Quorum Sensing Inhibitors Research Articles

Cracking the code of seasonal seawater biofouling: enhanced biofouling control with quorum sensing inhibitor-functionalized membranes

Membrane biofouling poses an ongoing challenge in seawater reverse osmosis (SWRO) desalination. Here we delved into the impact of seasonal variations in microbial communities on membrane biofouling and innovatively fabricated quorum sensing inhibitors (acylase (AC) and methyl anthranilate (MA))-modified membranes to combat it. Results indicated that Proteobacteria dominated in seawater and membrane biofilm across all seasons, while other phyla varied seasonally. At the class level, the two leading bacteria on the membrane were Gamma- and Alphaproteobacteria, constituting 14–48% and 4–27%, respectively. Genera like Arcobacter, Vibrio, and Rhodobacteraceae were identified as keystone species that exhibited a significant positive correlation with extracellular polymeric substance (EPS) and biofilm formation, leading to a substantive reduction in membrane flux by 70 to 77%. The introduction of AC and MA inhibitors on the membrane suppressed keystone bacteria Rhodobacteraceae and Arcobacter and affected their metabolism, thereby significantly reducing EPS by 65–69% and 55–59%, respectively, and alleviating membrane flux decline by 30–32% and 18–22%, respectively, compared to the pristine membrane. These findings shed new light on the seasonal patterns of membrane biofouling and provide valuable insights into anti-biofouling strategies based on QS inhibition for collaborative biofilm formation.

Design, synthesis and exploration of novel triazinoindoles as potent quorum-sensing inhibitors and radical quenchers.

Background: Antimicrobial resistance has become a critical health concern, and quorum-sensing exacerbates the resistance by facilitating cell-to-cell communication within the microbial community, leading to severe pathogenic outbreaks. Methods & results: Novel 1-(2-((5H-[1,2,4]-triazino[5,6-b]indol-3-yl)thio)acetyl)indoline-2,3-diones were synthesized. The title compounds exhibit outstanding anti-quorum-sensing efficacy, and compound 7g demonstrated the maximum proficiency (IC50=0.0504μg/ml). The hybrids displayed potent antioxidant action, and compound 7c showed the highest antioxidant ability (IC50=40.71μg/ml). Molecular docking of the isatin hybrids against DNA gyrase and quorum-sensing receptor CviR validated the observed in vitro findings. The befitting pharmacokinetic profile of the synthesized drug candidates was ascertained through absorption, distribution, metabolism, excretion and toxicity screening. Conclusion: The remarkable biocompetence of the synthesized triazinoindoles may help to combat drug-resistant infections.

Discovery of psoralen as a quorum sensing inhibitor suppresses Pseudomonas aeruginosa virulence

Pseudomonas aeruginosa is a common opportunistic pathogen with growing resistance and presents heightened treatment challenges. Quorum sensing (QS) is a cell-to-cell communication system that contributes to the production of a variety of virulence factors and is also related to biofilm formation of P. aeruginosa. Compared to traditional antibiotics which kill bacteria directly, the anti-virulence strategy by targeting QS is a promising strategy for combating pseudomonal infections. In this study, the QS inhibition potential of the compounds derived from the Traditional Chinese Medicines was evaluated by using in silico, in vitro, and in vivo analyses. The results showed that psoralen, a natural furocoumarin compound derived from Psoralea corylifolia L., was capable of simultaneously inhibiting the three main QS regulators, LasR, RhlR, and PqsR of P. aeruginosa. Psoralen had no bactericidal activity but could widely inhibit the production of extracellular proteases, pyocyanin, and biofilm, and the cell motilities of the model and clinical P. aeruginosa strains. RNA-sequencing and quantitative PCR analyses further demonstrated that a majority of QS-activated genes in P. aeruginosa were suppressed by psoralen. The supplementation of psoralen could protect Caenorhabditis elegans from P. aeruginosa challenge, especially for the hypervirulent strain PA14. Moreover, psoralen showed synergistic antibacterial effects with polymyxin B, levofloxacin, and kanamycin. In conclusions, this study identifies the anti-QS and antibiofilm effects of psoralen against P. aeruginosa strains and sheds light on the discovery of anti-pseudomonal drugs among Traditional Chinese Medicines.Key points• Psoralen derived from Psoralea corylifolia L. inhibits the virulence-related phenotypes of P. aeruginosa.• Psoralen simultaneously targets the three core regulators of P. aeruginosa QS system and inhibits the expression of a large part of downstream genes.• Psoralen protects C. elegans from P. aeruginosa challenge and enhances the susceptibility of P. aeruginosa to antibiotics.

