An innovative role for luteolin as a natural quorum sensing inhibitor in Pseudomonas aeruginosa

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.

Beyond antibiotics: Emerging antivirulence strategies to combat Pseudomonas aeruginosa in cystic fibrosis

Pseudomonas aeruginosa is an opportunistic pathogen that poses a significant threat to individuals suffering from cystic fibrosis (CF). The pathogen is highly prevalent in CF individuals and is responsible for chronic infection, resulting in severe tissue damage and poor patient outcome. Prolonged antibiotic administration has led to the emergence of multidrug resistance in P. aeruginosa. In this direction, antivirulence strategies achieving targeted inhibition of bacterial virulence pathways, including quorum sensing, efflux pumps, lectins, and iron chelators, have been explored against CF isolates of P. aeruginosa. Hence, this review article presents a bird's eye view on the pulmonary infections involving P. aeruginosa in CF patients by laying emphasis on factors contributing to bacterial colonization, persistence, and disease progression along with the current line of therapeutics against P. aeruginosa in CF. We further collate scientific literature and discusses various antivirulence strategies that have been tested against P. aeruginosa isolates from CF patients.

A Systematic Hierarchical Virtual Screening Model for RhlR Inhibitors Based on PCA, Pharmacophore, Docking, and Molecular Dynamics

RhlR plays a key role in the quorum sensing of Pseudomonas aeruginosa. The current structure-activity relationship (SAR) studies of RhlR inhibitors mainly focus on elucidating the functional groups. Based on a systematic review of previous research on RhlR inhibitors, this study aims to establish a systematic, hierarchical screening model for RhlR inhibitors. We initially established a database and utilized principal component analysis (PCA) to categorize the inhibitors into two classes. Based on the training set, pharmacophore models were established to elucidate the structural characteristics of ligands. Subsequently, molecular docking, molecular dynamics simulations, and the calculation of binding free energy and strain energy were performed to validate the crucial interactions between ligands and receptors. Then, the screening criteria for RhlR inhibitors were established hierarchically based on ligand structure characteristics, ligand-receptor interaction, and receptor affinity. Test sets were finally employed to validate the hierarchical virtual screening model by comparing it with the current SAR studies of RhlR inhibitors. The hierarchical screening model was confirmed to possess higher accuracy and a true positive rate, which holds promise for subsequent screening and the discovery of active RhlR inhibitors.

FTY720 Reduces the Biomass of Biofilms in Pseudomonas aeruginosa in a Dose-Dependent Manner

Pseudomonas aeruginosa, a nosocomial pathogen, has strong biofilm capabilities, representing the main source of infection in the human body. Repurposing existing drugs has been explored as an alternative strategy to combat emerging antibiotic-resistant pathogens. Fingolimod hydrochloride (FTY720), an immunomodulatory drug for multiple sclerosis, has shown promising antimicrobial effects against some ESKAPE pathogens. Therefore, the effects of FTY720 on the biofilm capabilities of Pseudomonas aeruginosa were investigated in this study. It was determined that FTY720 inhibited the growth of P. aeruginosa PAO1 at 100 µM. The significant reduction in PAO1 cell viability was observed to be dose-dependent. Additional cytotoxicity analysis on human cell lines showed that FTY720 significantly reduced viabilities at sub-inhibitory concentrations of 25-50 µM. Microtiter assays and confocal analysis confirmed reductions in biofilm mass and thickness and the cell survivability ratio in the presence of FTY720. Similarly, virulence production and biofilm-related gene expression (rhlA, rhlB, pilA, pilI, fliC, fliD and algR) were determined. The results demonstrate that pigment production was affected and quantitative real-time PCR analysis showed a variable degree of reduced gene expression in response to FTY720 at 12.5-50 µM. These findings suggest that FTY720 could be repurposed as an alternative antibiofilm agent against Pseudomonas aeruginosa.

