It is the time for quorum sensing inhibition as alternative strategy of antimicrobial therapy

From quorum sensing inhibition to antimicrobial defense: The dual role of eugenol-gold nanoparticles against carbapenem-resistant Pseudomonas aeruginosa

To address the pressing challenge of antibiotic resistance, particularly the robust defense mechanisms of Pseudomonas aeruginosa (P. aeruginosa) against conventional antibiotics, this study employs nanotechnology to enhance antimicrobial efficacy while ensuring good biocompatibility with the host. In this study, gold nanoparticles were chemically decorated with eugenol, a phenol-rich natural compound, using a one-pot synthesis method. The successful synthesis and functionalization of eugenol-decorated gold nanoparticles (Eugenol_Au NPs) were validated by comprehensive physicochemical analyses, demonstrating their stability and biocompatibility. These nanoparticles exhibited potent antimicrobial activity against both planktonic and biofilm-embedded carbapenem-resistant P. aeruginosa strains. Eugenol_Au NPs disrupted the bacterial quorum sensing system and stimulated intracellular reactive oxygen species production, which enhance their antibacterial effects. This dual mechanism of action has promising clinical implications for the treatment of infections associated with antibiotic-resistant P. aeruginosa. In vivo assessments in a murine peritoneal infection model showed that Eugenol_Au NPs significantly reduced bacterial loads and mitigated inflammatory responses, thereby improving survival rates. The study highlights the potential of Eugenol_Au NPs as an alternative strategy for refractory infections caused by carbapenem-resistant P. aeruginosa, and underscores the feasibility and promise of further clinical research and development of new therapeutic approaches targeting this resistant pathogen.

Molecular modelling and experimental validation of mangiferin and its related compounds as quorum sensing modulators of Pseudomonas aeruginosa

The LasR quorum sensing system regulates the virulence factors of Pseudomonas aeruginosa, a multi-drug resistant pathogen. Mangiferin and related compounds have been found to modulate this system as determined by in silico and in vitro experimental procedures. ZINCPharmer was used to compile a library of over 1000 metabolites that were screened to the top five based on shared pharmacophores and drug-like properties with mangiferin. Molecular docking and molecular dynamics simulation (140 ns) showed that ZINC E (- 55.64 ± 2.93 kcal/mol) and ZINC D (- 54.51 ± 2.82 kcal/mol) had significantly lower binding free energy compared to mangiferin-LasR (- 42.24 ± 3.94 kcal/mol) and the reference standard (azithromycin-LasR (- 40.01 ± 6.15 kcal/mol). ZINC D (95.16%) competed favorably with mangiferin (95.77%) as potential QS modulators at sub-minimum inhibitory concentrations relative to ZINC E (85.07%) and azithromycin (85.79%). These observations suggest mangiferin and related lead compounds as potential drug candidates for P. aeruginosa infection management.

Targeting AI-2 quorum sensing: harnessing natural products against Streptococcus suis biofilm infection

The biofilm acts as a protective layer for Streptococcus suis (S. suis), contributing to the development of drug resistance and chronic infections. Autoinducer 2 (AI-2) quorum sensing represents the primary regulatory pathway governing biofilm formation in S. suis. Consequently, targeting AI-2 quorum sensing to inhibit biofilm formation represents a promising strategy for preventing and managing drug resistance and chronic infections caused by S. suis. This study established a small natural product library by integrating commercial drug molecules with Chinese herbal medicine molecules. Consequently, two natural products, salvianolic acid A (SAA) and rhapontin (RH), which target S. suis AI-2 via quorum sensing, were identified. SAA and RH inhibit AI-2 synthesis through noncompetitive and competitive binding to S-ribosylhomocysteinase (LuxS). By inhibiting S. suis AI-2 quorum sensing, these compounds modulate the expression of adhesion genes and the synthesis of extracellular polysaccharides (EPS), reducing the adhesion ability of S. suis and ultimately inhibiting biofilm formation. Using LC‒MS/MS, we further analysed the impact of SAA and RH on the metabolic activity of S. suis, revealing the potential medicinal value of these compounds. Finally, the efficacy of SAA and RH against S. suis infection was validated in Galleria mellonella larvae, confirming their significant anti-infection effects.

Evaluation of ampicillin plus ceftobiprole combination therapy in treating Enterococcus faecalis infective endocarditis and bloodstream infection

