EGCG-Mediated Potential Inhibition of Biofilm Development and Quorum Sensing in Pseudomonas aeruginosa

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

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

Conjugation of Lysozyme and Epigallocatechin Gallate for Improving Antibacterial and Antioxidant Properties

One of the main interests in the food industry is the preservation of food from spoilage by microorganisms or lipid oxidation. A novel alternative is the development of additives of natural origin with dual activity. In the present study, a chemically modified lysozyme (Lys) with epigallocatechin gallate (EGCG) was developed to obtain a conjugate (Lys-EGCG) with antibacterial/antioxidant activity to improve its properties and increase its application potential. The modification reaction was carried out using a free radical grafting method for the Lys modification reaction, using ascorbic acid and hydrogen peroxide as radical initiators in an aqueous medium. The synthesis of Lys-EGCG conjugate was confirmed by spectroscopic (FT-IR, 1H-RMN, and XPS) and calorimetry differential scanning (DSC) analyses. The EGCG binding to the Lys biomolecule was quantified by the Folin-Ciocalteu method; the antibacterial activity was evaluated by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MCB) against Staphylococcus aureus and Pseudomonas fluorescens; the antioxidant activity was evaluated by ABTS, DPPH, and FRAP. The spectroscopic results showed that the Lys-EGCG conjugate was successfully obtained, and the DSC analysis revealed a 20 °C increase (P < 0.05) in the denaturation temperature of Lys due to EGCG modification. The EGCG concentration in Lys-EGCG was 97.97 ± 4.7 µmol of EGCG/g of sample. The antibacterial and antioxidant activity of the Lys-EGCG conjugate was higher (P < 0.05) than pure EGCG and Lys. The chemical modification of Lys with EGCG allows for the bioconjugate with a dual function (antibacterial/antioxidant), broadening the range of Lys and EGCG applications to different areas such as food, cosmetic, and pharmaceutical industries.

Computational and experimental strategies for combating MBL P. aeruginosa (MBLPA) biofilms using phytochemicals: Targeting the quorum sensing network

Pseudomonas aeruginosa is a Gram-negative opportunistic bacterium, ubiquitously found in nature and causative agent in many infections. Due to increased antibiotic resistance, there is a need to develop more robust antibacterial agents from natural sources. In this study, we worked on two metallo-β-lactamase (MBL) producing Pseudomonas aeruginosa strains and targeted the Quorum Sensing mechanism (QS) of these bacteria to combat antibiotic resistance. Our study aimed at using phytochemicals which have been used since centuries in herbal medicine. We used fifteen commercially available phytochemicals and check their effects on biofilm formation, quorum sensing and inter-related mechanisms. Sub-inhibitory concentration of isoliquiritin inhibited biofilm formation 55 % in P8 at day 6 and 48 % in P6 at day 6; quorum sensing 83 % in P6 and 61 % in P8 whereas sub-inhibitory concentration of 6-gingerol suppressed biofilm formation by 48 % in P8 at day 6 and 44 % in P6 at day 6; quorum sensing 69 % in P6 and 48 % in P8, respectively. The results indicated isoliquiritin, epigallocatechin gallate, eugenol, luteolin and chrysin to be the potential candidates in inhibiting QS and related mechanisms. Isoliquiritin which was never been used before against biofilm and QS related studies, showed remarkable results and found to be more efficient in inhibiting QS than 6-gingerol -a known QS inhibitor. For examining the molecular interaction between phytochemicals and QS, In-silico molecular docking was performed between phytoligands and four QS proteins (Las I, Las R, RhlI and Rhl R). In-silico docking analysis revealed that isoliquiritin showed strong bond with amino acids (Trp34, Asp35, Asp35, Tyr105, Arg104, Val138, Thr140) present at the active site of RhlI with binding energy value of -8.4 kcal/mol as compared to that of 6-gingerol with Rhl1 (-7.3 kcal/mol). In conclusion, our study may help in controlling nosocomial infections caused by carbapenem-resistant metallo beta-lactamase P. aeruginosa (MBL-PA) by utilizing these phytochemicals in biofilms disruption and quorum sensing inhibition. Moreover their synergism with antibiotics may help in lowering the MIC of carbapenem antibiotics against such Multi-drug resistant strains.

