Quorum Sensing Inhibition Activity Research Articles

EVALUATION OF ANTI-QUORUM SENSING ACTIVITY OF-HEXADECANOIC ACID PRODUCED BY PSEUDOMONAS STUTZERI SJ4 – A MARINE EPIBIOTIC BACTERIUM

Quorum sensing (QS) mechanism is cell communication that plays vital role in the development of infection by many pathogenic microorganisms. It controls multiple virulence factors such as pigmentation, biofilm formation, swarming motility, resistance towards antibiotics, extracellular polysaccharide production (EPS) and expression of several collective traits. The disruption of quorum sensing mechanism can be a solution to the emerging problem of multi-drug resistance among pathogenic bacteria. The effector molecule for Quorum sensing inhibition may be enzymatic or non- enzymatic in nature termed as Quorum Quenching (QQ) or Quorum sensing inhibitory (QSIs)/anti –QS compound, respectively. We used marine epibiotic bacteria as a source to obtained novel bacterial strain as QSI producer. One of the potent isolate, SJ4 was identified as Pseudomonas stutzeri SJ4, it is a short rod, gram negative bacterium. The ethyl acetate extract from P. stutzeri SJ4, showed highest QSI activity against monitor strain Chromobacterium violaceum (MTCC 5526). The extracted compound was tested against P. aeruginosa PAO1 at minimum inhibitiory concentration (MIC) and sub-MIC to study the effect on virulence factors. The significant inhibition of pycocyanin pigment, EPS production, rhamnolipid production and reduced swimming and swarming motility was observed. In addition, biofilm formation was notably inhibited which was confirmed by staining and spectometric method. Based on this observation, QS interption by extract which contain QSI remarkebly reduced the virulence of pathogen hence, can be use as therapeutic agents. The Thin Layer Chomatography (TLC) and Gas chrmoatography-Mass Spectrometry (GC-MS) identified major compound as n-Hexadecanoic acid. However, further research is required on purification of compound and its potential applications for the treatement of infections.

Alleviating the virulence of Pseudomonas aeruginosa and Staphylococcus aureus by ascorbic acid nanoemulsion

The high incidence of persistent multidrug resistant bacterial infections is a worldwide public health burden. Alternative strategies are required to deal with such issue including the use of drugs with anti-virulence activity. The application of nanotechnology to develop advanced Nano-materials that target quorum sensing regulated virulence factors is an attractive approach. Synthesis of ascorbic acid Nano-emulsion (ASC-NEs) and assessment of its activity in vitro against the virulence factors and its protective ability against pathogenesis as well as the effect against expression of quorum sensing genes of Pseudomonas aeruginosa and Staphylococcus aureus isolates. Ascorbic acid Nano-emulsion was characterized by DLS Zetasizer Technique, Zeta potential; Transmission Electron Microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The antibacterial activity of ASC-NEs was tested by the broth microdilution method and the activity of their sub-MIC against the expression of quorum sensing controlled virulence was investigated using phenotypic experiments and RT-PCR. The protective activity of ASC-NEs against P. aeruginosa as well as S. aureus pathogenesis was tested in vivo. Phenotypically, ASC-NEs had strong virulence inhibitory activity against the tested bacteria. The RT-PCR experiment showed that it exhibited significant QS inhibitory activity. The in vivo results showed that ASC-NEs protected against staphylococcal infection, however, it failed to protect mice against Pseudomonal infection. These results suggest the promising use of nanoformulations against virulence factors in multidrug resistant P. aeruginosa and S. aureus. However, further studies are required concerning the potential toxicity, clearance and phamacokinetics of the nanoformulations.

