The hierarchy quorum sensing network in Pseudomonas aeruginosa

Potential roles of quorum quenching in microbial aggregates during wastewater treatment

Quorum sensing-regulated microbial behaviors often negatively impact wastewater treatment, leading to issues such as biofouling in membrane bioreactors, filamentous bulking, and resistance gene transfer. Quorum quenching, which counteracts quorum sensing, offers a promising strategy to mitigate these problems. This review aims to highlight overlooked perspectives for its application in microbial aggregates during wastewater treatment. First, the review examines the quorum sensing network present in microbial aggregates and the regulatory role of different quorum sensing systems in bacterial function and behavior during wastewater treatment. The discussions cover hierarchical, parallel, and competitive quorum sensing systems to clarify the interactions among these pathways. A precise quorum quenching strategy is proposed to enhance efficiency based on the type of quorum sensing regulation. Additionally, a bridge is established between the physiological characteristics of quorum quenching bacteria and process parameters to achieve process control over bacterial function and behavior during wastewater treatment.

Targeting Pseudomonas aeruginosa PAO1 pathogenicity: The role of Glycyrrhiza glabra in inhibiting virulence factors and biofilms

Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative opportunistic pathogen posing serious risks to immunocompromised individuals due to its virulence factors and biofilm formation. This study evaluated the efficacy of methanol extract of Glycyrrhiza glabra (G. glabra) in mitigating P. aeruginosa PAO1 pathogenesis through in-vitro assays, including Minimum Inhibitory Concentration (MIC), biofilm assay, growth curve analysis, pyocyanin quantification, and molecular docking. The extract inhibited PAO1 growth at 5 mg/mL and demonstrated significant antibiofilm activity at sub-MIC levels, reducing biofilm formation by 50.22 %, 22.13 %, and 11.53 % at concentrations of 1.25 mg/mL, 0.625 mg/mL, and 0.312 mg/mL, respectively. Pyocyanin production was also significantly suppressed. Molecular docking revealed that 4-(4-Trifluoromethyl-benzoylamino)-benzoic acid and betulinic acid, identified in the extract, exhibited strong binding affinities (-6.4 kcal/mol and -6.9 kcal/mol) to the QS regulator 7XNJ. These findings underscore the potential of G. glabra as an antipathogenic agent against P. aeruginosa, warranting further investigation into its clinical applications.

c-di-GMP phosphodiesterase ProE interacts with quorum sensing protein PqsE to promote pyocyanin production in Pseudomonas aeruginosa

The universal bacterial second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) plays critical roles in regulating a variety of bacterial functions such as biofilm formation and virulence. The metabolism of c-di-GMP is inversely controlled by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs). Recently, increasing studies suggested that the protein-protein interactions between DGCs/PDEs and their partners appear to be a common way to achieve specific regulation. In this work, we showed that the PDE ProE can interact with PQS quorum sensing protein PqsE to regulate pyocyanin production in Pseudomonas aeruginosa. Our bacterial two-hybrid assay demonstrated that ProE directly interacts with PqsE, and isothermal titration calorimetry and surface plasmon resonance assay further confirmed that the binding affinity of ProE with PqsE is at micromolar level. Both ProE and PqsE negatively regulate intracellular c-di-GMP levels. Furthermore, our transcriptomic study showed that co-expression of ProE and PqsE significantly changes the gene expression profiles in P. aeruginosa, especially with increased expression of pyocyanin genes, and the qPCR and phenotypic results confirmed the transcriptome data. Taken together, our study suggested that the interaction between ProE and PqsE plays a critical role in regulation of pyocyanin production and highlights the importance of protein-protein interaction mediated c-di-GMP signaling in P. aeruginosa.IMPORTANCEc-di-GMP is pivotal in orchestrating various bacterial functions. In Pseudomonas aeruginosa, the nuanced balance of intracellular c-di-GMP is maintained by approximately 41 diguanylate cyclases (DGCs) and phosphodiesterases (PDEs). Emerging studies indicate that the c-di-GMP metabolic DGCs and PDEs may be involved in the signal transduction process by directly binding to the target protein, thus influencing downstream function. Despite their known importance, the precise functions of these proteins, especially their interacting partners, remain unclear. In this study, we identified that PQS quorum sensing system protein PqsE is a binding partner of c-di-GMP phosphodiesterase ProE; further analysis suggested that the ProE specifically interacts with PqsE to promote pyocyanin production. Our study extended the regulatory mechanism of the c-di-GMP signal transduction and quorum sensing in governing bacterial physiology.

Reprofiling lamivudine as an antibiofilm and anti-pathogenic agent against Pseudomonas aeruginosa

Resistance to antibiotics is a critical growing public health problem that needs urgent action to combat. To avoid the stress on bacterial growth that evokes the development of resistance, anti-virulence agents can be an attractive strategy as they do not target bacterial growth. There are FDA approved drugs have been screened for their anti-virulence activities. Lamivudine (LAM) is a synthetic nucleoside analogue used as an antiretroviral in treatment of HIV and can be used in treatment of HBV. The present study aimed to assess the anti-virulence activities of LAM against a clinically important pathogen Pseudomonas aeruginosa. The LAM's antibiofilm and anti-virulence activities were evaluated. The impact of LAM on the quorum sensing (QS) systems which control the production of these virulence factors was assessed virtually and by quantification of the expression of QS-encoding genes. Furthermore, in vivo mice protection assay was conducted to attest the LAM's anti-pathogenic activity. The current findings elaborated the promising anti-pathogenic and anti-QS activities of LAM. LAM interfered with biofilm formation in P. aeruginosa PAO1 strain. Moreover, swarming motility and production of pyocyanin and protease were significantly diminished. At the molecular level, LAM downregulated the QS-encoding genes LasI, LasR, RhlR, PqsA and PqsR. Additionally, the detailed in silico docking and molecular simulation studies showed the considered high LAM's ability to bind and hinder the QS receptors in the P. aeruginosa. In an agreement with in vitro and in silico, the in vivo results showed the LAM full protection of mice against P. aeruginosa. In conclusion, LAM could be repurposed to be employed as adjunct therapy with traditional antibiotics for treating serious pseudomonal infections.

Phenazine Scaffolds as a Potential Allosteric Inhibitor of LasR Protein in Pseudomonas aeruginosa

Millions of individuals suffer from chronic infections caused by bacterial biofilms, resulting in significant loss of life. Pseudomonas aeruginosa stands out as a major culprit in causing such chronic infections, largely due to its antibiotic resistance. This pathogen poses a considerable threat in healthcare settings, particularly to critically ill and immunocompromised patients. The persistence of chronic and recurrent bacterial infections is often attributed to bacterial biofilms. Therefore, there is an urgent need to discover novel small molecules capable of efficiently eliminating biofilms independent of bacterial growth. In this project, an in silico drug discovery approach was employed to identify nine halogenated-phenazine compounds as allosteric inhibitors of the LasR protein. The LasR is a key transcription factor that triggers other quorum-sensing systems and plays a crucial role in biofilm formation and activation of virulence genes. By inhibiting LasR, specifically targeting its allosteric site, the dimerization of LasR and subsequent biofilm formation could be prevented. Molecular docking and simulations, coupled with binding energy calculations, identified five compounds with potential as anti-biofilm agents. These compounds exhibited higher binding affinities to the distal site, suggesting their structural capability to interact with allosteric site residues of the LasR protein. Based on these findings, it is proposed that these compounds could serve as promising leads for the treatment of biofilm and quorum-sensing-related infections.

Inhibitors of the PqsR Quorum-Sensing Receptor Reveal Differential Roles for PqsE and RhlI in Control of Phenazine Production

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections and it is resistant to many current antibiotic therapies, making development of new anti-microbial treatments imperative. The cell-to-cell communication process called quorum sensing controls P. aeruginosa pathogenicity. Quorum sensing relies on the production, release, and group-wide detection of extracellular signal molecules called autoinducers. Quorum sensing enables bacteria to synchronize group behaviors. P. aeruginosa possesses multiple quorum-sensing systems that control overlapping regulons, including those required for virulence and biofilm formation. Interventions that target P. aeruginosa quorum-sensing receptors are considered a fruitful avenue to pursue for new therapeutic advances. Here, we developed a P. aeruginosa strain that carries a bioluminescent reporter fused to a target promoter that is controlled by two P. aeruginosa quorum-sensing receptors. The receptors are PqsR, which binds and responds to the autoinducer called PQS (2-heptyl-3-hydroxy-4(1H)-quinolone) and RhlR, which binds and responds to the autoinducer called C4-HSL (C4-homoserine lactone). We used this reporter strain to screen >100,000 compounds with the aim of identifying inhibitors of either or both the PqsR and RhlR quorum-sensing receptors. We report results for 30 PqsR inhibitors from this screen. All of the identified compounds inhibit PqsR with IC50 values in the nanomolar to low micromolar range and they are readily docked into the autoinducer binding site of the PqsR crystal structure, suggesting they function competitively. The majority of hits identified are not structurally related to previously reported PqsR inhibitors. Recently, RhlR was shown to rely on the accessory protein PqsE for full function. Specifically, RhlR controls different subsets of genes depending on whether it is bound to PqsE or to C4-HSL, however, the consequences of differential regulation on the quorum-sensing output response have not been defined. PqsR regulates pqsE. That feature of the system enabled us to exploit our new set of PqsR inhibitors to show that RhlR requires PqsE to activate the biosynthetic genes for pyocyanin, a key P. aeruginosa virulence factor, while C4-HSL is dispensable. These results highlight the promise of inhibition of PqsR as a possible P. aeruginosa therapeutic to suppress production of factors under RhlR-PqsE control.