Differential effects of theasinensins and epigallocatechin-3-O-gallate on phospholipid bilayer structure and liposomal aggregation

(-)-Epigallocatechin-3-O-gallate (EGCg), the major catechin responsible for the health-enhancing and disease-preventive effects of green tea, is susceptible to auto-oxidation at physiological pH levels. However, whether the oxidized EGCg resulting from its oral consumption possesses any bioactive functions remains unclear. This study presents a differential analysis of intact and oxidized EGCg regarding their interactions with phosphatidylcholine liposomes, serving as a simple biomembrane model. In the presence of ascorbic acid, pre-oxidized EGCg induced liposomal aggregation in a dose-dependent manner, whereas intact EGCg did not. Toxicity evaluation using calcein-loaded liposomes revealed that liposomal aggregation is associated with minimal membrane damage. Through fractionation of the oxidized EGCg sample, the fraction containing theasinensins showed high liposomal aggregation activity. Overall, these results suggest that oxidatively condensed EGCg dimers may stimulate various cells by altering the plasma membrane in a manner different from that of EGCg monomers.

Antibiofilm Activity of Combretum micranthum G. Don Catechin-Sugar Phytocomplex on Pseudomonas aeruginosa

Clinicians often have to face infections caused by microorganisms that are difficult to eradicate due to their resistance and/or tolerance to antimicrobials. Among these pathogens, Pseudomonas aeruginosa causes chronic infections due to its ability to form biofilms on medical devices, skin wounds, ulcers and the lungs of patients with Cystic Fibrosis. In this scenario, the plant world represents an important reservoir of natural compounds with antimicrobial and/or antibiofilm properties. In this study, an extract from the leaves of Combretum micranthum G. Don, named Cm4-p, which was previously investigated for its antimicrobial activities, was assayed for its capacity to inhibit biofilm formation and/or to eradicate formed biofilms. The model strain P. aeruginosa PAO1 and its isogenic biofilm hyperproducer derivative B13 were treated with Cm4-p. Preliminary IR, UV-vis, NMR, and mass spectrometry analyses showed that the extract was mainly composed of catechins bearing different sugar moieties. The phytocomplex (3 g/L) inhibited the biofilm formation of both the PAO1 and B13 strains in a significant manner. In light of the obtained results, Cm4-p deserves deeper investigations of its potential in the antimicrobial field.

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

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

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.

Potential of Flavonoids as Promising Phytotherapeutic Agents to Combat Multidrug-Resistant Infections

BACKGROUND

Considering the limited number of current effective treatments, Multidrug- Resistant (MDR) illnesses have grown to be a serious concern to public health. It has become necessary to look for new antimicrobial drugs because of the emergence of resistance to numerous kinds of antibiotics. The use of flavonoids is one phytotherapeutic strategy that has been researched as a potential remedy for this issue. Secondary plant compounds called flavonoids have been found to have an antibacterial effect against resistant microorganisms.

OBJECTIVE

This review seeks to give readers a glimpse into contemporary studies on flavonoids' potential to fight MDR infections.

METHODS

A systematic search was conducted on electronic databases (PubMed, Scopus, and Google Scholar) using relevant keywords such as flavonoids, MDR infections, antimicrobial activity, and resistance microbes. Studies that investigated the antimicrobial activity of flavonoids against resistant microbes were included in this review.

RESULTS

Most research found that flavonoids have antibacterial efficacy against resistant microorganisms, and some also showed that they have synergistic benefits with traditional antibiotics. The flavonoids quercetin, kaempferol, apigenin, and luteolin were the most often investigated ones. According to research, flavonoids affect microbial gene expression, inhibit microbial enzymes, and disrupt the integrity of microbial cell membranes. Additionally, a few studies have noted the flavonoids' low toxicity and safety.

CONCLUSION

For the treatment of infections that are resistant to many drugs, flavonoids constitute a promising class of phytotherapeutic agents. To develop flavonoid-based treatment methods for treating MDR illnesses and assess the potential of flavonoids as adjuvants to conventional antimicrobial drugs, more study is required.