Accelerated solvent extraction of red onion peel extract and its antimicrobial, antibiofilm, and quorum-sensing inhibition activities against Listeria monocytogenes and Chromobacteriumviolaceum

In this study, we used accelerated solvent extraction (ASE) to extract flavonoids and anthocyanins from dried red onion peels, producing red onion peel extract (ROPE). High-performance liquid chromatography analysis of ROPE obtained using ASE identified important flavonols and anthocyanins. Total flavonoid and anthocyanin contents measured from ROPE were 459.15 mg/g ± 16.45 (DW) and 33.14 mg/g ± 0.99 (DW), respectively. ROPE antimicrobial activity against L. monocytogenes showed strain-specific effects, where the minimum inhibitory concentration (MIC) for V7 was two-fold greater than for EGD and Scott A (i.e., 25.82 vs. 12.91 mg quercetin-3, 4′-diglucoside equivalents/gram [mg QdGE/g] ROPE). ROPE significantly inhibited (P < 0.05) biofilm formation by all three strains at sub-inhibitory concentrations (0.40–6.45 mg QdGE/g) in a concentration-dependent manner. Pre-formed biofilms of mixed L. monocytogenes strains on stainless steel were inactivated after 48 h at 22 °C only with higher concentrations of ROPE (25.82–56.63 mg QdGE/g). Sub-inhibitory concentrations of ROPE also inhibited L. monocytogenes motility and suppressed violacein pigment production in Chromobacterium violaceum ATCC 12472, suggesting that ROPE inhibited quorum sensing. Therefore, our data indicate that red onion peel waste has potential as a source of natural antibacterial compounds as an approach to food safety in the circular economy.

Antimicrobial and antiquorum-sensing activity of Conocarpus lancifolius Engl. (Combretaceae)

Multidrug resistance to antimicrobial agents is a rapidly increasing problem. New strategies are required to reduce microbial resistance and pathogenicity. These include inhibiting microbial virulence factors, such as quorum-sensing (QS). In this study, the leaf and fruit extracts of Conocarpus lancifolius Engl. were investigated for their antimicrobial and QS inhibitory activities. The ethyl acetate extract of the leaf (EAL) recorded a remarkable inhibition of the Gram-negative bacteria; Escherichia coli and Klebsiella pneumonia (23 and 20 mm, respectively), using the agar well diffusion assay. Also, it showed the highest antifungal effect against Candida albicans (20 mm). Meanwhile, the ethyl acetate extract of the fruit (EAF) showed significant inhibition of the Gram-positive bacteria; Staphylococcus aureus and Bacillus cereus (20 and 21 mm, respectively). Measurement of the minimum inhibitory concentration (MIC) by the broth microdilution method indicated that Gram-positive bacteria were more susceptible to the antimicrobial effect of the investigated extracts. Particularly, EAL and EAF showed comparable activity to ampicillin against B. cereus (MIC, 312.5 µg/mL). The highest antifungal activity was recorded for the petroleum ether extract of the leaf (MIC, 625 µg/mL). Measurement of the inhibition diameter of pigment (PID) produced by the reporter strain, Chromobacterium violaceum indicated that EAL demonstrated higher QS inhibition (6 mm) compared to the standard, catechin (4.8 mm). In addition, the leaf and fruit extracts showed comparable activity to catechin (5 mm). The current study reported that C. lancifolius could be a promising antimicrobial and anti-quorum sensing drug candidate.

Effect of traditional Chinese medicine monomers interfering with quorum-sensing on virulence factors of extensively drug-resistant Acinetobacter baumannii.

The antimicrobial resistance of Acinetobacter baumannii (A. baumannii) clinical isolates has emerged as a great threat to public health. Quorum sensing (QS) is one of the resistance mechanisms for drug-resistant A. baumannii. Interfering with QS is a promising strategy to combat infections caused by drug-resistant bacteria. This study explored the QS inhibition ability of thirty-four traditional Chinese medicine monomers (TCMMs) and assessed the effect of QS inhibitors (QSIs) on the virulence factors of twelve extensively drug-resistant A. baumannii (XDRAB) strains. Nine traditional Chinese medicine monomers, such as caffeic acid, cinnamic acid, and myricetin, were found to be able to inhibit the bacterial QS. Then, at 1/8 of the minimal inhibitory concentration, we found that these QSIs inhibited extensively drug-resistant A. baumannii adhesion and biofilm formation and downregulated the expression levels of virulence-associated genes (abaI, abaR, csuE, pgaA, and bap). In conclusion, nine traditional Chinese medicine monomers have QS inhibitory activity and may downregulate QS genes to interfere with the QS system, which could inhibit the expression of extensively drug-resistant A. baumannii virulence factors. These results suggest that traditional Chinese medicine monomers could develop as novel anti-virulence compounds to control extensively drug-resistant A. baumannii infections.