Multidimensional Criteria for Virtual Screening of PqsR Inhibitors Based on Pharmacophore, Docking, and Molecular Dynamics.

Pseudomonas aeruginosa is a clinically challenging pathogen due to its high resistance to antibiotics. Quorum sensing inhibitors (QSIs) have been proposed as a promising strategy to overcome this resistance by interfering with the bacterial communication system. Among the potential targets of QSIs, PqsR is a key regulator of quorum sensing in Pseudomonas aeruginosa. However, the current research on PqsR inhibitors is limited by the lack of diversity in the chemical structures and the screening methods. Therefore, this study aims to develop a multidimensional screening model for PqsR inhibitors based on both ligand- and receptor-based approaches. First, a pharmacophore model was constructed from a training set of PqsR inhibitors to identify the essential features and spatial arrangement for the activity. Then, molecular docking and dynamics simulations were performed to explore the core interactions between PqsR inhibitors and their receptor. The results indicate that an effective PqsR inhibitor should possess two aromatic rings, one hydrogen bond acceptor, and two hydrophobic groups and should form strong interactions with the following four amino acid residues: TYR_258, ILE_236, LEU_208, and GLN_194. Moreover, the docking score and the binding free energy should be lower than -8 kcal/mol and -40 kcal/mol, respectively. Finally, the validity of the multidimensional screening model was confirmed by a test set of PqsR inhibitors, which showed a higher accuracy than the existing screening methods based on single characteristics. This multidimensional screening model would be a useful tool for the discovery and optimization of PqsR inhibitors in the future.

Bioprospecting and Exploration of Phytochemicals as Quorum Sensing Inhibitors against Cariogenic Dental Biofilm

Dental caries is a polymicrobial infection affecting the dental hard tissues. Excessive carbohydrate intake leads to the accumulation of acid-producing and acid-resistant microorganisms in the oral region. It is a biofilm-dependent oral infection with cariogenic pathogens and the most prevalent disease globally. The prevention and control of caries play a vital role in global health management. Periodontal diseases and subgingival plaque etiology are due to the combined action of bacterial invasion and immune reaction, resulting in the devastation of periodontal tissues, culminating in tooth loss. The compact micro colony inhabiting the dental surfaces attaches with secreted polymer, forming a biofilm. Bacterial biofilm impervious to various drugs and chemicals poses a significant challenge in therapeutic scenarios of medical and odonatological infections. The quorum-sensing signaling mechanism in bacteria controls the metabolic and physiologic properties involved in bacterial existence, pathogenesis, and virulence. Hence, studies monitoring the molecular mechanism of quorum sensing and their restricted social interactions will be highly beneficial in the treatment regimen of the modern era. Natural bioactive compounds can be exploited for their medicinal value in combating oro-dental infections. Phytochemicals are promising candidates that could provide novel strategies for fighting infections. The current review highlights the mechanism of quorum sensing, plant products’ effect in controlling quorum sensing, and biofilm-induced dental infections like Periodontitis.

