Quorum Sensing Inhibition Activity Research Articles

Falcaria vulgaris extract: A mixture of quorum sensing inhibitors for controlling Pectobacterium carotovorum subsp. carotovorum

A promising strategy to control bacterial diseases involves using Quorum Sensing Inhibitor (QSI) compounds. This study aimed to evaluate the potential of Falcaria vulgaris plant extract to combat the phytopathogenic Pectobacterium carotovorum subsp. carotovorum (Pcc) via its QSI activity. Using biosensors and Minimum Inhibitory Concentration (MIC) assays, the QSI and antimicrobial aspects of the extract were assessed. Furthermore, the effect of the extract on the reduction of tuber maceration in potatoes was examined. Subsequently, homology modeling based on LasR was conducted to analyze interactions between ligand 3-oxo-C8-AHL, and ExpR2 protein. Docking studies were performed on all extract compounds identified via Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The extract effectively reduced maceration at sub-MIC concentrations across various pathogenic strains. Furthermore, Cyclopentadecanone, 2-hydroxy, showed more negative docking energy than the native ligand. Z,E−2,13-Octadecadien-1-ol showed energy equivalence to the native ligand. Additionally, this plant included certain compounds or their analogs that had previously been discovered as QSI compounds. These compounds included oleic acid, n-Hexadecanoic acid, cytidine, and linoleic acid, and they had energies that were comparable to that of the native ligand. In conclusion, the remarkable QSI property showed by this plant is likely attributed to a combination of compounds possessing this characteristic.

Design, Synthesis, and Biological Evaluation of 2-Phenoxyalkylhydrazide Benzoxazole Derivatives as Quorum Sensing Inhibitors with Strong Antibiofilm Effect.

With the increasing problem of bacterial resistance to traditional antibiotics, there is an urgent need for new antibacterial agents with novel mechanisms to treat infections caused by drug-resistant bacteria. In this paper, we designed and synthesized 2-phenoxyalkylhydrazide benzoxazole derivatives and evaluated their quorum sensing inhibition activity. Among them, 26c at a concentration of 102.4 μg/mL not only inhibited the production of pyocyanin and rhamnolipid by 45.6% and 38.3%, respectively, but also suppressed 76.6% of biofilm production at 32 μg/mL. In addition, 26c did not affect bacterial growth, but in a mouse model infected with P. aeruginosa PAO1, it could help ciprofloxacin effectively eliminate the living bacteria. In the targeting experiment, 26c could inhibit the fluorescence intensity of PAO1-lasB-gfp and PAO1-pqsA-gfp in a concentration-dependent manner, indicating that the compound acts on the quorum sensing system. Overall, 26c is worthy of further investigation as a quorum sensing inhibitor with strong antibiofilm effect.

An Investigation of Quorum Sensing Inhibitors against Bacillus cereus in The Endophytic Fungus Pithomyces sacchari of the Laurencia sp.

Bacillus cereus, a common food-borne pathogen, forms biofilms and generates virulence factors through a quorum sensing (QS) mechanism. In this study, six compounds (dankasterone A, demethylincisterol A3, zinnimidine, cyclo-(L-Val-L-Pro), cyclo-(L-Ile-L-Pro), and cyclo-(L-Leu-L-Pro)) were isolated from the endophytic fungus Pithomyces sacchari of the Laurencia sp. in the South China Sea. Among them, demethylincisterol A3, a sterol derivative, exhibited strong QS inhibitory activity against B. cereus. The QS inhibitory activity of demethylincisterol A3 was evaluated through experiments. The minimum inhibitory concentration (MIC) of demethylincisterol A3 against B. cereus was 6.25 μg/mL. At sub-MIC concentrations, it significantly decreased biofilm formation, hindered mobility, and diminished the production of protease and hemolysin activity. Moreover, RT-qPCR results demonstrated that demethylincisterol A3 markedly inhibited the expression of QS-related genes (plcR and papR) in B. cereus. The exposure to demethylincisterol A3 resulted in the downregulation of genes (comER, tasA, rpoN, sinR, codY, nheA, hblD, and cytK) associated with biofilm formation, mobility, and virulence factors. Hence, demethylincisterol A3 is a potentially effective compound in the pipeline of innovative antimicrobial therapies.