Outer membrane vesicles of Dinoroseobacter shibae transport a volatile aldehyde

Outer Membrane Vesicles (OMVs) of the Gram-negative marine bacterium Dinoroseobacter shibae, a member of the Roseobacteraceae, were investigated for the presence of volatile organic compounds (VOCs). Extracts of vesicles were analyzed by gas chromatography/mass spectrometry (GC/MS). In these analyses the short fatty acid (Z)-5-dodecenoic acid (1) and the related, more volatile aldehyde (Z)-5-dodecenal (8) were identified as VOCs of the OMVs. The aldehyde 8 has not yet been reported before from bacteria. Due to their possible function as signaling molecules, both compounds were tested for Quorum Sensing (QS) inhibition in a bioassay against the QS sensor strain Pseudomonas putida F117 (pKRC12) responsive to long-chain N-acylhomoserine lactones, the effectors of the sensor. Both compounds showed QS inhibitory activity. The potential function of VOCs in OMVs which has not been observed previously is discussed.

Exploration of the inhibitory effect of Cassia fistula on quorum sensing mediated virulence factor production and biofilm activity in Pseudomonas aeruginosa: an in vivo study in model organism Caenorhabditis elegans.

Introduction. Resistance to antibiotics is leading to challenges in the treatment of microbial diseases. One amongst the various approaches to control these pathogens is quorum sensing (QS), which is used to rectify resistance issues. Blocking the bacterial QS circuit is the most reliable anti-virulence therapy to control pathogenicity-associated genes. Pseudomonas aeruginosa is a contagious bacterium that proliferates in the host by using signalling molecules like acyl-homoserine lactones; these molecules generate and disseminate toxins and virulence factors for increasing host infection.Hypothesis. The herb Cassia fistula is known to have antimicrobial, antidiabetic, anti-inflammatory, antitumor medicinal properties amongst others. We hypothesize that its crude extracts will inhibit the QS circuit of Pseudomonas aeruginosa (P. aeruginosa).Aim. The research work was aimed at evaluating anti-quorum sensing and anti-biofilm activity of various crude extracts from Cassia fistula against P. aeruginosa.Methodology. Various extraction methods and solvents were availed for maximum separation, and the extracts were screened for anti-quorum sensing activity. The most potent Fruit Ethyl acetate (FEE) extract at non-inhibitory concentrations was found to interrupt both short-chain (RhlI/R) and long-chain (LasI/R) QS circuits and other virulence factors (P<0.05) such as elastase, protease, rhamnolipids and pyocyanin levels in P. aeruginosa. Biofilm inhibitory properties of FEE were demonstrated using atomic force microscopy, scanning electron microscope and confocal laser microscope. Caenorhabditis elegans infection model (Paralytic assay) was developed to determine the protective role of FEE by reducing the pathogenicity of P. aeruginosa.Results. The study results suggest that hot crude FEE extract interfered in the QS circuit, leading to comprehensive debilitation of QS-controlled virulence factors. The extract reduced virulence factor production in P. aeruginosa at 4 mg ml-1 concentration whilst paradoxically promoting biofilm formation. Possibly, higher sugar content in the extract promoted clump formation of biofilm architecture by increasing exopolysaccharide production. Moreover, in vivo analysis of bacterial pathogenesis on Caenorhabditis elegans reveals a drastic increase in survival rates in FEE treated worms compared to untreated control.Conclusions. FEE showed promising QS inhibitory activity against P. aeruginosa. In the future, additional purification of crude FEE is required to remove carbohydrates, and pure isolated phytochemicals from FEE could be used as therapeutic agents to control QS-mediated infections in P. aeruginosa.