Regulation of quorum sensing for the manipulation of conjugative transfer of antibiotic resistance genes in wastewater treatment system

The emergence and transmission of antibiotic resistance genes (ARGs) through plasmid-mediated conjugation has become a significant worldwide public health threat. Biofilms are widely recognized as the primary reservoirs for ARGs, providing favorable conditions for horizontal gene transfer. Quorum sensing (QS) plays a critical role in bacterial biofilm formation, which further influences the spread of bacterial resistance. In this study, we examined the effects of vanillin, a QS inhibitor (QSI), at subinhibitory concentrations (sub-MICs) ranging from 0 – 0.1 g/L, on the transfer of ARGs between Escherichia coli and Pseudomonas aeruginosa. Our findings indicated that vanillin at sub-MICs inhibited the conjugative transfer frequency of the RP4 plasmid. This inhibition was supported by the downregulation of plasmid transfer genes. The suppression of conjugation can mainly be attributed to the inhibition of biofilm formation, the synthesis of extracellular polymeric substances (EPS), and the secretion of virulence factors, all of which are regulated by the bacterial QS system. On the other hand, the levels of ROS and cell membrane permeability were not primary explanations for this phenomenon. Furthermore, vanillin also reduced the conjugative transfer frequency of ARGs in wastewater effluent, providing a potential approach to alleviate bacterial resistance in water environments. These findings underscore the regulatory role of QSI in controlling ARGs transfer and have significant implications for manipulating the dissemination of bacterial resistance in the environment.

Juglone as a Natural Quorum Sensing Inhibitor against Pseudomonas aeruginosa pqs-Mediated Virulence and Biofilms.

Pseudomonas aeruginosa is a notorious opportunistic pathogen associated with chronic biofilm-related infections, posing a significant challenge to effective treatment strategies. Quorum sensing (QS) and biofilm formation are critical virulence factors employed by P. aeruginosa, contributing to its pathogenicity and antibiotic resistance. Other than the homoserine-based QS systems, P. aeruginosa also possesses the quinolone-based Pseudomonas quinolone signal (PQS) QS signaling. Synthesis of the PQS signaling molecule is achieved by the pqsABCDEH operon, whereas the PQS signaling response was mediated by the PqsR receptor. In this study, we report the discovery of a novel natural compound, Juglone, with potent inhibitory effects on pqs QS and biofilm formation in P. aeruginosa. Through an extensive screening of natural compounds from diverse sources, we identified Juglone, a natural compound from walnut, as a promising candidate. We showed that Juglone could inhibit PqsR and the molecular docking results revealed that Juglone could potentially bind to the PqsR active site. Furthermore, Juglone could inhibit pqs-regulated virulence factors, such as pyocyanin and the PQS QS signaling molecule. Juglone could also significantly reduce both the quantity and quality of P. aeruginosa biofilms. Notably, this compound exhibited minimal cytotoxicity toward mammalian cells, suggesting its potential safety for therapeutic applications. To explore the clinical relevance of Juglone, we investigated its combinatorial effects with colistin, a commonly used antibiotic against P. aeruginosa infections. The Juglone-colistin combinatorial treatment could eliminate biofilms formed by wild-type P. aeruginosa PAO1 and its clinical isolates collected from cystic fibrosis patients. The Juglone-colistin combinatorial therapy dramatically improved colistin efficacy and reduced inflammation in a wound infection model, indicating its potential for clinical utility. In conclusion, the discovery of Juglone provides insights into the development of innovative antivirulence therapeutic strategies to combat P. aeruginosa biofilm-associated infections.

Application of Rosette Quorum Sensing Inhibitor in Fish Preservation

This study screened fish derived spoilage bacteria as the research object, and a development approach was used to determine the inhibitory effect of rose polyphenols on the secretion of the quorum sensing (QS) signal molecule N-acyl homoserine lactone (AHLs) by fish spoilage bacteria. The effect of rose QS inhibitors applied to fish preservation coatings on the putrefaction of spoilage bacteria was studied by measuring the changes in texture, pH, and thiobarbituric acid reactive substances (TBARS) during the storage process of fish. The findings demonstrated that the dominant strain causing fish spoilage was Sphingomonaspaucimobilis, and rose polyphenols could significantly inhibit the ability of the spoilage bacteria to secrete AHLs. The application of different concentrations (1 and 2 mg/mL) of rose polyphenols in fish preservation coatings can slow down the growth of TBARS, and 2 mg/mL of rose polyphenols has a better inhibitory effect on the oxidation of fish fat, By measuring the L*, a*, and b* values of different treatment groups, it was found that the addition of rose polyphenols delayed the decrease of L* and the increase of a* value in fish meat, but had no significant effect on b* value, The 2 mg/mL rose polyphenol coating treatment group had the slightest pH change, according on tracking measurements of pH changes during fish storage. The sensory assessment results of fish meat from different treatment groups during storage showed that the 2 mg/mL rose polyphenol treatment group decreased the least among all treatment groups, which means applying it to the fish meat preservation coating can effectively delay the rate of quality decline during storage. The findings of this work may serve as a theoretical foundation for the use of naturally occurring rose polyphenols, a QS inhibitor, in the preservation of fish.