Bacterial Biofilm in Chronic Wounds and Possible Therapeutic Approaches

Wound repair and skin regeneration is a very complex orchestrated process that is generally composed of four phases: hemostasis, inflammation, proliferation, and remodeling. Each phase involves the activation of different cells and the production of various cytokines, chemokines, and other inflammatory mediators affecting the immune response. The microbial skin composition plays an important role in wound healing. Indeed, skin commensals are essential in the maintenance of the epidermal barrier function, regulation of the host immune response, and protection from invading pathogenic microorganisms. Chronic wounds are common and are considered a major public health problem due to their difficult-to-treat features and their frequent association with challenging chronic infections. These infections can be very tough to manage due to the ability of some bacteria to produce multicellular structures encapsulated into a matrix called biofilms. The bacterial species contained in the biofilm are often different, as is their capability to influence the healing of chronic wounds. Biofilms are, in fact, often tolerant and resistant to antibiotics and antiseptics, leading to the failure of treatment. For these reasons, biofilms impede appropriate treatment and, consequently, prolong the wound healing period. Hence, there is an urgent necessity to deepen the knowledge of the pathophysiology of delayed wound healing and to develop more effective therapeutic approaches able to restore tissue damage. This work covers the wound-healing process and the pathogenesis of chronic wounds infected by biofilm-forming pathogens. An overview of the strategies to counteract biofilm formation or to destroy existing biofilms is also provided.

In silico and in vitro evaluation of the anti-virulence potential of patuletin, a natural methoxy flavone, against Pseudomonas aeruginosa

This study aimed to investigate the potential of patuletin, a rare natural flavonoid, as a virulence and LasR inhibitor against Pseudomonas aeruginosa. Various computational studies were utilized to explore the binding of Patuletin and LasR at a molecular level. Molecular docking revealed that Patuletin strongly interacted with the active pocket of LasR, with a high binding affinity value of -20.96 kcal/mol. Further molecular dynamics simulations, molecular mechanics generalized Born surface area (MM/GBSA), protein-ligand interaction profile (PLIP), and essential dynamics analyses confirmed the stability of the patuletin-LasR complex, and no significant structural changes were observed in the LasR protein upon binding. Key amino acids involved in binding were identified, along with a free energy value of -26.9 kcal/mol. In vitro assays were performed to assess patuletin's effects on P. aeruginosa. At a sub-inhibitory concentration (1/4 MIC), patuletin significantly reduced biofilm formation by 48% and 42%, decreased pyocyanin production by 24% and 14%, and decreased proteolytic activities by 42% and 20% in P. aeruginosa isolate ATCC 27853 (PA27853) and P. aeruginosa clinical isolate (PA1), respectively. In summary, this study demonstrated that patuletin effectively inhibited LasR activity in silico and attenuated virulence factors in vitro, including biofilm formation, pyocyanin production, and proteolytic activity. These findings suggest that patuletin holds promise as a potential therapeutic agent in combination with antibiotics to combat antibiotic-tolerant P. aeruginosa infections.

Furan-based Chalcone Annihilates the Multi-Drug-Resistant Pseudomonas aeruginosa and Protects Zebra Fish Against its Infection

The emergence of carbapenem-resistant Pseudomonas aeruginosa, a multi-drug-resistant bacteria, is becoming a serious public health concern. This bacterium infects immunocompromised patients and has a high fatality rate. Both naturally and synthetically produced chalcones are known to have a wide array of biological activities. The antibacterial properties of synthetically produced chalcone were studied against P. aeruginosa. In vitro, study of the compound (chalcone derivative named DKO1), also known as (2E)-1-(5-methylfuran-2-yl)-3-(4-nitrophenyl) prop-2-en-1-one, had substantial antibacterial and biofilm disruptive action. DKO1 effectively shielded against P. aeruginosa-induced inflammation, oxidative stress, lipid peroxidation, and apoptosis in zebrafish larvae. In adult zebrafish, the treatment enhanced the chances of survivability and reduced the sickness-like behaviors. Gene expression, biochemical analysis, and histopathology studies found that proinflammatory cytokines (TNF-α, IL-1β, IL-6, iNOS) were down regulated; antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) levels increased, and histoarchitecture was restored in zebrafish. The data indicate that DKO1 is an effective antibacterial agent against P. aeruginosa demonstrated both in vitro and in vivo.

Plant-derived virulence arresting drugs as novel antimicrobial agents: Discovery, perspective, and challenges in clinical use

Antimicrobial resistance (AMR) emerges as a severe crisis to public health and requires global action. The occurrence of bacterial pathogens with multi-drug resistance appeals to exploring alternative therapeutic strategies. Antivirulence treatment has been a positive substitute in seeking to circumvent AMR, which aims to target virulence factors directly to combat bacterial infections. Accumulated evidence suggests that plant-derived natural products, which have been utilized to treat infectious diseases for centuries, can be abundant sources for screening potential virulence-arresting drugs (VADs) to develop advanced therapeutics for infectious diseases. This review sums up some virulence factors and their actions in various species of bacteria, as well as recent advances pertaining to plant-derived natural products as VAD candidates. Furthermore, we also discuss natural VAD-related clinical trials and patents, the perspective of VAD-based advanced therapeutics for infectious diseases and critical challenges hampering clinical use of VADs, and genomics-guided identification for VAD therapeutic. These newly discovered natural VADs will be encouraging and optimistic candidates that may sustainably combat AMR.

