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In last two decades, the world has seen an exponential increase in the antimicrobial resistance (AMR), making the issue a serious threat to human health. The mortality caused by AMR is one of the leading causes of human death worldwide. Till the end of the twentieth century, a tremendous success in the discovery of new antibiotics was seen, but in last two decades, there is negligible progress in this direction. The increase in AMR combined with slow progress of antibiotic drug discovery has created an urgent demand to search for newer methods of intervention to combat infectious diseases. One of such approach is to look for biofilm and quorum sensing (QS) inhibitors. Plants are excellent source of wide class compounds that can be harnessed to look for the compounds with such properties. This study proves a broad-spectrum biofilm and QS inhibitory potential of umbelliferone. More than 85% reduction in violacein production Chromobacterium violaceum 12472 was found. All tested virulent traits of Pseudomonas aeruginosa PAO1 and Serratia marcescens MTCC 97 were remarkably inhibited that ranged from 56.62% to 86.24%. Umbelliferone also successfully prevented the biofilm of test bacteria at least by 67.68%. Umbelliferone interacted at the active site of many proteins of QS circuit, which led to the mitigation of virulent traits. The stable nature of complexes of umbelliferone with proteins further strengthens in vitro results. After examining the toxicological profile and other drug-like properties, umbelliferone could be potentially developed as new drug to target the infections caused by Gram - ve bacteria.Communicated by Ramaswamy H. Sarma.

The development of antibiotic resistant microbial pathogens has become a global health threat and a major concern in modern medicine. The problem of antimicrobial resistance (AMR) has majorly arisen due to sub-judicious use of antibiotics in health care and livestock industry. A slow progress has been made in last two decades in discovery of new antibiotics. A new strategy in combatting AMR is to modulate or disarm the microbes for their virulence and pathogenicity. Plants are considered as promising source for new drugs against AMR pathogens. In this study, fraction-based screening of the Cinnamomum zeylanicum extract was performed followed by detailed investigation of antiquorum sensing and antibiofilm activities of the most active fraction that is, C. zeylanicum hexane fraction (CZHF). More than 75% reduction in violacein pigment of C. violaceum 12472 was overserved. CZHF successfully modulated the virulence of Pseudomonas aeruginosa PAO1 by 60.46%-78.35%. A similar effect was recorded against Serratia marcescens MTCC 97. A broad-spectrum inhibition of biofilm development was found in presence of sub-MICs of CZHF. The colonization of bacteria onto the glass coverslips was remarkably reduced apart from the reduction in exopolymeric substances. Alkaloids and terpenoids were found in CZHF. GC/MS analysis revealed the presence of cinnamaldehyde dimethyl acetal, 2-propenal, coumarin, and α-copaene as major phytocompounds. This study provides enough evidence to support potency of C. zeylanicum extract in targeting the virulence of Gram -ve pathogenic bacteria. The plant extract or active compounds can be developed as successful drugs after careful in vivo examination to target microbial infections. RESEARCH HIGHLIGHTS: Hexane fraction of Cinnamomum zeylanicum is active against QS and biofilms. The broad-spectrum antibiofilm activity was further confirmed by microscopic analysis. Dimethyl acetal, 2-propenal, coumarin, α-copaene, and so forth are major phytocompounds., (© 2023 Wiley Periodicals LLC.)

Social cheating is the exploitation of public goods that are costly metabolites, like exoproteases. Exoprotease exploitation in Pseudomonas aeruginosa has been studied in reference strains. Experimental evolution with reference strains during continuous growth in casein has demonstrated that nonexoprotease producers that are lasR mutants are selected while they behave as social cheaters. However, noncanonical quorum-sensing systems exist in P. aeruginosa strains, which are diverse. In this work, the exploitation of exoproteases in the environmental strain ID4365 was evaluated; ID4365 has a nonsense mutation that precludes expression of LasR. ID4365 produces exoproteases under the control of RhlR, and harbors an inducible prophage. As expected, rhlR mutants of ID4365 behave as social cheaters, and exoprotease-deficient individuals accumulate upon continuous growth in casein. Moreover, in all continuous cultures, population collapses occur. However, this also sometimes happens before cheaters dominate. Interestingly, during growth in casein, ID4565's native prophage is induced, suggesting that the metabolic costs imposed by social cheating may increase its induction, promoting population collapses. Accordingly, lysogenization of the PAO1 lasR mutant with this prophage accelerated its collapse. These findings highlight the influence of temperate phages in social cheating., (© The Author(s) 2023. Published by Oxford University Press on behalf of FEMS.)

