxR receptor exhibits improved detection of Pseudomonas aeruginosa's biomarker molecule 2-aminoacetophenone

2-Aminoacetophneone (2-AA) is a volatile molecule produced in high amounts by the opportunistic pathogen Pseudomonas aeruginosa. We have previously shown that 2-AA activates the quorum sensing (QS) LuxR receptor of Aliivibrio fischeri. In the present study we were able to improve LuxR's affinity and detection limit for 2-AA by genetic modification of three amino acids within the binding pocket of the receptor. Expression of the modified LuxR receptor in a luminescent bacterial biosensor provided an efficient detection assay of 2-AA in clinical P. aeruginosa strains isolated from blood and lung infections, as well as in phlegm samples obtained from subjects suffering from lung infections.

Whole-organism phenotypic screening for anti-infectives promoting host health

To date, antibiotics have been identified on the basis of their ability to kill bacteria or inhibit their growth rather than directly for their capacity to improve clinical outcomes of infected patients. Although historically successful, this approach has led to the development of an antibiotic armamentarium that suffers from a number of shortcomings, including the inevitable emergence of resistance and, in certain infections, suboptimal efficacy leading to long treatment durations, infection recurrence, or high mortality and morbidity rates despite apparent bacterial sterilization. Conventional antibiotics fail to address the complexities of in vivo bacterial physiology and virulence, as well as the role of the host underlying the complex, dynamic interactions that cause disease. New interventions are needed, aimed at host outcome rather than microbiological cure. Here we review the role of screening models for cellular and whole-organism infection, including worms, flies, zebrafish, and mice, to identify novel therapeutic strategies and discuss their future implications.

Molecular Insights into Function and Competitive Inhibition of Pseudomonas aeruginosa Multiple Virulence Factor Regulator

New approaches to antimicrobial drug discovery are urgently needed to combat intractable infections caused by multidrug-resistant (MDR) bacteria. Multiple virulence factor regulator (MvfR or PqsR), a Pseudomonas aeruginosa quorum sensing transcription factor, regulates functions important in both acute and persistent infections. Recently identified non-ligand-based benzamine-benzimidazole (BB) inhibitors of MvfR suppress both acute and persistent P. aeruginosa infections in mice without perturbing bacterial growth. Here, we elucidate the crystal structure of the MvfR ligand binding domain (LBD) in complex with one potent BB inhibitor, M64. Structural analysis indicated that M64 binds, like native ligands, to the MvfR hydrophobic cavity. A hydrogen bond and pi interaction were found to be important for MvfR-M64 affinity. Surface plasmon resonance analysis demonstrated that M64 is a competitive inhibitor of MvfR. Moreover, a protein engineering approach revealed that Gln194 and Tyr258 are critical for the interaction between MvfR and M64. Random mutagenesis of the full-length MvfR protein identified a single-amino-acid substitution, I68F, at a DNA binding linker domain that confers M64 insensitivity. In the presence of M64, I68F but not the wild-type (WT) MvfR protein retained DNA binding ability. Our findings strongly suggest that M64 promotes conformational change at the DNA binding domain of MvfR and that the I68F mutation may compensate for this change, indicating allosteric inhibition. This work provides critical new insights into the molecular mechanism of MvfR function and inhibition that could aid in the optimization of anti-MvfR compounds and improve our understanding of MvfR regulation.

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes serious acute, persistent, and relapsing infections. New approaches to antimicrobial drug discovery are urgently needed to combat intractable infections caused by this pathogen. The Pseudomonas aeruginosa quorum sensing transcription factor MvfR regulates functions important in both acute and persistent infections. We used recently identified inhibitors of MvfR to perform structural studies and reveal important insights that would benefit the optimization of anti-MvfR compounds. Altogether, the results reported here provide critical detailed mechanistic insights into the function of MvfR domains that may benefit the optimization of the chemical, pharmacological, and safety properties of MvfR antagonist series.