Innovative application of ceftriaxone as a quorum sensing inhibitor in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium that has the potential to induce various healthcare-related infections through its array of virulence factors. The control of virulence factor expression is mainly regulated by a communication process among cells called quorum sensing (QS). Blocking QS could be a viable tactic to suppress virulence factors and reduce pathogenicity without impacting bacterial growth. This approach has the potential to significantly decrease the multiple drug resistance emergence. In this study, we explored the impact of ceftriaxone (CRO), which is a commonly used β-lactam antibiotic, and its metal derivatives on the QS system and virulence factors of both standard strains and clinical isolates of P. aeruginosa. The quorum sensing inhibitory (QSI) activity of CRO and ceftriaxone Nickel complex (CRON) was evaluated. The minimum inhibitory concentration (MIC) was determined and the effect of sub-MICs of CRO and CRON was assessed on P. aeruginosa strains virulence factors. CRO and CRON effectively suppressed the virulence factors of P. aeruginosa strains at sub-MICs, without altering bacterial viability. Additionally, a molecular docking investigation was carried out to identify potential mechanisms of QSI. CRO and CRON exhibited high ICM scores, potentially displacing natural ligands when interacting with LasR, LasI, and PqsR receptors.

Regulation of the H1 Type VI Secretion System by the Transcriptional Regulator NfxB in Pseudomonas aeruginosa

The type VI secretion system (T6SS) is a widely distributed molecular apparatus found in most Gram-negative bacteria. Studies show that T6SSs have functions in bacterial virulence, inter- and intra-bacterial competition, and environmental adaptation. Pseudomonas aeruginosa, an opportunistic pathogen, harbors three T6SS gene clusters that perform diverse roles in clinical infection. Herein, using DNA affinity chromatography of the H1-T6SS promoter, the fluoroquinolone antibiotic resistance regulator NfxB was identified. Further studies demonstrated that NfxB negatively regulates the expression of H1-T6SS by directly binding to its promoter region. T6SS expression and effector secretion are regulated by the fluoroquinolone antibiotic via NfxB, which enhances inter-bacterial competition in the complex bacterial ecology. Meanwhile, the deletion of nfxB alters carbenicillin resistance through an unknown pathway. This study provides new insights into the regulation of T6SS by environmental signals, and it provides data support for antibiotic resistance and inter-bacterial competition due to T6SSs.

Regulatory role of PA3299.1 small RNA in Pseudomonas aeruginosa biofilm formation via modulation of algU and mucA expression

Small RNAs (sRNAs) have emerged as key regulators of transcriptional factors and components within regulatory networks that govern bacterial biofilm formation. This study aimed to explore the regulatory role of the PA3299.1 sRNA in controlling biofilm formation in P. aeruginosa. Results showed that PA3299.1 expression was significantly elevated in both substratum-attached and colony biofilms compared to planktonic growth. Further investigation revealed that strains overexpressing PA3299.1 exhibited enhanced biofilm formation, while its deletion resulted in a substantial reduction in biofilm development. PA3299.1 was found to regulate the expression of AlgU and MucA, the sigma and anti-sigma factors, integral to the biofilm developmental network. In summary, this research identifies PA3299.1 as a critical regulator of biofilm formation and potentially a contributor to the pathogenicity of P. aeruginosa, that could help to develop new therapeutic strategies to manage biofilm-associated infections.

A plasmid-encoded inactive toxin-antitoxin system MtvT/MtvA regulates plasmid conjugative transfer and bacterial virulence in Pseudomonas aeruginosa

Plasmid-encoded toxin-antitoxin (TA) systems are known for their role in plasmid maintenance via post-segregational killing. Here, we identified an inactive type II TA system, MtvT/MtvA (MtvTA), encoded on the conjugative plasmid pPAD8 from the clinical Pseudomonas aeruginosa strain PAD8. Despite its annotation as a toxin, MtvT exhibited no detectable toxicity in our assays. Interestingly, the deletion of the MtvTA significantly increased the transfer efficiency of pPAD8 from PAD8 to P. aeruginosa strain PAO1. Functional assays revealed that the MtvTA complex negatively regulates plasmid transfer by binding to the promoters of dot/icm system genes. In addition, pPAD8ΔmtvTA attenuated the pathogenicity of the host strain compared to pPAD8, highlighting a regulatory role for MtvTA in virulence. Mechanistically, the MtvTA complex positively regulates the type III and type VI secretion systems and pyocyanin biosynthesis by directly binding to the promoters of exsA and rsmY/rsmZ and indirectly influencing lasI expression, respectively. These findings provide new insights into the regulatory roles of an inactive plasmid-encoded TA system, expanding our understanding of the interplay between plasmids and their bacterial hosts.

Quorum sensing regulation by the nitrogen phosphotransferase system in Pseudomonas aeruginosa

In the opportunistic pathogen Pseudomonas aeruginosa, the nitrogen-related phosphotransferase system (PTSNtr) influences multiple virulence behaviors. The PTSNtr is comprised of three enzymes: first PtsP, then the PtsO phosphocarrier, and the final PtsN phosphoacceptor. We previously showed that ptsP inactivation increases LasI-LasR quorum sensing, a system by which P. aeruginosa regulates genes in response to population density. LasI synthesizes a diffusible autoinducer that binds and activates the LasR receptor, which activates a feedback loop by increasing lasI expression. In this study, we examined the impact of the PTSNtr on quorum sensing. Disruption of ptsP increased the expression of some, but not all, tested quorum-controlled genes, including lasI, phzM (pyocyanin biosynthesis), hcnA (hydrogen cyanide biosynthesis), and, to a lesser extent, rsaL (quorum sensing regulator). Expression of these genes remained dependent on LasR and the autoinducer, whether provided endogenously or exogenously. Increased lasI expression in ΔptsP (or ΔptsO) cells was partly due to the presence of unphosphorylated PtsN, which alone was sufficient to elevate lasI expression. However, we observed residual increases in ΔptsP or ΔptsO cells even in the absence of PtsN, suggesting that PtsP and PtsO can regulate gene expression independent of PtsN. Indeed, genetically disrupting the PtsO phosphorylation site impacted gene expression in the absence of PtsN, and transcriptomic evidence suggested that PtsO and PtsN have distinct regulons. Our results expand our view of how the PTSNtr components function both within and apart from the classic phosphorylation cascade to regulate key virulence behaviors in P. aeruginosa.

Enhancement of aerobic sludge granulation by quorum sensing signaling molecules mediated by biomimetic bacterial extracellular vesicles

The addition of exogenous quorum sensing signaling molecules to the activated sludge system enables rapid sludge granulation. However, signaling molecules exposed to the environment are easily degraded, and their quorum sensing effects cannot be maintained in the long term. Therefore, they must be frequently added, which leads to an increase in operational costs. In this study, signaling molecules, acylated homoserine lactones (AHLs), were packaged into biomimetic bacterial extracellular vesicles-lipid vesicles (AHLs@ZZT), and the mediating role of lipid vesicles for AHLs was utilized to improve the utilization efficiency of signaling molecules. The results show that packaging of AHLs into vesicles slowed down the release of AHLs and protected them from degradation by porcine renal acylase. Moreover, the chemical properties of lipid vesicles are similar to the structure of bacterial cell walls, making it easier for the packaged AHLs to bind to target bacteria, thereby generating more EPS and accelerating the aggregation of microorganisms. After adding the lipid vesicles loaded with AHLs into the activated sludge system, the sludge granulation process was accelerated. Furthermore, the frequency of AHLs@ZZT addition was reduced by three times compared to that of unpackaged AHLs, resulting in a granular sludge with a smoother and denser surface. High-throughput sequencing of the sludge genome in the system indicated that adding AHLs@ZZT could promote microbial diversity and enrich functional microorganisms. Three-dimensional fluorescence spectra further revealed that the tryptophan and tyrosine proteins in extracellular polymeric substances secreted by these microorganisms facilitated sludge granulation. In summary, the lipid vesicle-mediated signaling molecular strategy can promote the rapid formation of granular sludge and maintain the long-term stability of the granular sludge structure, representing an economic and feasible regulation strategy.