Attenuation of Las/Rhl quorum sensing regulated virulence and biofilm formation in Pseudomonas aeruginosa PAO1 by Artocarpesin

The emergence of multidrug resistance and increased pathogenicity in microorganisms is conferred by the presence of highly synchronized cell density dependent signalling pathway known as quorum sensing (QS). The QS hierarchy is accountable for the secretion of virulence phenotypes, biofilm formation and drug resistance. Hence, targeting the QS phenomenon could be a promising strategy to counteract the bacterial virulence and drug resistance. In the present study, artocarpesin (ACN), a 6-prenylated flavone was investigated for its capability to quench the synthesis of QS regulated virulence factors. From the results, ACN showed significant inhibition of secreted virulence phenotypes such as pyocyanin (80%), rhamnolipid (79%), protease (69%), elastase (84%), alginate (88%) and biofilm formation (88%) in opportunistic pathogen, Pseudomonas aeruginosa PAO1. Further, microscopic observation of biofilm confirmed a significant reduction in biofilm matrix when P. aeruginosa PAO1 was supplemented with ACN at its sub-MIC concentration. Quantitative gene expression studies showed the promising aspects of ACN in down regulation of several QS regulatory genes associated with production of virulence phenotypes. Upon treatment with sub-MIC of ACN, the bacterial colonization in the gut of Caenorhabditis elegans was potentially reduced and the survival rate was greatly improved. The promising QS inhibition activities were further validated through in silico studies, which put an insight into the mechanism of QS inhibition. Thus, ACN could be considered as possible drug candidate targeting chronic microbial infections.

Quorum sensing inhibition activities of Philippine ethnobotanicals against multidrug-resistant pathogens

Alternative therapeutic approaches to target microbial multidrug resistance (MDR) have become an important thrust in research. One potential approach to manage antibiotic resistance and pathogenicity in MDR pathogens is through targeting quorum sensing (QS). Blocking the QS system does not affect bacterial growth while preventing bacteria from triggering virulence, reducing pathogenicity and selective pressure to survive, hence, reducing the resistance evolution. Recent ethnopharmacological research highlights the prospects of Philippine ethnobotanicals to discover novel molecules and approaches for targeting the QS system to control diseases and pathogens. In this review, two sets of Philippine ethnobotanicals utilized by ethnic communities - Ikalahan and Ilongot-E?ongot – are highlighted as QS inhibitors. Inhibition of QS-linked virulence factor production such as violacein, biofilm, DNase, α-Hemolysin, swarming motility and coagulase in MDR pathogens Pseudomonas aeruginosa, Staphylococcus aureus, Aeromonas hydrophila, Streptococcus agalactiae, Candida albicans and one QS reporter bacteria, Chromobacterium violaceum by the ethnobotanical extracts are presented. All Philippine ethnobotanicals from the two ethnic communities included in this review showed inhibition on one or more virulence factors highlighting their activities against QS and emphasizes their potential for in-depth research on QS-based drug development for antipathogenesis.

Antimicrobial and quorum sensing inhibitory activity of epiphytic bacteria isolated from the red alga Halymenia durvillei.

Halymenia durvillei is a red alga that is commonly utilized in the Philippines as food and as a source of high-value natural products for industrial applications. However, there are no studies regarding the microbial community associated with H. durvillei and its potential applications. This study aimed to isolate and identify the epiphytic bacteria of H. durvillei and determine their antimicrobial and quorum sensing inhibitory (QSI) effects. The thalli of H. durvillei were collected at the shores of Santa Fe, Bantayan, Cebu, Philippines. Bacterial isolates were identified using 16S rRNA, and their ethyl acetate (EtOAc) extracts were subjected to antimicrobial susceptibility tests against representative species of yeast and Gram-negative and Gram-positive bacteria. Their QSI activity against Chromobacterium violaceum was also determined. Fourteen distinct bacterial colonies belonging to four genera, namely Alteromonas (3), Bacillus (5), Oceanobacillus (1) and Vibrio (5), were successfully isolated and identified. All 14 bacterial isolates exhibited antibacterial effects. EPB9, identified as Bacillus safensis , consistently showed the strongest inhibition against Escherichia coli , Staphylococcus aureus and Staphylococcus epidermidis , with minimum inhibitory concentrations (MICs) ranging from 0.0625 to 1.0 mg ml-1. In contrast, all 14 isolates showed weak antifungal effects. Both B. safensis (EPB9) and Bacillus australimaris (EPB15) exhibited QSI effects at 100 mg ml-1, showing opaque zones of 3.1±0.9 and 3.8±0.4 mm, respectively. This study is the first to isolate and identify the distinct microbial epiphytic bacterial community of H. durvillei and its potential as an abundant resource for new antibacterial and QSI bioactives.