Enterococcus faecalis is responsible for numerous serious infections, and treatment options often include ampicillin combined with an aminoglycoside or dual beta-lactam therapy with ampicillin and a third-generation cephalosporin. The mechanism of dual beta-lactam therapy relies on the saturation of penicillin-binding proteins (PBPs). Ceftobiprole exhibits high affinity binding to nearly all E. faecalis PBPs, thus suggesting its potential utility in the treatment of severe E. faecalis infections. The availability of therapeutic drug monitoring (TDM) for ampicillin and ceftobiprole has prompted the use of this drug combination in our hospital. Due to the time-dependent antimicrobial properties of these antibiotics, an infusion administration longer than indicated was chosen. From January to December 2020, twenty-one patients were admitted to our hospital for severe E. faecalis infections and were treated with this approach. We retrospectively analyzed their clinical characteristics and pharmacological data. Most patients achieved an aggressive PK/PD target (T > 4-8 minimum inhibitory concentration, MIC) when this alternative drug combination regimen was used. Our analysis included the study of E. faecalis biofilm production, as well as the kinetics of bacterial killing of ceftobiprole alone or in combination with ampicillin. Time-kill experiments revealed strong bactericidal activity of ceftobiprole alone at concentrations four times higher than the MIC for some enterococcal strains. In cases where a bactericidal effect of ceftobiprole alone was not evident, synergism with ampicillin and bactericidal activity were demonstrated instead. The prolonged infusion of ceftobiprole, either alone or with ampicillin, emerges as a valuable option for the treatment of severe invasive E. faecalis infections.

Breaking the Phalanx: Overcoming Bacterial Drug Resistance with Quorum Sensing Inhibitors that Enhance Therapeutic Activity of Antibiotics

Antibiotic-resistant bacterial infections loom over humanity as an increasing deadly threat. There exists a dire need for new treatments, especially those that synergize with our existing arsenal of antibiotic drugs to help overcome the gap in antibiotic efficacy and attenuate the development of new antibiotic-resistance in the most dangerous pathogens. Quorum sensing systems in bacteria drive the formation of biofilms, increase surface motility, and enhance other virulence factors, making these systems attractive targets for the discovery of novel antibacterials. Quorum sensing inhibitors (QSIs) are hypothesized to synergize with existing antibiotics, making bacteria more sensitive to the effects of these drugs. In this study, we aimed to find the synergistic combinations between the QSIs and known antibiotics to combat the two deadliest hospital infections - Pseudomonas aeruginosa and Acinetobacter baumannii. We mined biochemical activity databases and literature to identify known, high efficacy QSIs against these bacteria. We used these data to develop and validate a Quantitative Structure-Activity Relationship (QSAR) model for predicting QSI activity and then employed this model to identify new potential QSIs from the Inxight database of approved and investigational drugs. We then tested binary mixtures of the identified QSIs with 11 existing antibiotics using a combinatorial matrix screening approach with ten (five of each) clinical isolates of P. aeruginosa and A. baumannii . Amongst explored drug combinations, 31 exhibited a synergistic effect, including mixtures involving naldemedine and telotristat, two drugs predicted by our model with previously undescribed QSI activity. Although no mixture inhibiting all the strains was found, piperacillin combined with curcumin, ketoprofen, indomethacin, and piroxicam demonstrated the broadest antimicrobial action. We anticipate that further preclinical investigation of these combinations of novel repurposed QSIs with a known antibiotic may lead to novel clinical candidates.

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Contribution of the infection ecosystem and biogeography to antibiotic failure in vivo

The acquisition of antibiotic resistance in bacteria, though a deeply concerning international issue, is reasonably well-understood at a mechanistic level. Less well-understood is why bacteria that are sensitive in vitro to well-established and widely-used antibiotics sometimes fail to respond to these agents in vivo. This is a particularly common problem in chronic, polymicrobial infection scenarios. Here, we discuss this in vitro-in vivo disconnect from the perspective of the bacterium, focusing in particular on how infection micro/macro-environment, biogeography, and the presence of co-habiting species affect the response to antibiotics. Using selected exemplars, we also consider interventions that might improve treatment outcomes, as well as ecologically 'eubiotic' approaches that have less of an impact on the patient's commensal microflora. In our view, the accrued data strongly suggest that we need a more comprehensive understanding of the in situ microbiology at infection sites.

Advancing Anti-Biofilm Strategies: Innovations to Combat Biofilm-Related Challenges and Enhance Efficacy

Biofilms are complex communities of microorganisms that can cause significant challenges in various settings, including industrial processes, environmental systems, and human health. The protective nature of biofilms makes them resistant to traditional anti-biofilm strategies, such as chemical agents, mechanical interventions, and surface modifications. To address the limitations of conventional anti-biofilm methods, researchers have explored emerging strategies that encompass the use of natural compounds, nanotechnology-based methods, quorum-sensing inhibition, enzymatic degradation, and antimicrobial photodynamic/sonodynamic therapy. There is an increasing focus on combining multiple anti-biofilm strategies to combat resistance and enhance effectiveness. Researchers are continuously investigating the mechanisms of biofilm formation and developing innovative approaches to overcome the limitations of conventional anti-biofilm methods. These efforts aim to improve the management of biofilms and prevent infections while preserving the environment. This study provides a comprehensive overview of the latest advancements in anti-biofilm strategies. Given the dynamic nature of this field, exploring new approaches is essential to stimulate further research and development initiatives. The effective management of biofilms is crucial for maintaining the health of industrial processes, environmental systems, and human populations.