Animal Models for Pseudomonas aeruginosa Quorum Sensing Studies

Quorum sensing (QS) systems play global regulatory roles in bacterial virulence. They synchronize the expression of multiple virulence factors and they control and modulate bacterial antibiotic tolerance systems and host defense mechanisms. Therefore, it is important to obtain knowledge about QS modes of action and to test putative therapeutics that may interrupt QS actions in the context of infections. This chapter describes methods to study bacterial pathogenesis in murine acute and persistent/relapsing infection models, using the Gram-negative bacterial pathogen Pseudomonas aeruginosa as an example. These infection models can be used to probe bacterial virulence functions and in mechanistic studies, as well as for the assessment of the therapeutic potential of antibacterials, including anti-virulence agents.

Pseudomonas aeruginosa quorum sensing modulates immune responses: An updated review article

Pseudomonas aeruginosa is an opportunistic bacterium which induces some complications in immunocompromised patients. Pseudomonas aeruginosa is a quorum-sensing using bacterium which regulates its genes expression. The bacterium uses two famous pathways for quorum sensing entitled LasI/LasR and RhlI/RhlR systems. It has been documented that the bacteria which use quorum sensing are able to overcome immune responses. This review article aims to present recent information regarding the effects of Pseudomonas aeruginosa quorum sensing systems on the host immune responses.

NF-κBp50 and HDAC1 Interaction Is Implicated in the Host Tolerance to Infection Mediated by the Bacterial Quorum Sensing Signal 2-Aminoacetophenone

Some bacterial quorum sensing (QS) small molecules are important mediators of inter-kingdom signaling and impact host immunity. The QS regulated small volatile molecule 2-aminoacetophenone (2-AA), which has been proposed as a biomarker of Pseudomonas aeruginosa colonization in chronically infected human tissues, is critically involved in "host tolerance training" that involves a distinct molecular mechanism of host chromatin regulation through histone deacetylase (HDAC)1. 2-AA's epigenetic reprogramming action enables host tolerance to high bacterial burden and permits long-term presence of P. aeruginosa without compromising host survival. Here, to further elucidate the molecular mechanisms of 2-AA-mediated host tolerance/resilience we investigated the connection between histone acetylation status and nuclear factor (NF)-κB signaling components that together coordinate 2-AA-mediated control of transcriptional activity. We found increased NF-κBp65 acetylation levels in 2-AA stimulated cells that are preceded by association of CBP/p300 and increased histone acetyltransferase activity. In contrast, in 2-AA-tolerized cells the protein-protein interaction between p65 and CBP/p300 is disrupted and conversely, the interaction between p50 and co-repressor HDAC1 is enhanced, leading to repression of the pro-inflammatory response. These results highlight how a bacterial QS signaling molecule can establish a link between intracellular signaling and epigenetic reprogramming of pro-inflammatory mediators that may contribute to host tolerance training. These new insights might contribute to the development of novel therapeutic interventions against bacterial infections.

Polypharmacology Approaches against the Pseudomonas aeruginosa MvfR Regulon and Their Application in Blocking Virulence and Antibiotic Tolerance

Pseudomonas aeruginosa is an important nosocomial pathogen that is frequently recalcitrant to available antibiotics, underlining the urgent need for alternative therapeutic options against this pathogen. Targeting virulence functions is a promising alternative strategy as it is expected to generate less-selective resistance to treatment compared to antibiotics. Capitalizing on our nonligand-based benzamide-benzimidazole (BB) core structure compounds reported to efficiently block the activity of the P. aeruginosa multiple virulence factor regulator MvfR, here we report the first class of inhibitors shown to interfere with PqsBC enzyme activity, responsible for the synthesis of the MvfR activating ligands HHQ and PQS, and the first to target simultaneously MvfR and PqsBC activity. The use of these compounds reveals that inhibiting PqsBC is sufficient to block P. aeruginosa's acute virulence functions, as the synthesis of MvfR ligands is inhibited. Our results show that MvfR remains the best target of this QS pathway, as we show that antagonists of this target block both acute and persistence-related functions. The structural properties of the compounds reported in this study provide several insights that are instrumental for the design of improved MvfR regulon inhibitors against both acute and persistent P. aeruginosa infections. Moreover, the data presented offer the possibility of a polypharmacology approach of simultaneous silencing two targets in the same pathway. Such a combined antivirulence strategy holds promise in increasing therapeutic efficacy and providing alternatives in the event of a single target's resistance development.