Jingfang granule alleviates Pseudomonas aeruginosa-induced acute lung inflammation through suppression of STAT3/IL-17/NF-κB pathway based on network pharmacology analysis and experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Pseudomonas aeruginosa is an opportunistic bacterial pathogen which is the second leading cause of hospital-acquired pneumonia. Jingfang granule (JFG) is an herbal formula of Traditional Chinese medicine (TCM) widely used in treatment of acute respiratory tract infections in China. However, the molecular mechanisms of JFG in treatment of P. aeruginosa-induced acute pneumonia are not clear.

AIM OF STUDY

This study aimed to investigate the mechanisms underlying the effects of JFG on P. aeruginosa-induced acute inflammation using a mouse model of bacterial acute pneumonia.

MATERIALS AND METHODS

The chemical components and targets of JFG were retrieved from Traditional Chinese Medicine Systems Pharmacology (TCMSP) database, and the P. aeruginosa pneumonia-related targets were obtained from the disease databases, including Online Mendelian Inheritance in Man (OMIM), GeneCards and DisGeNet. The protein-protein interaction (PPI) network was constructed using STRING database. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed using the Database for Annotation, Visualization and Integrated Discovery (DAVID). Molecular docking was performed using AutoDockTools 1.5.6. Further in vivo experiments employed a mouse model of P. aeruginosa acute pneumonia to verify the target proteins and signaling pathways affected by JFG, which were predicted by the network pharmacology analysis.

RESULTS

A total of 218 active components and 257 targets of JFG were retrieved from TCMSP database. Moreover, 99 intersectant targets were obtained between the 257 JFG targets and 694 disease targets. Among the intersectant targets, STAT3, IL-6, AKT1, TNF, MAPK1, MAPK3 and EGFR were identified to be the key therapeutic targets through PPI network analysis, and STAT3 was in the center of the network, which is a key regulator of IL-17 expression. KEGG pathway enrichment analysis suggested that IL-17 signaling pathway was one of the crucial inflammatory pathways affected by JFG in treatment of P. aeruginosa pneumonia. Furthermore, the in vivo experiments demonstrated that the JFG-treated mice displayed reduced proinflammatory cytokine production (IL-17, IL-1β, IL-6 and TNF), diminished neutrophil infiltration and decreased mortality, compared with the non-drug-treated mice during P. aeruginosa lung infection. Moreover, the expression or phosphorylation levels of the key regulators in STAT3/IL-17/NF-κB axis including STAT3, ERK1/2 (MAPK3/1), AKT, NF-κB p65 and RORγt were significantly reduced in the lung tissues of the JFG-treated mice.

CONCLUSION

JFG was effective in treatment of P. aeruginosa acute lung infection, which reduced inflammatory responses through suppressing STAT3/IL-17/NF-κB pathway.

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

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

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

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

Antibiofilm potential of luteolin against multidrug-resistant Staphylococcus aureus isolated from dairy goats and farm environments

Staphylococcus aureus (S. aureus) is a prominent pathogen responsible for mastitis in dairy goats, and capable of contaminating farm environments. Luteolin is a naturally derived flavonoid found in many plant types. To our best of knowledge, this study involved the initial investigation into the prevalence of S. aureus and screened the multidrug-resistant (MDR) S. aureus from raw milk samples and farm environments. Furthermore, we explored the antimicrobial and antibiofilm activities of luteolin against MDR S. aureus. Antibiofilm activity was evaluated via crystal violet staining and confocal laser scanning microscopy (CLSM). Bacterial morphology and biofilm microstructure were observed via scanning electron microscopy (SEM), and the antibiofilm mechanisms were further explored based on extracellular polymeric substance (EPS) production, extracellular DNA (eDNA) content, and quantitative reverse transcription PCR (qRT-PCR). In total, 28 and 43 S. aureus isolates were isolated from raw milk and environmental samples, respectively. Raw milk samples had the highest prevalence of S. aureus (58.33%), followed by sewage sludge (35.42%), soil (27.78%), excrement (19.44%), bulk tank (12.50%), milking parlor (11.11%), and feed (7.50%). Among the isolated strains, 40 isolates (56.34%) expressed the MDR phenotype. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of luteolin against MDR S. aureus were 8-32 μg/mL and 16-64 μg/mL, respectively. Compared to that in the untreated control isolate, the number of dead cells increased, while the auto-aggregation and cell surface hydrophobicity decreased. Moreover, the cell membrane dissolved with the increase in luteolin concentration. Luteolin down-regulated the transcription of seven biofilm related genes: icaA, icaD, icab, hld, hla, agrA and RNAIII. These results indicated that S. aureus coexisted in raw milk and goat farm environments, and also suggested the potential of luteolin as a promising antibiofilm agent against MDR S. aureus.