Discovery of Melittin as Triple-Action Agent: Broad-Spectrum Antibacterial, Anti-Biofilm, and Potential Anti-Quorum Sensing Activities.

The development of antibiotic-resistant microorganisms is a major global health concern. Recently, there has been an increasing interest in antimicrobial peptides as a therapeutic option. This study aimed to evaluate the triple-action (broad-spectrum antibacterial, anti-biofilm, and anti-quorum sensing activities) of melittin, a membrane-active peptide present in bee venom. The minimum inhibitory concentration and minimum bactericidal concentration of the melittin were determined using the microdilution method and agar plate counting. Growth curve analysis revealed that melittin showed a concentration-dependent antibacterial activity. Scanning electron microscope analysis revealed that melittin treatment altered the morphology. Confocal laser scanning microscope revealed that melittin increased the membrane permeability and intracellular ROS generation in bacteria, all of which contribute to bacterial cell death. In addition, the crystal violet (CV) assay was used to test the anti-biofilm activity. The CV assay demonstrated that melittin inhibited biofilm formation and eradicated mature biofilms. Biofilm formation mediated by quorum sensing (QS) plays a major role in this regard, so molecular docking and molecular dynamics analysis confirmed that melittin interacts with LasR receptors through hydrogen bonds, and further evaluates the anti-QS activity of melittin through the production of virulence factors (pyocyanin, elastase, and rhamnolipid), exopolysaccharides secretion, and bacterial motility, that may be the key to inhibiting the biofilm formation mechanism. The present findings highlight the promising role of melittin as a broad-spectrum antibacterial, anti-biofilm agent, and potential QS inhibitor, providing a new perspective and theoretical basis for the development of alternative antibiotics.

Ketoprofen attenuates Las/Rhl quorum-sensing (QS) systems of Pseudomonas aeruginosa: molecular and docking studies.

Quorum sensing (QS) is the leading cause of persistent infections and recalcitrance to antibiotic treatment of Pseudomonas aeruginosa. Hence, QS inhibitors are promising agents for the potential treatment of P. aeruginosa infections. Herein, the reducing effect of ketoprofen on virulence factors production including protease, hemolysin, pyocyanin, hydrogen cyanide, biofilm, and motility of P. aeruginosa strains was investigated. Furthermore, the quorum quenching activity of ketoprofen at the molecular level was examined by real-time PCR assessment. Our results showed that ketoprofen significantly attenuates virulence factors and biofilm formation in P. aeruginosa strains. Moreover, ketoprofen down-regulated the expression of lasI, lasR, rhlI, and rhlR genes, by 35-47, 22-48, 34-67, and 43-56%, respectively. As well, molecular docking simulation showed a high binding affinity of ketoprofen with QS regulatory proteins. Consequently, this study confirmed the quorum quenching activity of ketoprofen, which could be employed as a useful agent for the treatment of P. aeruginosa infections.

Inhibition of Pseudomonas aeruginosa quorum sensing by chemical induction of the MexEF-oprN efflux pump.