Peptides as Quorum Sensing Molecules: Measurement Techniques and Obtained Levels In vitro and In vivo

The expression of certain bacterial genes is regulated in a cell-density dependent way, a phenomenon called quorum sensing. Both Gram-negative and Gram-positive bacteria use this type of communication, though the signal molecules (auto-inducers) used by them differ between both groups: Gram-negative bacteria use predominantly N-acyl homoserine lacton (AHL) molecules (autoinducer-1, AI-1) while Gram-positive bacteria use mainly peptides (autoinducer peptides, AIP or quorum sensing peptides). These quorum sensing molecules are not only involved in the inter-microbial communication, but can also possibly cross-talk directly or indirectly with their host. This review summarizes the currently applied analytical approaches for quorum sensing identification and quantification with additionally summarizing the experimentally found in vivo concentrations of these molecules in humans.

Role of intestinal microbiota and metabolites on gut homeostasis and human diseases

Background

A vast diversity of microbes colonizes in the human gastrointestinal tract, referred to intestinal microbiota. Microbiota and products thereof are indispensable for shaping the development and function of host innate immune system, thereby exerting multifaceted impacts in gut health.

Methods

This paper reviews the effects on immunity of gut microbe-derived nucleic acids, and gut microbial metabolites, as well as the involvement of commensals in the gut homeostasis. We focus on the recent findings with an intention to illuminate the mechanisms by which the microbiota and products thereof are interacting with host immunity, as well as to scrutinize imbalanced gut microbiota (dysbiosis) which lead to autoimmune disorders including inflammatory bowel disease (IBD), Type 1 diabetes (T1D) and systemic immune syndromes such as rheumatoid arthritis (RA).

Results

In addition to their well-recognized benefits in the gut such as occupation of ecological niches and competition with pathogens, commensal bacteria have been shown to strengthen the gut barrier and to exert immunomodulatory actions within the gut and beyond. It has been realized that impaired intestinal microbiota not only contribute to gut diseases but also are inextricably linked to metabolic disorders and even brain dysfunction.

Conclusions

A better understanding of the mutual interactions of the microbiota and host immune system, would shed light on our endeavors of disease prevention and broaden the path to our discovery of immune intervention targets for disease treatment.

A quorum-sensing signal promotes host tolerance training through HDAC1-mediated epigenetic reprogramming

The mechanisms by which pathogens evade elimination without affecting host fitness are not well understood. For the pathogen Pseudomonas aeruginosa, this evasion appears to be triggered by excretion of the quorum sensing (QS) molecule 2-aminoacetophenone (2-AA), which dampens host immune responses and modulates host metabolism, thereby enabling the bacteria to persist at a high burden level. Here, we examined how 2-AA trains host tissues to become tolerant to a high bacterial burden, without compromising host fitness. We found that 2-AA regulates histone deacetylase1 (HDAC1) expression and activity, resulting in hypoacetylation of lysine 18 of histone H3 (H3K18) at pro-inflammatory cytokine loci. Specifically, 2-AA induced reprogramming of immune cells occurs via alterations in histone acetylation of immune cytokines in vivo and in vitro. This host epigenetic reprograming, which was maintained for up to 7 days, dampened host responses to subsequent exposure to 2-AA or other pathogen-associated molecules. The process was found to involve a distinct molecular mechanism of host chromatin regulation. Inhibition of HDAC1 prevented the immunomodulatory effects of 2-AA. These observations provide the first mechanistic example of a QS molecule regulating a host epigenome to enable tolerance of infection. These insights have enormous potential for developing preventive treatments against bacterial infections.