There has been tremendous spread of antimicrobial resistance globally, mainly due to the excessive and unnecessary use of antibiotics, making the situation alarming. This has created a need for the development of alternative strategies to selectively target the bacterial pathogenicity without exerting selection pressure for the development of antimicrobial resistance. Targeting quorum sensing (QS)-mediated virulence and biofilms by nontoxic natural products is gaining importance as new control strategy to combat the virulence and biofilms of pathogenic bacteria. In this study, the crude extract of Plumbago zeylanica was fractioned in different solvents using liquid-liquid partitioning to obtain the most bioactive fraction. The inhibitory effect of the bioactive extract of P. zeylanica on QS at sub-minimum inhibitory concentrations (MICs) was studied against Chromobacterium violaceum 12472, Pseudomonas aeruginosa PAO1, and Serratia marcescens MTCC 97. Biofilm inhibition was studied using microtiter plate assay, scanning electron microscopy, and confocal laser scanning microscopy. Major phytocompounds detected were cinnamaldehyde dimethyl acetal, plumbagin, asarone, 4-chromanol, phthalic acid, palmitic acid, ergost-5-en-3-ol, stigmasterol, and β-sitosterol. The violacein production in C. violaceum 12472 was reduced by >80% in the presence of P. zeylanica hexane fraction (PZHF; 200 μg/ml). The most active PZHF inhibited QS-mediated virulence factors of P. aeruginosa PAO1 such as pyocyanin, pyoverdin, rhamnolipid production, motility, etc., significantly at sub-MICs. Similarly, PZHF showed 59 to 76% inhibition of biofilm formation of above test pathogens. The findings revealed that active fraction of P. zeylanica was effective against the QS-regulated functions and biofilms development of Gram -ve pathogenic bacteria., (© 2021 Wiley Periodicals LLC.)

The global rise in antimicrobial resistance and lack of discovery of new antimicrobials have created serious concerns. Targeting quorum sensing (QS) and biofilms of pathogenic bacteria is considered a promising approach in antimicrobial drug discovery. This study explored the inhibitory effect of plumbagin against biofilms and QS of Chromobacterium violaceum , Serratia marcescens and Pseudomonas aeruginosa . Violacein production in C. violaceum 12472 was reduced by >80%. The virulent traits of P. aeruginosa PAO1 such as pyocyanin, rhamnolipid and proteases were also inhibited at sub-minimum inhibitory concentrations. Moreover, the biofilms of the test bacteria were reduced by 56-70%. Plumbagin reduced the bacterial adherence and colonization on solid surface. Computational studies gave closer insights regarding the possible modes of action. Molecular dynamics simulations revealed that the protein complexes were quite stable under physiological conditions. This study provides both experimental and computational evidence regarding the efficacy of plumbagin against biofilms and the QS-controlled virulence factors of Gram-negative bacteria.