Potential quorum-sensing inhibitor of Hafnia alvei H4-theaflavin-3,3´-digallate analyzed by virtual screening and molecular simulation

Hafnia species can cause food spoilage via the quorum-sensing (QS) system. Thus, strategies that target QS in these bacteria might be a good approach to safeguard the quality of processed food. In this study, the amino acid sequence of the LasI Ha protein, a key QS regulator from Hafnia alvei H4, was used to construct its 3D structure for the virtual screening of potential QS inhibitors (QSIs) from the Bioactive Compound database. Four potential QSIs were obtained, and these were all theaflavins (TFs). Among them, theaflavin-3,3´-digallate (TF3) was found to outperform the others, displaying a higher docking score according to molecular docking analysis, and required only a sub-minimal inhibitory concentration (31.25 mM) to cause a significant decrease in the production of the autoinducer N-acyl homoserine lactone in H. alvei H4 and up to 60.5% inhibition of its motility. Furthermore, molecular simulation results indicated that TF3 could stably bind to a cavity within LasI Ha to form stable hydrogen bonds and hydrophobic interactions with various key residues of the protein to exert the inhibitory effect. Thus, TF3 may be considered a potential compound to protect against food spoilage caused by H. alvei H4 via the quorum quenching. IMPORTANCE Hafnia alvei, the main strain studied in this paper, is often isolated from spoiled foods, especially refrigerated protein-based raw foods, and is generally considered to be a spoilage bacterium whose spoilage-causing properties may be closely related to its own very strong population-sensing activity, so the strategy of quorum quenching against H. alvei H4 may be a good way to guarantee the quality of processed foods. Given the current global requirements for food safety and quality, coupled with negative consumer perceptions of the excessive inclusion of synthetic chemicals in food products, the use of natural compounds as QSIs in the storage of aquatic food products would seem more attractive.

Research hotspot and trend of chronic wounds: A bibliometric analysis from 2013 to 2022

Chronic wounds have been confirmed as a vital health problem facing people in the global population aging process. While significant progress has been achieved in the study of chronic wounds, the treatment effect should be further improved. The number of publications regarding chronic wounds has been rising rapidly. In this study, bibliometric analysis was conducted to explore the hotspots and trends in the research on chronic wounds. All relevant studies on chronic wounds between 2013 and 2022 were collected from the PubMed database of the Web of Science (WOS) and the National Center for Biotechnology Information (NCBI). The data were processed and visualised using a series of software. On that basis, more insights can be gained into hotspots and trends of this research field. Wound Repair and Regeneration has the highest academic achievement in the field of chronic wound research. The United States has been confirmed as the most productive country, and the University of California System ranks high among other institutions. Augustin, M. is the author of the most published study, and Frykberg, RG et al. published the most cited study. Furthermore, the hotspots of wound research over the last decade were identified (e.g., bandages, infection and biofilms, pathophysiology and therapy). This study will help researchers gain insights into chronic wound research's hotspots and trends accurately and quickly. Moreover, the exploration of bacterial biofilm and the pathophysiological mechanism of the chronic wound will lay a solid foundation and clear direction for treating chronic wounds.