Attenuation of biofilm and quorum sensing regulated virulence factors of an opportunistic pathogen Pseudomonas aeruginosa by phytofabricated silver nanoparticles

Green-synthesized nanoparticles provide an effective strategy for inhibiting microbial pathogenesis by affecting biofilm formation, quorum sensing (QS), and other surface properties of microorganisms. QS is a density-dependent communication signaling cascade that regulates biofilm formation and other pathogenic factors of Pseudomonas aeruginosa. In this context, the effect of phytofabricated silver nanoparticles (CC-AgNPs) synthesized using Cuphea carthagenensis extract on biofilm, QS, and QS-dependent virulence factors of P. aeruginosa were evaluated in this study. CC-AgNPs demonstrated significant attenuation of biofilm, QS, and QS-dependent virulence factors at sub-MICs. A significant inhibition of 88.39 ± 4.32 %, 79.64 ± 3.31 %, 73.07 ± 3.0 %, and 61.67 ± 1.5 % of biofilm formation, quorum sensing, pyocyanin, and LasB elastase, respectively was reported in the study at 20 μg/mL. The study also demonstrated a significant reduction of LasA Staphylolytic activity and 91.37 ± 1.05 % exoprotease production in comparison to untreated control. The lower concentrations of CC-AgNPs also demonstrated significant attenuation of biofilm and other virulence factors suggesting the strong potency of NPs against P. aeruginosa. XTT analysis reported the effect of CC-AgNPs on sessile cells of P. aeruginosa without impacting growth of planktonic cells at sub-MICs. Cell-proliferation study in human cell lines (HEK 293 and Caco-2 cells) demonstrated the safe nature of CC-AgNPs at tested concentrations. This study is novel in a way that environmentally friendly CC-AgNPs were used to inhibit QS at sub-MICs without killing the tested strains, therefore, could be developed as an anti-virulent drug to overcome biofilm and antimicrobial resistance problems.

Inhibition of biofilm formation, quorum sensing and virulence factor production in Pseudomonas aeruginosa PAO1 by selected LasR inhibitors

The quorum sensing network of Pseudomonas aeruginosa mediates the regulation of genes controlling biofilm formation and virulence factors. The rise of drug resistance to Pseudomonas aeruginosa infections has made quorum sensing-regulated biofilm formation in clinical settings a major issue. In the present study, LasR inhibitors identified in our previous study were evaluated for their antibiofilm and antiquorum sensing activities against P. aeruginosa PAO1. The compounds selected were (3-[2-(3,4-dimethoxyphenyl)-2-(1H-indol-3-yl)ethyl]-1-(2-fluorophenyl)urea) (C1), (3-(4-fluorophenyl)-2-[(3-methylquinoxalin-2-yl)methylsulfanyl]quinazolin-4-one) (C2) and (2-({4-[4-(2-methoxyphenyl)piperazin-1-yl]pyrimidin-2-yl}sulfanyl)-N-(2,4,6-trimethylphenyl)acetamide) (C3). The minimum inhibitory concentrations of C1 and C2 were 1000 μM, whereas that of C3 was 500 μM. At sub-MICs, the compounds showed potent antibiofilm activity without affecting the growth of P. aeruginosa PAO1. Electron microscopy confirmed the disruption of biofilm by the selected compounds. The antiquorum sensing activity of the compounds was revealed by the inhibition of violacein in Chromobacterium violaceum and the inhibition of swimming and swarming motilities in P. aeruginosa PAO1. Furthermore, the compounds also attenuated the production of quorum sensing-mediated virulence factors. The qRT-PCR revealed the downregulation of quorum sensing regulatory genes, namely lasI, lasR, rhlI, rhlR, lasB, pqsA and pqsR. The selected compounds also exhibited lower cytotoxicity against peripheral blood lymphocytes. Thus, this study could pave a way to explore these compounds for the development of therapeutic agent against Pseudomonas aeruginosa biofilm-related infections.

The antivirulence activity, transcriptomics of EGCG and its protective effects on zebrafish infected by Aeromonas hydrophila

Background

Aeromonas hydrophila is an important pathogen that mainly harms aquatic animals and exhibits resistance to a variety of antibiotics. This study investigated the effect of epigallocatechin-3-gallate (EGCG) on the virulence factors of A.hydrophila and its impact on adhesion, invasion, and cytotoxicity in Caco-2 cells. The potential mechanism of antibacterial activity of EGCG was investigated by transcriptomic analysis.