Evidence for Direct Control of Virulence and Defense Gene Circuits by the Pseudomonas aeruginosa Quorum Sensing Regulator, MvfR

Pseudomonas aeruginosa defies eradication by antibiotics and is responsible for acute and chronic human infections due to a wide variety of virulence factors. Currently, it is believed that MvfR (PqsR) controls the expression of many of these factors indirectly via the pqs and phnAB operons. Here we provide strong evidence that MvfR may also bind and directly regulate the expression of additional 35 loci across the P. aeruginosa genome, including major regulators and virulence factors, such as the quorum sensing (QS) regulators lasR and rhlR, and genes involved in protein secretion, translation, and response to oxidative stress. We show that these anti-oxidant systems, AhpC-F, AhpB-TrxB2 and Dps, are critical for P. aeruginosa survival to reactive oxygen species and antibiotic tolerance. Considering that MvfR regulated compounds generate reactive oxygen species, this indicates a tightly regulated QS self-defense anti-poisoning system. These findings also challenge the current hierarchical regulation model of P. aeruginosa QS systems by revealing new interconnections between them that suggest a circular model. Moreover, they uncover a novel role for MvfR in self-defense that favors antibiotic tolerance and cell survival, further demonstrating MvfR as a highly desirable anti-virulence target.

Electrochemistry provides a simple way to monitor Pseudomonas aeruginosa metabolites

Pseudomonas aeruginosa is one of the most common bacteria responsible for nosocomial infections. To imagine new therapies, understanding virulence mechanisms and the associated communication system of the bacterium (its quorum sensing) is a target of the first importance. Electrochemistry is a promising tool for real-time in situ monitoring of electroactive species issued from P. aeruginosa communication system. This contribution deals with the electrochemical characterization of the main bacteria electroactive metabolites: Pseudomonas Quinolone Signal, pyocyanin and 2'-aminoacetophenone. These metabolites were electrochemically characterized and further detected in supernatant of P. aeruginosa PA01 strain grown in LB medium.

Considerations and caveats in anti-virulence drug development

As antibiotic resistance remains a major public health threat, anti-virulence therapy research is gaining interest. Hundreds of potential anti-virulence compounds have been examined, but very few have made it to clinical trials and none have been approved. This review surveys the current anti-virulence research field with a focus on the highly resistant and deadly ESKAPE pathogens, especially Pseudomonas aeruginosa. We discuss timely considerations and caveats in anti-virulence drug development, including target identification, administration, preclinical development, and metrics for success in clinical trials. Development of a defined pipeline for anti-virulence agents, which differs in important ways from conventional antibiotics, is imperative for the future success of these critically needed drugs.

Bacterial-excreted small volatile molecule 2-aminoacetophenone induces oxidative stress and apoptosis in murine skeletal muscle

Oxidative stress induces mitochondrial dysfunction and facilitates apoptosis, tissue damage or metabolic alterations following infection. We have previously discovered that the Pseudomonas aeruginosa (PA) quorum sensing (QS)-excreted small volatile molecule, 2-aminoacetophenone (2-AA), which is produced in infected human tissue, promotes bacterial phenotypes that favor chronic infection, while also compromising muscle function and dampens the pathogen-induced innate immune response, promoting host tolerance to infection. In this study, murine whole-genome expression data have demonstrated that 2-AA affects the expression of genes involved in reactive oxygen species (ROS) homeostasis, thus producing an oxidative stress signature in skeletal muscle. The results of the present study demonstrated that the expression levels of genes involved in apoptosis signaling pathways were upregulated in the skeletal muscle of 2-AA-treated mice. To confirm the results of our transcriptome analysis, we used a novel high-resolution magic-angle-spinning (HRMAS), proton (¹H) nuclear magnetic resonance (NMR) method and observed increased levels of bisallylic methylene fatty acyl protons and vinyl protons, suggesting that 2-AA induces skeletal muscle cell apoptosis. This effect was corroborated by our results demonstrating the downregulation of mitochondrial membrane potential in vivo in response to 2-AA. The findings of the present study indicate that the bacterial infochemical, 2-AA, disrupts mitochondrial functions by inducing oxidative stress and apoptosis signaling and likely promotes skeletal muscle dysfunction, which may favor chronic/persistent infection.