The cell-to-cell communication system quorum sensing (QS), used by various pathogenic bacteria to synchronize gene expression and increase host invasion potentials, is studied as a potential target for persistent infection control. To search for novel molecules targeting the QS system in the Gram-negative opportunistic pathogen Pseudomonas aeruginosa, a chemical library consisting of 3,280 small compounds from LifeArc was screened. A series of 10 conjugated phenones that have not previously been reported to target bacteria were identified as inhibitors of QS in P. aeruginosa. Two lead compounds (ethylthio enynone and propylthio enynone) were re-synthesized for verification of activity and further elucidation of the mode of action. The isomeric pure Z-ethylthio enynone was used for RNA sequencing, revealing a strong inhibitor of QS-regulated genes, and the QS-regulated virulence factors rhamnolipid and pyocyanin were significantly decreased by treatment with the compounds. A transposon mutagenesis screen performed in a newly constructed lasB-gfp monitor strain identified the target of Z-ethylthio enynone in P. aeruginosa to be the MexEF-OprN efflux pump, which was further established using defined mex knockout mutants. Our data indicate that the QS inhibitory capabilities of Z-ethylthio enynone were caused by the drainage of intracellular signal molecules as a response to chemical-induced stimulation of the MexEF-oprN efflux pump, thereby inhibiting the autogenerated positive feedback and its enhanced signal-molecule synthesis.

The regulation effect of preventing soil nitrogen loss using microbial quorum sensing inhibitors

Preventing soil nitrogen (N) losses driven by microbial nitrification and denitrification contributes to improving global environmental concerns caused by NO3−-N leaching and N2O emission. Quorum sensing (QS) signals regulate nitrification and denitrification of N-cycling bacteria in pure culture and water treatment systems, and mediate the composition of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in activated sludge. However, whether disrupting QS could prevent soil N losses remains unclear. This study explored the feasibility of applying quorum sensing inhibitors (QSIs) as an innovative strategy to reduce N losses from agricultural soils. The two QSIs, penicillic acid and 4-iodo-N-[(3S)-tetrahydro-2-oxo-3-furanyl]-benzeneacetamide (4-iodo PHL), were more effective in reducing N losses than traditional inhibitors, including N-(n-butyl) thiophosphoric triamide and 3,4-dimethylpyrazole phosphate. After 36 days of aerobic incubation, penicillic acid and 4-iodo PHL inhibited nitrification by 39% and 68%, respectively. The inhibitory effects are attributed to the fact that 4-iodo PHL decreased the abundance of archaeal and bacterial amoA genes, as well as the relative abundance of Candidatus Nitrocosmicus (AOA), Candidatus Nitrososphaera (AOA), and Nitrospira (nitrite-oxidizing bacteria/comammox), while penicillic acid reduced archaeal amoA abundance and the relative abundance of Nitrosospira (AOB) and the microbes listed above. Penicillic acid also strongly inhibited denitrification (33%) and N2O emissions (61%) at the peak of N2O production (day 4 of anaerobic incubation) via decreasing nitrate reductase gene (narG) abundance and increasing N2O reductase gene (nosZ) abundance, respectively. Furthermore, the environmental risks of QSIs to microbial community structure and network stability, CO2 emissions, and soil animals were acceptable. Overall, QSIs have application potential in agriculture to reduce soil N losses and the associated effect on climate change. This study established a new method to mitigate N losses from the perspective of QS, and can serve as important basis of decreasing the environmental risks of agricultural non-point source pollution.

Embelia ribes Burm.f. fruit extract inhibit quorum sensing-dependent production of virulence factors and biofilm formation: An integrated in vitro and in silico approach

Quorum sensing (QS) is a cell-to-cell signaling method that allows bacteria to control gene expression and regulate a variety of physiological processes, particularly the synthesis of virulence factors and biofilm formation. Inhibition of QS has been proposed as a promising strategy in attenuating the pathogenicity and enhancing the efficacy of antimicrobial drugs targeting bacterial infections. This study investigated the potential utilization of Embelia ribes fruit extract (ERFE) as an inhibitor of QS-dependent virulence factors and biofilm development in Gram negative pathogens. Further, the results were correlated with the inhibition of biofilms. High performance thin-layer chromatography (HPTLC), followed by analysis of phytochemicals using gas chromatography-mass spectrometry (GC–MS) was conducted. Analyzing ADMET (absorption, distribution, metabolism, excretion and toxicity) profiles, PAINS (Pan-assay interference compounds), and molecular docking analyses of selected potential phytochemicals were performed against proteins participating in QS and formation of biofilm. In-vitro analysis of anti-QS activity of ERFE against Chromobacterium violaceum (violacein production), Pseudomonas aeruginosa (pyocyanin production) and Serratia marcescens (prodigiosin production) demonstrated significant dose-dependent interference in pigment formation at sub-MIC concentrations. The development of biofilm was significantly reduced by 84.10, 85.52 and 70.64% over control at the highest sub-MIC levels for C. violaceum, P. aeruginosa and S. marcescens, respectively. Furthermore, in the presence of ERFE, swarming motility and exopolysaccharide production (EPS) were also reduced. As a result, further insights have been gained into the mechanism underlying the anti-QS activity. Further investigations with in-vivo studies are warranted to fully explore the therapeutic applications of this natural compound in managing the bacterial pathogenicity and biofilm-related infections.