Efficient Recovery Strategy of Luteolin from Agricultural Waste Peanut Shells and Activity Evaluation of Its Functional Biomolecules

Peanut shells (PSs) generated from agricultural waste contain valuable compounds with bioactive properties such as anti-aging, antimicrobial, and antioxidant properties, making it desirable to recycle them as a sustainable resource. The aim of this study is to design an effective luteolin recovery process as the first step of an integrated biorefinery utilizing PSs as raw material. The major extraction variables and their ranges for luteolin recovery from PSs were determined (0-60 °C, 1-5 h, 0-100% MeOH concentration) and a predictive model was derived through a response surface methodology (RSM). Based on the predictive model, the equation determined for the maximal extraction of luteolin at 1 h was as follows: y = -1.8475x + 159.57, and the significant range of variables was as follows: 33.8 °C ≤ temperature (x) ≤ 48.5 °C and 70.0% ≤ MeOH concentration (y) ≤ 97.5%, respectively. High antioxidant and elastase inhibitory activities of PS extracts were confirmed, and these results support their potential to be used as functional materials. In addition, 39.2% of the solid residue after extraction was carbohydrate, which has potential as a carbon source for fermentation. This study provides a useful direction on an integrated biorefinery approach for sustainable agricultural waste valorization.

7-Ethoxycoumarin rescued Caenorhabditis elegans from infection of COPD derived clinical isolate Pseudomonas aeruginosa through virulence and biofilm inhibition via targeting Rhl and Pqs quorum sensing systems

Pseudomonas aeruginosa is an ambidextrous Gram-negative contagium with density convoluted network defined quorum sensing, which enables the persistent survival within the host environment, contributing to various lung related diseases including Chronic Obstructive Pulmonary Disease (COPD). It is clear that P. aeruginosa is a powerful, exquisite pathogen that has adopted a variety of virulence properties through quorum sensing (QS) regulated phenomenon and that it dominates both in the development and exacerbations of COPD. Interestingly, 7-Ethoxycoumarin (7-EC), a compound that adequately mimics QS signaling molecule of P. aeruginosa, was introduced as part of the process of developing novel ways to treat the severe exacerbations. The results showed that, introduction of 7-EC significantly decreased exopolysaccharide-mediated biofilm development of strains isolated from COPD sputum, as evidenced by SEM analysis. Furthermore, 7-EC was able to modulate a variety of virulence factors and motility without subjecting planktonic cells to any selection pressure. Bacterial invasion assay revealed the potential activity of the 7-EC in preventing the active entry to A549 cells without causing any damage to the cells and found functionally active in protecting the C. elegans from P. aeruginosa infection and being non-toxic to the worms. Docking analysis was further proved that 7-EC to be the potential anti-QS compound competing specifically with Rhl and Pqs Systems. Therefore, 7-EC in the utilisation against the P. aeruginosa based infections, may open an avenue for the futuristic mechanistic study in chronic respiratory diseases and a initiator for the development of non-antibiotic based antibacterial therapy.

Evaluating Biofilm Inhibitory Potential in Fish Pathogen, Aeromonas hydrophila by Agricultural Waste Extracts and Assessment of Aerolysin Inhibitors Using In Silico Approach

Aeromonas hydrophila, an opportunistic bacteria, causes several devastating diseases in humans and animals, particularly aquatic species. Antibiotics have been constrained by the rise of antibiotic resistance caused by drug overuse. Therefore, new strategies are required to prevent appropriate antibiotic inability from antibiotic-resistant strains. Aerolysin is essential for A. hydrophila pathogenesis and has been proposed as a potential target for inventing drugs with anti-virulence properties. It is a unique method of disease prevention in fish to block the quorum-sensing mechanism of A. hydrophila. In SEM analysis, the crude solvent extracts of both groundnut shells and black gram pods exhibited a reduction of aerolysin formation and biofilm matrix formation by blocking the QS in A. hydrophila. Morphological changes were identified in the extracts treated bacterial cells. Furthermore, in previous studies, 34 ligands were identified with potential antibacterial metabolites from agricultural wastes, groundnut shells, and black gram pods using a literature survey. Twelve potent metabolites showed interactions between aerolysin and metabolites during molecular docking analysis, in that H-Pyran-4-one-2,3 dihydro-3,5 dihydroxy-6-methyl (-5.3 kcal/mol) and 2-Hexyldecanoic acid (-5.2 kcal/mol) showed promising results with potential hydrogen bond interactions with aerolysin. These metabolites showed a better binding affinity with aerolysin for 100 ns in molecular simulation dynamics. These findings point to a novel strategy for developing drugs using metabolites from agricultural wastes that may be feasible pharmacological solutions for treating A. hydrophila infections for the betterment of aquaculture.