PqsBC, a Condensing Enzyme in the Biosynthesis of the Pseudomonas aeruginosa Quinolone Signal: CRYSTAL STRUCTURE, INHIBITION, AND REACTION MECHANISM

Pseudomonas aeruginosa produces a number of alkylquinolone-type secondary metabolites best known for their antimicrobial effects and involvement in cell-cell communication. In the alkylquinolone biosynthetic pathway, the β-ketoacyl-(acyl carrier protein) synthase III (FabH)-like enzyme PqsBC catalyzes the condensation of octanoyl-coenzyme A and 2-aminobenzoylacetate (2-ABA) to form the signal molecule 2-heptyl-4(1H)-quinolone. PqsBC, a potential drug target, is unique for its heterodimeric arrangement and an active site different from that of canonical FabH-like enzymes. Considering the sequence dissimilarity between the subunits, a key question was how the two subunits are organized with respect to the active site. In this study, the PqsBC structure was determined to a 2 Å resolution, revealing that PqsB and PqsC have a pseudo-2-fold symmetry that unexpectedly mimics the FabH homodimer. PqsC has an active site composed of Cys-129 and His-269, and the surrounding active site cleft is hydrophobic in character and approximately twice the volume of related FabH enzymes that may be a requirement to accommodate the aromatic substrate 2-ABA. From physiological and kinetic studies, we identified 2-aminoacetophenone as a pathway-inherent competitive inhibitor of PqsBC, whose fluorescence properties could be used for in vitro binding studies. In a time-resolved setup, we demonstrated that the catalytic histidine is not involved in acyl-enzyme formation, but contributes to an acylation-dependent increase in affinity for the second substrate 2-ABA. Introduction of Asn into the PqsC active site led to significant activity toward the desamino substrate analog benzoylacetate, suggesting that the substrate 2-ABA itself supplies the asparagine-equivalent amino function that assists in catalysis.

PqsE of Pseudomonas aeruginosa Acts as Pathway-Specific Thioesterase in the Biosynthesis of Alkylquinolone Signaling Molecules

Pseudomonas aeruginosa uses the alkylquinolones PQS (2-heptyl-3-hydroxy-4(1H)-quinolone) and HHQ (2-heptyl-4(1H)-quinolone) as quorum-sensing signal molecules, controlling the expression of many virulence genes as a function of cell population density. The biosynthesis of HHQ is generally accepted to require the pqsABCD gene products. We now reconstitute the biosynthetic pathway in vitro, and demonstrate that in addition to PqsABCD, PqsE has a role in HHQ synthesis. PqsE acts as thioesterase, hydrolyzing the biosynthetic intermediate 2-aminobenzoylacetyl-coenzyme A to form 2-aminobenzoylacetate, the precursor of HHQ and 2-aminoacetophenone. The role of PqsE can be taken over to some extent by the broad-specificity thioesterase TesB, explaining why the pqsE deletion mutant of P. aeruginosa still synthesizes HHQ. Interestingly, the pqsE mutant produces increased levels of 2,4-dihydroxyquinoline, resulting from intramolecular cyclization of 2-aminobenzoylacetyl-coenzyme A. Overall, our data suggest that PqsE promotes the efficiency of alkylquinolone signal molecule biosynthesis in P. aeruginosa and balances the levels of secondary metabolites deriving from the alkylquinolone biosynthetic pathway.

Prediction of multiple infections after severe burn trauma: a prospective cohort study

OBJECTIVE

To develop predictive models for early triage of burn patients based on hypersusceptibility to repeated infections.

BACKGROUND

Infection remains a major cause of mortality and morbidity after severe trauma, demanding new strategies to combat infections. Models for infection prediction are lacking.

METHODS

Secondary analysis of 459 burn patients (≥16 years old) with 20% or more total body surface area burns recruited from 6 US burn centers. We compared blood transcriptomes with a 180-hour cutoff on the injury-to-transcriptome interval of 47 patients (≤1 infection episode) to those of 66 hypersusceptible patients [multiple (≥2) infection episodes (MIE)]. We used LASSO regression to select biomarkers and multivariate logistic regression to built models, accuracy of which were assessed by area under receiver operating characteristic curve (AUROC) and cross-validation.

