Pseudomonas aeruginosa Quorum Sensing

Pathogenicity and virulence of Pseudomonas aeruginosa: Recent advances and under-investigated topics

Pseudomonas aeruginosa is a model for the study of quorum sensing, protein secretion, and biofilm formation. Consequently, it has become one of the most intensely reviewed pathogens, with many excellent articles in the current literature focusing on these aspects of the organism's biology. Here, though, we aim to take a slightly different approach and consider some less well appreciated (but nonetheless important) factors that affect P. aeruginosa virulence. We start by reminding the reader of the global importance of P. aeruginosa infection and that the "virulome" is very niche-specific. Overlooked but obvious questions such as "what prevents secreted protein products from being digested by co-secreted proteases?" are discussed, and we suggest how the nutritional preference(s) of the organism might dictate its environmental reservoirs. Recent studies identifying host genes associated with genetic predisposition towards P. aeruginosa infection (and even infection by specific P. aeruginosa strains) and the role(s) of intracellular P. aeruginosa are introduced. We also discuss the fact that virulence is a high-risk strategy and touch on how expression of the two main classes of virulence factors is regulated. A particular focus is on recent findings highlighting how nutritional status and metabolism are as important as quorum sensing in terms of their impact on virulence, and how co-habiting microbial species at the infection site impact on P. aeruginosa virulence (and vice versa). It is our view that investigation of these issues is likely to dominate many aspects of research into this WHO-designated priority pathogen over the next decade.

Interplay of Mycobacterium abscessus and Pseudomonas aeruginosa in experimental models of coinfection: Biofilm dynamics and host immune response

The incidence of infection by nontuberculous mycobacteria, mainly Mycobacterium abscessus, is increasing in patients with cystic fibrosis and other chronic pulmonary diseases, leading to an accelerated lung function decline. In most cases, M. abscessus coinfects Pseudomonas aeruginosa, the most common pathogen in these conditions. However, how these two bacterial species interact during infection remains poorly understood. This study explored their behaviour in three relevant pathogenic settings: dual-species biofilm development using a recently developed method to monitor individual species in dual-species biofilms, coinfection in bronchial epithelial cells, and in vivo coinfection in the Galleria mellonella model. The results demonstrated that both species form stable mixed biofilms and reciprocally inhibit single-biofilm progression. Coinfections in bronchial epithelial cells significantly decreased cell viability, whereas in G. mellonella, coinfections induced lower survival rates than individual infections. Analysis of the immune response triggered by each bacterium in bronchial epithelial cell assays and G. mellonella larvae revealed that P. aeruginosa induces the overexpression of proinflammatory and melanization cascade responses, respectively. In contrast, M. abscessus and P. aeruginosa coinfection significantly inhibited the immune response in both models, resulting in worse consequences for the host than those generated by a single P. aeruginosa infection. Overall, this study highlights the novel role of M. abscessus in suppressing immune responses during coinfection with P. aeruginosa, emphasizing the clinical implications for the management of cystic fibrosis and other pulmonary diseases. Understanding these interactions could inform the development of new therapeutic strategies to mitigate the severity of coinfections in vulnerable patients.

Assessment of furobenzopyran from Ammi visnaga in disrupting Pseudomonas aeruginosa biofilms and suppressing associated virulence factors

Ammi visnaga, an herbal plant containing the furobenzopyran derivative (khellin) with therapeutic effects, remains unexplored for its potential to disrupt the biofilm formation and suppress the virulence factors mediated through the Las quorum-sensing system in Pseudomonas aeruginosa. The current study investigates the efficacy of khellin in inhibiting biofilm formation, suppressing biofilm-associated virulence factors at sub-minimum inhibitory concentration (sub-MIC) levels of ≤9 μg/mL, and its interactions with LasR are evaluated through molecular docking and dynamics simulation. In-silico analysis using the 'aBiofilm' web tool predicted a strong antibiofilm potential for khellin, with no prior reports of such activity. This prediction was supported by confocal laser scanning microscopy, which demonstrated significant biofilm inhibition at 9 μg/mL, along with noticeable microbial distortion. Further assessments showed that sub-MIC levels of khellin effectively reduced biofilm-associated virulence factors, including swimming and swarming motility, rhamnolipid content, cell surface hydrophobicity, alginate, and exopolysaccharide production, in a dose-dependent manner, though the extent of inhibition varied among these factors. Molecular docking analysis yielded a score of -7.285 kcal/mol, indicating a favorable binding, and 'Molecular Mechanics Generalized Born Surface Area' binding free energy of -28.32 kcal/mol confirms a stable and energetically favorable interaction with the target protein. The stability of the khellin-protein complex was validated through a 100 ns molecular dynamics simulation using the 'Optimized Potentials for Liquid Simulations-All Atom' force field model. Results of root mean square deviation, root mean square fluctuation, radius of gyration, intramolecular hydrogen bonds, molecular surface area, solvent accessible surface area, and polar surface area confirmed that khellin maintained stable interactions throughout the simulation. These findings suggest khellin as a potential candidate for treating Pseudomonas-associated biofilm infections and provide strong evidence that khellin may function as a quorum-sensing inhibitor of the P.aeruginosa's LasR protein.

In silico analysis of quorum sensing modulators: Insights into molecular docking and dynamics and potential therapeutic applications

Quorum sensing (QS) regulates bacterial functions like virulence and biofilm formation, mediated by proteins such as LasI and QscR in Pseudomonas aeruginosa. This study investigates the structural dynamics of LasI and QscR proteins in complex with Sulfamerazine and Sulfaperin, using AiiA lactonase as a negative control, through molecular dynamics (MD) simulations to identify potential QS modulators. Molecular docking and MD simulations assessed binding affinity and structural dynamics, analyzing parameters like docking scores, root-mean-square deviation (RMSD), root-mean-square fluctuation (RMSF), solvent-accessible surface area (SASA), radius of gyration (Rg), principal component analysis (PCA), and covariance analysis. Sulfamerazine exhibited the highest binding affinity for LasI based on docking scores, indicating strong ligand-protein interactions. MD simulations revealed stability in the LasI-Sulfamerazine complex, with lower RMSD compared to LasI-Sulfaperin and QscR complexes. RMSF analysis indicated greater flexibility in ligand-binding regions of LasI-Sulfaperin and QscR complexes, suggesting weaker binding. SASA showed a decrease in solvent-accessible surface area for the LasI-Sulfamerazine complex, supporting a compact structure. Rg values confirmed this, with the LasI-Sulfamerazine complex being more compact (~2.00 nm) than QscR-ligand complexes (2.10-2.30 nm). PCA revealed significant conformational changes in the LasI-Sulfamerazine complex, with PC1 explaining 57.26% variance. Covariance analysis indicated stronger residue coupling in the LasI-Sulfamerazine complex, suggesting higher rigidity, while LasI-Sulfaperin and QscR complexes exhibited flexible dynamics. AiiA lactonase was used as a negative control due to its established quorum quenching activity, which hydrolyzes AHL molecules and disrupts QS signaling. Unlike LasI and QscR, AiiA does not rely on small molecule binding for activation. However, a known LasI or QscR inhibitor would have served as a more appropriate positive control, which will be considered in future studies. These findings suggest the LasI-Sulfamerazine complex's stability and rigidity make Sulfamerazine a promising QS modulator. Computational analyses highlight its potential to disrupt bacterial communication. Further experimental validation is needed to confirm its therapeutic implications.