Antiquorum and Antibiofilm Activities of Piper bogotense C. DC. against Pseudomonas aeruginosa and Identification of Bioactive Compounds

The present study describes the anti-biofilm and quorum sensing (QS) inhibitory potential of extracts and chemical constituents from Piper bogotense. Antibiofilm potential was determined through crystal violet assay against Pseudomonas aeruginosa, while QS inhibition efficacy was determined through violacein inhibition assay using Chromobacterium violaceum as a bacterial model. Additionally, this study reports the effects of the chemical constituents isolated in P. bogotense against various virulent factors associated with QS, such as the percentage decrease in pyocyanin, elastase, and protease production. The chemical study led to the isolation and identification of two prenylated benzoic acids (1 and 2) and a prenylated hydroquinone 3, of which compounds 1 and 2 are reported for the first time for P. bogotense. The ethanolic extract and the DCM fraction from P. bogotense stand out for reducing violacein production in C. violaceum, as well as the biofilm formation in P. aeruginosa. Compounds 2 and 3 stand out for having the lowest violacein production (43.8% and 68.3%), as well as the lowest production of virulence factors such as elastase (60.2% and 51.4%) and pyocyanin (39.7% and 33.2%). These results demonstrate the potential of P. bogotense components to be used as an alternative control against multidrug-resistant P. aeruginosa.

Luteolin, a promising quorum quencher mitigates virulence factors production in Pseudomonas aeruginosa - In vitro and in vivo approach

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes healthcare-associated infection and high mortality in immunocompromised patients. It produces several virulence factors through quorum sensing (QS) mechanisms that is essential for subverting host immune system. Even front-line antibiotics are unable to control PA pathogenicity due to the emergence of antibiotic resistance. Luteolin is a naturally derived compound that has proven to be the effective drug to annihilate pathogens through quorum quenching mechanism. In this study, the protective effect of luteolin against the PA-mediated inflammation was demonstrated using zebrafish model. Luteolin protects zebrafish from PA infection and increases their survival rate. It was found that PA-mediated ROS, lipid peroxidation, and apoptosis were also significantly reduced in luteolin-treated zebrafish larvae. Open field test (OFT) reveals that luteolin rescued PA-infected zebrafish from retarded swimming behavior. Furthermore, luteolin increases SOD and CAT levels and decreases LDH and NO levels in PA-infected zebrafish compare to control group. Histological and gene expression analysis reveals that luteolin protects PA-infected zebrafish by decreasing gut inflammation and altering the expression of inflammatory (TNF-α, IL-1β, IL-6) and antioxidant markers (iNOS, SOD, CAT). Thus, luteolin was found to have dual effect in protecting PA-infected zebrafish by decreasing virulence factors production in PA and stimulating host immune system. This is the first study demonstrating the protective effect of luteolin using animal model. Hence, luteolin could be used as a future therapeutic drug to control multi-drug resistant PA.

Phytochemicals, Biological Activities, Molecular Mechanisms, and Future Prospects of Plantago asiatica L

Plantago asiatica L. has been used as a vegetable and nutritious food in Asia for thousands of years. According to recent phytochemical and pharmacological research, the active compositions of the plant contribute to various health benefits, such as antioxidant, anti-inflammatory, antibacterial, antiviral, and anticancer. This article reviews the 87 components of the plant and their structures, as well as their biological activities and molecular research progress, in detail. This review provides valuable reference material for further study, production, and application of P. asiatica, as well as its components in functional foods and therapeutic agents.

Molecular Mechanisms and Applications of N-Acyl Homoserine Lactone-Mediated Quorum Sensing in Bacteria

Microbial biodiversity includes biotic and abiotic components that support all life forms by adapting to environmental conditions. Climate change, pollution, human activity, and natural calamities affect microbial biodiversity. Microbes have diverse growth conditions, physiology, and metabolism. Bacteria use signaling systems such as quorum sensing (QS) to regulate cellular interactions via small chemical signaling molecules which also help with adaptation under undesirable survival conditions. Proteobacteria use acyl-homoserine lactone (AHL) molecules as autoinducers to sense population density and modulate gene expression. The LuxI-type enzymes synthesize AHL molecules, while the LuxR-type proteins (AHL transcriptional regulators) bind to AHLs to regulate QS-dependent gene expression. Diverse AHLs have been identified, and the diversity extends to AHL synthases and AHL receptors. This review comprehensively explains the molecular diversity of AHL signaling components of Pseudomonas aeruginosa, Chromobacterium violaceum, Agrobacterium tumefaciens, and Escherichia coli. The regulatory mechanism of AHL signaling is also highlighted in this review, which adds to the current understanding of AHL signaling in Gram-negative bacteria. We summarize molecular diversity among well-studied QS systems and recent advances in the role of QS proteins in bacterial cellular signaling pathways. This review describes AHL-dependent QS details in bacteria that can be employed to understand their features, improve environmental adaptation, and develop broad biomolecule-based biotechnological applications.