RESULTS

Three predictive models were developed using covariates of (1) clinical characteristics; (2) expression profiles of 14 genomic probes; (3) combining (1) and (2). The genomic and clinical models were highly predictive of MIE status [AUROCGenomic = 0.946 (95% CI: 0.906-0.986); AUROCClinical = 0.864 (CI: 0.794-0.933); AUROCGenomic/AUROCClinical P = 0.044]. Combined model has an increased AUROCCombined of 0.967 (CI: 0.940-0.993) compared with the individual models (AUROCCombined/AUROCClinical P = 0.0069). Hypersusceptible patients show early alterations in immune-related signaling pathways, epigenetic modulation, and chromatin remodeling.

CONCLUSIONS

Early triage of burn patients more susceptible to infections can be made using clinical characteristics and/or genomic signatures. Genomic signature suggests new insights into the pathophysiology of hypersusceptibility to infection may lead to novel potential therapeutic or prophylactic targets.

Exploring the chemical space of ureidothiophene-2-carboxylic acids as inhibitors of the quorum sensing enzyme PqsD from Pseudomonas aeruginosa

Pseudomonas aeruginosa employs a quorum sensing (QS) communication system that makes use of small diffusible molecules. Among other effects, the QS system coordinates the formation of biofilm which decisively contributes to difficulties in the therapy of Pseudomonas infections. The present work deals with the structure-activity exploration of ureidothiophene-2-carboxylic acids as inhibitors of PqsD, a key enzyme in the biosynthetic pathway of signal molecules in the Pseudomonas QS system. We describe an improvement of the inhibitory activity by successfully combining features from two different PqsD inhibitor classes. Furthermore the functional groups, which are responsible for the inhibitory potency, were identified. Moreover, the inability of the new inhibitors, to prevent signal molecule formation in whole cell assays, is discussed.

Role of bacterial volatile compounds in bacterial biology

Bacterial interactions with neighboring microorganisms via production of small metabolites enable bacteria to respond and adapt to environmental changes. The study of intercellular interactions primarily focused on soluble metabolites, but bacteria also produce and release into their headspace a wide variety of volatile secondary metabolites, the ecological roles of which have generally been overlooked. However, bacterial volatile compounds are known to contribute to interkingdom interactions (plant, fungi and nematodes), and recent studies also identified their at-a-distance influence on bacterial behavior. The present review describes the biological roles of bacterial volatile compounds in inter- and intraspecies bacterial interactions, a new and yet unexplored research area, with potential clinical and industrial applications.

Cyclo(Phe-Pro) produced by the human pathogen Vibrio vulnificus inhibits host innate immune responses through the NF-κB pathway

Cyclo(Phe-Pro) (cFP) is a secondary metabolite produced by certain bacteria and fungi. Although recent studies highlight the role of cFP in cell-to-cell communication by bacteria, its role in the context of the host immune response is poorly understood. In this study, we investigated the role of cFP produced by the human pathogen Vibrio vulnificus in the modulation of innate immune responses toward the pathogen. cFP suppressed the production of proinflammatory cytokines, nitric oxide, and reactive oxygen species in a lipopolysaccharide (LPS)-stimulated monocyte/macrophage cell line and in bone marrow-derived macrophages. Specifically, cFP inhibited inhibitory κB (IκB) kinase (IKK) phosphorylation, IκBα degradation, and nuclear factor κB (NF-κB) translocation to the cell nucleus, indicating that cFP affects the NF-κB pathway. We searched for genes that are responsible for cFP production in V. vulnificus and identified VVMO6_03017 as a causative gene. A deletion of VVMO6_03017 diminished cFP production and decreased virulence in subcutaneously inoculated mice. In summary, cFP produced by V. vulnificus actively suppresses the innate immune responses of the host, thereby facilitating its survival and propagation in the host environment.