RhlR-mediated cooperation in cystic fibrosis-adapted isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa uses quorum sensing (QS) to regulate the expression of dozens of genes, many of which encode shared products, called "public goods." P. aeruginosa possesses two complete acyl-homoserine lactone (AHL) QS circuits: the LasR-I and RhlR-I systems. Canonically, these systems are hierarchically organized: RhlR-I activity depends on LasR-I activation. However, in contrast to laboratory strains, isolates from people with cystic fibrosis can engage in AHL QS using only the transcription factor RhlR. In these isolates, RhlR regulates AHL QS and the production of secreted public goods, such as the exoprotease elastase, which are accessible to both producing and non-producing cells. When P. aeruginosa strains that use LasR to regulate elastase production are grown on casein as the sole carbon and energy source, LasR-null mutant "cheaters" commonly arise in populations due to a selective growth advantage. We asked if these social dynamics might differ in "RhlR cooperators": populations that use RhlR, not LasR, to regulate public goods. We passaged RhlR cooperators from several genetic backgrounds in casein broth. We found that cheaters emerged among most RhlR cooperators. However, in one isolate background, E90, RhlR-null mutants were dramatically outcompeted by RhlR cooperators. In this background, the mechanism by which RhlR mutants are outcompeted by RhlR cooperators is AHL-dependent and occurs in stationary phase but is not the same as previously described "policing" mechanisms. Our data suggest that cheating, or the lack thereof, does not explain the lack of RhlR mutants observed in most infection environments.IMPORTANCEQuorum sensing (QS) mutants arise in a variety of populations of bacteria, but mutants of the gene encoding the transcription factor RhlR in Pseudomonas aeruginosa appear to be infrequent. Our work provides insight on the mechanisms through which RhlR-mediated cooperation is maintained in a LasR-null population of P. aeruginosa. Characterizing the selective pressure(s) that disfavor mutations from occurring in RhlR may enhance our understanding of P. aeruginosa evolution in chronic infections and potentially guide the development of therapeutics targeting the RhlR-I QS circuit.

Quorum Sensing Coordinates Carbon and Nitrogen Metabolism to Optimize Public Goods Production in Pseudomonas fluorescens 2P24

The coordination of public and private goods production is essential for bacterial adaptation to environmental changes. Quorum sensing (QS) regulates this balance by mediating the trade-off between the communal benefits of "public goods," such as siderophores and antibiotics, and the individual metabolic needs fulfilled by "private goods," such as intracellular metabolites utilized for growth and survival. Pseudomonas fluorescens 2P24 harbors a LasI/LasR-type QS system, MupI/MupR, which regulates mupirocin production through signaling molecules. This study explores how QS coordinates carbon and nitrogen metabolism to optimize the production of key secondary metabolites, including 2,4-diacetylphloroglucinol (2,4-DAPG), mupirocin, and siderophores, which serve as public goods. Loss of QS disrupts this balance by enhancing the Krebs cycle, denitrification, pyruvate anaplerosis, and ammonium assimilation, lead to halted 2,4-DAPG and mupirocin synthesis and increased siderophore production. In the absence of QS, elevated siderophore production compensates for iron acquisition, ensuring rapid cellular growth. Under nutrient-limited or high cell density conditions, MupR regulates carbon and nitrogen fluxes to sustain public goods production. These findings highlight QS as a key environmental sensor that fine-tunes resource allocation, bacterial fitness, and adaptation to ecological and nutritional conditions, suggesting the potential for QS-targeted approaches to enhance antibiotic production and agricultural sustainability.

Arsenic-induced modulation of virulence and drug resistance in Pseudomonas aeruginosa

Arsenic contamination of water sources, whether from natural or industrial origins, represents a significant risk to human health. However, its impact on waterborne pathogens remains understudied. This research explores the effects of arsenic exposure on the opportunistic pathogen Pseudomonas aeruginosa, a bacterium found in diverse environments. The arsenic exposure at concentrations of 0.12-20 mg/L As(III) resulted in rapid growth arrest of P. aeruginosa. Moreover, arsenic exposure significantly reduced the production of key virulence factors such as elastase (by 1.48- to 9.24-fold), pyocyanin, and flagella while increasing siderophore and extracellular polysaccharide production (by 1.44-1.75 and 1.36-2.59 times, respectively). Proteomic analysis revealed that both low (0.12 mg/L) and high (1.2 mg/L) As(III) levels activated an antioxidant defense response, with upregulation of Fnr-2, TrxB2, and Ohr. Furthermore, arsenic-induced the overexpression of multidrug resistance efflux proteins MexAB-OprM, MexCD-OprJ, and MexEF-OprN. At the same time, proteins associated with quorum sensing (QS), type III secretion system (T3SS), pyocyanin biosynthesis, and flagellar assembly were downregulated. In vitro assays confirmed that arsenic reduced bacterial virulence and significantly enhanced survival and proliferation under antibiotic treatment. These results indicate that arsenic exposure modulates the virulence and antibiotic resistance of P. aeruginosa, raising concerns about the public health risks posed by the convergence of arsenic-contaminated water and multidrug-resistant bacteria.

Diversity-Oriented Synthesis and Antibiofilm Evaluation of Furan-2-Carboxamides

A diversity-oriented collection of furan-2-carboxamides with antibiofilm activity against P. aeruginosa is reported. The design involved the bioisosteric replacement of the labile furanone ring by a furan-2-carboxamide moiety to explore its influence on biological activity. After evaluation, carbohydrazides and triazoles showed significant antibiofilm activity, and 4b resulted in the most remarkable compound (58 % inhibition). Furthermore, treating P. aeruginosa with three active carboxamides reduced some virulence factors (pyocyanin and proteases), confirming the anti-quorum sensing properties of the derivatives and suggesting LasR as a plausible target. Molecular docking proposed that carbohydrazides share a similar binding mode to related furanones inside LasR with an excellent docking score, while higher derivatives diminished in silico affinity.

Dual RNA sequencing of a co-culture model of Pseudomonas aeruginosa and human 2D upper airway organoids

Pseudomonas aeruginosa is a Gram-negative bacterium that is notorious for airway infections in cystic fibrosis (CF) subjects. Bacterial quorum sensing (QS) coordinates virulence factor expression and biofilm formation at population level. Better understanding of QS in the bacterium-host interaction is required. Here, we set up a new P. aeruginosa infection model, using 2D upper airway nasal organoids that were derived from 3D organoids. Using dual RNA-sequencing, we dissected the interaction between organoid epithelial cells and WT or QS-mutant P. aeruginosa strains. Since only a single healthy individual and a single CF subject were used as donors for the organoids, conclusions about CF-specific effects could not be deduced. However, P. aeruginosa induced epithelial inflammation, whereas QS signaling did not affect the epithelial airway cells. Conversely, the epithelium influenced infection-related processes of P. aeruginosa, including QS-mediated regulation. Comparison of our model with samples from the airways of CF subjects indicated that our model recapitulates important aspects of infection in vivo. Hence, the 2D airway organoid infection model is relevant and may help to reduce the future burden of P. aeruginosa infections in CF.

Exploring daidzein dimethyl ether from Albizzia lebbeck as a novel quorum sensing inhibitor against Pseudomonas aeruginosa: Insights from in vitro and in vivo studies

Infections of multidrug-resistant pathogens including Pseudomonas aeruginosa, cause a high risk of mortality in immunocompromised patients and underscore the need for novel natural antibacterial drugs. In this study, common phytochemicals prevalent in fruits and vegetables have been demonstrated for their ability to inhibit quorum sensing (QS) in Pseudomonas aeruginosa PAO1 (PA). Ten compounds were screened virtually by molecular docking, among which, daidzein dimethyl ether originally from Albizzia lebbeck showed the most significant inhibitory effect on the formation of biofilm and the accumulation of virulence factors, including elastase, pyocyanin and rhamnolipid in PA. Further, both qRT-PCR analysis of key QS components including LasR in PA and luminescence detection of LasR as a reporter in a heterologous system revealed that daidzein dimethyl ether at 10 µM significantly inhibited the transcription of lasR and its downstream targeting genes. At the same time, MD simulations also showed that daidzein dimethyl ether could reduce the stability of LasR. Furthermore, the protective effect of daidzein dimethyl ether against PA infection was demonstrated using zebrafish infection model. It was found to reduce significantly the inflammation in the PA-infected zebrafish and increase their survival rate by inhibiting prominently the accumulation of reactive oxygen species (ROS) and reducing fish mortality in PA-infected zebrafish larvae. Additionally, open field tests suggested that PA-infected zebrafish were observed with impaired swimming behaviour, but daidzein dimethyl ether-treatment rescued zebrafish from such swimming abnormalities. Histopathological analysis revealed that zebrafish treated with both PA and daidzein dimethyl ether showed obvious integrity in intestine tissues, compared to those with only PA treatment. This study firstly demonstrated the preventive advantages of daidzein dimethyl ether in an animal model against PA infection. It is worthwhile to explore further its potential therapeutic intervention as an antimicrobial agent.