Results

EGCG not only inhibited the production of biofilm, hemolytic activity, motility, and protease activity of A.hydrophila, but also reduced its adhesion, invasion, and cytotoxicity in Caco-2 cells. Transcriptomic analysis indicated that the antimicrobial activity of EGCG may be achieved by weakening the chemotaxis and stress response of the bacteria, as well as inhibiting the TonB system. Animal studies demonstrated that EGCG can significantly improve the survival rate and organs damage of zebrafish infected with A.hydrophila.

Conclusion

EGCG would be a potential alternative drug for the prevention and treatment of A. hydrophila infections by anti-virulence mechanism.

Recent advances on the regulation of bacterial biofilm formation by herbal medicines

Biofilm formation is a fundamental part of life cycles of bacteria which affects various aspects of bacterial-host interactions including the development of drug resistance and chronic infections. In clinical settings, biofilm-related infections are becoming increasingly difficult to treat due to tolerance to antibiotics. Bacterial biofilm formation is regulated by different external and internal factors, among which quorum sensing (QS) signals and nucleotide-based second messengers play important roles. In recent years, different kinds of anti-biofilm agents have been discovered, among which are the Chinese herbal medicines (CHMs). CHMs or traditional Chinese medicines have long been utilized to combat various diseases around the world and many of them have the ability to inhibit, impair or decrease bacterial biofilm formation either through regulation of bacterial QS system or nucleotide-based second messengers. In this review, we describe the research progresses of different chemical classes of CHMs on the regulation of bacterial biofilm formation. Though the molecular mechanisms on the regulation of bacterial biofilm formation by CHMs have not been fully understood and there are still a lot of work that need to be performed, these studies contribute to the development of effective biofilm inhibitors and will provide a novel treatment strategy to control biofilm-related infections.

Metabolomics and proteomics analyses revealed mechanistic insights on the antimicrobial activity of epigallocatechin gallate against Streptococcus suis

Streptococcus suis (S. suis) is a highly virulent zoonotic pathogen and causes severe economic losses to the swine industry worldwide. Public health security is also threatened by the rapidly growing antimicrobial resistance in S. suis. Therefore, there is an urgent need to develop new and safe antibacterial alternatives against S. suis. The green tea polyphenol epigallocatechin gallate (EGCG) with a number of potential health benefits is known for its antibacterial effect; however, the mechanism of its bactericidal action remains unclear. In the present, EGCG at minimal inhibitory concentration (MIC) showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. EGCG also reduced S. suis pathogenicity in Galleria mellonella larvae in vivo. Metabolomics and proteomics analyses were performed to investigate the underlying mechanism of antibacterial activity of EGCG at MIC. Many differentially expressed proteins involved in DNA replication, synthesis of cell wall, and cell membrane, and virulence were down-regulated after the treatment of S. suis with EGCG. EGCG not only significantly reduced the hemolytic activity of S. suis but also down-regulated the expression of suilysin (Sly). The top three shared KEGG pathways between metabolomics and proteomics analysis were ABC transporters, glycolysis/gluconeogenesis, and aminoacyl-tRNA biosynthesis. Taken together, these data suggest that EGCG could be a potential phytochemical compound for treating S. suis infection.

Epigallocatechin-3-gallate ameliorates liver injury secondary to Pseudomonas aeruginosa pneumonia

Pseudomonas aeruginosa is a dangerous pathogen causing nosocomial pneumonia. P. aeruginosa infection-induced liver damage is another fatal threat, and antibiotic treatment is not effective in relieving P. aeruginosa virulence-triggered damage. We here evaluated the protective effect of epigallocatechin gallate (EGCG), a substance that inhibits virulence of P. aeruginosa through quorum quenching, on liver damage secondary to P. aeruginosa infection. Mice were pretreated with EGCG (20, 40, and 80 mg/kg) for 3 days, and then infected with P. aeruginosa through intratracheal instillation to model acute pneumonia. The mice were sacrificed after 24 h of infection, and samples were harvested for subsequent analysis. EGCG significantly decreased the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Histopathological changes of liver were significantly ameliorated by EGCG. It also significantly reduced oxidative stress that induced liver damage in P. aeruginosa infection, which relied not on the activation of the Nrf₂-HO-1 pathway but on the upregulation of the activity of antioxidative enzymes. Then, the inflammatory response in the liver was tested. EGCG inhibited the release of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) by blocking the inflammation regulating signaling of the TLR4-myD88-NF-κB pathway. EGCG upregulated the activation of nuclear receptors to stronger the liver protective activity against P. aeruginosa infection. Conclusively, EGCG exhibited a significant hepatoprotective effective against P. aeruginosa infection.