Methyl gallate from Camellia nitidissima Chi flowers reduces quorum sensing related virulence and biofilm formation against Aeromonas hydrophila

Aeromonas hydrophila, a Gram-negative zoonotic bacterium, causes high mortality in fish farming and immunocompromised patients. This study aimed to extract methyl gallate (MG) from the flowers of Camellia nitidissima Chi and evaluate its potential as a quorum sensing inhibitor (QSI) against Aeromonas hydrophila SHAe 115. MG reduced QS-associated virulence factors, including hemolysis, protease, and lipase, while impairing swimming motility and biofilm formation. Additionally, MG down-regulated positive regulatory genes (ahyR, fleQ) and up-regulated negative regulators (litR, fleN). This highlights MG's promise as a potent QSI for A. hydrophila SHAe 115, advancing strategies against infections in aquaculture and human health.

Acute toxicity of binary mixtures for quorum sensing inhibitors and sulfonamides against Aliivibrio fischeri: QSAR investigations and joint toxic actions

Quorum sensing inhibitors (QSIs), as a kind of ideal antibiotic substitutes, have been recommended to be used in combination with traditional antibiotics in medical and aquaculture fields. Due to the co-existence of QSIs and antibiotics in environmental media, it is necessary to evaluate their joint risk. However, there is little information about the acute toxicity of mixtures for QSIs and antibiotics. In this study, 10 QSIs and 3 sulfonamides (SAs, as the representatives for traditional antibiotics) were selected as the test chemicals, and their acute toxic effects were determined using the bioluminescence of Aliivibrio fischeri (A. fischeri) as the endpoint. The results indicated that SAs and QSIs all induced S-shaped dose-responses in A. fischeri bioluminescence. Furthermore, SAs possessed greater acute toxicity than QSIs, and luciferase (Luc) might be the target protein of test chemicals. Based on the median effective concentration (EC50) for each test chemical, QSI-SA mixtures were designed according to equitoxic (EC50(QSI):EC50(SA) = 1:1) and non-equitoxic ratios (EC50(QSI):EC50(SA) = 1:10, 1:5, 1:0.2, and 1:0.1). It could be observed that with the increase of QSI proportion, the acute toxicity of QSI-SA mixtures enhanced while the corresponding TU values decreased. Furthermore, QSIs contributed more to the acute toxicity of test binary mixtures. The joint toxic actions of QSIs and SAs were synergism for 23 mixtures, antagonism for 12 mixtures, and addition for 1 mixture. Quantitative structure–activity relationship (QSAR) models for the acute toxicity QSIs, SAs, and their binary mixtures were then constructed based on the lowest CDOCKER interaction energy (Ebind-Luc) between Luc and each chemical and the component proportion in the mixture. These models exhibited good robustness and predictive ability in evaluating the toxicity data and joint toxic actions of QSIs and SAs. This study provides reference data and applicable QSAR models for the environmental risk assessment of QSIs, and gives a new perspective for exploring the joint effects of QSI-antibiotic mixtures.

Identification of novel phenylalanine derivatives bearing a hydroxamic acid moiety as potent quorum sensing inhibitors.