Identification of anti-virulence compounds that disrupt quorum-sensing regulated acute and persistent pathogenicity

Etiological agents of acute, persistent, or relapsing clinical infections are often refractory to antibiotics due to multidrug resistance and/or antibiotic tolerance. Pseudomonas aeruginosa is an opportunistic Gram-negative bacterial pathogen that causes recalcitrant and severe acute chronic and persistent human infections. Here, we target the MvfR-regulated P. aeruginosa quorum sensing (QS) virulence pathway to isolate robust molecules that specifically inhibit infection without affecting bacterial growth or viability to mitigate selective resistance. Using a whole-cell high-throughput screen (HTS) and structure-activity relationship (SAR) analysis, we identify compounds that block the synthesis of both pro-persistence and pro-acute MvfR-dependent signaling molecules. These compounds, which share a benzamide-benzimidazole backbone and are unrelated to previous MvfR-regulon inhibitors, bind the global virulence QS transcriptional regulator, MvfR (PqsR); inhibit the MvfR regulon in multi-drug resistant isolates; are active against P. aeruginosa acute and persistent murine infections; and do not perturb bacterial growth. In addition, they are the first compounds identified to reduce the formation of antibiotic-tolerant persister cells. As such, these molecules provide for the development of next-generation clinical therapeutics to more effectively treat refractory and deleterious bacterial-human infections.

Antibiotic resistant and tolerant bacterial pathogens are responsible for acute, chronic and persistent human infections recalcitrant to any current treatments. Therefore, there is an urgent need to identify new antimicrobial drugs that will help circumvent the current antibiotic resistance crisis. Bacterial pathogens often develop resistance to antibiotic drugs that target bacterial growth or viability. In contrast, strategies that specifically target virulence pathways non-essential for growth could limit selective resistance, and thus are candidates for the development of next-generation antimicrobial therapeutics. In this study we target the bacterial communication system MvfR (PqsR), which is known to control virulence of the opportunistic bacterial pathogen Pseudomonas aeruginosa. We identified and improved upon new small molecules that effectively silence the MvfR communication system, and as a result block P. aeruginosa virulence both in vitro and in vivo. Moreover, these new compounds are the first known to restrict the ability of bacteria to form antibiotic-tolerant cells and consequently proved to be very effective at preventing persistent infection in a mammalian infection model. Because of their ability to simultaneously block acute and persistent infections, these new molecules may provide a very strong basis for the development of next generation antimicrobials.

Limiting damage during infection: lessons from infection tolerance for novel therapeutics

In the field of infectious disease control, novel therapies are focusing on reducing illness caused by pathogens rather than on reducing the pathogen burden itself. Here, Vale and colleagues highlight some potential consequences of such therapeutics for pathogen spread and evolution.

Assessing Pseudomonas aeruginosa Persister/antibiotic tolerant cells

Bacterial persistence, which is observed in a broad range of microbial species, is the capacity of a bacterial cell subpopulation called "persisters" to tolerate exposure to normally lethal concentrations of bactericidal antibiotics. This ability, which is not due to antibiotic-resistant mutants, has been implicated in antibiotic treatment failures and may account for latent, chronic, and relapsing infections. Antibiotic tolerant/Persister (AT/P) cells have been notoriously difficult to study due to their low frequency and transient nature. This chapter describes the main methods used to isolate and study Pseudomonas aeruginosa AT/P cells and discusses new technologies that may ease research of P. aeruginosa persisters in the near future.