Curcumin and 10-undecenoic acid as natural quorum sensing inhibitors of LuxS/AI-2 of Bacillus subtilis and LasI/LasR of Pseudomonas aeruginosa

The quorum sensing (QS) system is related to cell-to-cell communication as a function of population density, which regulates several physiological functions including biofilm formation and virulence gene expression. QS inhibitors have emerged as a promising strategy to tackle virulence and biofilm development. Among a wide variety of phytochemicals, many of them have been described as QS inhibitors. Driven by their promising clues, this study aimed to identify active phytochemicals against LuxS/autoinducer-2 (AI-2) (as the universal QS system) from Bacillus subtilis and LasI/LasR (as a specific QS system) of Pseudomonas aeruginosa, through in silico analysis followed by in vitro validation. The optimized virtual screening protocols were applied to screen a phytochemical database containing 3479 drug-like compounds. The most promising phytochemicals were curcumin, pioglitazone hydrochloride, and 10-undecenoic acid. In vitro analysis corroborated the QS inhibitory activity of curcumin and 10-undecenoic acid, however, pioglitazone hydrochloride showed no relevant effect. Inhibitory effects on LuxS/AI-2 QS system triggered reduction of 33–77% by curcumin (at 1.25–5 µg/mL) and 36–64% by 10-undecenoic acid (at 12.5–50 µg/mL). Inhibition of LasI/LasR QS system was 21% by curcumin (at 200 µg/mL) and 10–54% by 10-undecenoic acid (at 15.625–250 µg/mL). In conclusion, in silico analysis allowed the identification of curcumin and, for the first time, 10-undecenoic acid (showing low cost, high availability, and low toxicity) as alternatives to counteract bacterial pathogenicity and virulence, avoiding the imposition of selective pressure usually related to classic industrial disinfection and antibiotics therapy.

Triple combination of SPR741, clarithromycin, and erythromycin against Acinetobacter baumannii and its tolerant phenotype.

Extensively drug-resistant (XDR) Acinetobacter baumannii poses a severe threat to public health due to its ability to form biofilms and persister cells, which contributes to critical drug resistance and refractory device-associated infections. A novel strategy to alleviate such an emergency is to identify promising compounds that restore the antimicrobial susceptibility of existing antibiotics against refractory infections. Here, we found a significant synergy among three combinations of SPR741, clarithromycin and erythromycin with a potent antimicrobial activity against XDR A. baumannii (SPR741/CLA/E at 8/10/10 μg ml-1 for XDR AB1069 and at 10/16/10 μg ml-1 for XDR AB1208, respectively). Moreover, the triple combination therapy exhibits a significant antipersister and antibiofilm effect against XDR strains. Mechanistic studies demonstrate that SPR741 may promote intracellular accumulation of macrolides by permeabilizing the outer membrane as well as disrupting membrane potential and further enhance the quorum sensing inhibition activity of the macrolides against XDR A. baumannii and its biofilms. In addition, the triple combination of SPR741 with clarithromycin and erythromycin was not easy to induce resistance in A. baumannii and had effective antimicrobial activity with low toxicity in vivo. Collectively, these results reveal the potential of SPR741 in combination with clarithromycin and erythromycin as a clinical therapy for refractory infections caused by XDR A. baumannii.

Antibacterial and anti-quorum sensing activities of the different solvent extracts of Embelia ruminata