Cyclic Diguanylate G-Quadruplex Inducer-Quorum Sensing Inhibitor Hybrids as Bifunctional Anti-biofilm and Anti-virulence Agents Against Pseudomonas aeruginosa

The release of virulence factors and biofilm formation by Pseudomonas aeruginosa are pivotal drivers of its severe pathogenicity and antibiotic resistance. Based on our prior findings, cyclic di-GMP (c-di-GMP) G-quadruplex inducers are promising biofilm inhibitors and that quorum sensing systems are central regulators of virulence, we aimed to design and synthesize c-di-GMP G-quadruplex inducer-quorum sensing inhibitor hybrids. These hybrids were envisioned as bifunctional agents with both antibiofilm and antivirulence capabilities. Hybrids A7 and A11, characterized by their quinoline and 3-indole rings, emerged as potent inhibitors. They achieve this dual action by inducing c-di-GMP G-quadruplex formation and disrupting the las and pqs signaling system. Additionally, hybrids A7 and A11 attenuated virulence factors and inhibited the motility phenotypes of P. aeruginosa. Furthermore, when tested in in vivo Caenorhabditis elegans infection models, these hybrids, in combination with antibiotics such as tetracycline, improved survival rates, all while maintaining a favorable biosafety profile.

An insight on the powerful of bacterial quorum sensing inhibition

Bacteria have their own language through which they communicate with one another like all higher organisms. So, many researchers are working hard to identify and comprehend the components of this bacterial communication, known as quorum sensing (QS). In quorum sensing, bacteria use signaling molecules called autoinducers (AIs) to exchange information. Many natural compounds and extraction techniques have been intensively studied to disrupt bacterial signaling and examine their effectiveness for bacterial pathogenesis control. Quorum sensing inhibitors can interfere with QS and block the action of AI signaling molecules. Recent research indicates that quorum sensing inhibitors (QSIs) and quorum quenching enzymes (QQEs) show great promise in reducing the pathogenicity of bacteria and inhibiting biofilm synthesis. In addition, the effectiveness of QQEs and QSIs in experimental animal models was demonstrated. These are taken into account in the development of innovative medical devices, such as dressings and catheters, to prevent bacterial infections. The present review highlights this aspect with a prospective vision for its development and application.

Modulation of Vibrio cholerae gene expression through conjugative delivery of engineered regulatory small RNAs

The increase in antibiotic resistance in bacteria has prompted the efforts in developing new alternative strategies for pathogenic bacteria. We explored the feasibility of targeting Vibrio cholerae by neutralizing bacterial cellular processes rather than outright killing the pathogen. We investigated the efficacy of delivering engineered regulatory small RNAs (sRNAs) to modulate gene expression through DNA conjugation. As a proof of concept, we engineered several sRNAs targeting the type VI secretion system (T6SS), several of which were able to successfully knockdown the T6SS activity at different degrees. Using the same strategy, we modulated exopolysaccharide production and motility. Lastly, we delivered an sRNA targeting T6SS into V. cholerae via conjugation and observed a rapid knockdown of the T6SS activity. Coupling conjugation with engineered sRNAs represents a novel way of modulating gene expression in V. cholerae opening the door for the development of novel prophylactic and therapeutic applications.

IMPORTANCE

Given the prevalence of antibiotic resistance, there is an increasing need to develop alternative approaches to managing pathogenic bacteria. In this work, we explore the feasibility of modulating the expression of various cellular systems in Vibrio cholerae using engineered regulatory sRNAs delivered into cells via DNA conjugation. These sRNAs are based on regulatory sRNAs found in V. cholerae and exploit its native regulatory machinery. By delivering these sRNAs conjugatively along with a real-time marker for DNA transfer, we found that complete knockdown of a targeted cellular system could be achieved within one cell division cycle after sRNA gene delivery. These results indicate that conjugative delivery of engineered regulatory sRNAs is a rapid and robust way of precisely targeting V. cholerae.

Critical review on plant-derived quorum sensing signaling inhibitors in pseudomonas aeruginosa

Pseudomonas aeruginosa, a biofilm-forming organism with complex quorum mechanisms (Las, Rhl, PQS, and IQS), poses an imminent danger to the healthcare sector and renders current treatment options for chemotherapy ineffectual. The pathogen's diverse pathogenicity, antibiotic resistance, and biofilms make it difficult to eradicate it effectively. Quorum sensing, a complex system reliant on cell density, controls P. aeruginosa's pathogenesis. Quorum-sensing genes are key components of P. aeruginosa's pathogenic arsenal, and their expression determines how severe the spread of infection becomes. Over the past ten years, there has been a noticeable increase in the quest for and development of new antimicrobial medications. Quorum sensing may be an effective treatment for infections triggered by bacteria. Introducing quorum-sensing inhibitors as an anti-virulent strategy might be an intriguing therapeutic method that can be effectively employed along with current medications. Amongst the several speculated processes, a unique anti-virulence strategy using anti-quorum sensing and antibiofilm medications for targeting pseudomonal infestations seems to be at the forefront. Due to their noteworthy quorum quenching capabilities, biologically active phytochemicals have become more well-known in the realm of science in this context. Recent research showed how different phytochemical quorum quenching actions affect P. aeruginosa's QS-dependent pathogenicity. This review focuses on the most current data supporting the implementation of plant bio-actives to treat P.aeruginosa-associated diseases, as well as the benefits and future recommendationsof employing them in anti-virulence therapies as a supplementary drug development approach towards conventional antibiotic approaches.