Rhodiola rosea Reduces Intercellular Signaling in Campylobacter jejuni

Campylobacter jejuni is a major foodborne pathogen and the leading cause of bacterial gastroenteritis, i.e., campylobacteriosis. Besides searching for novel antimicrobials, identification of new targets for their action is becoming increasingly important. Rhodiola rosea has long been used in traditional medicine. Ethanolic extracts from the roots and rhizomes of the plant contain a wide range of bioactive compounds with various pharmacological activities. In this study, cultivated plant materials have been used, i.e., "Mattmark" and "Rosavine". Through optimized protocols, we obtained fractions of the initial ethanolic extracts rich in most important bioactive compounds from R. rosea, including salidroside, rosavins, proanthocyanidins (PACs), and flavonoids. The antimicrobial activity in relation to the chemical composition of the extracts and their fractions was studied with an emphasis on C. jejuni AI-2-mediated intercellular signaling. At concentration 15.625 mg/L, bioluminescence reduction rates varied from 27% to 72%, and the membrane remained intact. Fractions rich in PACs had the strongest antimicrobial effect against C. jejuni, with the lowest minimal inhibitory concentrations (MICs) (M F3 40%: 62.5 mg/L; R F3 40%: 250 mg/L) and the highest intercellular signaling reduction rates (M F3 40%: 72%; R F3 40%: 65%). On the other hand, fractions without PACs were less effective (MICs: M F5 PVP: 250 mg/L; R F5 PVP: 1000 mg/L and bioluminescence reduction rates: M F5 PVP: 27%; R F5 PVP: 43%). Additionally, fractions rich in flavonoids had strong antimicrobial activity (MICs: M F4 70%: 125 mg/L; R F4 70%: 250 mg/L and bioluminescence reduction rates: M F4 70%: 68%; R F4 70%: 50%). We conclude that PACs and flavonoids are crucial compound groups responsible for the antimicrobial activity of R. rosea roots and rhizomes in C. jejuni.

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.

Design, Synthesis, and Biological Evaluation of N-Acyl-Homoserine Lactone Analogs of Quorum Sensing in Pseudomonas aeruginosa

Quorum sensing plays a necessary role in the production of virulence factors and the formation of biofilm on Pseudomonas aeruginosa. Thus, the development of inhibition of quorum sensing is one of the most promising methods to control bacterial infection and antibiotic resistance. In this work, nine novel AHL analogs were designed, synthesized, and evaluated as potential quorum sensing inhibitors. The results depicted that structural modifications have significant effects on quorum sensing inhibition activity of AHL molecules. Without inhibiting the growth of P. aeruginosa, 2-(4-bromophenyl)-N-(2-oxotetrapyridinefuran-3-yl) butanamide (compound no.10) showed the excellent performance in inhibiting biofilm formation and virulence factor production among all the compounds through robustly suppressing the expression of QS related genes. In a molecular docking study, compound no.10 exhibited a higher affinity toward LasR than other AHL analogs. In addition, compound no.10 also exhibits the best inhibition effect on virulence production in the Caenorhabditis elegans infection model.

Paeonol Interferes With Quorum-Sensing in Pseudomonas aeruginosa and Modulates Inflammatory Responses In Vitro and In Vivo

Developing quorum-sensing (QS) based anti-infection drugs is one of the most powerful strategies to combat multidrug-resistant bacteria. Paeonol has been proven to attenuate the QS-controlled virulence factors of P. aeruginosa by down-regulating the transcription of QS signal molecules. This research aimed to assess the anti-virulence activity and mechanism of paeonol against P. aeruginosa infection in vitro and in vivo. In this study, paeonol was found to reduce the adhesion and invasion of P.aeruginosa to macrophages and resist the cytotoxicity induced by P.aeruginosa. Paeonol reduced the expression of virulence factors of P.aeruginosa by inhibiting QS, thereby reducing the LDH release and damage of P.aeruginosa-infected macrophages. Paeonol can inhibit bacterial virulence and enhance the ability of macrophages to clear P.aeruginosa. In addition, paeonol exerts anti-inflammatory activity by reducing the expression of inflammatory cytokines and increasing the production of anti-inflammatory cytokines. Paeonol treatment significantly inhibited the activation of TLR4/MyD88/NF-κB signaling pathway and decreased the inflammation response of P. aeruginosa-infected macrophages. Paeonol also significantly reduced the ability of P.aeruginosa to infect mice and reduced the inflammatory response. These data suggest that paeonol can inhibit the virulence of P.aeruginosa and decrease the inflammation response in P.aeruginosa-infected macrophages and mice, which can decrease the damage induced by P.aeruginosa infection and enhance the ability of macrophages to clear bacteria. This study supports the further development of new potential anti-infective drugs based on inhibition of QS and virulence factors.