The rise of antibiotic resistance has resulted in an intense drive to screen plants and their secondary metabolites for their antibacterial activity as alternatives to conventional antibiotics. Furthermore, research has focused on plant sources that can curtail the development of drug resistance and the expression of bacterial virulence factors by attenuation of quorum sensing (QS). Thus, the present study investigated the phytochemical profile together with the antibacterial potential of a southern African plant species, Embelia ruminata (E.Mey. ex A.DC.) Mez. against a panel of Gram-negative and Gram-positive strains. Additionally, the study evaluated the QS inhibitory potential of E. ruminata using Chromobacterium subtsugae CV017 (short chain autoinducer) and Chromobacterium violaceum ATCC 12472 (long chain autoinducer). The results of the preliminary phytochemical tests showed the presence of benzoquinone, alkaloids, triterpenoids, flavonoids, phenolic compounds, quinones anthraquinones and resin compounds in the different solvent extracts. In the gas chromatography-mass spectrophotometer analyses, thirty bioactive compounds were identified including the benzoquinone compound, embelin in the hexane and chloroform fruit and seed extracts. In the antibacterial assays, extracts tested at 400 and 800 µg produced limited antibacterial activity against the Gram-negative bacteria, with the fruit extracts demonstrating greatest activity against selected bacterial strains. The methanolic stem bark extracts showed promising activity against selected Gram-positive strains, particularly methicillin-resistant Staphylococcus aureus. In the anti-QS violacein inhibition assay, the chloroform leaf, hexane and methanolic seed extracts displayed inhibition of both biosensor strains suggesting that these extracts possess broad-spectrum QS inhibitory activity. Furthermore, the methanolic seed extracts demonstrated the most potent violacein inhibitory activity against both biosensor strains compared to the other plant organ extracts. This study provides insight into the bioactivity of E. ruminata extracts as possible anti-virulence agents targeting resistant bacterial strains.

Design, synthesis and evaluation of oxazolopyridinone derivatives as quorum sensing inhibitors

The antibiotic crisis is associated with the appearance of multidrug resistant (MDR) pathogens, which has caused severe bacterial infections and imposed a huge burden on modern society. Therefore, there is an urgent need to develop new antibacterial drugs with novel mechanism of action. Here we designed and synthesized three series of benzoxazolone, oxazolopyridinone and 3-(2-hydroxyphenyl)hydantoin derivatives and evaluated their activity as novel quorum sensing (QS) inhibitors. We found that benzoxazolone and oxazolopyridinone derivatives had promising QS inhibitory activity in the minimum inhibitory concentration, pyocyanin and rhamnolipid inhibition assays. In particular, A10 and B20 at 256 μg/mL not only suppressed pyocyanin production regulated by QS in P. aeruginosa PAO1 by 36.55% and 46.90%, respectively, but also showed the strongest rhamnolipid inhibitory activity with the IC50 values of 66.35 and 56.75 µg/mL, respectively. Further studies demonstrated that B20 at 64 μg/mL inhibited biofilm formation in P. aeruginosa PAO1 by 40%, and weakened its swarming motility. More importantly, the bacterial mortality of B20 combined with ciprofloxacin and clarithromycin against P. aeruginosa were 48.27% and 49.79%, respectively, while ciprofloxacin and clarithromycin had only 16.99% and 29.11% of bacterial mortality against P. aeruginosa when used alone. Mechanistic studies indicated that B20 directly inhibited the QS pathway based on the GFP reporter strain assay. Overall, this compound with oxazolopyridinone core could serve as an antibacterial lead of QS inhibitor for further evaluation of its drug-likeness.

Novel quinoline-based derivatives as the PqsR inhibitor against Pseudomonas aeruginosa PAO1.

The emerging of drug resistant Pseudomonas aeruginosa is a critical challenge and renders an urgent action to discover innovative antimicrobial interventions. One of these interventions is to disrupt the pseudomonas quinolone signal (pqs) quorum sensing (QS) system, which governs multiple virulence traits and biofilm formation. This study aimed to investigate the QS inhibitory activity of a series of new PqsR inhibitors bearing a quinoline scaffold against Ps. aeruginosa. The results showed that compound 1 suppressed the expression of QS-related genes and showed the best inhibitory activity to the pqs system of wild-type Ps. aeruginosa PAO1 with an IC50 of 20.22 μmol L-1 . The virulence factors including pyocyanin, total protease, elastase and rhamnolipid were significantly suppressed in a concentration-dependent manner with the compound. In addition, compound 1 in combination with tetracycline inhibited synergistically the bacterial growth and suppressed the biofilm formation of PAO1. The molecular docking studies also suggested that compound 1 could potentially interact with the ligand-binding domain of the Lys-R type transcriptional regulator PqsR as a competitive antagonist. The quinoline-based derivatives were found to interrupt the quorum sensing system via the pqs pathway and thus the production of virulence factors was inhibited and the antimicrobial susceptibility of Ps. aeruginosa was enhanced. The study showed that the quinoline-based derivatives could be used as an anti-virulence agent for treating Ps. aeruginosa infections.