Theophylline as a quorum sensing and biofilm inhibitor in Pseudomonas aeruginosa and Chromobacterium violaceum

Quorum sensing (QS) is pivotal in coordinating virulence factors and biofilm formation in various pathogenic bacteria, making it a prime target for disrupting bacterial communication. Pseudomonas aeruginosa is a member of the "ESKAPE" group of bacterial pathogens known for their association with antimicrobial resistance and biofilm formation. The current antibiotic arsenal falls short of addressing biofilm-related infections effectively, highlighting the urgent need for novel therapeutic agents. In this study, we explored the anti-QS and anti-biofilm properties of theophylline against two significant pathogens, Chromobacterium violaceum and P. aeruginosa. The production of violacein, pyocyanin, rhamnolipid, and protease was carried out, along with the evaluation of biofilm formation through methods including crystal violet staining, triphenyl tetrazolium chloride assay, and fluorescence microscopy. Furthermore, computational analyses were conducted to predict the targets of theophylline in the QS pathways of P. aeruginosa and C. violaceum. Our study demonstrated that theophylline effectively inhibits QS activity and biofilm formation in C. violaceum and P. aeruginosa. In P. aeruginosa, theophylline inhibited the production of key virulence factors, including pyocyanin, rhamnolipid, protease, and biofilm formation. The computational analyses suggest that theophylline exhibits robust binding affinity to CviR in C. violaceum and RhlR in P. aeruginosa, key participants in the QS-mediated biofilm pathways. Furthermore, theophylline also displays promising interactions with LasR and QscR in P. aeruginosa. Our study highlights theophylline as a versatile anti-QS agent and offers a promising avenue for future research to develop novel therapeutic strategies against biofilm-associated infections.

Vascular catheter-related infections: an endemic disease in healthcare institutions. An opinion paper of the Spanish Society of Cardiovascular Infections (SEICAV)

Catheter-related infections (CRI) are a serious healthcare problem due to their potential to cause serious complications, including bacteraemia or infective endocarditis, and to increase patient morbidity and mortality. In addition, these in fections significantly prolong hospital stay and cost. Preventing CRI is crucial and is considered a criterion for quality and safety in healthcare. For these reasons, the Spanish Society of Cardiovascular Infections (SEICAV) has considered it pertinent to review this topic, with experts in different areas including clinical microbiologists, infectious disease specialists, surgeons and nurses. The data were presented at a session held at the Ramón Areces Foundation, which was organised in the form of specific questions grouped into three round tables. The first panel analysed the scale of the problem including epidemiological, clinical and diagnostic aspects; the second panel addressed advances in the treatment of CRI; and the third panel reviewed developments in the prevention of CRI. The recorded session is available on the Areces Foundation website and we believe it maybe of interest not only to health professionals, but also to any non-expert citizen interested in the subject.

Beyond Antibiotics: What the Future Holds

The prevalence of multidrug resistance (MDR) and stagnant drug-development pipelines have led to the rapid rise of hard-to-treat antibiotic-resistant bacterial infections. These infectious diseases are no longer just nosocomial but are also becoming community-acquired. The spread of MDR has reached a crisis level that needs immediate attention. The landmark O'Neill report projects that by 2050, mortality rates associated with MDR bacterial infections will surpass mortality rates associated with individuals afflicted with cancer. Since conventional antimicrobials are no longer very reliable, it is of great importance to investigate different strategies to combat these life-threatening infectious diseases. Here, we provide an overview of recent advances in viable alternative treatment strategies mainly targeting a pathogen's virulence capability rather than viability. Topics include small molecule and immune inhibition of virulence factors, quorum sensing (QS) quenching, inhibition of biofilm development, bacteriophage-mediated therapy, and manipulation of an individual's macroflora to combat MDR bacterial infections.

Falcaria vulgaris extract: A mixture of quorum sensing inhibitors for controlling Pectobacterium carotovorum subsp. carotovorum

A promising strategy to control bacterial diseases involves using Quorum Sensing Inhibitor (QSI) compounds. This study aimed to evaluate the potential of Falcaria vulgaris plant extract to combat the phytopathogenic Pectobacterium carotovorum subsp. carotovorum (Pcc) via its QSI activity. Using biosensors and Minimum Inhibitory Concentration (MIC) assays, the QSI and antimicrobial aspects of the extract were assessed. Furthermore, the effect of the extract on the reduction of tuber maceration in potatoes was examined. Subsequently, homology modeling based on LasR was conducted to analyze interactions between ligand 3-oxo-C8-AHL, and ExpR2 protein. Docking studies were performed on all extract compounds identified via Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The extract effectively reduced maceration at sub-MIC concentrations across various pathogenic strains. Furthermore, Cyclopentadecanone, 2-hydroxy, showed more negative docking energy than the native ligand. Z,E-2,13-Octadecadien-1-ol showed energy equivalence to the native ligand. Additionally, this plant included certain compounds or their analogs that had previously been discovered as QSI compounds. These compounds included oleic acid, n-Hexadecanoic acid, cytidine, and linoleic acid, and they had energies that were comparable to that of the native ligand. In conclusion, the remarkable QSI property showed by this plant is likely attributed to a combination of compounds possessing this characteristic.