Acyl-Homoserine Lactone Enhances the Resistance of Anammox Consortia under Heavy Metal Stress: Quorum Sensing Regulatory Mechanism

Anaerobic ammonium oxidation (anammox) represents an energy-efficient process for the removal of biological nitrogen from ammonium-rich wastewater. However, the susceptibility of anammox bacteria to coexisting heavy metals considerably restricts their use in engineering practices. Here, we report that acyl-homoserine lactone (AHL), a signaling molecule that mediates quorum sensing (QS), significantly enhances the nitrogen removal rate by 24% under Cu2+ stress. A suite of macro-/microanalytical and bioinformatic analyses was exploited to unravel the underlying mechanisms of AHL-induced Cu2+ resistance. Macro-/microanalytical evidence indicated that AHL regulations on the production, spatial distribution, and functional groups of extracellular polymeric substances were not significant, ruling out extracellular partitioning and complexation as a principal mechanism. Meanwhile, molecular biological evidence showed that AHL upregulated the transcriptional levels of resistance genes (sod, kat, cysQ, and czcC responsible for antioxidation defense, Cu2+ sequestration, and transport) to appreciable extents, indicating intracellular resistance as the primary mechanism. This study yielded a mechanistic understanding of the regulatory roles of AHL in extracellular and intracellular resistance of anammox consortia, providing a fundamental basis for utilizing QS regulation for efficient nitrogen removal in wastewaters with heavy metal stress.

Anti-Biofilm Agents to Overcome Pseudomonas aeruginosa Antibiotic Resistance

Pseudomonas aeruginosa is one of world's most threatening bacteria. In addition to the emerging prevalence of multi-drug resistant (MDR) strains, the bacterium also possesses a wide variety of virulence traits that worsen the course of the infections. Particularly, its ability to form biofilms that protect colonies from antimicrobial agents is a major cause of chronic and hard-to-treat infections in immune-compromised patients. This protective barrier also ensures cell growth on abiotic surfaces and thus enables bacterial survival on medical devices. Hence, as the WHO alerted to the need to develop new treatments, the use of anti-biofilm agents (ABAs) appeared as a promising approach. Given the selection pressure imposed by conventional antibiotics, a new therapeutic strategy has emerged that aims at reducing bacterial virulence without inhibiting cell growth. So-called anti-virulence agents (AVAs) would then restore the efficacy of conventional antibiotics (ATBs) or potentiate the effectiveness of the immune system. The last decade has seen the development of ABAs as AVAs against P. aeruginosa. This review aims to highlight the design strategy and critical features of these molecules to pave the way for further discoveries of highly potent compounds.

Exploring the antivirulence potential of phenolic compounds to inhibit quorum sensing in Pseudomonas aeruginosa

Bacteria coordinate gene expression in a cell density-dependent manner in a communication process called quorum sensing (QS). The expression of virulence factors, biofilm formation and enzyme production are QS-regulated phenotypes that can interfere in human health. Due to this importance, there is great interest in inhibiting QS, comprising an anti-virulence strategy. This work aimed to evaluate the effect of selected phenolic compounds on the inhibition of QS-regulated phenotypes in Pseudomonas aeruginosa PAO1, using concentrations that do not interfere in bacterial growth. This is one of the main premises for studying the effect of compounds on QS. Firstly, an in-silico study with the LasR and RhlR proteins of P. aeruginosa by molecular docking of 82 phenolic compounds was performed. Then, a screening with 13 selected phenolic compounds was performed, using biosensor strains P. aeruginosa lasB-gfp and P. aeruginosa rhlA-gfp, which emit fluorescence when the QS system is activated. From this assay, eight compounds were selected and evaluated for inhibition of pyocyanin, rhamnolipids, proteases, elastase, and motility. The compounds variably inhibited the evaluated virulence factors. The greatest inhibitions were observed for swarming motility, achieving inhibition rates of up to 50% for baicalein (500 µM) and curcumin (50 µM). Notably, curcumin showed satisfactory inhibition for all phenotypes even at lower concentrations (12.5 to 50 µM) compared to the other compounds (125 to 500 µM). Four compounds - rosmarinic acid, baicalein, curcumin, and resveratrol - were finally tested against biofilm formation observed by optical microscopy. This study demonstrated that phenolic compounds exhibit strong in silico binding to P. aeruginosa LasR and RhlR proteins and variably inhibit QS-regulated phenotypes in vitro. Although no biofilm inhibition was observed, future studies combining compounds and exploring molecular mechanisms are recommended. These findings highlight the biotechnological potential of phenolic compounds for future applications in the food, clinical, and pharmaceutical fields.

Traditional Chinese Medicine Monomer Bakuchiol Attenuates the Pathogenicity of Pseudomonas aeruginosa via Targeting PqsR

As the antibiotic resistance of pathogens becomes increasingly severe, it is becoming more feasible to use methods that suppress the virulence of pathogens rather than exerting selective pressure on their growth. Pseudomonas aeruginosa, a dangerous opportunistic pathogen, infects hosts by producing multiple virulence factors, which are regulated by quorum-sensing (QS) systems, including the las systems, rhl systems, and pqs systems. This study used the chromosome lacZ transcription fusion reporter model to screen the traditional Chinese medicine monomer library and found that bakuchiol can effectively inhibit the pqs system and related virulence phenotypes of P. aeruginosa, including the production of virulence factors (pyocyanin, hydrogen cyanide, elastase, and lectin) and motility (swarming, swimming, and twitching motility) without affecting its growth. Subsequently, through genetic complementation analysis, we found that bakuchiol inhibited the function of the transcriptional activation protein PqsR of the pqs system in P. aeruginosa in a concentration-dependent manner. Furthermore, molecular dynamics simulation study results indicated that bakuchiol can target PqsR of the pqs system, thereby inhibiting the pqs system. Among the amino acids in PqsR, ALA-168 may be a key amino acid residue in the hydrophobic interaction between PqsR protein and bakuchiol. Finally, in vivo experiments demonstrated that bakuchiol attenuated the pathogenicity of P. aeruginosa to Chinese cabbage (Brassica pekinensis) and Caenorhabditis elegans. In summary, this study suggests that bakuchiol is an effective inhibitor that targets the pqs system of P. aeruginosa, providing a new strategy for addressing P. aeruginosa infections.

Regulatory Mechanisms and Physiological Impacts of Quorum Sensing in Gram-Negative Bacteria

The Quorum sensing (QS) system is a widely existing communication mechanism, which regulates bacterial community behaviors and the expression of specific genes. The most common pathogenic bacteria in clinical infections are gram-negative bacteria, and QS plays an important regulatory role in the production of virulence factors and development of antibiotic resistance. This article reviews the QS systems of gram-negative bacteria and provides an overview of how they regulate their physiological functions.

Quercetin: a promising virulence inhibitor of Pseudomonas aeruginosa LasB in vitro

With the inappropriate use of antibiotics, antibiotic resistance has emerged as a major dilemma for patients infected with Pseudomonas aeruginosa. Elastase B (LasB), a crucial extracellular virulence factor secreted by P. aeruginosa, has been identified as a key target for antivirulence therapy. Quercetin, a natural flavonoid, exhibits promising potential as an antivirulence agent. We aim to evaluate the impact of quercetin on P. aeruginosa LasB and elucidate the underlying mechanism. Molecular docking and molecular dynamics simulation revealed a rather favorable intermolecular interaction between quercetin and LasB. At the sub-MICs of ≤256 μg/ml, quercetin was found to effectively inhibit the production and activity of LasB elastase, as well as downregulate the transcription level of the lasB gene in both PAO1 and clinical strains of P. aeruginosa. Through correlation analysis, significant positive correlations were shown between the virulence gene lasB and the QS system regulatory genes lasI, lasR, rhlI, and rhlR in clinical strains of P. aeruginosa. Then, we found the lasB gene expression and LasB activity were significantly deficient in PAO1 ΔlasI and ΔlasIΔrhlI mutants. In addition, quercetin significantly downregulated the expression levels of regulated genes lasI, lasR, rhlI, rhlR, pqsA, and pqsR as well as effectively attenuated the synthesis of signaling molecules 3-oxo-C12-HSL and C4-HSL in the QS system of PAO1. Quercetin was also able to compete with the natural ligands OdDHL, BHL, and PQS for binding to the receptor proteins LasR, RhlR, and PqsR, respectively, resulting in the formation of more stabilized complexes. Taken together, quercetin exhibits enormous potential in combating LasB production and activity by disrupting the QS system of P. aeruginosa in vitro, thereby offering an alternative approach for the antivirulence therapy of P. aeruginosa infections. KEY POINTS: • Quercetin diminished the content and activity of LasB elastase of P. aeruginosa. • Quercetin inhibited the QS system activity of P. aeruginosa. • Quercetin acted on LasB based on the QS system.

Dopamine, an exogenous quorum sensing signaling molecule or a modulating factor in Pseudomonas aeruginosa?