Interception of Epoxide ring to quorum sensing system in Enterococcus faecalis and Staphylococcus aureus

Quorum sensing inhibitor (QSI) has been attracting attention as anti-virulence agent which disarms pathogens of their virulence rather than killing them. QSI marking cyclic peptide-mediated QS in Gram-positive bacteria is an effective tool to overcome the crisis of antibiotic-dependent chemotherapy due to the emergence of drug resistance strain, e.g., methicillin resistant Staphylococcus aureus (MRSA) and Vancomycin resistant Enterococci (VRE). From a semi-large-scale screening thus far carried out, two Epoxide compounds, Ambuic acid and Synerazol, have been found to efficiently block agr and fsr QS systems, suggesting that the Epoxide group is involved in the mode of action of these QSIs. To address this notion, known natural Epoxide compounds, Cerulenin and Fosfomycin were examined for QSI activity for the agr and fsr systems in addition to in silico and SAR studies. As a result, most of investigated Epoxide containing antibiotics correlatively interfere with QSI activity for the agr and fsr systems under sublethal concentrations.

Bactericidal effect of Iberin combined with photodynamic antimicrobial chemotherapy against Pseudomonas aeruginosa biofilm cultured on ex vivo wound model

Wounds infected by Pseudomonas aeruginosa (P. aeruginosa) biofilms are characterized by poor healing and by being long lasting. Pyocyanin and pyoverdine are exotoxins that contribute to P. aeruginosa pathogenicity in wound infections and are known as virulence factors. Despite the usefulness of antimicrobial photodynamic therapy (PDT) in the management of wound infections, biofilms are hurdle for microbial photoinactivation. Quorum sensing (QS) is a cell density-dependent chemical signaling system P. aeruginosa uses to regulate biofilm formation and virulence factors production. In the current study, QS attenuation was used in combination with PDT against P. aeruginosa biofilm cultured on skin explant. Iberin is a QS inhibitor that attenuates P. aeruginosa virulence and affects biofilm integrity. The antibiofilm and QS inhibitory activities of iberin in combination with either riboflavin or 5,10,15,20-Tetrakis(1-methyl-4-pyridinio) porphyrin tetra p-toluenesulfonate (TMP) mediated PDT were investigated using viable count method and pyocyanin and pyoverdine assays, respectively.No bactericidal activity was reported when iberin was added to a mature biofilm (24 h) followed by PDT. When added to a growing biofilm at multiple time points (0 h, 24 h and 48 h), iberin inhibited P. aeruginosa biofilm QS signaling system. This inhibitory effect resulted in an observable decrease in the levels of the QS-regulated virulence factors, pyocyanin and pyoverdine, without any effect on the growth of the biofilm cultures. These changes in biofilm virulence were associated with a decrease in biofilm resistance to PDT and caused bactericidal effect upon photosensitizers treatment and irradiation. Iberin-treated-riboflavin-mediated PDT resulted in a significant 1.3 log reduction in biofilm population. Similarly, iberin-treated-TMP-mediated PDT caused a significant 1.8 log reduction in biofilm population. The combination of QS inhibitor with PDT is a promising alternative antimicrobial therapy for the management of biofilms.

Attenuation of quorum sensing regulated virulence functions and biofilm of pathogenic bacteria by medicinal plant Artemisia annua and its phytoconstituent 1, 8-cineole.

The emergence of multidrug resistance (MDR) in bacterial pathogens is a serious public health concern. A significant therapeutic target for MDR infections is the quorum sensing-regulated bacterial pathogenicity. Determining the anti-quorum sensing abilities of certain medicinal plants against bacterial pathogens as well as the in-silico interactions of particular bioactive phytocompounds with QS and biofilm-associated proteins were the objectives of the present study. In this study, 6 medicinal plants were selected based on their ethnopharmacological usage, screened for Anti-QS activity and Artemisia annua leaf extract (AALE) demonstrated pigment inhibitory activity against Chromobacterium violaceum CV12472. Further, the methanol active fraction significantly inhibited the virulence factors (pyocyanin, pyoverdine, rhamnolipid and swarming motility) of Pseudomonas aeruginosa PAO1 and Serratia marcescens MTCC 97 at respective sub-MICs. The inhibition of biofilm was determined using a microtiter plate test and scanning electron microscopy. Biofilm formation was impaired by 70%, 72% and 74% in P. aeruginosa, C. violaceum and S. marcescens, respectively at 0.5xMIC of the extract. The phytochemical content of the extract was studied using GC-MS and 1, 8-cineole was identified as major bioactive compound. Furthermore, 1, 8-cineole was docked with quorum sensing (QS) proteins (LasI, LasR, CviR, and rhlR) and biofilm proteins (PilY1 and PilT). In silico docking and dynamics simulations studies suggested interactions with QS-receptors CviR', LasI, LasR, and biofilm proteins PilY1, PilT for anti-QS activity. Further, 1, 8-cineole demonstrated 66% and 51% reduction in violacein production and biofilm formation, respectively to validate the findings of computational analysis. Findings of the present investigation suggests that 1, 8-cineole plays a crucial role in the QS and biofilm inhibitory activity demonstrated by Artemisia annua extract. RESEARCH HIGHLIGHTS: Artemisia annua leaf extract (AALE) methanol fraction demonstrated broad-spectrum QS and biofilm inhibition Scanning electron microscopy (SEM) confirmed biofilm inhibition Molecular docking and simulation studies suggested positive interactions of 1,8-cineol with QS-receptors and biofilm proteins.