Quorum Sensing Inhibitors: An Alternative Strategy to Win the Battle against Multidrug-Resistant (MDR) Bacteria

Antibiotic resistance is a major problem and a major global health concern. In total, there are 16 million deaths yearly from infectious diseases, and at least 65% of infectious diseases are caused by microbial communities that proliferate through the formation of biofilms. Antibiotic overuse has resulted in the evolution of multidrug-resistant (MDR) microbial strains. As a result, there is now much more interest in non-antibiotic therapies for bacterial infections. Among these revolutionary, non-traditional medications is quorum sensing inhibitors (QSIs). Bacterial cell-to-cell communication is known as quorum sensing (QS), and it is mediated by tiny diffusible signaling molecules known as autoinducers (AIs). QS is dependent on the density of the bacterial population. QS is used by Gram-negative and Gram-positive bacteria to control a wide range of processes; in both scenarios, QS entails the synthesis, identification, and reaction to signaling chemicals, also known as auto-inducers. Since the usual processes regulated by QS are the expression of virulence factors and the creation of biofilms, QS is being investigated as an alternative solution to antibiotic resistance. Consequently, the use of QS-inhibiting agents, such as QSIs and quorum quenching (QQ) enzymes, to interfere with QS seems like a good strategy to prevent bacterial infections. This review sheds light on QS inhibition strategy and mechanisms and discusses how using this approach can aid in winning the battle against resistant bacteria.

Quercetin disrupts biofilm formation and attenuates virulence of Aeromonas hydrophila

Aeromonas hydrophila poses significant health and economic challenges in aquaculture owing to its pathogenicity and prevalence. Overuse of antibiotics has led to multidrug resistance and environmental pollution, necessitating alternative strategies. This study investigated the antibacterial and antibiofilm potentials of quercetin against A. hydrophila. Efficacy was assessed using various assays, including antibacterial activity, biofilm inhibition, specific growth time, hemolysis inhibition, autoaggregation, and microscopic evaluation. Additionally, docking analysis was performed to explore potential interactions between quercetin and virulence proteins of A. hydrophila, including proaerolysin, chaperone needle-subunit complex of the type III secretion system, and alpha-pore forming toxin (PDB ID: 1PRE, 2Q1K, 6GRK). Quercetin exhibited potent antibacterial activity with 21.1 ± 1.1 mm zone of inhibition at 1.5 mg mL-1. It also demonstrated significant antibiofilm activity, reducing biofilm formation by 46.3 ± 1.3% at the MIC and attenuating autoaggregation by 55.9 ± 1.5%. Hemolysis was inhibited by 41 ± 1.8%. Microscopic analysis revealed the disintegration of the A. hydrophila biofilm matrix. Docking studies indicated active hydrogen bond interactions between quercetin and the targeted virulence proteins with the binding energy -3.2, -5.6, and -5.1 kcal mol⁻1, respectively. These results suggest that quercetin is an excellent alternative to antibiotics for combating A. hydrophila infection in aquaculture. The multifaceted efficacy of quercetin in inhibiting bacterial growth, biofilm formation, virulence factors, and autoaggregation highlights the potential for aquaculture health and sustainability. Future research should delve into the precise mechanisms of action and explore synergistic combinations with other compounds for enhanced efficacy and targeted interventions.

Relevance of the Adjuvant Effect between Cellular Homeostasis and Resistance to Antibiotics in Gram-Negative Bacteria with Pathogenic Capacity: A Study of Klebsiella pneumoniae

Antibiotic resistance has become a global issue. The most significant risk is the acquisition of these mechanisms by pathogenic bacteria, which can have a severe clinical impact and pose a public health risk. This problem assumes that bacterial fitness is a constant phenomenon and should be approached from an evolutionary perspective to develop the most appropriate and effective strategies to contain the emergence of strains with pathogenic potential. Resistance mechanisms can be understood as adaptive processes to stressful conditions. This review examines the relevance of homeostatic regulatory mechanisms in antimicrobial resistance mechanisms. We focus on the interactions in the cellular physiology of pathogenic bacteria, particularly Gram-negative bacteria, and specifically Klebsiella pneumoniae. From a clinical research perspective, understanding these interactions is crucial for comprehensively understanding the phenomenon of resistance and developing more effective drugs and treatments to limit or attenuate bacterial sepsis, since the most conserved adjuvant phenomena in bacterial physiology has turned out to be more optimized and, therefore, more susceptible to alterations due to pharmacological action.