Pseudomonas aeruginosa is recognized globally as an opportunistic pathogen of considerable concern due to its high virulence and pathogenicity, especially in immunocompromised individuals. While research has identified several endogenous quorum sensing (QS) signaling molecules that enhance the virulence and pathogenicity of P. aeruginosa, investigations on exogenous QS signaling molecules or modulating factors remain limited. This study found that dopamine serves as an exogenous QS signaling molecule or modulating factor of P. aeruginosa PAO1, enhancing the production of virulence factors and biofilms. Compared to the control group, treatment with 40 μM dopamine resulted in a 33.1 % increase in biofilm formation, 68.1 % increase in swimming mobility, 63.1 % increase in swarming mobility, 147.2 % increase in the signaling molecule 3-oxo-C12-HSL, and 50.5 %, 28.5 %, 27.0 %, and 33.2 % increases in the virulence factors alginate, rhamnolipids, protease, and pyocyanin, respectively. This study further explored the mechanism of dopamine regulating the biofilm formation and virulence of P. aeruginosa PAO1 through transcriptome and metabolome. Transcriptomic analysis showed that dopamine promoted the expression of virulence genes psl, alg, lasA, rhlABC, rml, and phz in P. aeruginosa PAO1. Metabolomic analysis revealed changes in the concentrations of tryptophan, pyruvate, ethanolamine, glycine, 3-hydroxybutyric acid, and alizarin. Furthermore, KEGG enrichment analysis of altered genes and metabolites indicated that dopamine enhanced phenylalanine, tyrosine, and tryptophan in P. aeruginosa PAO1. The results of this study will contribute to the development of novel exogenous QS signaling molecules or modulating factors and advance our understanding of the interactions between P. aeruginosa and the host environment.

Combatting biofilm-mediated infections in clinical settings by targeting quorum sensing

Biofilm-associated infections constitute a significant challenge in managing infectious diseases due to their high resistance to antibiotics and host immune responses. Biofilms are responsible for various infections, including urinary tract infections, cystic fibrosis, dental plaque, bone infections, and chronic wounds. Quorum sensing (QS) is a process of cell-to-cell communication that bacteria use to coordinate gene expression in response to cell density, which is crucial for biofilm formation and maintenance.. Its disruption has been proposed as a potential strategy to prevent or treat biofilm-associated infections leading to improved treatment outcomes for infectious diseases. This review article aims to provide a comprehensive overview of the literature on QS-mediated disruption of biofilms for treating infectious diseases. It will discuss the mechanisms of QS disruption and the various approaches that have been developed to disrupt QS in reference to multiple clinical pathogens. In particular, numerous studies have demonstrated the efficacy of QS disruption in reducing biofilm formation in various pathogens, including Pseudomonas aeruginosa and Staphylococcus aureus. Finally, the review will discuss the challenges and future directions for developing QS disruption as a clinical therapy for biofilm-associated infections. This includes the development of effective delivery systems and the identification of suitable targets for QS disruption. Overall, the literature suggests that QS disruption is a promising alternative to traditional antibiotic treatment for biofilm-associated infections and warrants further investigation.

Synergism Between α-Terpineol and Terpinen-4-ol Potentiates Antivirulence Response Against Pseudomonas aeruginosa

Antivirulence strategies have emerged as next-generation therapies that are now becoming refractory to the use of traditional antimicrobial approaches. Considering the global medical burden associated with Pseudomonas aeruginosa infections, there is a pressing need to explore therapeutic alternatives. In this direction, the current study was aimed at investigating the combinational effects of α-terpineol (α-T) and terpinen-4-ol (T-4-ol), the principal bioactive components of tea tree oil, against P. aeruginosa. The phytochemical combination was examined for synergistic interaction and various biological properties, including antibacterial, quorum quenching (QQ), and antivirulence potential. α-T and T-4-ol displayed synergism and harbored profuse antibacterial properties against P. aeruginosa. The phytochemicals inhibited quorum sensing (QS) in biosensor strains of Agrobacterium tumefaciens and Chromobacterium violaceum by suppressing lacZ and diminishing violacein production, respectively. Moreover, α-T and T-4-ol, independently and in combination, extended antivirulence response by significantly reducing hemolysin, pyocyanin, pyochelin, and total protease production in P. aeruginosa PAO1 and PA14. Hence, this study suggests that the phytochemical combination of α-T and T-4-ol can be used as a potent antivirulence elixir over antibiotics to combat P. aeruginosa.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-024-01189-7.

PA5402-5407 of Pseudomonas aeruginosa Regulate the Expression of the Aa3-Type Oxidases and Their Growth Under Carbon Starvation and High-Density Conditions

Our previous studies identified PA5407 in Pseudomonas aeruginosa as a new regulatory protein for bacterial division and named it ZapAL. This protein enhances the assembly of the key bacterial division protein FtsZ and participates in the assembly of the bacterial Z-ring, but its physiological function is not clear. ZapAL is in the same gene cluster as PA5402-5406, and in this study, we found that these genes are involved in the regulation of bacterial growth under nutrient deficiency and high-density conditions. The expression of Aa3 oxidase increases significantly at the end of the stationary phase of bacterial growth under aerobic conditions, and appropriately accelerate energy intake to adapt to the adversity. In our study, we found that the knockout of PA5402-5407 in P. aeruginosa promotes the further expression of Aa3 oxidase and its expression increased more and faster than the wild type, especially under carbon starvation and high-density conditions. This results in a larger bacteria population, but the average length of the bacteria is abnormally reduced. In summary, our study found that the P. aeruginosa gene cluster PA5402-5407 regulated the expression of Aa3 oxidase in the late stationary phase, and these genes balance energy intake, growth and division of bacteria under adverse conditions.

Assembly of functional microbial ecosystems: from molecular circuits to communities

Microbes compete and cooperate with each other via a variety of chemicals and circuits. Recently, to decipher, simulate, or reconstruct microbial communities, many researches have been engaged in engineering microbiomes with bottom-up synthetic biology approaches for diverse applications. However, they have been separately focused on individual perspectives including genetic circuits, communications tools, microbiome engineering, or promising applications. The strategies for coordinating microbial ecosystems based on different regulation circuits have not been systematically summarized, which calls for a more comprehensive framework for the assembly of microbial communities. In this review, we summarize diverse cross-talk and orthogonal regulation modules for de novo bottom-up assembling functional microbial ecosystems, thus promoting further consortia-based applications. First, we review the cross-talk communication-based regulations among various microbial communities from intra-species and inter-species aspects. Then, orthogonal regulations are summarized at metabolites, transcription, translation, and post-translation levels, respectively. Furthermore, to give more details for better design and optimize various microbial ecosystems, we propose a more comprehensive design-build-test-learn procedure including function specification, chassis selection, interaction design, system build, performance test, modeling analysis, and global optimization. Finally, current challenges and opportunities are discussed for the further development and application of microbial ecosystems.

Trends and implications of antimicrobial resistance in Pseudomonas aeruginosa: Insights from a 19-year study in Zhejiang Province

This study aimed to elucidate the resistance trends of P. aeruginosa isolates from 2005 to 2023 in Zhejiang Province, emphasizing the impact of Coronavirus disease 2019 (COVID-19) on antimicrobial resistance patterns and clinical management. We retrospectively analyzed 7326 P. aeruginosa isolates collected from diverse clinical sources in a tertiary hospital in Zhejiang Province from 2005 to 2023. Identification and antibiotic susceptibility testing of each isolate were performed using the VITEK-32 automated system and the disk diffusion method, following Clinical and Laboratory Standards Institute guidelines. We assessed resistance patterns for key antibiotic classes relevant to P. aeruginosa treatment, including carbapenems, β-lactams, aminoglycosides, and quinolones. Statistical analyses, including trend evaluations and resistance determinant assessments, were conducted in R software (version 4.2.2), with visualizations generated through ggplot2 to illustrate resistance trends over time. This study focused on key anti-pseudomonal agents including carbapenems (imipenem and meropenem), β-lactams (piperacillin), and quinolones (ciprofloxacin and levofloxacin). We observed a progressive increase in resistance to imipenem from 6.8% in 2005 to 48.2% in 2023 and meropenem from 25.4% to 44.2% over the same period. Conversely, resistance rates to aminoglycosides declined, with gentamicin resistance dropping from 22.0% in 2005 to 5.0% in 2019. Cephalosporins exhibited variable trends, with cefepime resistance peaking at 40.4% in 2013 before declining to 12.1% in 2023. The findings indicated a progressive increase in resistance rates for these antibiotics, with notable peaks coinciding with changes in clinical practices and the COVID-19 pandemic. The analysis demonstrated that shifts in prescription habits, particularly during the COVID-19 pandemic, influenced resistance patterns, underscoring the need for context-specific antimicrobial stewardship strategies. This study identifies significant, evolving resistance patterns in P. aeruginosa over a 19-year period, with marked increases in resistance to critical antibiotics, including carbapenems (imipenem, meropenem), quinolones (levofloxacin, ciprofloxacin), and certain β-lactams (piperacillin). These findings underscore an urgent need for dynamic, tailored infection control measures, emphasizing the importance of robust antibiotic stewardship programs, localized treatment guidelines, and proactive monitoring of resistance trends. Implementing these strategies is essential to effectively counter the challenges posed by multi-drug resistant P. aeruginosa, improve patient outcomes, and sustain the efficacy of vital antibiotic therapies.

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.