Synergistic chemo-/photothermal therapy based on supercritical technology-assisted chitosan-indocyanine green/luteolin nanocomposites for wound healing

Despite the success, it is highly challenging to battle against pathogenic biofilms-based chronic bacterial infections by conventional antibiotic therapy. Herein, we report a near-infrared (NIR)/acid-induced nanoplatform based on chitosan (CS)-coated indocyanine green (ICG, photosensitizer)/luteolin (LUT, a natural quorum sensing inhibitor) nanocomposites (ICG/LUT-CS) as antibacterial and antibiofilm agents for skin wound healing. Initially, the ICG/LUT nanoplatforms are prepared by the supercritical antisolvent technology and coated with the CS layer. The obtained ICG/LUT-CS with ultra-high encapsulation efficiency exhibited more favorable photothermal conversion effects and improved NIR laser/acid dual-induced drug release behavior than individual modalities, achieving exceptional bacteria-killing and biofilm elimination effects. Moreover, the ICG/LUT-CS realized the synergetic effects of chemotherapy and photothermal therapy outcomes for wound healing. Together, our findings provided an appealing strategy for the rapid preparation and future translational application of ICG/LUT-CS as an ideal agent for fighting against biofilm infections.

Molecular Basis for Luteolin as a Natural TatD DNase Inhibitor in Trueperella pyogenes

TatD960 and TatD825 are DNases that contribute to biofilm formation and virulence in Trueperella pyogenes (T. pyogenes). Luteolin is a natural flavonoid commonly found in plants that exhibits antimicrobial capacity. Our study aims to investigate the effects of luteolin on TatD DNases as a natural inhibitor. In this research, the expression of tatD genes and TatD proteins in T. pyogenes treated with luteolin was detected, and then the effect of luteolin on the hydrolysis of DNA by TatD DNases was analyzed using agarose gel electrophoresis. Moreover, the interactions between luteolin and TatD DNases were tested using surface plasmon resonance (SPR) assays and molecular docking analysis. After 1/2 MIC luteolin treatment, the transcription of tatD genes and expression of TatD proteins appeared to be reduced in 80–90% of T. pyogenes (n = 20). The gel assay revealed that luteolin can inhibit the activity of TatD DNases. The SPR assay showed that the KD values of luteolin to TatD960 and TatD825 were 6.268 × 10⁻⁶ M and 5.654 × 10⁻⁶ M, respectively. We found through molecular docking that hydrogen bonding is predominant in the interaction of luteolin and TatD DNases. Our data indicate that luteolin inhibited the ability of TatD DNases by decreasing their binding to DNA. The current study provides an insight into the development of luteolin as a DNase inhibitor in preventing biofilm formation and virulence in T. pyogenes.

The Molecular Architecture of Pseudomonas aeruginosa Quorum-Sensing Inhibitors

The survival selection pressure caused by antibiotic-mediated bactericidal and bacteriostatic activity is one of the important inducements for bacteria to develop drug resistance. Bacteria gain drug resistance through spontaneous mutation so as to achieve the goals of survival and reproduction. Quorum sensing (QS) is an intercellular communication system based on cell density that can regulate bacterial virulence and biofilm formation. The secretion of more than 30 virulence factors of P. aeruginosa is controlled by QS, and the formation and diffusion of biofilm is an important mechanism causing the multidrug resistance of P. aeruginosa, which is also closely related to the QS system. There are three main QS systems in P. aeruginosa: las system, rhl system, and pqs system. Quorum-sensing inhibitors (QSIs) can reduce the toxicity of bacteria without affecting the growth and enhance the sensitivity of bacterial biofilms to antibiotic treatment. These characteristics make QSIs a popular topic for research and development in the field of anti-infection. This paper reviews the research progress of the P. aeruginosa quorum-sensing system and QSIs, targeting three QS systems, which will provide help for the future research and development of novel quorum-sensing inhibitors.