Modeling reciprocal adaptation of Staphylococcus aureus and Pseudomonas aeruginosa co-isolates in artificial sputum medium

Co-infections by Staphylococcus aureus and Pseudomonas aeruginosa are frequent in the airways of patients with cystic fibrosis. These co-infections show higher antibiotic tolerance in vitro compared to mono-infections. In vitro models have been developed to study the interspecies interactions between P. aeruginosa and S. aureus. However, these model systems fail to incorporate clinical isolates with diverse phenotypes, do not reflect the nutritional environment of the CF airway mucus, and/or do not model the biofilm mode of growth observed in the CF airways. Here, we established a dual-species biofilm model grown in artificial sputum medium, where S. aureus was inoculated before P. aeruginosa to facilitate the maintenance of both species over time. It was successfully applied to ten pairs of clinical isolates exhibiting different phenotypes. Co-isolates from individual patients led to robust, stable co-cultures, supporting the theory of cross-adaptation in vivo. Investigation into the cross-adaptation of the VBB496 co-isolate pair revealed that both the P. aeruginosa and S. aureus isolates had reduced antagonism, in part due to reduced production of P. aeruginosa secondary metabolites as well as higher tolerance to those metabolites by S. aureus. Together, these results indicate that the two-species biofilm model system provides a useful tool for exploring interspecies interactions of P. aeruginosa and S. aureus in the context of CF airway infections.

Two cinnamic acid derivatives as inhibitors of Pseudomonas aeruginosa las and pqs quorum-sensing systems: Impact on biofilm formation and virulence factors

INTRODUCTION

Quorum sensing (QS) is a bacterial communication mechanism that regulates gene expression, playing a crucial role in various physiological processes. Interfering with this signalling pathway is a promising strategy to control bacterial pathogenicity and virulence.

OBJECTIVES

This study evaluated the potential of two cinnamic acid derivatives, ferulic and sinapic acids, to inhibit the las and pqs systems in Pseudomonas aeruginosa. Their effects on biofilm architecture, virulence factor production and bacterial motility were also investigated.

METHODS

Bioreporter strains and bioluminescence-based assays were used to evaluate the modulation of QS-activity by cinnamic acid-type phenolic acids. In addition, in silico docking analysis was performed to validate the binding interactions of the cinnamic acid derivatives with QS-receptors. The biofilm architecture was analysed by optical coherence tomography, and virulence factors production (pyoverdine, pyocyanin, total proteases, lipases, gelatinases and siderophores) and motility were measured by absorbance measurement and plate agar method.

RESULTS

Ferulic and sinapic acids at 1000 µg mL-1 inhibited the las and pqs systems by 90 % and 80 %, respectively. The N-3-oxododecanoyl-homoserine lactone production was reduced by 70 % (6.25 µg mL-¹). In silico analysis demonstrated that cinnamic acid derivatives exhibited comparable interactions and higher docking scores than reference ligands and inhibitors. Biofilm thickness decreased from 96 µm to 11 µm, and virulence factors and swarming motility were significantly impaired. The comparable anti-QS activity of cinnamic acid derivatives suggests that the additional methoxy group in sinapic acid does not directly contribute to its anti-QS effect.

CONCLUSION

Ferulic and sinapic acids compromised the biofilm architecture and virulence of P. aeruginosa through QS inhibition.

A comprehensive analysis of the effect of quorum-sensing molecule 3-oxo-C12-homoserine lactone on Candida auris and Candida albicans

Candida auris occupies similar niches in various infections as Pseudomonas aeruginosa; however, the details of their interspecies communication remain largely unknown. To gain deeper insights into this relationship, phenotypic and transcriptomic analyses were conducted in the presence of the primary P. aeruginosa quorum-sensing molecule, N-(3-oxododecanoyl)-l-homoserine lactone (HSL), against C. auris, with the results compared to those of C. albicans. Our findings indicate that HSL-induced effects are not specific to C. albicans; additionally, several characteristics are present in C. auris but not in C. albicans following HSL exposure. Significant HSL-induced reduction was observed in growth and adhesion of C. auris cells in time -and concentration-dependent way (p < 0.01-0.001). Moreover, HSL reduced intracellular iron and zinc levels (p < 0.05-0.001); furthermore, it modulated C. auris metabolism toward beta-oxidation, which may be associated with the observed reduction in in vivo virulence at lower HSL concentrations compared with C. albicans. RNA-sequencing transcriptome analysis of C. auris revealed 67 and 306 upregulated genes, as well as 111 and 168 downregulated genes, in response to 100 and 200-μM HSL, respectively. We identified 45 overlapping upregulated and 25 overlapping downregulated genes between the two HSL concentrations. Similar to other Candida-derived C12 compounds (e.g., farnesol), HSL reduces several C. auris survival strategies, which may significantly influence the nature of P. aeruginosa-C. auris co-habitation. In conclusion, the obtained findings on C. auris do not provide clear evidence that HSL mediated effects have any favourable consequences in terms of P. aeruginosa-C. auris co-colonisation and/or co-infections.

Temperature controls LasR regulation of piv expression in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa causes debilitating lung infections in people with cystic fibrosis, as well as eye, burn, and wound infections in otherwise immunocompetent individuals. Many of P. aeruginosa's virulence factors are regulated by environmental cues, such as temperature and cell density. One such virulence factor is protease IV. Prior studies have shown that piv expression is higher at ambient temperatures (22°C-28°C) compared to human body temperature (37°C) and also upregulated by the LasRI quorum sensing system, although it is unclear how. We found that piv expression was thermoregulated at stationary phase, but not exponential phase, and that piv is thermoregulated at the level of transcription. Using a transcriptional reporter for piv, we show that LasR activates piv expression more at 25°C at stationary phase than at 37°C. We show that key components of the LasRI quorum sensing system are not upregulated at 25°C, suggesting that LasR regulatory activity is not higher intrinsically at this temperature. We also identified sequences within the piv promoter that are important for its thermoregulation. We propose that LasR upregulates piv more at 25°C than at 37°C. The finding that temperature controls LasR regulation of piv highlights the complex nature of gene regulatory systems in P. aeruginosa.IMPORTANCEPseudomonas aeruginosa is a versatile opportunistic pathogen capable of causing many different types of infections that are often difficult to treat, such as lung infections in people with cystic fibrosis. Temperature regulates the expression of many virulence factors that contribute to P. aeruginosa's ability to cause infection, yet our mechanistic understanding of virulence factor thermoregulation is poor. In this study, we show that the virulence factor protease IV is thermoregulated at the level of transcription through the quorum sensing regulator, LasR. Mechanistic studies of virulence factor thermoregulation will expand our understanding of how P. aeruginosa experiences different environments, including the mammalian host. Our work also highlights the importance of growth conditions in studying gene regulation, as it better elucidates the regulation of protease IV by LasR, which was previously not well understood.

Inhibitory effects of reumycin produced by Streptomyces sp. TPMA0082 on virulence factors of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen that causes a wide range of infections. The increasing multidrug-resistance of P. aeruginosa poses a critical challenge for medical care. P. aeruginosa employs virulence factors and biofilms to establish infections in humans and protect itself from environmental stress or antibiotics. These factors are regulated by a quorum sensing mechanism involving multiple regulatory systems that act interdependently through signaling molecules. Therefore, interference with quorum sensing systems can suppress the pathogenicity of P. aeruginosa. In this study, quorum sensing inhibitors were explored from secondary metabolites derived from 111 strains of actinomycetes by targeting the las system, which is thought to be upstream of the quorum sensing cascade in P. aeruginosa. As a result, reumycin was isolated from the culture broth of Streptomyces sp. TPMA0082. Reumycin, a molecule containing a pyrimidotriazine ring, inhibited the binding of the autoinducer to the LasR receptor in the las system, thereby suppressing the production of P. aeruginosa virulence factors, including pyocyanin, rhamnolipids, elastase, motility, and biofilms, without affecting bacterial growth. Toxoflavin, a reumycin derivative with a methyl group at the N1 position, exhibited strong antibacterial activity. Fervenulin, a reumycin derivative with a methyl group at the N8 position, had a negative impact on the logarithmic growth phase of the bacteria and exhibited lower inhibitory activity against virulence factor production compared to reumycin. These findings suggest that the position and number of methyl groups attached to the pyrimidotriazine structure significantly influence its biological activity, exerting distinct effects on quorum sensing inhibition and antibacterial activity.