Antimicrobial Potency of Nor-Pyochelin Analogues and Their Cation Complexes against Multidrug-Resistant Pathogens

The opportunistic pathogen Pseudomonas aeruginosa develops increasing resistance toward even the most potent antibiotics. Like other bacteria, the pathogen produces a number of virulence factors including metallophores, which constitute an important group. Pseudomonads produce the iron-chelating metallophore (siderophore) pyochelin, which, in addition to its iron-scavenging ability, is an effector for the transcriptional regulator PchR in its FeIII-bound form (ferripyochelin). In the present study, docking studies predicted a major ferripyochelin binding site in PchR, which prompted the exploration of nor-pyochelin analogues to produce tight binding to PchR, and thereby upregulation of the pyochelin metabolism. In addition, we investigated the effects of using the analogues to bind the antimicrobial cations GaIII and InIII. Selected analogues of nor-pyochelin were synthesized, and their GaIII- and InIII-based complexes were assessed for antimicrobial activity. The results indicate that the GaIII complexes inhibit the pathogens under iron-limited conditions, while the InIII-based systems are more effective in iron-rich media. Several of the GaIII complexes were shown to be highly effective against a multidrug-resistant P. aeruginosa clinical isolate, with minimum inhibitory concentrations (MICs) of ≤1 μg/mL. Similarly, two of the InIII-based systems were particularly effective against the isolate, with an MIC of 8 μg/mL. These results show high promise in comparison with other, traditionally potent antibiotics, as the compounds generally indicated low cytotoxicity toward mammalian cells. Preliminary mechanistic investigations using pseudomonal transposon mutants suggested that the inhibitory effects of the InIII-based systems could be due to acute iron deficiency as a result of InIII-bound bacterioferritin.

Polymicrobial interactions between Staphylococcus aureus and Pseudomonas aeruginosa promote biofilm formation and persistence in chronic wound infections

Chronic, non-healing wounds are a leading cause of prolonged patient morbidity and mortality due to biofilm- associated, polymicrobial infections. Staphylococcus aureus and Pseudomonas aeruginosa are the most frequently co-isolated pathogens from chronic wound infections. Competitive interactions between these pathogens contribute to enhanced virulence, persistence, and antimicrobial tolerance. P. aeruginosa utilizes the extracellular proteases LasB, LasA, and AprA to degrade S. aureus surface structures, disrupt cellular physiology, and induce cell lysis, gaining a competitive advantage during co-infection. S. aureus evades P. aeruginosa by employing aggregation mechanisms to form biofilms. The cell wall protein SasG is implicated in S. aureus biofilm formation by facilitating intercellular aggregation upon cleavage by an extracellular protease. We have previously shown that proteolysis by a host protease can induce aggregation. In this study, we report that P. aeruginosa proteases LasA, LasB, and AprA cleave SasG to induce S. aureus aggregation. We demonstrate that SasG contributes to S. aureus biofilm formation in response to interactions with P. aeruginosa proteases by quantifying aggregation, SasG degradation, and proteolytic kinetics. Additionally, we assess the role of SasG in influencing S. aureus biofilm architecture during co-infection in vivo, chronic wound co-infections. This work provides further knowledge of some of the principal interactions that contribute to S. aureus persistence within chronic wounds co-infected with P. aeruginosa, and their impact on healing and infection outcomes.

Strategies for quorum sensing inhibition as a tool for controlling Pseudomonas aeruginosa infections

Antibiotic resistance is one of the most important concerns in global health today. A growing number of infections are becoming harder to treat with conventional drugs and fewer new antibiotics are being developed. In this context, strategies based on blocking or attenuating virulence pathways that do not focus on eradication of bacteria are potential therapeutic approaches that should reduce the selective pressure exerted on the pathogen. This virulence depletion can be achieved by inhibiting the conserved quorum sensing (QS) system, a mechanism that enables bacteria to communicate with one another in a density-dependent manner. QS regulates gene expression, leading to the activation of important processes such as virulence and biofilm formation. This review highlights the approaches reported so far for disrupting different steps of the QS system of the multiresistant pathogen Pseudomonas aeruginosa. The authors describe different types of molecules (including enzymes, natural and synthetic small molecules, and antibodies) already identified as P. aeruginosa quorum quenchers (QQs) or QS inhibitors (QSIs), grouped according to the QS circuit that they block (Las, Rhl, Pqs and some examples from the controversial pathway Iqs). The discovery of new QQs and QSIs is expected to help reduce antibiotic doses, or at least to provide options that act as adjuvants to enhance the effect of antibiotic treatment. Moreover, this article outlines the advantages and possible drawbacks of each strategy and provides perspectives on the potential developments in this field in the future.

Isovanillin decreases the virulence regulated by the quorum sensing system of Pseudomonas aeruginosa

The quorum-sensing (QS) system of Pseudomonas aeruginosa dominates the pathogenicity of the acute or chronic infection process. Hence, curbing the pathogenicity of P. aeruginosa by targeting QS system is an ideal strategy. This study aims to identify potential anti-virulence compounds that can effectively disrupt the QS system of P. aeruginosa using a combination of virtual screening and experimental validation techniques. We explored inhibitory effect of isovanillin obtained by virtual screening on P. aeruginosa QS regulated virulence factors extracellular protease, biofilm, and pyocyanin. Results displayed that isovanillin could inhibit the virulence phenotypes regulated by the las- and pqs-QS systems of P. aeruginosa. The synthesis of extracellular proteases, pyocyanin, and biofilm formation by P. aeruginosa were dramatically inhibited by sub-MICs doses of isovanillin. The results of RNA sequencing and quantitative PCR revealed that the QS-activated genes down-regulated by subinhibitory isovanillin in the transcriptional evels. Furthermore, the presence of isovanillin increased the susceptibility of drug-resistant P. aeruginosa to kanamycin, meropenem, and polymyxin B. Treatment of isovanillin as a monotherapy significantly decreased the mortality of C. elegans in P. aeruginosa PAO1 or UCBPP-PA14 (PA14) infection. Our study reported the anti-virulence activity of isovanillin against P. aeruginosa, and provided a structural foundation for developing anti-virulence drugs targeting the QS system of P. aeruginosa.

Novel benzothiazole derivatives target the Gac/Rsm two-component system as antibacterial synergists against Pseudomonas aeruginosa infections

The management of antibiotic-resistant, bacterial biofilm infections in skin wounds poses an increasingly challenging clinical scenario. Pseudomonas aeruginosa infection is difficult to eradicate because of biofilm formation and antibiotic resistance. In this study, we identified a new benzothiazole derivative compound, SN12 (IC50 = 43.3 nmol/L), demonstrating remarkable biofilm inhibition at nanomolar concentrations in vitro. In further activity assays and mechanistic studies, we formulated an unconventional strategy for combating P. aeruginosa-derived infections by targeting the two-component (Gac/Rsm) system. Furthermore, SN12 slowed the development of ciprofloxacin and tobramycin resistance. By using murine skin wound infection models, we observed that SN12 significantly augmented the antibacterial effects of three widely used antibiotics-tobramycin (100-fold), vancomycin (200-fold), and ciprofloxacin (1000-fold)-compared with single-dose antibiotic treatments for P. aeruginosa infection in vivo. The findings of this study suggest the potential of SN12 as a promising antibacterial synergist, highlighting the effectiveness of targeting the two-component system in treating challenging bacterial biofilm infections in humans.

Tracing the path of Quorum sensing molecules in cystic fibrosis mucus in a biomimetic in vitro permeability platform

P. aeruginosa employs specific quorum sensing (QS) mechanisms to orchestrate biofilm formation, enhancing resistance to host defences. In physiological conditions, QS molecules permeate the lung environment and cellular membrane to reach the cytoplasmic Aryl Hydrocarbon Receptor (AhR) that is pivotal for activating the immune response against infection. In pathological conditions like cystic fibrosis (CF) this interkingdom communication is altered, favouring P. aeruginosa persistence and chronic infection. Here, we aim to investigate the molecular journey of QS molecules from CF-like environments to the cytoplasm by quantifying via HPLC-MS the permeability of selected QS molecules (quinolones, lactones, and phenazines) through in vitro models of the two main biological lung barriers: CF-mucus and cellular membrane. While QS molecules not activating AhR exhibit intermediate permeability through the cellular membrane model (PAMPA) (1.0-4.0 × 10-6 cm/s), the AhR-activating molecule (pyocyanin) shows significantly higher permeability (8.6 ± 1.4 × 10-6 cm/s). Importantly, combining the CF mucus model with PAMPA induces a 50% decrease in pyocyanin permeability, indicating a strong mucus-shielding effect with pathological implications in infection eradication. This study underscores the importance of quantitatively describing the AhR-active bacterial molecules, even in vitro, to offer new perspectives for understanding P. aeruginosa virulence mechanisms and for proposing new antibacterial therapeutic approaches.