A quorum sensing small volatile molecule promotes antibiotic tolerance in bacteria

Bacteria can be refractory to antibiotics due to a sub-population of dormant cells, called persisters that are highly tolerant to antibiotic exposure. The low frequency and transience of the antibiotic tolerant “persister” trait has complicated elucidation of the mechanism that controls antibiotic tolerance. In this study, we show that 2’ Amino-acetophenone (2-AA), a poorly studied but diagnostically important small, volatile molecule produced by the recalcitrant gram-negative human pathogen Pseudomonas aeruginosa, promotes antibiotic tolerance in response to quorum-sensing (QS) signaling. Our results show that 2-AA mediated persister cell accumulation occurs via alteration of the expression of genes involved in the translational capacity of the cell, including almost all ribosomal protein genes and other translation-related factors. That 2-AA promotes persisters formation also in other emerging multi-drug resistant pathogens, including the non 2-AA producer Acinetobacter baumannii implies that 2-AA may play an important role in the ability of gram-negative bacteria to tolerate antibiotic treatments in polymicrobial infections. Given that the synthesis, excretion and uptake of QS small molecules is a common hallmark of prokaryotes, together with the fact that the translational machinery is highly conserved, we posit that modulation of the translational capacity of the cell via QS molecules, may be a general, widely distributed mechanism that promotes antibiotic tolerance among prokaryotes.

The end of an old hypothesis: the pseudomonas signaling molecules 4-hydroxy-2-alkylquinolines derive from fatty acids, not 3-ketofatty acids

Groups of pathogenic bacteria use diffusible signals to regulate their virulence in a concerted manner. Pseudomonas aeruginosa uses 4-hydroxy-2-alkylquinolines (HAQs), including 4-hydroxy-2-heptylquinoline (HHQ) and 3,4-dihydroxy-2-heptylquinoline (PQS), as unique signals. We demonstrate that octanoic acid is directly incorporated into HHQ. This finding rules out the long-standing hypothesis that 3-ketofatty acids are the precursors of HAQs. We found that HAQ biosynthesis, which requires the PqsABCD enzymes, proceeds by a two-step pathway: (1) PqsD mediates the synthesis of 2-aminobenzoylacetate (2-ABA) from anthraniloyl-coenzyme A (CoA) and malonyl-CoA, then (2) the decarboxylating coupling of 2-ABA to an octanoate group linked to PqsC produces HHQ, the direct precursor of PQS. PqsB is tightly associated with PqsC and required for the second step. This finding uncovers promising targets for the development of specific antivirulence drugs to combat this opportunistic pathogen.

A small volatile bacterial molecule triggers mitochondrial dysfunction in murine skeletal muscle

Mitochondria integrate distinct signals that reflect specific threats to the host, including infection, tissue damage, and metabolic dysfunction; and play a key role in insulin resistance. We have found that the Pseudomonas aeruginosa quorum sensing infochemical, 2-amino acetophenone (2-AA), produced during acute and chronic infection in human tissues, including in the lungs of cystic fibrosis (CF) patients, acts as an interkingdom immunomodulatory signal that facilitates pathogen persistence, and host tolerance to infection. Transcriptome results have led to the hypothesis that 2-AA causes further harm to the host by triggering mitochondrial dysfunction in skeletal muscle. As normal skeletal muscle function is essential to survival, and is compromised in many chronic illnesses, including infections and CF-associated muscle wasting, we here determine the global effects of 2-AA on skeletal muscle using high-resolution magic-angle-spinning (HRMAS), proton (¹H) nuclear magnetic resonance (NMR) metabolomics, in vivo³¹P NMR, whole-genome expression analysis and functional studies. Our results show that 2-AA when injected into mice, induced a biological signature of insulin resistance as determined by ¹H NMR analysis-, and dramatically altered insulin signaling, glucose transport, and mitochondrial function. Genes including Glut4, IRS1, PPAR-γ, PGC1 and Sirt1 were downregulated, whereas uncoupling protein UCP3 was up-regulated, in accordance with mitochondrial dysfunction. Although 2-AA did not alter high-energy phosphates or pH by in vivo³¹P NMR analysis, it significantly reduced the rate of ATP synthesis. This affect was corroborated by results demonstrating down-regulation of the expression of genes involved in energy production and muscle function, and was further validated by muscle function studies. Together, these results further demonstrate that 2-AA, acts as a mediator of interkingdom modulation, and likely effects insulin resistance associated with a molecular signature of mitochondrial dysfunction in skeletal muscle. Reduced energy production and mitochondrial dysfunctional may further favor infection, and be an important step in the establishment of chronic and persistent infections.