Molecular simulation-based investigation of thiazole derivatives as potential LasR inhibitors of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa), a very resilient pathogen, demonstrates a diverse array of virulence factors, the expression of which is closely linked to the quorum sensing(QS) mechanism, which facilitates cell-cell interaction. Quorum sensing (QS) inhibition is a promising strategy for combating bacterial infections. LasR, a transcriptional factor that controls the mechanism of QS in P. aeruginosa, is a promising target for therapeutic development, because a lot of research has been done on its structure. It has already been established that thiazoles and their compounds have anti-QS potential against P aeruginosa. The study aims to identify new LasR quorum sensing inhibitors (QSIs) derived from novel thiazoles utilizing a structure-based virtual screening technique using the ZINC database. A complete set of 800 molecules (a novel thiazole derivative library) were docked inside the active region of the LasR receptor before being screened using pharmacokinetic and toxicology studies. Among the derivatives that were examined, compounds D_152, D_153, and L_331 were selected as potential inhibitors of LasR in P. aeruginosa and further studied to obtain a crucial understanding of the binding interactions that take place between inhibitor ligands and LasR. The findings indicated that the pharmacophoric characteristics of the derivative D_152 were comparable to those of the reference thiazole molecule (TC). Moreover, the molecular docking investigations showed that derivative D_152 and reference compound TC both fit the LasR protein's active area well. Furthermore, TC and D_152's amino acid interaction graphs with LasR and CviR are nearly identical. Furthermore, compound D_152's ability to engage with the LasR binding site through the dissolution of the protein's dimer was demonstrated by molecular dynamics modeling tests conducted over a 50 ns time span, demonstrating its function as a LasR antagonist. Additionally, Density Functional Theory (DFT) study was conducted on compound D_152 in order to determine the electron density of a molecule. According to the research findings, the recently produced thiazole derivative (D_152) has the potential to be used as a QSI against the LasR receptor, which would speed up the fight against the pathogenicity of P. aeruginosa that is resistant to multiple drugs.

Pseudomonas aeruginosa Quorum Signals; Associations with Virulence, and Impact of Therapeutic Gamma Radiation Doses

Quorum sensing (QS) signals are the fundamental regulators of P. aeruginosa cellular machinery. From this perspective, this study aimed to analyze a pathogenic Pseudomonas aeruginosa isolate quorum signals profile prior and following exposure to therapeutic gamma radiation doses, and associate them with their virulence. Analysis of quorum signals was conducted utilizing GC-Mass spectroscopy and CFM-ID 4.0 mass spectra prediction webserver. The correlation between these signals and P. aeruginosa virulence was investigated through in vitro and computational methods. The isolates pyocyanin, biosurfactant, and biofilm productions were quantified before and after gamma irradiation and the STRING-DB were used to scrutinize the QS synthesizing proteins interactions. Further, the Cytoscape software statistically analyzed the QS proteins-proteins interaction networks. The study reported the recovery of acyl-homoserine lactones (C2, C4, C6, and C12-HSLs) and fatty acid signals (DSFs) from the P. aeruginosa isolate ethyl acetate extract and proposed the potential isolation of longer-chain HSLs (> C12-HSLs). New functional associations were identified for QS synthesizing proteins, which involve spermidine, fatty acids, and siderophores biosynthesis. The irradiated P. aeruginosa extracts GC-MS chromatograms exhibited notable changes in the retention times of QS signals and their mass spectra with the retrieval of different forms of fatty acids esters. Additionally, irradiated P. aeruginosa demonstrated a modest increase in the production of both biofilms and biosurfactants. This finding indicated that changes in quorum signals profile post irradiation boosted P. aeruginosa virulence mechanisms, which may potentially lead to an exacerbation of infection pathogenesis following the application of therapeutic gamma radiation doses.

Quorum sensing inhibitors (QSIs): a patent review (2019-2023)

INTRODUCTION

The collective behavior of bacteria is regulated by Quorum Sensing (QS), in which bacteria release chemical signals and express virulence genes in a cell density-dependent manner. Quorum Sensing inhibitors (QSIs) are a large class of natural and synthetic compounds that have the potential to competitively inhibit the Quorum Sensing (QS) systems of several pathogens blocking their virulence mechanisms. They are considered promising compounds to deal with antimicrobial resistance, providing an opportunity to develop new drugs against these targets.

AREAS COVERED

The present review represents a comprehensive analysis of patents and patent applications available on Espacenet and Google Patent, from 2019 to 2023 referring to the therapeutic use of Quorum Sensing inhibitors.

EXPERT OPINION

Unlike classical antibiotics, which target the basic cellular metabolic processes, QSIs provide a promising alternative to attenuating virulence and pathogenicity without putting selective pressure on bacteria. The general belief is that QSIs pose no or little selective pressure on bacteria since these do not affect their growth. To date, QSIs are seen as the most promising alternative to traditional antibiotics. The next big step in this area of research is its succession to the clinical stage.

Antioxidant capacities and in vitro anti-microbial activities of rice (Oryza sativa var Bajong) from Borneo

Rice contains antioxidants and phenolic components that exert anti-inflammatory and anticancer properties. Different geographical areas produce rice with various chemical constituents and phytochemicals, in turn these confer differential protective effects including antimicrobial and anticancer properties. Sarawak rice, Oryza sativa var Bajong (Bajong), a fragrant dark purple rice grain harvested from two locations in Sarawak, namely interior Lubok Nibong (LN) and coastal Sri Aman (SA), was assessed for their antioxidant properties and antimicrobial activities. The rice was extracted using methanol solvent and evaluated for total phenolic content (TPC), total flavonoid contents (TFC), as well as their antioxidant and antimicrobial activities based on the Folin-Ciocalteu assay, the aluminium calorimetric method, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity and disk diffusion assay, respectively. Using dual-wavelength measurement, Bajong LN showed 2.16% higher amylose content than Bajong SA. Furthermore, 24-h extract of Bajong LN and 48-h extract of Bajong SA exhibited high antioxidant properties (34-70 µg/mL) and were rich in phenolic (46.54 ± 2.62 mg GAE/g; 25.28 ± 3.91 mg GAE/g) and flavonoid contents (5.53 ± 0.36 mg QCE/g; 7.7 ± 2.19 mg QCE/g) respectively. It is interesting to note that 72-h Bajong extract exhibited the largest zone of inhibition (9-9.3 mm) against Gram-negative Pseudomonas aeruginosa (Ps. aeruginosa), which correlated to the high TPC and TFC despite a reduction of antioxidant activity due to prolonged extraction hours. These significant results conferred added value to a staple, health-promoting Bajong had warranted it to be further investigated as a nutraceutical and pharmaceutical crop.

Influence of Amino Acids on Quorum Sensing-Related Pathways in Pseudomonas aeruginosa PAO1: Insights from the GEM iJD1249

BACKGROUND/OBJECTIVES

Amino acids (AAs) play a critical role in diseases such as cystic fibrosis where Pseudomonas aeruginosa PAO1 adapts its metabolism in response to host-derived nutrients. The adaptation influences virulence and complicates antibiotic treatment mainly for the antimicrobial resistance context. D- and L-AAs have been analyzed for their impact on quorum sensing (QS), a mechanism that regulates virulence factors. This research aimed to reconstruct the genome-scale metabolic model (GEM) of P. aeruginosa PAO1 to investigate the metabolic roles of D- and L-AAs in QS-related pathways.

METHODS

The updated GEM, iJD1249, was reconstructed by using protocols to integrate data from previous models and refined with well-standardized in silico media (LB, M9, and SCFM) to improve flux balance analysis accuracy. The model was used to explore the metabolic impact of D-Met, D-Ala, D-Glu, D-Ser, L-His, L-Glu, L-Arg, and L-Ornithine (L-Orn) at 5 and 50 mM in QS-related pathways, focusing on the effects on bacterial growth and carbon flux distributions.