A review of chemical signaling mechanisms underlying quorum sensing and its inhibition in Staphylococcus aureus

Staphylococcus aureus is a significant bacterium responsible for multiple infections and is a primary cause of fatalities among patients in hospital environments. The advent of pathogenic bacteria such as methicillin-resistant S. aureus revealed the shortcomings of employing antibiotics to treat bacterial infectious diseases. Quorum sensing enhances S. aureus's survivability through signaling processes. Targeting the key components of quorum sensing has drawn much interest nowadays as a promising strategy for combating infections caused by bacteria. Concentrating on the accessory gene regulator quorum-sensing mechanism is the most commonly suggested anti-virulence approach for S.aureus. Quorum quenching is a common strategy for controlling illnesses triggered by microorganisms since it reduces the pathogenicity of bacteria and improves bacterial biofilm susceptibility to antibiotics, thus providing an intriguing prospect for drug discovery. Quorum sensing inhibition reduces selective stresses and constrains the emergence of antibiotic resistance while limiting bacterial pathogenicity. This review examines the quorum sensing mechanisms involved in S. aureus, quorum sensing targets and gene regulation, environmental factors affecting quorum sensing, quorum sensing inhibition, natural products as quorum sensing inhibitory agents and novel therapeutical strategies to target quorum sensing in S. aureus as drug developing technique to augment conventional antibiotic approaches.

Quorum sensing-related activities of beneficial and pathogenic bacteria have important implications for plant and human health

Eukaryotic organisms coevolved with microbes from the environment forming holobiotic meta-genomic units. Members of host-associated microbiomes have commensalic, beneficial/symbiotic, or pathogenic phenotypes. More than 100 years ago, Lorenz Hiltner, pioneer of soil microbiology, introduced the term 'Rhizosphere' to characterize the observation that a high density of saprophytic, beneficial, and pathogenic microbes are attracted by root exudates. The balance between these types of microbes decide about the health of the host. Nowadays we know, that for the interaction of microbes with all eukaryotic hosts similar principles and processes of cooperative and competitive functions are in action. Small diffusible molecules like (phyto)hormones, volatiles and quorum sensing signals are examples for mediators of interspecies and cross-kingdom interactions. Quorum sensing of bacteria is mediated by different autoinducible metabolites in a density-dependent manner. In this perspective publication, the role of QS-related activities for the health of hosts will be discussed focussing mostly on N-acyl-homoserine lactones (AHL). It is also considered that in some cases very close phylogenetic relations exist between plant beneficial and opportunistic human pathogenic bacteria. Based on a genome and system-targeted new understanding, sociomicrobiological solutions are possible for the biocontrol of diseases and the health improvement of eukaryotic hosts.

MzmL, a novel marine derived N-acyl homoserine lactonase from Mesoflavibacter zeaxanthinifaciens that attenuates Pectobacterium carotovorum subsp. carotovorum virulence

Quorum sensing (QS) is a conserved cell-cell communication mechanism widely distributed in bacteria, and is oftentimes tightly correlated with pathogen virulence. Quorum quenching enzymes, which interfere with QS through degrading the QS signaling molecules, could attenuate virulence instead of killing the pathogens, and thus are less likely to induce drug resistance. Many Gram-negative bacteria produce N-acyl homoserine lactones (AHLs) for interspecies communication. In this study, we isolated and identified a bacterial strain, Mesoflavibacter zeaxanthinifaciens XY-85, from an Onchidium sp. collected from the intertidal zone of Dapeng Reserve in Shenzhen, China, and found it had strong AHL degradative activity. Whole genome sequencing and blast analysis revealed that XY-85 harbors an AHL lactonase (designated MzmL), which is predicted to have an N-terminal signal peptide and share the "HXHXDH" motif with known AHL lactonases belonging to the Metallo-β-lactamase superfamily. Phylogenetic studies showed MzmL was closest to marine lactonase cluster members, MomL and Aii20J, instead of the AiiA type lactonases. Ultra performance liquid chromatography-mass spectrometry analysis confirmed that MzmL functions as an AHL lactonase catalyzing AHL degradation through lactone hydrolysis. MzmL could degrade both short- and long-chain AHLs with or without a substitution of oxo-group at the C-3 position, and retained full bioactivity under a wide range of temperatures (28-100°C) and pHs (4-11). Furthermore, MzmL significantly reduced Pectobacterium carotovorum subsp. carotovorum virulence factor production in vitro, such as biofilm formation and plant cell wall degrading enzyme production, and inhibited soft rot development on potato slices. These results demonstrated that MzmL may be a novel type of AHL lactonase with good environmental stability, and has great potential to be developed into a novel biological control agent for bacterial disease management.

Molecular Aspects of the Functioning of Pathogenic Bacteria Biofilm Based on Quorum Sensing (QS) Signal-Response System and Innovative Non-Antibiotic Strategies for Their Elimination

One of the key mechanisms enabling bacterial cells to create biofilms and regulate crucial life functions in a global and highly synchronized way is a bacterial communication system called quorum sensing (QS). QS is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small signalling molecules called autoinducers (AIs). In bacteria, QS controls the biofilm formation through the global regulation of gene expression involved in the extracellular polymeric matrix (EPS) synthesis, virulence factor production, stress tolerance and metabolic adaptation. Forming biofilm is one of the crucial mechanisms of bacterial antimicrobial resistance (AMR). A common feature of human pathogens is the ability to form biofilm, which poses a serious medical issue due to their high susceptibility to traditional antibiotics. Because QS is associated with virulence and biofilm formation, there is a belief that inhibition of QS activity called quorum quenching (QQ) may provide alternative therapeutic methods for treating microbial infections. This review summarises recent progress in biofilm research, focusing on the mechanisms by which biofilms, especially those formed by pathogenic bacteria, become resistant to antibiotic treatment. Subsequently, a potential alternative approach to QS inhibition highlighting innovative non-antibiotic strategies to control AMR and biofilm formation of pathogenic bacteria has been discussed.