Antibiofilm and Quorum Sensing Inhibition (QSI) Potential of Lagerstroemia speciosa Leaves Extract

Disruption of quorum sensing pathway of pathogenic microbes is considered as novel approach to fight against infectious diseases. The current study was planned to evaluate the antibiofilm and quorum sensing inhibitory potential of Lagerstroemia speciosa. Antibacterial and antibiofilm potential of L. speciosa extracts was determined through agar well diffusion and crystal violet assay against sinusitis isolates, that is, Staphylococcus aureus, Enterococcus faecalis, Proteus mirabilis, and Klebsiella pneumoniae, while quorum sensing inhibition efficacy of L. speciosa extracts was determined through violacein inhibition assay using Chromobacterium pseudoviolaceum as bacterial model. The methanolic extract of L. speciosa presented the highest antimicrobial activity against E. faecalis and antibiofilm activity against K. pneumoniae (77.42 ± 1.51%), while n-hexane extract was found to be least active against all tested bacterial strains. Quorum sensing inhibition activity of L. speciosa extracts against C. pseudoviolaceum showed significant dose-dependent inhibition in violacein production by different concentrations of methanolic extract. Furthermore, none of the extracts of L. speciosa showed any hemolytic activity against human RBCs and hold considerable thrombolytic potential in comparison to streptokinase (75.9 ± .46%). In conclusion, findings suggest that L. speciosa leaves are excellent source of phytochemicals with potent antibiofilm and quorum sensing inhibition potential.

Three New Xanthones from Hypericum scabrum and Their Quorum Sensing Inhibitory Activities against Chromobacterium violaceum.

Quorum sensing (QS) plays an important role in the production of virulence factors and pathogenicity in pathogenic bacteria and is, therefore, a hopeful target to fight against bacterial infections. During our search for natural QS inhibitors, two new xanthonolignoids (1 and 2), each existing as a racemic mixture, one new simple oxygenated xanthone (7), and eight known analogs (3–6, 8–11) were isolated from Hypericum scabrum Linn. Chiral separation of 1 yielded a pair of enantiomers 1a and 1b. The structures of these compounds were elucidated by spectroscopic analysis and ECD (electrostatic circular dichroism) calculations. All isolates were evaluated for their QS inhibitory activity against Chromobacterium violaceum. Both 9 and 10 exhibited the most potent QS inhibitory effects with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 31.25 and 62.5 μM, respectively. Crystal violet staining was used to further evaluate the biofilm inhibition potential of compounds 7, 9 and 10, and the formation of biofilms increased with decreasing drug concentration in a classic dose-dependent manner. The results of a cytotoxicity assay revealed that compounds 7, 9 and 10 exhibited no cytotoxic activity on PC-12 cells at the tested concentration.

Diallyl trisulfide attenuates Pseudomonas aeruginosa virulence via inhibiting quorum sensing

Diallyl trisulfide (DATS), diallyl disulfide (DADS), and diallyl sulfide (DAS), three sulfur-rich compounds commonly found in garlic, can inhibit Pseudomonas aeruginosa quorum sensing (QS). We previously reported the inhibitory effects of DAS and DADS on the PAO1 QS system. To delineate any differences in QS inhibitory mechanisms among these three compounds and further verify their functional chemical groups, the QS-inhibitory effects and mechanism of DATS on P. aeruginosa PAO1 were investigated based on transcriptomic analysis, qRT-PCR, and physiological and chemical experiments in this study. The results indicated that DATS was mildly toxic to P. aeruginosa PAO1 and inhibited its growth slightly in a dose-dependent manner. Furthermore, DATS downregulated the transcriptional levels of all key genes involved in PAO1 QS systems, including lasI/lasR, rhlI/rhlR, and pqsABCDEH/pqsR, and downregulated the transcriptional levels of some related virulence genes, including the genes encoding exoprotease, elastase, lectin, and rhamnolipids, as well as those involved in PQS, pyocyanin biosynthesis, and biofilm formation. As a result, the production of related virulence factors by the PAO1 strain decreased upon DATS exposure. Therefore, DATS attenuated P. aeruginosa virulence and pathogenicity by inhibiting its QS systems. Through a comparative analysis of the QS-inhibitory effects of DATS, DADS, and DAS on the PAO1 strain, DATS was found to have the strongest QS-inhibitory activity, followed by DADS and DAS. In conclusion, the inhibitory activities of these sulfur compounds against P. aeruginosa QS and virulence were related to the thioether and disulfide groups, which increase with an increase in the number of sulfur atoms in the chemical formula. These findings are of great significance for the control of P. aeruginosa virulence and pathogenicity in the future.