RESULTS

Among the tested AAs, D-Met was the only one that did not enhance the growth rate of P. aeruginosa PAO1, while L-Arg and L-Orn increased fluxes in the L-methionine biosynthesis pathway, influencing the metH gene. These findings suggest a differential metabolic role for D-and L-AAs in QS-related pathways.

CONCLUSIONS

Our results shed some light on the metabolic impact of AAs on QS-related pathways and their potential role in P. aeruginosa virulence. Future studies should assess D-Met as a potential adjuvant in antimicrobial strategies, optimizing the concentration in combination with antibiotics to maximize its therapeutic effectiveness.

Modulation of the Pseudomonas aeruginosa quorum sensing cascade by MexT-regulated factors

Pseudomonas aeruginosa (Pa) uses quorum sensing (QS), a cell-cell communication system that enables it to sense cell density and to alter gene expression. Pa has three complete QS circuits controlled by the regulators LasR, RhlR, and PqsR, that together activate hundreds of genes. In the well-studied strain PAO1, QS is organized hierarchically, with PqsR and RhlR activity dependent on LasR. This hierarchy depends on the non-QS transcription factor MexT; deletion of mexT allows for RhlR activity in the absence of LasR. We aimed to identify how MexT modulates the Pa QS architecture. We compared the transcriptome of PAO1 to that of PAO1ΔmexT and determined a MexT regulon. We identified two MexT-regulated operons that may affect the QS hierarchy: the efflux pump genes mexEF-oprN and the Pseudomonas quinolone signal (PQS) synthesis genes pqsABCDE. We tested whether the products of these genes affected the QS hierarchy. A mexEF knockout mutant, like a mexT deletion mutant, exhibited RhlR activity earlier, and to a higher magnitude, than wild-type PAO1. MexEF-OprN is known to export quinolones, and we found that exogenous addition of PQS, through PqsE, also resulted in earlier and higher magnitude of RhlR activity compared to wild-type PAO1. We also discovered alternate QS architectures in clinical isolates, where RhlR activity is not fully dependent on LasR. In these isolates, surprisingly, MexT does not influence the relationship between LasR and RhlR. Our work reveals a new suite of factors that regulate QS in Pa, with implications for bacterial behaviors in environmental and clinical settings.

Chronic suppurative otitis media: disrupted host-microbial interactions and immune dysregulation

Recent research has uncovered new mechanisms that disrupt the balance between the host and microbes in the middle ear, potentially leading to dysbiosis and chronic suppurative otitis media (CSOM). Dysbiotic microbial communities, including core pathogens such as persister cells, are recognized for displaying cooperative virulence. These microbial communities not only evade the host's immune defenses but also promote inflammation that leads to tissue damage. This leads to uncontrolled disorder and pathogen proliferation, potentially causing hearing loss and systemic complications. In this discussion, we examine emerging paradigms in the study of CSOM that could provide insights into other polymicrobial inflammatory diseases. Additionally, we underscore critical knowledge gaps essential for developing a comprehensive understanding of how microbes interact with both the innate and adaptive immune systems to trigger and maintain CSOM.

LasB activation in Pseudomonas aeruginosa: Quorum sensing-mediated release of an auto-activation inhibitor

Pseudomonas aeruginosa secretes three major proteases: elastase B (LasB), protease IV (PIV), and elastase A (LasA), which play crucial roles in infection and pathogenesis. These proteases are activated sequentially from LasB in a proteolytic cascade, and LasB was previously thought to undergo auto-activation. However, our previous study suggested that LasB cannot auto-activate independently but requires additional quorum sensing (QS)-dependent factors for activation, as LasB remained inactive in QS-deficient P. aeruginosa (QS-) even under artificial overexpression. In this study, we provide evidence for the existence of a LasB inhibitor in QS- mutants: inactive LasB overexpressed in QS- strains was in its processed form and could be reactivated upon purification; when full-length LasB was overexpressed in Escherichia coli, a heterologous bacterium lacking both LasB activators and inhibitors, the protein underwent normal processing and activation; and purified active LasB was significantly inhibited by culture supernatant (CS) from QS- strains but not by CS from QS+ strains. These findings demonstrate that a LasB inhibitor exists in QS- strains, and in its absence, LasB can undergo auto-activation without requiring an activator. Based on these results, we propose an updated hypothesis: the QS-dependent LasB activator functions by removing the LasB inhibitor rather than acting directly on LasB itself, thus preventing premature LasB activation until QS response is initiated.

Design and synthesis of new quinazolinone derivatives: investigation of antimicrobial and biofilm inhibition effects

New quinazolin-4-ones 9-32 were synthesized in an attempt to overcome the life-threatening antibiotic resistance phenomenon. The antimicrobial screening revealed that compounds 9, 15, 16, 18, 19, 20 and 29 are the most broad spectrum antimicrobial agents in this study with safe profile on human cell lines. Additionally, compounds 19 and 20 inhibited biofilm formation in Pseudomonas aeruginosa, which is regulated by quorum sensing system, at sub-minimum inhibitory concentrations (sub-MICs) with IC50 values 3.55 and 6.86 µM, respectively. By assessing other pseudomonal virulence factors suppression, it was found that compound 20 decreased cell surface hydrophobicity compromising bacterial cells adhesion, while both compounds 19 and 20 curtailed the exopolysaccharide production which constitutes the major component of the matrix binding biofilm components together. Also, at sub-MICs Pseudomonas cells twitching motility was impeded by compounds 19 and 20, a trait which augments the cells pathogenicity and invasion potential. Molecular docking study was performed to further evaluate the binding mode of candidates 19 and 20 as inhibitors of P. aeruginosa quorum sensing transcriptional regulator PqsR. The achieved results demonstrate that both compounds bear promising potential for discovering new anti-biofilm and quorum quenching agents against Pseudomonas aeruginosa without triggering resistance mechanisms as the normal bacterial life cycle is not disturbed.

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.

Essential oils modulate virulence phenotypes in a multidrug-resistant pyomelanogenic Pseudomonas aeruginosa clinical isolate

Pyomelanogenic P. aeruginosa, frequently isolated from patients with urinary tract infections and cystic fibrosis, possesses the ability to withstand oxidative stress, contributing to virulence and resulting in persistent infections. Whole genome sequence analysis of U804, a pyomelanogenic, multidrug-resistant, clinical isolate, demonstrates the mechanism underlying pyomelanin overproduction. Seven essential oils (EOs) were screened for pyomelanin inhibition. Garlic, cinnamon and thyme EOs were selected for further studies based on their significant anti-virulent properties, like inhibition of pyomelanin production and biofilm formation. Additionally, downregulation of the expression of virulence genes regulated by quorum sensing (QS) and a decrease in levels of the QS signaling molecule, C12-HSL, were also observed. The EO treatment inhibited the survival of U804 in human blood and increased survival of C. elegans, a whole animal model of pathogenesis. EO treatment also resulted in a significant reduction of efflux pump activity, indicative of their effect on antibiotic sensitization. Garlic oil enhanced the permeability of the bacterial membrane, resulting in decreased survival, when combined with sub-MIC concentrations of colistin. This study demonstrates that thyme, cinnamon and garlic EOs can attenuate pyomelanogenic P. aeruginosa virulence traits. Additionally, garlic potentiates drug sensitivity, suggesting its promising therapeutic use in combating pyomelanogenic MDR infections.