Weak selection for resistance to quorum sensing inhibition during multiple host infection cycles

Quorum sensing (QS) inhibition is a promising novel approach to control bacterial infections. However, it is not clear whether QS inhibition will impose selective pressure for the spread of resistance against QS inhibition in pathogen populations. Previous research tried to answer this question by using synthetic growth media, and this revealed that whether or not resistance will spread completely depends on the environment in which it is studied. Therefore, the spread of resistance should be studied in the environment where it ultimately matters: in vivo during infection of a host. Here, using QS inhibitor-susceptible and -resistant mimics, we show that resistance to QS inhibition does not spread in host-associated populations of Vibrio campbellii during up to 35 cycles of infection and transmission if the initial frequency of the resistance is low in the pathogen population, whereas it further increases to 100% if it is already prevalent. However, even in the latter case, the resistance spreads at a slower pace than resistance to antibiotics spreads under the same conditions.

Hexadecanoic acid analogs as potential CviR-mediated quorum sensing inhibitors in Chromobacterium violaceum: an in silico study

Chromobacterium violaceum is a Gram-negative, rod-shaped and opportunistic human pathogen. C. violaceum is resistant to various antibiotics due to the production of quorum sensing (QS)-controlled virulence factor and biofilm formation. Hence, we need to find alternative strategies to overcome the antimicrobial resistance and biofilm formation in Gram-negative bacteria. QS is a mechanism in which bacteria's ability to regulate the virulence factors and biofilm formations leads to disease progression. Previously, hexadecanoic acid was identified as a CviR-mediated quorum-sensing inhibitor. In this study, we aimed to discover potential analogs of hexadecanoic acid as a CviR-mediated quorum-sensing inhibitor against C. violaceum by using ADME/T prediction, density functional theory, molecular docking, molecular dynamics and free energy binding calculations. ADME/T properties predicted for analogs were acceptable for human oral absorption and feasibility. The highest occupied molecular orbitals and lowest unoccupied molecular orbitals gap energies predicted and found oleic acid with -0.3748 energies. Docosatrienoic acid exhibited the highest binding affinity -8.15 Kcal/mol and strong and stable interactions with the amino acid residues on the active site of the CviR protein. These compounds on MD simulations for 100 ns show strong hydrogen-bonding interactions with the protein and remain stable inside the active site. Our results suggest hexadecanoic acid analogs could serve as anti-QS and anti-biofilm molecules for treating C. violaceum infections. However, further validation and investigation of these inhibitors against CviR are needed to claim their candidacy for clinical trials.Communicated by Ramaswamy H. Sarma.

A review of chemical signaling pathways in the quorum sensing circuit of Pseudomonas aeruginosa

Pseudomonas aeruginosa, an increasingly common competitive and biofilm organism in healthcare infection with sophisticated, interlinked and hierarchic quorum systems (Las, Rhl, PQS, and IQS), creates the greatest threats to the medical industry and has rendered prevailing chemotherapy medications ineffective. The rise of multidrug resistance has evolved into a concerning and potentially fatal occurrence for human life. P. aeruginosa biofilm development is assisted by exopolysaccharides, extracellular DNA, proteins, macromolecules, cellular signaling and interaction. Quorum sensing is a communication process between cells that involves autonomous inducers and regulators. Quorum-induced infectious agent biofilms and the synthesis of virulence factors have increased disease transmission, medication resistance, infection episodes, hospitalizations and mortality. Hence, quorum sensing may be a potential therapeutical target for bacterial illness, and developing quorum inhibitors as an anti-virulent tool could be a promising treatment strategy for existing antibiotics. Quorum quenching is a prevalent technique for treating infections caused by microbes because it diminishes microbial pathogenesis and increases microbe biofilm sensitivity to antibiotics, making it a potential candidate for drug development. This paper examines P. aeruginosa quorum sensing, the hierarchy of quorum sensing mechanism, quorum sensing inhibition and quorum sensing inhibitory agents as a drug development strategy to supplement traditional antibiotic strategies.