Methoxyisoflavan derivative from Trigonella stellata inhibited quorum sensing and virulence factors of Pseudomonas aeruginosa

The number of deaths caused by multidrug-resistant Pseudomonas aeruginosa has risen in the recent decade. The development of quorum sensing inhibition (QSI) is a promising approach for controlling Pseudomonas infection. Therefore, this study mainly aimed to investigate how a plant-source material inhibits QSI to produce an antipathogenic effect for fighting microbial infections. The QSI effect of Trigonella stellata was assessed by using Chromobacterium violaceum ATCC 12472 reporter strain. Trigonella stellata exhibited high QSI activity, and an ethanolic extract of T. stellata was prepared for phytochemical isolation of the most active QSI compound. Nine pure compounds were isolated and identified as kaempferitrin (1), soyasaponin I (2), β-sitosterol-3-O-glucoside (3), dihydromelilotoside (4), astrasikokioside I (5), methyl dihydromelilotoside (6), (3R, 4S)-4, 2′, 4′-trihydroxy-7-methoxy-4′-O-β-d-glucopyranosylisoflavan (7), (3S, 4R)-4, 2′, 4′-trihydroxy-7-methoxyisoflavan (8, TMF), and (+)-d-pinitol (9). These compounds were screened against C. violaceum ATCC 12472, and TMF exhibited a potent QSI. The effect of TMF at sub-minimum inhibitory concentrations (MICs) was assessed against P. aeruginosa virulence factors, including biofilm, pyocyanin formation protease and hemolysin activity. TMF induced significant elimination of QS-associated virulence behavior. In addition, TMF at sub-MICs significantly reduced the relative expression of lasI, lasR, rhlI, and rhlR compared with that in untreated cells. Furthermore, molecular docking was performed to predict structural basis of the QSI activity of TMF. The study demonstrated the importance of T. stellata as a signal modulator and inhibitor of P. aeruginosa pathogenesis.

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.

Biosynthesized Silver Nanoparticles from Eruca sativa Miller Leaf Extract Exhibits Antibacterial, Antioxidant, Anti-Quorum-Sensing, Antibiofilm, and Anti-Metastatic Activities.