Antimicrobial resistance among pathogenic bacteria has become a global threat to human health. Due to poor progress in development of new antimicrobial drugs, there is a need for the development of novel alternative strategies to combat the problem of multidrug resistance. Moreover, there is focus on ecofriendly approach for the synthesis nanoparticles having efficient medicinal properties including antivirulence properties to tackle the emergence of multi-drug resistance. Targeting quorum sensing controlled virulence factors and biofilms has come out to be a novel anti-infective drug target. The silver nanoparticles (Ag@CC-NPs) were synthesized from aqueous extract of Carum copticum and characterized using UV-vis absorption spectroscopy, fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Ag@CC-NPs were checked for its ability to inhibit quorum sensing-mediated virulence factors and biofilms against three test pathogens at sub-MIC values. There was ~75% inhibition of violacein production by Ag@CC-NPs against C. violaceum. The P. aeruginosa virulence factors such as pyocyanin production, pyoverdin production, exoprotease activity, elastase activity, swimming motility and rhamnolipid production were inhibited by 76.9, 49.0, 71.1, 53.3, 89.5, and 60.0% at sub-MIC. Moreover, virulence factors of S. marcescens viz. prodigiosin production, exoprotease activity, and swarming motility was reduced by 78.4, 67.8, and 90.7%. Ag@CC-NPs also exhibited broad-spectrum antibiofilm activity with 77.6, 86.3, and 75.1% inhibition of biofilms of P. aeruginosa, S. marcescens, and C. violaceum respectively. The biofilm formation on glass coverslip was reduced remarkably as evident from SEM and CLSM analysis. The findings revealed the in vitro efficacy of Ag@CC-NPs against bacterial pathogens and can be exploited in the development of alternative therapeutic agent in management of bacterial infections for topical application, mainly wound infection, or coating of surfaces to prevent bacterial adherence on medical devices., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The present study evaluated the efficacy of Y 2 O 3 :Tb (core) and Y 2 O 3 :Tb@SiO 2 nanospheres (core/shell NSs) against virulence functions regulated by quorum sensing (QS) and biofilm formation in pathogenic bacteria. Scanning electron microscope (SEM) images were used to study the size, shape, and morphology. The images clearly displayed spherical shaped, mono-dispersed particles with narrow size distribution and an average grain size of 110-130 nm. The chemical composition of the samples was determined by using energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). We determined the impact of core and core/shell NSs on QS using sensor strains of Chromobacterium violaceum CVO26 and Pseudomonas aeruginosa PAO1 in a comparative study. Sub-MICs of core and core/shell NSs substantially suppressed QS-controlled violacein production in C. violaceum. Similar concentration-dependent effect of sub-MICs of synthesized core and core/shell NSs was observed in the QS-regulated virulence functions (elastase, total protease, pyocyanin production, swarming motility, and exopolysaccharide production) in PAO1. A concentration-dependent decrease (14-60%) was recorded in the biofilm forming capability of PAO1, upon treatment with core and core/shell NSs. Moreover, core/shell NSs were more effective in inhibiting biofilm at higher tested concentrations as compared to core-NSs. The synthesized NSs demonstrated significantly impaired attachment of cells to the microtiter plate indicating that NSs target biofilm inhibition at the attachment stage. Based on these results, we predict that core and core/shell NSs may be an alternative to combat the threat of drug-resistant pathogenic bacteria.

The emergence of multi-drug resistance in pathogenic bacteria in clinical settings as well as food-borne infections has become a serious health concern. The problem of drug resistance necessitates the need for alternative novel therapeutic strategies to combat this menace. One such approach is targeting the quorum-sensing (QS) controlled virulence and biofilm formation. In this study, we first screened different fractions of Psoralea corylifolia (seed) for their anti-QS property in the Chromobacterium violaceum 12472 strain. The methanol fraction was found to be the most active fraction and was selected for further bioassays. At sub-inhibitory concentrations, the P. corylifolia methanol fraction (PCMF) reduced QS-regulated virulence functions in C. violaceum CVO26 (violacein); Pseudomonas aeruginosa (elastase, protease, pyocyanin, chitinase, exopolysaccharides (EPS), and swarming motility), A. hydrophila (protease, EPS), and Serratia marcescens (prodigiosin). Biofilm formation in all the test pathogens was reduced significantly ( p ≤ 0.005) in a concentration-dependent manner. The β-galactosidase assay showed that the PCMF at 1,000 μg/ml downregulated las -controlled transcription in PAO1. In vivo studies with C. elegans demonstrated increased survival of the nematodes after treatment with the PCMF. Bakuchiol, a phytoconstituent of the extract, demonstrated significant inhibition of QS-regulated violacein production in C. violaceum and impaired biofilm formation in the test pathogens. The molecular docking results suggested that bakuchiol efficiently binds to the active pockets of LasR and RhlR, and the complexes were stabilized by several hydrophobic interactions. Additionally, the molecular dynamics simulation of LasR, LasR-bakuchiol, RhlR, and RhlR-bakuchiol complexes for 50 ns revealed that the binding of bakuchiol to LasR and RhlR was fairly stable. The study highlights the anti-infective potential of the PCMF and bakuchiol instead of bactericidal or bacteriostatic action, as the extract targets QS-controlled virulence and the biofilm.