Phenylalanine derivatives are a well-known small moiety responsible for controlling the virulence factors of several bacteria. Herein, for the first time, we report novel structures of phenylalanine derivatives bearing a hydroxamic acid moiety which were designed, synthesized, and evaluated for use as quorum sensing inhibitors. Biological results reveal that six compounds showed good quorum sensing inhibitors properties with an IC50 ranging from 7.12 ± 2.11 μM-92.34 ± 2.09 μM (4NPO, a reference compound, IC50 = 29.13 ± 0.88 μM). In addition, three out of the six compounds (4a, 4c, 4h) showed strong anti-biofilm formation and CviR inhibitory activity when compared to that of 4NPO. These biological data were also confirmed by computational studies. In this series of compounds, 4h is the most promising compound for future drug development targeting quorum sensing. Our results concluded that the fragment-based drug design is a good approach for the discovery of novel quorum-sensing inhibitors in the future.

Triblock copolymer micelles enhance solubility, permeability and activity of a quorum sensing inhibitor against Pseudomonas aeruginosa biofilms.

Antimicrobial resistance is a threat to public health for which new treatments are urgently required. The capability of bacteria to form biofilms is of particular concern as it enables high bacterial tolerance to conventional therapies by reducing drug diffusion through the dense, exopolymeric biofilm matrix and the upregulation of antimicrobial resistance machinery. Quorum sensing (QS), a process where bacteria use diffusible chemical signals to coordinate group behaviour, has been shown to be closely interconnected with biofilm formation and bacterial virulence in many top priority pathogens including Pseudomonas aeruginosa. Inhibition of QS pathways therefore pose an attractive target for new therapeutics. We have recently reported a new series of pqs quorum sensing inhibitors (QSIs) that serve as potentiators for antibiotics in P. aeruginosa infections. The impact on biofilms of some reported QSIs was however hindered by their poor penetration through the bacterial biofilm, limiting the potential for clinical translation. In this study we developed a series of poly(β-amino ester) (PBAE) triblock copolymers and evaluated their ability to form micelles, encapsulate a QSI and enhance subsequent delivery to P. aeruginosa biofilms. We observed that the QSI could be released from polymer micelles, perturbing the pqs pathway in planktonic P. aeruginosa. In addition, one of the prepared polymer variants increased the QSIs efficacy, leading to an enhanced potentiation of ciprofloxacin (CIP) action and therefore improved reduction in biofilm viability, compared to the non-encapsulated QSI. Thus, we demonstrate QSI encapsulation in polymeric particles can enhance its efficacy through improved biofilm penetration.

Inhibition of Quorum Sensing to Mitigate the Risks of Membrane Biofouling in Biological Wastewater Treatment

Membrane-based systems play a pivotal role in various applications, providing efficient separation, purification, and filtration processes across diverse industries such as water purification and desalination. However, this system faces major challenge of membrane biofouling impacting the efficiency and sustainability of such systems. Biofouling occurs when various microorganisms like bacteria, fungi, etc. adheres to the surface of membrane and form biofilm which results in reducing membrane permeability and increasing its operational cost. Various physical, chemical and biological strategies are known to prevent biofouling. Inhibition of quorum sensing is a recent trend based on the researches that shows quorum sensing as an integral part of biofilm formation. Bacteria’s uses cell to cell communication mechanisms known as Quorum sensing, plays an important role in formation of virulence factors, biofilm. It is regulated by quorum sensing signalling molecules known as autoinducers like Autoinducing peptides, acyl homoserine lactones, Autoinducer-2. Various strategies can be adopted to inhibit quorum sensing: inhibition of Autoinducer synthase which is responsible for synthesizing autoinducers; inhibition/degradation of autoinducers and interfering with signal receptors. This article provides deeper knowledge of Quorum sensing (QS), methods of QS inhibition: Quorum quenching which involves the enzymatic degradation of QS signaling molecules, and the use of Quorum sensing inhibitor compounds in preventing membrane biofouling are discussed in detail. This article delves into the potential of disrupting quorum sensing pathways to prevent or reduce biofilm formation, thereby enhancing the performance and longevity of membranes in wastewater treatment. The mitigation of biofouling can revolutionize membrane-based systems, ensuring their sustainability and efficacy in water treatment processes

Discovery and evaluation of 3-(2-isocyanobenzyl)-1H-indole derivatives as potential quorum sensing inhibitors for the control of Pseudomonas aeruginosa infections in vitro.