New 24-Membered Macrolactines from an Arctic Bacterium Bacillus amyloliquefaciens SCSIO 41392 and Their Anti-Pathogenicity Evaluation

Three new 24-membered macrolactines, amylomacrolactines A-C (1-3), along with two known compounds 4 and 5, were isolated from the Arctic bacteria Bacillus amyloliquefaciens SCSIO 41392. The configurations of 1-3 were assigned by a combination of coupling constants, NOESY, and analysis of MM2-optimized conformation, as well as by comparison with reports in the literature. Compounds 1 and 2 showed quorum sensing (QS) inhibitory activities against the Pseudomonas aeruginosa (P. aeruginosa) PQS system and suppressed PQS-regulated virulence factor pyocyanin synthesis. In addition, compounds 3-5 affected the production of another essential virulence factor, siderophore of pyoverdine (PVD), in P. aeruginosa. More importantly, compound 5 showed an anti-biofilm activity against P. aeruginosa. Altogether, the isolated compounds displayed multiple bacterial virulence inhibition activities, which is worthy of further exploration for novel analogues in antimicrobial drug development.

New LsrK Ligands as AI-2 Quorum Sensing Interfering Compounds against Biofilm Formation

Antimicrobial resistance (AMR) represents a critical global health crisis. An innovative strategy to deal with AMR is to interfere with biofilm formation and bacterial quorum sensing (QS). In this study, newly designed autoinducer-2 (AI-2)-inspired compounds in targeting biofilm-associated infections were evaluated for their ability to inhibit biofilm formation in Staphylococcus aureus and Pseudomonas aeruginosa. The most effective compounds, 5d, 5e, and 7b, exhibited potent antibiofilm activity with minimal inhibitory concentrations in the low microgram per mL range. Detailed biological assays confirmed that the antibiofilm activity was primarily driven through AI-2 QS inhibition rather than direct antimicrobial effects. The combination of different spectroscopic techniques, such as differential scanning fluorimetry, intrinsic tryptophan fluorescence, circular dichroism, and nuclear magnetic resonance, elucidated the binding between the compounds and the LsrK enzyme, a key player in AI-2 mediated QS. Our findings highlight the potential of these novel QS inhibitors as promising therapeutic agents against biofilm-associated infections.

Synergistic effect of the combination of phenolic compounds and tobramycin on the inhibition of Pseudomonas aeruginosa biofilm

Bacteria coordinate gene expression in a cell density-dependent manner using a communication process called quorum sensing (QS). The expression of virulence factors, biofilm formation and enzyme production are examples of QS-regulated phenotypes that can interfere with food quality and safety. Due to the importance of these phenotypes, the inhibition of bacterial communication as an anti-virulence strategy is of great interest. This work aimed to evaluate the effect of phenolic compounds on the inhibition of biofilm formation by Pseudomonas aeruginosa PAO1, using concentrations that do not interfere in bacterial growth. The synergistic effect of rosmarinic acid, baicalein, curcumin and resveratrol with tobramycin and between the phenolics themselves was evaluated. The tested combinations proved to be a good strategy for reducing the dose of antibiotics used in treatments and obtaining satisfactory results against P. aeruginosa biofilms. The combination of the four compounds at the highest concentration (500 μM) completely inhibited biofilm formation. The obtained results contribute to understanding the effect of phenolic compounds on QS inhibition, which may help to define the mechanism of inhibition, in addition to expanding the biotechnological potential of these compounds for future applications in the food, pharmaceutical and medical fields.

Quorum sensing and antibiotic resistance in polymicrobial infections

Quorum sensing (QS) is a critical bacterial communication system regulating behaviors like biofilm formation, virulence, and antibiotic resistance. This review highlights QS's role in polymicrobial infections, where bacterial species interactions enhance antibiotic resistance. We examine QS mechanisms, such as acyl-homoserine lactones (AHLs) in Gram-negative bacteria and autoinducing peptides (AIPs) in Gram-positive bacteria, and their impact on biofilm-associated antibiotic resistance. The challenges uniquely associated with polymicrobial infections, such as those found in cystic fibrosis lung infections, chronic wound infections, and medical device infections, are also summarized. Furthermore, we explore various laboratory models, including flow cells and dual-species culture models, used to study QS interactions in polymicrobial environments. The review also discusses promising quorum sensing inhibitors (QSIs), such as furanones and AHL analogs, which have demonstrated efficacy in reducing biofilm formation and virulence in laboratory and clinical studies. By addressing the interplay between QS and antibiotic resistance, this paper aims to advance therapeutic strategies that disrupt bacterial communication and improve antibiotic efficacy, ultimately mitigating the global challenge of antibiotic resistance in polymicrobial infections.

Mucosal sugars delineate pyrazine vs pyrazinone autoinducer signaling in Klebsiella oxytoca

Virulent Klebsiella oxytoca strains are associated with gut and lung pathologies, yet our understanding of the molecular signals governing pathogenesis remains limited. Here, we characterized a family of K. oxytoca pyrazine and pyrazinone autoinducers and explored their roles in microbial and host signaling. We identified the human mucin capping sugar Neu5Ac as a selective elicitor of leupeptin, a protease inhibitor prevalent in clinical lung isolates of K. oxytoca, and leupeptin-derived pyrazinone biosynthesis. Additionally, we uncovered a separate pyrazine pathway, regulated by general carbohydrate metabolism, derived from a broadly conserved PLP-dependent enzyme. While both pyrazine and pyrazinone signaling induce iron acquisition responses, including enterobactin biosynthesis, pyrazinone signaling enhances yersiniabactin virulence factor production and selectively activates the proinflammatory human histamine receptor H4 (HRH4). Our findings suggest that the availability of specific carbohydrates delineates distinct autoinducer pathways in K. oxytoca that may have differential effects on bacterial virulence and host immune responses.

Free-swimming bacteria transcriptionally respond to shear flow

Surface-attached cells can sense and respond to shear flow, but planktonic (free-swimming) cells are typically assumed to be oblivious to any flow that carries them. Here, we find that planktonic bacteria can transcriptionally respond to flow, inducing expression changes that are beneficial in flow. Specifically, we use microfluidic experiments and quantitative modeling to show that in the presence of flow, planktonic Pseudomonas aeruginosa induce shear rate-dependent genes that promote growth in low-oxygen environments. Untangling this mechanism revealed that in flow, motile P. aeruginosa spatially redistribute, leading to cell density changes that activate quorum sensing, which in turn enhances the oxygen uptake rate. In diffusion-limited environments, including those commonly encountered by bacteria, flow-induced cell density gradients also independently generate oxygen gradients that alter gene expression. Mutants deficient in this flow-responsive mechanism exhibit decreased fitness in flow, suggesting that this dynamic coupling of biological and mechanical processes can be physiologically significant.

Novel humanized anti-PcrV monoclonal antibody COT-143 protects mice from lethal Pseudomonas aeruginosa infection via inhibition of toxin translocation by the type III secretion system

Treatment of Pseudomonas aeruginosa infection is challenging due to its intrinsic and acquired antibiotic resistance. As the number of current therapeutic options for P. aeruginosa infections is limited, developing novel treatments against the pathogen is an urgent clinical priority. The suppression of virulence of P. aeruginosa could be a new therapeutic option, and the type III secretion system (T3SS), which enables the bacteria to translocate various kinds of toxins into host cells and inhibits cellular functions, is considered as one possible target. In this report, we examined T3SS inhibition by COT-143/INFEX702, a humanized monoclonal antibody against PcrV, T3SS component, and present the crystal structure of the antibody-PcrV complex. COT-143 inhibited T3SS-dependent cytotoxicity and protected mice from the mortality caused by P. aeruginosa infection. The inhibition of cytotoxicity coincided with inhibition of translocon formation in a host cell membrane, which is necessary for T3SS intoxication. COT-143 protected murine neutrophils and facilitated phagocytosis of P. aeruginosa. These results suggest that COT-143 facilitates P. aeruginosa clearance by protecting neutrophil via inhibition of T3SS-dependent toxin translocation. This is the first report to show that an anti-PcrV antibody directly interferes with translocon formation to inhibit intoxication of host cells.

Fuzheng Touxie Jiedu Huayu Decoction inhibits the MexAB-OprM efflux pump and quorum sensing-mediated biofilm formation in difficult-to-treat multidrug resistance Pseudomonas aeruginosa

ETHNOPHARMACOLOGICAL RELEVANCE

Fuzheng Touxie Jiedu Huayu Decoction (FTJHD) is a commonly used clinical formula that has been found effective in resisting multidrug resistance-Pseudomonas aeruginosa in previous in vivo and in vitro studies.

AIM OF THE STUDY

To investigate the antimicrobial effects of FTJHD and its drug-containing serum alone or in combination with ceftazidime on difficult-to-treat multidrug resistance-P. aeruginosa (DTMDR-P. aeruginosa).

MATERIALS AND METHODS

The antibacterial effects of FTJHD and its drug-containing alone or in combination with ceftazidime against DTMDR-P. aeruginosa were examined by the tube dilution method and bacterial growth curves. The changes in the bacterial ultrastructure were examined by transmission electron microscopy. The biofilm formation ability of bacteria was examined by crystal violet staining and scanning electron microscopy. The expression of the MexAB-OprM efflux pump and quorum sensing system genes were validated through quantitative polymerase chain reaction. Molecular docking was used to evaluate the interaction between active components and the MexAB-OprM efflux pump.