Quorum sensing (QS) plays an important role in virulence, biofilm formation and survival of many pathogenic bacteria including Pseudomonas aeruginosa. This signalling pathway is considered as novel and promising target for anti-infective agents. In the present investigation, effect of the Sub-MICs of clove oil on QS regulated virulence factors and biofilm formation was evaluated against P. aeruginosa PAO1 and Aeromonas hydrophila WAF-38 strain. Sub-inhibitory concentrations of the clove oil demonstrated statistically significant reduction of las- and rhl-regulated virulence factors such as LasB, total protease, chitinase and pyocyanin production, swimming motility and exopolysaccharide production. The biofilm forming capability of PAO1 and A. hydrophila WAF-38 was also reduced in a concentration-dependent manner at all tested sub-MIC values. Further, the PAO1-preinfected Caenorhabditis elegans displayed an enhanced survival when treated with 1.6 percent v/v of clove oil. The above findings highlight the promising anti-QS-dependent therapeutic function of clove oil against P. aeruginosa.

Inhibition of quorum sensing (QS)-regulated virulence factors including biofilm is a recognized anti-pathogenic drug target. The search for safe and effective anti-QS agents is expected to be useful to combat diseases caused by multidrug-resistant bacteria. In this study, effect of a commonly used antibiotic, doxycycline on QS was evaluated using sensor strains of Chromobacterium violaceum (ATCC 12472 and CVO26) and Pseudomonas aeruginosa PAO1. Sub-MICs of doxycycline reduced QS-controlled violacein production in C. violaceum to a significant degree (70 %) and showed a significant reduction of LasB elastase (67.2 %), pyocyanin (69.1 %), chitinase (69.8 %) and protease (65 %) production and swarming motility (74 %) in P. aeruginosa PAO1 over untreated controls. Similar results were also recorded against a clinical strain of P. aeruginosa (PAF-79). Interestingly, doxycycline at respective sub-MICs (4 and 32 μg ml(-1)) significantly reduced the biofilm-forming capability and exopolysaccharide production in both the strains of P. aeruginosa (PAO1 and PAF-79) over untreated controls. The results of this study highlight the multiple actions of doxycycline against QS-linked traits/virulence factors and its potential to attenuate virulence of P. aeruginosa.

Discovery of quorum sensing (QS) system to coordinate virulence and biofilm formation in bacterial pathogens has triggered search for safe, stable and non-toxic anti-QS compounds from natural products. Ethanolic extracts of 24 Indian medicinal plants were tested by agar well and disc diffusion assay for anti-QS activity using Chromobacterium violaceum (CV12472 and CVO26) reporter strains. AHL from C. violaceum CV31532 was isolated and partially purified for its use in CVO26 based bioassay. Effect on swarming-motility of Pseudomonas aeruginosa (PAO1) was also recorded at sub-MIC concentrations of extracts. Of the 24 medicinal plants screened Hemidesmus indicus (L.) Schult (root), Holarrhena antidysenterica (Roth) A.DC. (bark), Mangifera indica L. (seed) Punica granatum L. (pericarp) and Psoralea corylifolia L. (seed) demonstrated varying level of inhibition of violacein production in the reporter strains. Moreover, a significant reduction in swarms was recorded over control. The inhibition of violacein production and swarming motility may be due to direct or indirect interference on QS by active constituents or the interactive effect of different phytocompounds present in the extracts. These plant extracts may be selected for activity guided fractionation to identify and characterize the active principle.

Aims: To evaluate quorum sensing (QS) inhibitory activity of plant essential oils using strains of Chromobacterium violaceum (CV12472 and CVO26) and Pseudomonas aeruginosa (PAO1)., Methods and Results: Inhibition of QS-controlled violacein production in C. violaceum was assayed using disc diffusion and agar well diffusion method. Of the 21 essential oils, four oils showed varying levels of anti-QS activity. Syzygium aromaticum (Clove) oil showed promising anti-QS activity on both wild and mutant strains with zones of pigment inhibition 19 and 17 mm, respectively, followed by activity in cinnamon, lavender and peppermint oils. The effect of clove oil on the extent of violacein production was estimated photometrically and found to be concentration dependent. At sub-MICs of clove oil, 78.4% reduction in violacein production over control and up to 78% reduction in swarming motility in PAO1 over control were recorded. Gas chromatography-mass spectrometry analysis of clove oil indicated presence of many phytocompounds. Eugenol, the major constituent of clove oil could not exhibit anti-QS activity., Conclusions: Presence of anti-QS activity in clove oil and other essential oils has indicated new anti-infective activity. The identification of anti-QS phytoconstituents is needed to assess the mechanism of action against both C. violaceum and Ps. aeruginosa., Significance and Impact of the Study: Essential oils having new antipathogenic drugs principle because of its anti-QS activity might be important in reducing virulence and pathogenicity of drug-resistant bacteria in vivo.