Insights into the diverse roles of the terminal oxidases in Burkholderia cenocepacia H111

Burkholderia cenocepacia H111 is an obligate aerobic bacterium which has been isolated from a cystic fibrosis (CF) patient. In CF lungs the environment is considered micro-oxic or even oxygen-depleted due to bacterial activities and limited oxygen diffusion in the mucus layer. To adapt to low oxygen concentrations, bacteria possess multiple terminal oxidases. In this study, we identified six terminal oxidases of B. cenocepacia H111 and constructed reporter strains to monitor their expression in different environments. While the heme-copper oxidase aa3 (cta) was constitutively expressed, the bd-1 oxidase (cyd) was induced under oxygen-limited growth conditions. The cyanide-insensitive bd-type terminal oxidase (cio-1) was mainly expressed in cells grown on the surface of solid medium or in liquid cultures in presence of cyanide, which is known to be produced in the CF lung by the often co-residing CF pathogen Pseudomonas aeruginosa. Indeed, a cio-1 insertional mutant was not able to grow in the presence of cyanide confirming the important role of Cio-1 in cyanide resistance. The caa3 oxidase (caa), was only expressed under nutrient limitation when cells were grown on the surface of solid medium. We also investigated the involvement of two regulatory systems, Anr and RoxS/RoxR, in the expression of cio-1 and cyd. Our data suggest, that, given that Cio-1 is only present in prokaryotes and plays an important role in the defense against cyanide-producing P. aeruginosa, it may be a valuable drug target for treatment of polymicrobial infections in CF patients.

Interspecies Crosstalk via LuxI/LuxR-Type Quorum Sensing Pathways Contributes to Decreased Nematode Survival in Coinfections of Pseudomonas aeruginosa and Burkholderia multivorans

Quorum sensing (QS) is a prominent chemical communication mechanism used by common bacteria to regulate group behaviors at high cell density, including many processes important in pathogenesis. There is growing evidence that certain bacteria can use QS to sense not only themselves but also other species and that this crosstalk could alter collective behaviors. In the current study, we report the results of culture-based and in vivo coinfection experiments that probe interspecies interactions between the opportunistic pathogens Pseudomonas aeruginosa and Burkholderia multivorans involving their LuxI/LuxR-type QS circuits. Using a Caenorhabditis elegans infection model, we show that infections with both species result in poorer host outcomes compared with monoinfections. We use genetic mutants and a transwell infection assay to establish that crosstalk via LuxR-type receptors and signals is important for this coinfection pathogenicity. Using laboratory cocultures with cell-based reporter systems, we show that the RhlR and CepR receptors in P. aeruginosa and B. multivorans, respectively, can each recognize a QS signal produced by the other species. Lastly, we apply chemical biology to complement our genetic approach and demonstrate the potential to regulate interspecies interactions between the wild-type strains of P. aeruginosa and B. multivorans through the application of synthetic compounds that modulate RhlR and CepR activities. Overall, this study reveals that interspecies interaction via QS networks is possible between P. aeruginosa and B. multivorans and that it can contribute to coinfection severity with these two species.

Pseudomonas aeruginosa quorum sensing and biofilm attenuation by a di-hydroxy derivative of piperlongumine (PL-18)

Bacterial communication, Quorum Sensing (QS), is a target against virulence and prevention of antibiotic-resistant infections. 16 derivatives of Piperlongumine (PL), an amide alkaloid from Piper longum L., were screened for QS inhibition. PL-18 had the best QSI activity. PL-18 inhibited the lasR-lasI, rhlR-rhlI, and pqs QS systems of Pseudomonas aeruginosa. PL-18 inhibited pyocyanin and rhamnolipids that are QS-controlled virulence elements. Iron is an essential element for pathogenicity, biofilm formation and resilience in harsh environments, its uptake was inhibited by PL-18. Pl-18 significantly reduced the biofilm biovolume including in established biofilms. PL-18-coated silicon tubes significantly inhibited biofilm formation. The transcriptome study of treated P. aeruginosa showed that PL-18 indeed reduced the expression of QS and iron homeostasis related genes, and up regulated sulfur metabolism related genes. Altogether, PL-18 inhibits QS, virulence, iron uptake, and biofilm formation. Thus, PL-18 should be further developed against bacterial infection, antibiotic resistance, and biofilm formation.

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.

Evolutionary loss of an antibiotic efflux pump increases Pseudomonas aeruginosa quorum sensing mediated virulence in vivo

Antibiotic resistance is one of the most pressing threats to human health, yet recent work highlights how loss of resistance may also drive pathogenesis in some bacteria. In two recent studies, we found that β-lactam antibiotic and nutrient stresses faced during infection selected for the genetic inactivation of the Pseudomonas aeruginosa (Pa) antibiotic efflux pump mexEFoprN. Unexpectedly, efflux pump mutations increased Pa virulence during infection; however, neither the prevalence of efflux pump inactivating mutations in real human infections, nor the mechanisms driving increased virulence of efflux pump mutants are known. We hypothesized that human infection would select for efflux pump mutations that drive increased virulence in Pa clinical isolates. Using genome sequencing of hundreds of Pa clinical isolates, we show that mexEFoprN efflux pump inactivating mutations are enriched in Pa cystic fibrosis isolates relative to Pa intensive care unit clinical isolates. Combining RNA-seq, metabolomics, genetic approaches, and infection models we show that efflux pump mutants have elevated expression of two key Pa virulence factors, elastase and rhamnolipids, which increased Pa virulence and lung damage during both acute and chronic infections. Increased virulence factor production was driven by higher Pseudomonas quinolone signal levels in the efflux pump mutants. Finally, genetic restoration of the efflux pump in a representative ICU clinical isolate and the notorious CF Pa Liverpool epidemic strain reduced their virulence. Together, our findings suggest that mutations inactivating antibiotic resistance mechanisms could lead to greater patient mortality and morbidity.

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.

The battle within: how Pseudomonas aeruginosa uses host-pathogen interactions to infect the human lung

Pseudomonas aeruginosa is a versatile Gram-negative pathogen known for its ability to invade the respiratory tract, particularly in cystic fibrosis patients. This review provides a comprehensive analysis of the multifaceted strategies for colonization, virulence, and immune evasion used by P. aeruginosa to infect the host. We explore the extensive protein arsenal of P. aeruginosa, including adhesins, exotoxins, secreted proteases, and type III and VI secretion effectors, detailing their roles in the infective process. We also address the unique challenge of treating diverse lung conditions that provide a natural niche for P. aeruginosa on the airway surface, with a particular focus in cystic fibrosis. The review also discusses the current limitations in treatment options due to antibiotic resistance and highlights promising future approaches that target host-pathogen protein-protein interactions. These approaches include the development of new antimicrobials, anti-attachment therapies, and quorum-sensing inhibition molecules. In summary, this review aims to provide a holistic understanding of the pathogenesis of P. aeruginosa in the respiratory system, offering insights into the underlying molecular mechanisms and potential therapeutic interventions.

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.

Antimicrobial and antibiofilm properties of procyanidins: potential for clinical and biotechnological applications

Procyanidins (PCs) have emerged as agents with potential antimicrobial and antibiofilm activities, although their mechanisms of action and structure-activity relationships remain poorly understood. This review assessed the potential mechanisms of action and applications of these compounds to explore these aspects. Studies on the antimicrobial properties of PCs suggest that they are involved in osmotic imbalance, DNA interactions and metabolic disruption. Although less studied, their antibiofilm activities include antiadhesive effects and the modulation of mobility and quorum sensing. However, most research has used uncharacterized plant extracts for in vitro assays, limiting the understanding of the structure-activity relationships of PCs and their in vivo mechanisms. Clinical trials on the antimicrobial and antibiofilm properties of PCs have not clarified these issues due to nonstandardized methodologies, inadequate chemical characterization, and the limited number of studies, preventing a consensus and evaluation of the in vivo effects. Additionally, patent analysis revealed that technological developments in the antimicrobial and antibiofilm uses of PCs are concentrated in health care and dental care, but new biotechnological uses are emerging. Therefore, while PCs are promising antimicrobial and antibiofilm compounds, further research into their chemical structures and mechanisms of action is crucial for evidence-based applications in biotechnology and health care.