Epigallocatechin-3-Gallate Ameliorates Acute Lung Damage by Inhibiting Quorum-Sensing-Related Virulence Factors of Pseudomonas aeruginosa

The superbug Pseudomonas aeruginosa is among the most formidable antibiotic-resistant pathogens. With declining options for antibiotic-resistant infections, new medicines are of utmost importance to combat with P. aeruginosa. In our previous study, we demonstrated that Epigallocatechin-3-gallate (EGCG) can inhibit the production of quorum sensing (QS)-regulated virulence factors in vitro. Accordingly, the protective effect and molecular mechanisms of EGCG against P. aeruginosa-induced pneumonia were studied in a mouse model. The results indicated that EGCG significantly lessened histopathological changes and increased the survival rates of mice infected with P. aeruginosa. EGCG effectively alleviated lung injury by reducing the expression of virulence factors and bacterial burden. In addition, EGCG downregulated the production of pro-inflammatory cytokines, such as TNF-α, IL-1, IL-6, and IL-17, and increased the expression of anti-inflammatory cytokines IL-4 and IL-10. Thus, the experimental results supported for the first time that EGCG improved lung damage in P. aeruginosa infection by inhibiting the production of QS-related virulence factors in vivo.

Drug repurposing to overcome microbial resistance

Infections are a growing global threat, and the number of resistant species of microbial pathogens is alarming. However, the rapid development of cross-resistant or multidrug-resistant strains and the development of so-called 'superbugs' are in stark contrast to the number of newly launched anti-infectives on the market. In this review, I summarize the causes of antimicrobial resistance, briefly discuss different approaches to the discovery and development of new anti-infective drugs, and focus on drug repurposing strategy, which is discussed from all possible perspectives. A comprehensive overview of drugs of other indications tested for their in vitro antimicrobial activity to support existing anti-infective therapeutics is provided, including several critical remarks on this strategy of repurposing non-antibiotics to antibacterial drugs.

Beneficial Effects of Green Tea EGCG on Skin Wound Healing: A Comprehensive Review

Epigallocatechin gallate (EGCG) is associated with various health benefits. In this review, we searched current work about the effects of EGCG and its wound dressings on skin for wound healing. Hydrogels, nanoparticles, micro/nanofiber networks and microneedles are the major types of EGCG-containing wound dressings. The beneficial effects of EGCG and its wound dressings at different stages of skin wound healing (hemostasis, inflammation, proliferation and tissue remodeling) were summarized based on the underlying mechanisms of antioxidant, anti-inflammatory, antimicrobial, angiogenesis and antifibrotic properties. This review expatiates on the rationale of using EGCG to promote skin wound healing and prevent scar formation, which provides a future clinical application direction of EGCG.

Quorum-sensing regulation of virulence factors in bacterial biofilm

Chronic polymicrobial wound infections are often characterized by the presence of bacterial biofilms. They show considerable structural and functional heterogeneity, which influences the choice of antimicrobial therapy and wound healing dynamics. The hallmarks of biofilm-associated bacterial infections include elevated antibiotic resistance and extreme pathogenicity. Biofilm helps bacteria to evade the host defense mechanisms and persist longer in the host. Quorum-sensing (QS)-mediated cell signaling primarily regulates biofilm formation in chronic infections and plays a major role in eliciting virulence. This review focuses on the QS mechanisms of two major bacterial pathogens, Staphylococcus aureus and Pseudomonas aeruginosa and explains how they interact in the wound microenvironment to regulate biofilm development and virulence. The review also provides an insight into the treatment modalities aimed at eradicating polymicrobial biofilms. This information will help us develop better diagnostic modalities and devise effective treatment regimens to successfully manage and overcome severe life-threatening bacterial infections.