Worldwide, the primary problem today is the proliferation of cancer and secondary bacterial infections caused by biofilms, as they are the principal causes of death due to the lack of effective drugs. A great deal of biological activities of silver nanoparticles (AgNPs) have made them a brilliant choice for the development of new drugs in recent years. The present study was conducted to evaluate the anticancer, antibacterial, anti-QS, and antibiofilm effects of AgNPs synthesized from Eruca sativa (E. sativa) leaf extract. The ultraviolet–visible (UV–Vis) spectra showed a peak of surface plasmon resonance at 424 nm λmax, which corresponded to AgNP formation. The Fourier transform infrared spectroscopy (FT-IR) confirmed that biological moieties are involved for the development of AgNPs. Moreover, transmission electron microscopy (TEM) analyses confirmed the spherical shape and uniform size (8.11 to 15 nm) of the AgNPs. In human lung cancer cells (A549), the anticancer potential of AgNPs was examined by the MTT [3-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, scratch assay, and invasion assay. The results indicated that AgNPs inhibit the migration of A549 cells. The synthesized AgNPs showed MIC values of 12.5 µg/mL against Chromobacterium violaceum (C. violaceum) and 25 µg/mL against Pseudomonas aeruginosa (P. aeruginosa), which demonstrated their antibacterial abilities. Biological compounds that disable the QS system are being investigated as potential strategies for preventing bacterial infections. Thus, we analyzed the potential effectiveness of synthesized AgNPs in inhibiting QS-regulated virulence factors and biofilm formation in both strains of bacteria. In C. violaceum, the synthesized AgNPs significantly inhibited both violacein (85.18% at 1/2 × MIC) and acyl homoserine lactone (78.76% at 1/2 × MIC). QS inhibitory activity was also demonstrated in P. aeruginosa at a sub-MIC concentration (1/2 × MIC) by a reduction in pyocyanin activity (68.83%), total protease (68.50%), LasA activity (63.91%), and LasB activity (56.40%). Additionally, the exopolysaccharide production was significantly reduced in both C. violaceum (65.79% at 1/2 × MIC) and P. aeruginosa (57.65% at 1/2 × MIC). The formation of biofilm was also significantly inhibited at 1/2 × MIC in C. violaceum (76.49%) and in P. aeruginosa (65.31%). Moreover, a GC–MS analysis confirmed the presence of different classes of bioactive phytochemical constituents present in the leaf extract of E. sativa. On the basis of our results, we conclude that biologically synthesized AgNPs showed numerous multifunctional properties and have the potential to be used against human cancer and bacterial biofilm-related infections.

Isolation, Biosynthetic Investigation, and Biological Evaluation of Maniwamycin G, an Azoxyalkene Compound from Streptomyces sp. TOHO-M025.

A new maniwamycin analogue, maniwamycin G, was isolated from Streptomyces sp. TOHO-M025 as a major product. Maniwamycin G has a molecular formula of C12H22N2O4, and its extensive NMR analysis revealed that maniwamycin G contains a methoxycarbonyl group instead of an amide as found in maniwamycin F. Its C-2 and C-3 configurations were determined to be (2R, 3R) by circular dichroism spectrum and a modified Mosher method, respectively. The biosynthetic origin of maniwamycin G was investigated using isotope-labeled compounds. The carbon source of maniwamycin G is four acetate units (C-1', C-2'; C-3', C-4'; C-5', C-6'; and C-4, C-5) and l-serine (C-1 to C-3). The nitrogen atom attached at C-2 (Nα) originates from serine, whereas the nitrogen atom of a hexen-1-yl amine unit (Nβ) is derived from glutamic acid. The quorum-sensing inhibitory activity of maniwamycin G was 2-fold lower than that of maniwamycin F.

A high-throughput screening approach for bacterial quorum sensing inhibitors (QSIs) against Aeromonas hydrophila infection

Bacterial quorum sensing (QS) is a well-known behavior for bacterial communication and plays an important role in various bacterial biological functions. Several approaches have been developed to interrupt the QS mechanism in bacterial pathogens. This study developed a novel, high-throughput screening method combined with phage peptide display libraries and a QS biosensor system (PDQBS) to identify quorum-sensing inhibitors (QSIs). We screened 11 hit peptide candidates for QSI activity, which inhibited the C4-AHL mediated quorum-sensing system. Although the synthetic peptides showed moderate inhibitory effects and six candidate peptides ligated with a cell-penetrating peptide (CPP) dramatically inhibited QS signals. The protective efficacies of candidate DNA expression vector ligated with CPP-QSIs were tested against Aeromonas hydrophila infection in the zebrafish model. The obtained result revealed that at least two peptides (CPP21 and CPP23) exhibited an increased protective ability against A. hydrophila infection with RPSs of >50%. Furthermore, the three candidates CPP-QSIs (CPP21, CPP23, and CPP24), also showed high protective abilities with RPSs of >50% against A. hydrophila infection in the mice model. The qPCR analysis further confirmed that these selected CPP-QSIs might stimulate host immunity and inhibit the virulence of A. hydrophila. Finally, the results of dot blot and ELISA assays indicated that these CPP-QSI peptides could bind to the QS receptor protein, AhyR/CviR. Overall, this study provides a promising approach to screening novel QSI candidates for controlling QS-mediated bacterial infections.