The human microbiome in space: parallels between Earth-based dysbiosis, implications for long-duration spaceflight, and possible mitigation strategies

SUMMARYThe human microbiota encompasses the diverse communities of microorganisms that reside in, on, and around various parts of the human body, such as the skin, nasal passages, and gastrointestinal tract. Although research is ongoing, it is well established that the microbiota exert a substantial influence on the body through the production and modification of metabolites and small molecules. Disruptions in the composition of the microbiota-dysbiosis-have also been linked to various negative health outcomes. As humans embark upon longer-duration space missions, it is important to understand how the conditions of space travel impact the microbiota and, consequently, astronaut health. This article will first characterize the main taxa of the human gut microbiota and their associated metabolites, before discussing potential dysbiosis and negative health consequences. It will also detail the microbial changes observed in astronauts during spaceflight, focusing on gut microbiota composition and pathogenic virulence and survival. Analysis will then turn to how astronaut health may be protected from adverse microbial changes via diet, exercise, and antibiotics before concluding with a discussion of the microbiota of spacecraft and microbial culturing methods in space. The implications of this review are critical, particularly with NASA's ongoing implementation of the Moon to Mars Architecture, which will include weeks or months of living in space and new habitats.

Pseudomonas aeruginosa: metabolic allies and adversaries in the world of polymicrobial infections

Pseudomonas aeruginosa (PA), an opportunistic human pathogen that is frequently linked with chronic infections in immunocompromised individuals, is also metabolically versatile, and thrives in diverse environments. Additionally, studies report that PA can interact with other microorganisms, such as bacteria, and fungi, producing unique metabolites that can modulate the host immune response, and contribute to disease pathogenesis. This review summarizes the current knowledge related to the metabolic interactions of PA with other microorganisms (Staphylococcus, Acinetobacter, Klebsiella, Enterococcus, and Candida) and human hosts, and the importance of these interactions in a polymicrobial context. Further, we highlight the potential applications of studying these metabolic interactions toward designing better diagnostic tools, and therapeutic strategies to prevent, and treat infections caused by this pathogen.

Drug-Drug Interactions in Nosocomial Infections: An Updated Review for Clinicians

Prevention, assessment, and identification of drug-drug interactions (DDIs) represent a challenge for healthcare professionals, especially in nosocomial settings. This narrative review aims to provide a thorough assessment of the most clinically significant DDIs for antibiotics used in healthcare-associated infections. Complex poly-pharmaceutical regimens, targeting multiple pathogens or targeting one pathogen in the presence of another comorbidity, have an increased predisposition to result in life-threatening DDIs. Recognising, assessing, and limiting DDIs in nosocomial infections offers promising opportunities for improving health outcomes. The objective of this review is to provide clinicians with practical advice to prevent or mitigate DDIs, with the aim of increasing the safety and effectiveness of therapy. DDI management is of significant importance for individualising therapy according to the patient, disease status, and associated comorbidities.

In-silico and in-vitro assessment of the antibiofilm potential of azo dye, carmoisine against Pseudomonas aeruginosa

Biofilm is a community of microorganisms attached to the substrate and plays a significant role in microbial pathogenesis and medical device-related infection. Pseudomonas aeruginosa (PA) is a highly infectious gram-negative opportunistic biofilm-forming bacterium with high antibiotic resistance. Several reports underscore the antimicrobial activity of natural and synthetic food coloring agents, including carmoisine, turmeric dye, red amaranth dye, and phloxine B. However, their ability to suppress the PA biofilm is not clearly understood. Carmoisine is a red-colored synthetic azo dye containing naphthalene subunits and sulfonic groups and is widely used as a food coloring agent. This study investigated the antibiofilm potential and possible mechanism of biofilm inhibition by carmoisine against PA. Computational studies through molecular docking revealed that carmoisine strongly binds to QS regulator LasR (-12.7) and relatively less strongly but significantly with WspR (-6.9). Further analysis of the docked LasR-carmoisine complex using 100 ns MD simulation (Desmond, Schrödinger) validated the bonding strength and stability. Crystal violet assay, triphenyl tetrazolium chloride salt assay, and confocal microscopic studies were adopted for biofilm quantification, and the results indicated the dose-dependent antibiofilm activity of carmoisine against PA. We hypothesise that the carmoisine-mediated reduction of biofilm in PA is due to its interaction with LasR and interference with the QS system. The computational and biochemical analysis of another compound, 1,2-naphthoquinone-4-sulphonic acid, reiterated the role of the naphthalene ring in biofilm inhibition. Hence, this work will pave the way for the future discovery of antibiofilm drugs based on naphthalene ring-based lead compounds.Communicated by Ramaswamy H. Sarma.

Pseudomonas aeruginosa Biofilm Lifecycle: Involvement of Mechanical Constraints and Timeline of Matrix Production

Pseudomonas aeruginosa is an opportunistic pathogen causing acute and chronic infections, especially in immunocompromised patients. Its remarkable adaptability and resistance to various antimicrobial treatments make it difficult to eradicate. Its persistence is enabled by its ability to form a biofilm. Biofilm is a community of sessile micro-organisms in a self-produced extracellular matrix, which forms a scaffold facilitating cohesion, cell attachment, and micro- and macro-colony formation. This lifestyle provides protection against environmental stresses, the immune system, and antimicrobial treatments, and confers the capacity for colonization and long-term persistence, often characterizing chronic infections. In this review, we retrace the events of the life cycle of P. aeruginosa biofilm, from surface perception/contact to cell spreading. We focus on the importance of extracellular appendages, mechanical constraints, and the kinetics of matrix component production in each step of the biofilm life cycle.

N-Acyl Homoserine Lactone Production by the Marine Isolate, Dasania marina

Dasania marina (isolate SD1D, with 98.5% sequence similarity to Dasania marina DMS 21967 KOPRI 20902) is a marine bacterium that was isolated from ballast tank fluids as part of a biofilm study in 2014. Our previous work indicated that although this strain produced no detectable biofilm, it was the only isolate to produce N-acyl homoserine lactones (AHLs) in assays using the broad-range reporter strain, Agrobacterium tumefaciens KYC55. The goal of the current study was to determine the types of AHL molecules produced by the D. marina isolate using gas chromatography-mass spectroscopy (GCMS) and C4- to C14-AHL as standards. A time course assay indicated that the D. marina strain produced the highest level of AHLs at 20 h of growth. When extracts were subjected to GCMS, detectable levels of C8- and C10-AHL and higher levels of C12-AHL were observed. Interestingly, several biofilm-forming isolates obtained from the same source also produced detectable amounts of several AHLs. Of the isolates tested, a strain designated SD5, with 99.83% sequence similarity to Alteromonas tagae BCRC 17571, produced unstable biofilms, yet detectable levels of C6-, C8-, C10- and C12-AHL, and isolate SD8, an Alteromonas oceani S35 strain (98.85% sequence similarity), produced robust and stable biofilms accompanied by detectable levels of C8- and C12-AHL. All isolates tested produced C12-AHL at higher levels than the other AHLs. Results from this study suggest that quorum sensing and biofilm formation are uncoupled in D. marina. Whether the suite of AHLs produced by this isolate could modulate biofilm formation in other strains requires further study.

Exploring rose absolute and phenylethyl alcohol as novel quorum sensing inhibitors in Pseudomonas aeruginosa and Chromobacterium violaceum

Inter-cellular signaling, referred to as quorum sensing (QS), regulates the production of virulence factors in numerous gram-negative bacteria, such as the human pathogens Pseudomonas aeruginosa and Chromobacterium violaceum. QS inhibition may provide an opportunity for the treatment of bacterial infections. This represents the initial study to examine the antibiofilm and antivirulence capabilities of rose absolute and its primary component, phenylethyl alcohol. QS inhibition was assessed by examining extracellular exopolysaccharide synthesis, biofilm development, and swarming motility in P. aeruginosa PAO1, along with violacein production in C. violaceum ATCC 12472. Molecular docking analysis was conducted to explore the mechanism by which PEA inhibits QS. Our results indicate that rose absolute and PEA caused decrease in EPS production (60.5-33.5%), swarming motility (94.7-64.5%), and biofilm formation (98.53-55.5%) in the human pathogen P. aeruginosa PAO1. Violacein production decreased by 98.1% and 62.5% with an absolute (0.5 v/v %) and PEA (2 mM). Moreover, the molecular docking analysis revealed a promising competitive interaction between PEA and AHLs. Consequently, this study offers valuable insights into the potential of rose absolute and PEA as inhibitors of QS in P. aeruginosa and C. violaceum.