Luteolin Binds Streptolysin O Toxin and Inhibits Its Hemolytic Effects and Cytotoxicity

Group A streptococcus (GAS, Streptococcus pyogenes) is a common pathogen that can cause a variety of human diseases. Streptolysin O (SLO) is an exotoxin produced by GAS. It is a pore-forming toxin (PFT) that exhibits high in vivo toxicity. SLO enables GAS to evade phagocytosis and clearance by neutrophils, induces eukaryotic cell lysis, and activates inflammatory bodies. Luteolin is a natural compound that is produced by a wide range of plant species, and recent studies have shown that luteolin can inhibit the growth and alter the morphological of GAS. Here, we reported that luteolin can weaken the cytotoxicity and hemolytic activity of SLO in vitro. Briefly, luteolin bound SLO with high affinity, inhibited its dissolution of erythrocytes, affected its conformational stability and inhibited the formation of oligomers. To further verify the protective effect of luteolin, we used an in vitro SLO-induced human laryngeal carcinoma epithelial type-2 cells (HEp-2) model. Notably, our results showed luteolin protected HEp-2 cells from SLO induced cytotoxicity and changed in cell membrane permeability. In addition, we explored the role of luteolin in protecting mice from GAS-mediated injury using an aerosolized lung delivery model, and our results indicate that luteolin increases murine survival rate following inoculation with a lethal dose of GAS, and that survival was also associated with decreased pathological damage to lung tissue. Our results suggest that luteolin may be a novel drug candidate for the treatment of GAS infection.

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Plant-derived nanotherapeutic systems to counter the overgrowing threat of resistant microbes and biofilms

Since antiquity, the survival of human civilization has always been threatened by the microbial infections. An alarming surge in the resistant microbial strains against the conventional drugs is quite evident in the preceding years. Furthermore, failure of currently available regimens of antibiotics has been highlighted by the emerging threat of biofilms in the community and hospital settings. Biofilms are complex dynamic composites rich in extracellular polysaccharides and DNA, supporting plethora of symbiotic microbial life forms, that can grow on both living and non-living surfaces. These enforced structures are impervious to the drugs and lead to spread of recurrent and non-treatable infections. There is a strong realization among the scientists and healthcare providers to work out alternative strategies to combat the issue of drug resistance and biofilms. Plants are a traditional but rich source of effective antimicrobials with wider spectrum due to presence of multiple constituents in perfect synergy. Other than the biocompatibility and the safety profile, these phytochemicals have been repeatedly proven to overcome the non-responsiveness of resistant microbes and films via multiple pathways such as blocking the efflux pumps, better penetration across the cell membranes or biofilms, and anti-adhesive properties. However, the unfavorable physicochemical attributes and stability issues of these phytochemicals have hampered their commercialization. These issues of the phytochemicals can be solved by designing suitably constructed nanoscaled structures. Nanosized systems can not only improve the physicochemical features of the encapsulated payloads but can also enhance their pharmacokinetic and therapeutic profile. This review encompasses why and how various types of phytochemicals and their nanosized preparations counter the microbial resistance and the biofouling. We believe that phytochemical in tandem with nanotechnological innovations can be employed to defeat the microbial resistance and biofilms. This review will help in better understanding of the challenges associated with developing such platforms and their future prospects.

Quorum Quenching Enzyme (PF-1240) Capable to Degrade AHLs as a Candidate for Inhibiting Quorum Sensing in Food Spoilage Bacterium Hafnia alvei

Quorum sensing (QS) is widely present in microorganisms in marine aquatic products. Owing to the use of antibiotics, many spoilage bacteria in aquatic products are drug resistant. In order to slow down this evolutionary trend, the inhibition of spoilage phenotype of spoilage bacteria by interfering with QS has become a research hot spot in recent years. In this study, we found a new QS quenching enzyme, PF-1240; it was cloned and expressed in Pseudomonas fluorescens 08. Sequence alignment showed that its similarity with N-homoserine lactone (AHL) acylase QuiP protein of Pseudomonas fluorescens (Pf 0-1) was 78.4%. SDS-PAGE confirmed that the protein is a dimer composed of two subunits, which is similar to the structure of AHL acylases. The concentration of heterologous expression in Escherichia coli (DE3) was 26.64 μg/mL. Unlike most AHL acylases, PF-1240 can quench AHLs with different carbon chain lengths and inhibit the quorum sensing of the aquatic spoilage bacterium Hafnia alvei. It can significantly reduce the formation rate of biofilm of H. alvei to 44.4% and the yield of siderophores to 54%, inhibit the production of protease and lipase, and interfere with the motility of H. alvei. Through these corruption phenotypes, the specific application effect of PF-1240 can be further determined to provide a theoretical basis for its application in the preservation of practical aquatic products.