Quorum sensing (QS) inhibition stands out as an innovative therapeutic strategy for combating infections caused by drug-resistant pathogens. In this study, we assessed the potential of 3-(2-isocyanobenzyl)-1H-indole derivatives as novel quorum sensing inhibitors (QSIs). Initial screenings of their QS inhibitory activities were conducted against Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum CV026. Notably, six 3-(2-isocyanobenzyl)-1H-indole derivatives (4, 12, 25, 28, 32, and 33) exhibited promising QS, biofilms, and pyocyanin inhibitory activities under minimum inhibitory concentrations (MICs) against P. aeruginosa PAO1. Among them, 3-(2-isocyano-6-methylbenzyl)-1H-indole (IMBI, 32) emerged as the most promising candidate, demonstrating superior biofilm and pyocyanin inhibition. Further comprehensive studies revealed that derivative 32 at 25 μg mL-1 inhibited biofilm formation by 70% against P. aeruginosa PAO1, as confirmed by scanning electron microscopy (SEM). Additionally, derivative 32 substantially increased the susceptibility of mature biofilms, leading to a 57% destruction of biofilm architecture. In terms of interfering with virulence factors in P. aeruginosa PAO1, derivative 32 (25 μg mL-1) displayed remarkable inhibitory effects on pyocyanin, protease, and extracellular polysaccharides (EPS) by 73%, 51%, and 37%, respectively, exceeding the positive control resveratrol (RSV). Derivative 32 at 25 μg mL-1 also exhibited effective inhibition of swimming and swarming motilities. Moreover, it downregulated the expressions of QS-related genes, including lasI, lasR, rhlI, rhlR, pqsR, sdhB, sucD, sodB, and PA5439, by 1.82- to 10.87-fold. Molecular docking, molecular dynamics simulations (MD), and energy calculations further supported the stable binding of 32 to LasR, RhlI, RhlR, EsaL, and PqsR antagonizing the expression of QS-linked traits. Evaluation of the toxicity of derivative 32 on HEK293T cells via CCK-8 assay demonstrated low cytotoxicity. Overall, this study underscores the efficacy of derivative 32 in inhibiting virulence factors in P. aeruginosa. Derivative 32 emerges as a potential QSI for controlling P. aeruginosa PAO1 infections in vitro and an anti-biofilm agent for restoring or enhancing drug sensitivity in drug-resistant pathogens.

Quorum sensing inhibition activities of Philippine ethnobotanicals against multidrug-resistant pathogens

Alternative therapeutic approaches to target microbial multidrug resistance (MDR) have become an important thrust in research. One potential approach to manage antibiotic resistance and pathogenicity in MDR pathogens is through targeting quorum sensing (QS). Blocking the QS system does not affect bacterial growth while preventing bacteria from triggering virulence, reducing pathogenicity and selective pressure to survive, hence, reducing the resistance evolution. Recent ethnopharmacological research highlights the prospects of Philippine ethnobotanicals to discover novel molecules and approaches for targeting the QS system to control diseases and pathogens. In this review, two sets of Philippine ethnobotanicals utilized by ethnic communities - Ikalahan and Ilongot-E?ongot – are highlighted as QS inhibitors. Inhibition of QS-linked virulence factor production such as violacein, biofilm, DNase, α-Hemolysin, swarming motility and coagulase in MDR pathogens Pseudomonas aeruginosa, Staphylococcus aureus, Aeromonas hydrophila, Streptococcus agalactiae, Candida albicans and one QS reporter bacteria, Chromobacterium violaceum by the ethnobotanical extracts are presented. All Philippine ethnobotanicals from the two ethnic communities included in this review showed inhibition on one or more virulence factors highlighting their activities against QS and emphasizes their potential for in-depth research on QS-based drug development for antipathogenesis.