Emerging trends in the inhibition of bacterial molecular communication: An overview

Quorum sensing (QS) is a molecular cell-cell communication utilized by several bacteria and some fungi. It involves cell density dependent gene expression that includes extra polymeric substance production, sporulation, antibiotic production, motility, competence, symbiosis and conjugation. These expressions were carried out by different signaling molecules like acyl homo-serine lactone (AHL) and auto-inducing peptides (AIPs) which was effluxed by gram negative and gram positive bacteria. Pathogenic bacteria and biofilms often exhibit high resistance to antibiotics, attributed to the presence of antibiotic efflux pumps, reduced membrane permeability, and enzymes that deactivate quorum sensing (QS) inhibitors. To counteract virulence and multi-drug resistance (MDR), novel strategies such as employing quorum sensing (QS) inhibitors and quorum quenchers are employed. It targets signaling molecules with synthesis and prevents the signal from binding to receptors. In this present review, the mechanisms of QS along with inhibitors from different sources are described. These strategies potentially interfere with QS and it can be applied in different fields, mainly in hospitals and marine environments where the pathogenic infections and biofilm formation are highly involved.

Inhibition of Pseudomonas aeruginosa quorum sensing by methyl gallate from Mangifera indica

Antipathogenic drugs are a potential source of therapeutics, particularly following the emergence of multiple drug-resistant pathogenic microorganisms in the last decade. The inhibition of quorum sensing (QS) is an advanced antipathogenic approach for suppression of bacterial virulence and dissemination. This study aimed to investigate the inhibitory effect of some Egyptian medicinal plants on the QS signaling system of Pseudomonas aeruginosa. Among the tested plants, Mangifera indica exhibited the highest quorum sensing inhibition (QSI) activity against Chromobacterium violaceum ATCC 12472. Four pure compounds were extracted and identified; of these, methyl gallate (MG) showed the most potent QSI. MG had a minimum inhibitory concentration (MIC) of 512 g/mL against P. aeruginosa strains PAO1, PA14, Pa21, Pa22, Pa23, Pa24, and PAO-JP2. The virulence factors of PAO1, PA14, Pa21, Pa22, Pa23, and Pa24 were significantly inhibited by MG at 1/4 and 1/2 sub-MICs without affecting bacterial viability. Computational insights were performed by docking the MG compound on the LasR receptor, and the QSI behavior of MG was found to be mediated by three hydrogen bonds: Trp60, Arg61, and Thr75. This study indicates the importance of M. indica and MG in the inhibition and modulation of QS and QS-related virulence factors in P. aeruginosa.

Streptococcal peptides and their roles in host-microbe interactions

The genus Streptococcus encompasses many bacterial species that are associated with hosts, ranging from asymptomatic colonizers and commensals to pathogens with a significant global health burden. Streptococci produce numerous factors that enable them to occupy their host-associated niches, many of which alter their host environment to the benefit of the bacteria. The ability to manipulate host immune systems to either evade detection and clearance or induce a hyperinflammatory state influences whether bacteria are able to survive and persist in a given environment, while also influencing the propensity of the bacteria to cause disease. Several bacterial factors that contribute to this inter-species interaction have been identified. Recently, small peptides have become increasingly appreciated as factors that contribute to Streptococcal relationships with their hosts. Peptides are utilized by streptococci to modulate their host environment in several ways, including by directly interacting with host factors to disrupt immune system function and signaling to other bacteria to control the expression of genes that contribute to immune modulation. In this review, we discuss the many contributions of Streptococcal peptides in terms of their ability to contribute to pathogenesis and disruption of host immunity. This discussion will highlight the importance of continuing to elucidate the functions of these Streptococcal peptides and pursuing the identification of new peptides that contribute to modulation of host environments. Developing a greater understanding of how bacteria interact with their hosts has the potential to enable the development of techniques to inhibit these peptides as therapeutic approaches against Streptococcal infections.

Synthesis, in Silico Study and Biological Evaluation of N-(Benzothiazol/Thiazol-2-yl)benzamide Derivatives as Quorum Sensing Inhibitors against Pseudomonas aeruginosa

The development of bacterial resistance to chemical therapy poses a severe danger to efficacy of treating bacterial infections. One of the key factors for resistance to antimicrobial medications is growth of bacteria in biofilm. Quorum sensing (QS) inhibition was created as an alternative treatment by developing novel anti-biofilm medicines. Cell-cell communication is impeded by QS inhibition, which targets QS signaling pathway. The goal of this work is to develop newer drugs that are effective against Pseudomonas aeruginosa by decreasing QS and acting as anti-biofilm agents. In this investigation, N-(benzo[d]thiazol-2-yl)benzamide/N-(thiazol-2-yl)benzamide derivatives 3a-h were designed and synthesized in good yields. Further, molecular docking analyses revealed that binding affinity values were founded -11.2 to -7.6 kcal/mol that were moderate to good. The physicochemical properties of these prepared compounds were investigated through in-silico method. Molecular dynamic simulation was also used to know better understanding of stability of the protein and ligand complex. Comparing N-(benzo[d]thiazol-2-yl)benzamide 3a to salicylic acid (4.40±0.10) that was utilised as standard for quorum sensing inhibitor, the anti-QS action was found greater for N-(benzo[d]thiazol-2-yl)benzamide 3a (4.67±0.45) than salicylic acid (4.40±0.10). Overall, research results suggested that N-(benzo[d]thiazol-2-yl)benzamide/N-(thiazol-2-yl)benzamide derivatives 3a-h may hold to develop new quorum sensing inhibitors.