Discovery of 2,5-diketopiperazine alkaloids with quorum sensing inhibitory activity from the marine fungus Penicillium sp. ZJUT-34

One new 2,5-DKP derivative O-dihydroxycyclopenol (1) and seven known congeners 2–8 were isolated from the marine fungus Penicillium sp. ZJUT-34 cultured on rice medium. The planar structure of 1 was established by extensive spectroscopic analysis, including 1D, 2D NMR and HR-ESI-MS, while the relative configuration of 1 was determined by quantum chemical calculation. In the QS inhibitory assay, 1 significantly inhibited the production of violacein in Chromobacterium violaceum ATCC12472 (20.65%) at a concentration of 6.25 μg/mL without affecting the growth of the strain, as compared with norharmane (22.14%), a quorum sensing inhibitor (QSI) identified in our previous study. It represented the first report on the QS inhibitory activity of the seven-membered 2,5-DKPs. In addition, compounds 1–8 were subjected to antibacterial assay against six pathogenic bacteria Compound 8 exhibited comparable antibacterial activity against Enterococcus faecalis FA2-2 (MIC = 96 μg/mL) with the positive control gentamicin (MIC = 80 μg/mL).

Design, synthesis and biological evaluation of triazole, sulfonamide and sulfonyl urea derivatives of N-acylhomoserine lactone as quorum sensing inhibitors

Triazole, sulfonamide and sulfonyl urea derivatives of N-acylhomoserine lactones (AHLs) have been prepared from homoserine lactone hydrobromide which in turn is derived from l-methionine. The molecules were screened against Chromobacterium violaceum ATCC 12472 for their quorum sensing inhibitory (QSI) activity. Among them, compounds 6, 7 and 14 were exhibited comparable antibacterial activities with reference to penicillin and streptomycin as 37.5 µg/mL, while compounds 7, 13 and 17 exhibited promising QSI activity. These compounds represent a synthetically accessible class of AHL analogs could find utility to improve their potency.

Screening and Identification of a Streptomyces Strain with Quorum-Sensing Inhibitory Activity and Effect of the Crude Extracts on Virulence Factors of Pseudomonas aeruginosa.

Quorum-sensing (QS) is involved in numerous physiological processes in bacteria, such as biofilm formation, sporulation, and virulence formation. Therefore, the search for new quorum-sensing inhibitors (QSI) is a promising strategy that opens up a new perspective for controlling QS-mediated bacterial pathogens. To explore new QSIs, a strain named Streptomyces sp. D67 with QS inhibitory activity was isolated from the soil of the arid zone around the Kumutag Desert in Xinjiang. Phylogenetic analyses demonstrated that strain D67 shared the highest similarity with Streptomyces ardesiacus NBRC 15402T (98.39%), which indicated it represented a potential novel species in the Streptomyces genus. The fermentation crude extracts of strain D67 can effectively reduce the violacein production produced by Chromobacterium violaceum CV026 and the swarming and swimming abilities of Pseudomonas aeruginosa. It also has significant inhibitory activity on the production of virulence factors such as biofilm, pyocyanin, and rhamnolipids of P. aeruginosa in a significant concentration-dependent manner, but not on protease activity. A total of 618 compounds were identified from the fermentation crude extracts of strain D67 by LC-MS, and 19 compounds with significant QS inhibitory activity were observed. Overall, the strain with QS inhibitory activity was screened from Kumutag Desert in Xinjiang for the first time, which provided a basis for further research and development of new QSI.

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.