Pseudomonas aeruginosa Isolates from Water Samples of the Gulf of Mexico Show Similar Virulence Properties but Different Antibiotic Susceptibility Profiles than Clinical Isolates

Pseudomonas aeruginosa is an opportunistic pathogen found in a wide variety of environments, including soil, water, and habitats associated with animals, humans, and plants. From a One Health perspective, which recognizes the interconnectedness of human, animal, and environmental health, it is important to study the virulence characteristics and antibiotic susceptibility of environmental bacteria. In this study, we compared the virulence properties and the antibiotic resistance profiles of seven isolates collected from the Gulf of Mexico with those of seven clinical strains of P. aeruginosa. Our results indicate that the marine and clinical isolates tested exhibit similar virulence properties; they expressed different virulence factors and were able to kill Galleria mellonella larvae, an animal model commonly used to analyze the pathogenicity of many bacteria, including P. aeruginosa. In contrast, the clinical strains showed higher antibiotic resistance than the marine isolates. Consistently, the clinical strains exhibited a higher prevalence of class 1 integron, an indicator of anthropogenic impact, compared with the marine isolates. Thus, our results indicate that the P. aeruginosa marine strains analyzed in this study, isolated from the Gulf of Mexico, have similar virulence properties, but lower antibiotic resistance, than those from hospitals.

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.

Veratryl Alcohol Attenuates the Virulence and Pathogenicity of Pseudomonas aeruginosa Mainly via Targeting las Quorum-Sensing System

Pseudomonas aeruginosa is an opportunistic pathogen that usually causes chronic infections and even death in patients. The treatment of P. aeruginosa infection has become more challenging due to the prevalence of antibiotic resistance and the slow pace of new antibiotic development. Therefore, it is essential to explore non-antibiotic methods. A new strategy involves screening for drugs that target the quorum-sensing (QS) system. The QS system regulates the infection and drug resistance in P. aeruginosa. In this study, veratryl alcohol (VA) was found as an effective QS inhibitor (QSI). It effectively suppressed the expression of QS-related genes and the subsequent production of virulence factors under the control of QS including elastase, protease, pyocyanin and rhamnolipid at sub-inhibitory concentrations. In addition, motility activity and biofilm formation, which were correlated with the infection of P. aeruginosa, were also suppressed by VA. In vivo experiments demonstrated that VA could weaken the pathogenicity of P. aeruginosa in Chinese cabbage, Drosophila melanogaster, and Caenorhabditis elegans infection models. Molecular docking, combined with QS quintuple mutant infection analysis, identified that the mechanism of VA could target the LasR protein of the las system mainly. Moreover, VA increased the susceptibility of P. aeruginosa to conventional antibiotics of tobramycin, kanamycin and gentamicin. The results firstly demonstrate that VA is a promising QSI to treat infections caused by P. aeruginosa.

Taming Pseudomonas aeruginosa AM26 the barbarian: Targeting the PQS quorum sensing network using crude mandarin extract

Pseudomonas aeruginosa, one of the most notorious organisms, causes fatal diseases like-, meningitis, pneumonia as well as worsens the prognosis of cystic fibrosis patients. It is also multi-drug resistant and resists a wide range of antibiotics. Attempts have been made to reduce its virulence/pathogenic potential using a number of organic compounds. For this purpose, the Quorum sensing (QS) system of P. aeruginosa was targeted, which regulates its virulence. Pseudomonas Quinolone System (PQS), one of the four quorum sensing systems, producing pyocyanin pigment was chosen. 2-heptyl-3-hydroxy-4-quinolone (HHQ) is a ligand which binds to PQS protein is responsible for pyocyanin pigment production. Attempts were made to find a compound analogous to HHQ which could bind to PQS active site and inhibit the pigment formation. In-silico analysis was performed to estimate possible interactions and to find/predict the possible PQS inhibitors.

A Comparative Transcriptome Analysis Unveils the Mechanisms of Response in Feather Degradation by Pseudomonas aeruginosa Gxun-7

Microbial degradation of feathers offers potential for bioremediation, yet the microbial response mechanisms warrant additional investigation. In prior work, Pseudomonas aeruginosa Gxun-7, which demonstrated robust degradation of feathers at elevated concentrations, was isolated. However, the molecular mechanism of this degradation remains only partially understood. To investigate this, we used RNA sequencing (RNA-seq) to examine the genes that were expressed differentially in P. aeruginosa Gxun-7 when exposed to 25 g/L of feather substrate. The RNA-seq analysis identified 5571 differentially expressed genes; of these, 795 were upregulated and 603 were downregulated. Upregulated genes primarily participated in proteolysis, amino acid, and pyruvate metabolism. Genes encoding proteases, as well as those involved in sulfur metabolism, phenazine synthesis, and type VI secretion systems, were notably elevated, highlighting their crucial function in feather decomposition. Integration of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) taxonomies, combined with a review of the literature, led us to propose that metabolic feather degradation involves environmental activation, reducing agent secretion, protease release, peptide/amino acid uptake, and metabolic processes. Sulfite has emerged as a critical activator of keratinase catalysis, while cysteine serves as a regulatory mediator. qRT-PCR assay results for 11 selected gene subset corroborated the RNA-seq findings. This study enhances our understanding of the transcriptomic responses of P. aeruginosa Gxun-7 to feather degradation and offers insights into potential degradation mechanisms, thereby aiding in the formulation of effective feather waste management strategies in poultry farming.

Abiotic Small Molecule Inhibitors and Activators of the LasR Quorum Sensing Receptor in Pseudomonas aeruginosa with Potencies Comparable or Surpassing N-Acyl Homoserine Lactones

The opportunistic pathogen Pseudomonas aeruginosa controls almost 10% of its genome, including myriad virulence genes, via a cell-to-cell chemical communication system called quorum sensing (QS). Small molecules that either inhibit or activate QS in P. aeruginosa represent useful research tools to study the role of this signaling pathway in infection and interrogate its viability as an antivirulence target. However, despite active research in this area over the past 20+ years, there are relatively few synthetic compounds known to strongly inhibit or activate QS in P. aeruginosa. Most reported QS modulators in this pathogen are of low potency or have structural liabilities that limit their application in biologically relevant environments such as mimics of the native N-acyl l-homoserine lactone (AHL) signals. Here, we report the results of a high-throughput screen for abiotic small molecules that target LasR, a key QS regulator in P. aeruginosa. We screened a 25,000-compound library and discovered four new structural classes of abiotic LasR modulators. These compounds include antagonists that surpass the potency of all known AHL-type compounds and mimetics thereof, along with an agonist with potency approaching that of LasR's native ligand. The novel structures of this compound set, along with their anticipated robust physicochemical profiles, underscore their potential value as probe molecules to interrogate the roles of QS in this formidable pathogen.