RESULTS

FTJHD-containing serums at 1-, 2-, 4-, and 8-fold concentrations reduced the minimal inhibitory concentration (MIC) of ceftazidime against DTMDR-P. aeruginosa from 128 μg/mL to 64 μg/mL. Sub-inhibitory concentrations of ceftazidime in combination with FTJHD and FTJHD-containing serum prolonged the lag period of bacterial growth and reduced bacterial numbers. Additionally, 1/2 MIC of ceftazidime combined with FTJHD-containing serum significantly inhibited the activity of the MexAB-OprM efflux pump and quorum sensing system, thus reducing biofilm formation while causing more severe damage to the bacteria. Molecular docking revealed a strong affinity of quercetin, baicalein, luteolin, kaempferol, and β-sitosterol for the efflux pump regulatory proteins OprM and MexR.

CONCLUSION

FTJHD can exert synergistic anti-DTMDR-P. aeruginosa effects with ceftazidime by inhibiting biofilm formation mediated by the MexAB-OprM efflux pump and quorum sensing.

Mutation of Pseudomonas aeruginosa lasI/rhlI diminishes its cytotoxicity, oxidative stress, inflammation, and apoptosis on THP-1 macrophages

The management of Pseudomonas aeruginosa (P. aeruginosa) infections presents a substantial challenge to clinics and public health, emphasizing the urgent need for innovative strategies to address this issue. Quorum sensing (QS) is an intercellular communication mechanism that coordinates bacterial activities involved in various virulence mechanisms, such as acquiring host nutrients, facilitating biofilm formation, enhancing motility, secreting virulence factors, and evading host immune responses, all of which play a crucial role in the colonization and infection of P. aeruginosa. The LasI/R and RhlI/R sub-systems dominate in the QS system of P. aeruginosa. Macrophages play a pivotal role in the host's innate immune response to P. aeruginosa invasion, particularly through phagocytosis as the initial host defense mechanism. This study investigated the effects of P. aeruginosa's QS system on THP-1 macrophages. Mutants of PAO1 with lasI/rhlI deletion, as well as their corresponding complemented strains, were obtained, and significant downregulation of QS-related genes was observed in the mutants. Furthermore, the ΔlasI and ΔlasIΔrhlI mutants exhibited significantly attenuated virulence in terms of biofilm formation, extracellular polymeric substances synthesis, bacterial adhesion, motility, and virulence factors production. When infected with ΔlasI and ΔlasIΔrhlI mutants, THP-1 macrophages exhibited enhanced scavenging ability against the mutants and demonstrated resistance to cytotoxicity, oxidative stress, inflammatory response, and apoptosis induced by the culture supernatants of these mutant strains. These findings offer novel insights into the mechanisms underlying how the lasI/rhlI mutation attenuates cytotoxicity, oxidative stress, inflammation, and apoptosis in macrophages induced by P. aeruginosa.IMPORTANCEP. aeruginosa is classified as one of the ESKAPE pathogens and poses a global public health concern. The QS system of this versatile pathogen contributes to a broad spectrum of virulence, thereby constraining therapeutic options for serious infections. This study illustrated that the lasI/rhlI mutation of the QS system plays a prominent role in attenuating the virulence of P. aeruginosa by affecting bacterial adhesion, biofilm formation, extracellular polymeric substances synthesis, bacterial motility, and virulence factors' production. Notably, THP-1 macrophages infected with mutant strains exhibited increased phagocytic activity in eliminating intracellular bacteria and enhanced resistance to cytotoxicity, oxidative stress, inflammation, and apoptosis. These findings suggest that targeted intervention toward the QS system is anticipated to diminish the pathogenicity of P. aeruginosa to THP-1 macrophages.

The anti-quorum sensing and biofilm inhibitory potential of Piper betle L. leaf extract and prediction of the roles of the potent phytocompounds

The leaves of Piper betle L., known as betel leaf, have immense medicinal properties. It possesses potent antimicrobial efficacies and can be a valuable tool to combat drug-resistant microorganisms. Quorum sensing (QS) inhibition is one of the best strategies to combat drug resistance. The present study investigates the anti-quorum sensing and biofilm inhibitory potential of Piper betle L. leaf extract against two bacterial strains, Chromobacterium violaceum and Pseudomonas aeruginosa. The extract produced substantial QS-inhibition zones in a biosensor strain of C. violaceum (CV026), indicating interference with quorum-sensing signals. The Results demonstrated significant inhibition in biofilm formation and different QS-regulated virulence factors (violacein, exopolysaccharides, pyocyanin, pyoverdine, elastase) in both C. violaceum and P. aeruginosa at sub-MIC concentrations of the extract and tetracycline, an antibiotic with known anti-QS activity. The quantitative real-time PCR (qRT-PCR) revealed decreased gene expression in different QS-related genes in C. violaceum (cviI, cviR, and vioA) and P. aeruginosa (lasI, lasR, lasB, rhlI, rhlR, and rhlA) strains after treatment. Gas Chromatography-Mass Spectrometry (GC-MS) analysis identified the significant phytocompounds, mainly derivatives of chavicol and eugenol, in the extract. Of these compounds, chavicol acetate (affinity: -7.00 kcal/mol) and acetoxy chavicol acetate (affinity: -7.87 kcal/mol) showed the highest potential to bind with the CviR and LasR protein, respectively, as evident from the in-silico molecular docking experiment. The findings of this endeavour highlight the promising role of Piper betle L. as a source of natural compounds with anti-quorum sensing properties against pathogenic bacteria, opening avenues for developing novel therapeutic agents to combat bacterial infections.

Wake biofilm up to enhance suicidal uptake of gallium for chronic lung infection treatment

The hypometabolic and nutrient-limiting condition of dormant bacteria inside biofilms reduces their susceptibility to antibacterial agents, making the treatment of biofilm-dominating chronic infections difficult. Herein, we demonstrate an intratracheal aerosolized maltohexaose-modified catalase-gallium integrated nanosystem that can 'wake up' dormant Pseudomonas aeruginosa biofilm to increase the metabolism and nutritional iron demand by reconciling the oxygen gradient. The activated bacteria then enhance suicidal gallium uptake since gallium acts as a 'Trojan horse' to mimic iron. The internalized gallium ions disrupt biofilms by interfering with the physiological processes of iron ion acquisition and utilization, biofilm formation, and quorum sensing. Furthermore, aerosol microsprayer administration and bacteria-specific maltohexaose modification enable accumulation at biofilm-infected lung and targeted release of gallium into bacteria to improve the therapeutic effect. This work provides a potential strategy for treating infection by reversing the dormant biofilm's resistance condition.

Novel Insights into Cr(VI)-Induced Rhamnolipid Production and Gene Expression in Pseudomonas aeruginosa RW9 for Potential Bioremediation

Rhamnolipid (RL) is renowned for its efficacy in bioremediating several types of organic and metal contaminants. Nevertheless, there has been a scarcity of studies specifically examining the relationship between this substance and metals, especially in terms of their impact on RL formation and the underlying interaction processes. This study addresses this gap by investigating the RL mechanism in Cr (VI) remediation and evaluating its effect on RL production in Pseudomonas aeruginosa RW9. In this study, P. aeruginosa RW9 was grown in the presence of 10 mg l-1 Cr (VI). We monitored RL yield, congeners distribution, and their ratios, as well as the transcriptional expression of the RL-encoded genes: rhlA, rhlB, and rhlC. Our results revealed that RL effectively reduced Cr (VI) to Cr (III), with RL yield increasing threefold, although with a slight delay in synthesis compared to control cells. Furthermore, Cr (VI) exposure induced the transcriptional expression of the targeted genes, leading to a significant increase in di-RL production. The findings confirm that Cr (VI) significantly impacts RL production, altering its structural compositions and enhancing the transcriptional expression of RL-encoded genes in P. aeruginosa RW9. This study represents a novel exploration of Cr (VI)'s influence on RL production, providing valuable insights into the biochemical pathways involved and supporting the potential of RL in Cr (VI) bioremediation.

Hybrids of 3-Hydroxypyridin-4(1H)-ones and Long-Chain 4-Aminoquinolines as Potent Biofilm Inhibitors of Pseudomonas aeruginosa Potentiate Tobramycin and Polymyxin B Activity

The biofilm formation of Pseudomonas aeruginosa involves multiple complex regulatory pathways; thus, blocking a single pathway is unlikely to achieve the desired antibiofilm efficacy. Herein, a series of hybrids of 3-hydroxypyridin-4(1H)-ones and long-chain 4-aminoquinolines were synthesized as biofilm inhibitors against P. aeruginosa based on a multipathway antibiofilm strategy. Comprehensive structure-activity relationship studies identified compound 30b as the most valuable antagonist, which significantly inhibited P. aeruginosa biofilm formation (IC50 = 5.8 μM) and various virulence phenotypes. Mechanistic studies revealed that 30b not only targets the three quorum sensing systems but also strongly induces iron deficiency signals in P. aeruginosa. Furthermore, 30b demonstrated a favorable in vitro and in vivo safety profile. Moreover, 30b specifically enhanced the antibacterial activity of tobramycin and polymyxin B in in vitro and in vivo combination therapy. Overall, these results highlight the potential of 30b as a novel anti-infective candidate for treating P. aeruginosa infections.