RsaL is a self-regulatory switch that controls alternative biosynthesis of two AHL-type quorum sensing signals in Pseudomonas aeruginosa PA1201

Pseudomonas aeruginosa is a ubiquitous and metabolically versatile microorganism naturally found in soil and water. It is also an opportunistic pathogen in plants, insects, animals, and humans. In response to increasing cell density, P. aeruginosa uses two acyl-homoserine lactone (AHL) quorum-sensing (QS) signals (i.e., N-3-oxo-dodecanoyl homoserine lactone [3-oxo-C12-HSL] and N-butanoyl-homoserine lactone [C4-HSL]), which regulate the expression of hundreds of genes. However, how the biosynthesis of these two QS signals is coordinated remains unknown. We studied the regulation of these two QS signals in the rhizosphere strain PA1201. PA1201 sequentially produced 3-oxo-C12-HSL and C4-HSL at the early and late growth stages, respectively. The highest 3-oxo-C12-HSL-dependent elastase activity was observed at the early stage, while the highest C4-HSL-dependent rhamnolipid production was observed at the late stage. The atypical regulator RsaL played a pivotal role in coordinating 3-oxo-C12-HSL and C4-HSL biosynthesis and QS-associated virulence. RsaL repressed lasI transcription by binding the -10 and -35 boxes of the lasI promoter. In contrast, RsaL activated rhlI transcription by binding the region encoding the 5'-untranslated region of the rhlI mRNA. Further, RsaL repressed its own expression by binding a nucleotide motif located in the -35 box of the rsaL promoter. Thus, RsaL acts as a molecular switch that coordinates the sequential biosynthesis of AHL QS signals and differential virulence in PA1201. Finally, C4-HSL activation by RsaL was independent of the Las and Pseudomonas quinolone signal (PQS) QS signaling systems. Therefore, we propose a new model of the QS regulatory network in PA1201, in which RsaL represents a superior player acting at the top of the hierarchy.

Regulation of virulence in Chromobacterium violaceum and strategies to combat it

Chromobacterium is a rod-shaped, Gram-negative, facultatively anaerobic bacteria with a cosmopolitan distribution. Just about 160 Chromobacterium violaceum incidents have been reported globally, but then once infected, it has the ability to cause deadly septicemia, and infections in the lungs, liver, brain, spleen, and lymphatic systems that might lead to death. C. violaceum produces and utilizes violacein to kill bacteria that compete with it in an ecological niche. Violacein is a hydrophobic bisindole that is delivered through an efficient transport route termed outer membrane vesicles (OMVs) through the aqueous environment. OMVs are small, spherical segments detached from the outer membrane of Gram-negative bacteria. C. violaceum OMV secretions are controlled by a mechanism called the quorum sensing system CviI/CviR, which enables cell-to-cell communication between them and regulation of various virulence factors such as biofilm formation, and violacein biosynthesis. Another virulence factor bacterial type 3 secretion system (T3SS) is divided into two types: Cpi-1 and Cpi-2. Cpi-1's needle and rod effector proteins are perhaps recognized by NAIP receptors in humans and mice, activating the NLRC4 inflammasome cascade, effectively clearing spleen infections via pyroptosis, and cytotoxicity mediated by IL-18-driven Natural killer (NK) cells in the liver. In this paper, we attempt to interrelate quorum-controlled biofilm formation, violacein production, violacein delivery by OMVs and T3SS effector protein production and host mediated immunological effects against the Cpi1 of T3SS. We suggest a research path with natural bioactive molecule like palmitic acid that can act as an anti-quorum agent by reducing the expression of virulence factors as well as an immunomodulatory agent that can augment innate immune defense by hyperactivation of NLRC4 inflammasome hence dramatically purge C. violaceum infections.

Modified N-acyl-L-homoserine lactone compounds abrogate Las-dependent quorum-sensing response in human pathogen Pseudomonas aeruginosa

Quorum sensing (QS) is a mode of cell-cell communication that bacteria use to sense population density and orchestrate collective behaviors. The common opportunistic human pathogen Pseudomonas aeruginosa employs QS to regulate a large set of genes involved in virulence and host-pathogen interactions. The Las circuit positioned on the top of the QS hierarchy in P. aeruginosa makes use of N-acyl-L-homoserine lactones (AHLs) as signal molecules, like N-3-oxo-dodecanoyl-L-homoserine lactone (3O-C12-HSL). Disabling QS circuits by certain small-molecule compounds, known as quorum-sensing inhibitors (QSIs), has been proposed as a strategy to attenuate bacterial pathogenicity. In this study, four new AHL analogs were designed by incorporating a tert-butoxycarbonyl Boc group in amide and β-keto (3-oxo) moiety. Compounds were evaluated on a molecular and phenotypic basis as a QSI using the screening strategy linked to the assignment of the Las QS system in P. aeruginosa. Using a LasR-based bioreporter, we found that the compounds decreased LasR-controlled light activity and competed efficiently with natural 3O-C12-HSL. The compounds reduced the production of the cognate 3O-C12-HSL and certain virulence traits, like total protease activity, elastase activity, pyocyanin production, and extracellular DNA release. Furthermore, a quantitative proteomic approach was used to study the effect of the compounds on QS-regulated extracellular proteins. Among the four compounds tested, one of them showed the most significant difference in the appearance of the 3O-C12-HSL-responsive reference proteins related to QS communication and virulence, i.e., a distinct activity as a QSI. Moreover, by combining experimental data with computational chemistry, we addressed the effect of LasR protein flexibility on docking precision and assessed the advantage of using a multi-conformational docking procedure for binding mode prediction of LasR modulators. Thus, the four new AHL compounds were tested for their interaction with the AHL-binding site in LasR to identify the key interferences with the activity of LasR. Our study provides further insight into molecular features that are required for small-molecule modulation of LasR-dependent QS communication in P. aeruginosa. This should facilitate rational design of the next generation of antivirulence tools to study and manipulate QS-controlled fitness in bacteria and, thereby, handle bacterial infections in a new way.

Synthesis and Biological Evaluation of New Quinoline and Anthranilic Acid Derivatives as Potential Quorum Sensing Inhibitors

Inhibiting quorum sensing (QS), a central communication system, is a promising strategy to combat bacterial pathogens without antibiotics. Here, we designed novel hybrid compounds targeting the PQS (Pseudomonas quinolone signal)-dependent quorum sensing (QS) of Pseudomonas aeruginosa that is one of the multidrug-resistant and highly virulent pathogens with urgent need of new antibacterial strategies. We synthesized 12 compounds using standard procedures to combine halogen-substituted anthranilic acids with 4-(2-aminoethyl/4-aminobuthyl)amino-7-chloroquinoline, linked via 1,3,4-oxadiazole. Their antibiofilm activities were first pre-screened using Gram-negative Chromobacterium violaceum-based reporter, which identified compounds 15-19 and 23 with the highest anti-QS and minimal bactericidal effects in a single experiment. These five compounds were then evaluated against P. aeruginosa PAO1 to assess their ability to prevent biofilm formation, eradicate pre-formed biofilms, and inhibit virulence using pyocyanin as a representative marker. Compound 15 displayed the most potent antibiofilm effect, reducing biofilm formation by nearly 50% and pre-formed biofilm masses by 25%. On the other hand, compound 23 exhibited the most significant antivirulence effect, reducing pyocyanin synthesis by over 70%. Thus, our study highlights the potential of 1,3,4-oxadiazoles 15 and 23 as promising scaffolds to combat P. aeruginosa. Additionally, interactive QS systems should be considered to achieve maximal anti-QS activity against this clinically relevant species.

Transcriptional Regulators Controlling Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a pathogen capable of colonizing virtually every human tissue. The host colonization competence and versatility of this pathogen are powered by a wide array of virulence factors necessary in different steps of the infection process. This includes factors involved in bacterial motility and attachment, biofilm formation, the production and secretion of extracellular invasive enzymes and exotoxins, the production of toxic secondary metabolites, and the acquisition of iron. Expression of these virulence factors during infection is tightly regulated, which allows their production only when they are needed. This process optimizes host colonization and virulence. In this work, we review the intricate network of transcriptional regulators that control the expression of virulence factors in P. aeruginosa, including one- and two-component systems and σ factors. Because inhibition of virulence holds promise as a target for new antimicrobials, blocking the regulators that trigger the production of virulence determinants in P. aeruginosa is a promising strategy to fight this clinically relevant pathogen.