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Antimicrobial resistance (AMR) is an urgent worldwide health concern, requiring the exploration for novel antimicrobial interventions. A Gram-negative bacterium, Chromobacterium violaceum, synthesizes quorum-sensing-regulated violacein pigment, develops resilient biofilms, and is often used for the screening of anti-infective drugs. The aim of this work is to assess the antibacterial and antibiofilm properties of three polyphenols: 1,4-naphthoquinone, caffeic acid, and piperine. The determination of antibacterial activity was conducted by the agar overlay and broth microdilution techniques. Analysis of membrane rupture was conducted by crystal violet uptake and β-galactosidase assay. Inhibition of biofilm was evaluated using a 96-well microtiter plate assay. Biofilm structures were visualized using light, scanning electron microscopy (SEM), and confocal laser scanning electron microscopy (CLSM). Among the phytochemicals, 1,4-naphthoquinone exhibited the highest antibacterial action (25 mm zone of inhibition). The minimum inhibitory concentration of 1,4-naphthoquinone was determined to be 405 µM. Outer and inner membrane permeability was enhanced by 52.01% and 1.28 absorbance, respectively. Violacein production was reduced by 74.85%, and biofilm formation was suppressed by 63.25% at sub-MIC levels (202.5 µM). Microscopic analyses confirmed reduced adhesion on surfaces. Hemolytic activity of 1,4-naphthoquinone showed a concentration-dependent effect, with 32.16% haemolysis at 202.5 µM. Molecular docking revealed significant interactions of 1,4-naphthoquinone with DNA gyrase followed by CviR. These findings highlight 1,4-naphthoquinone's potent antibacterial efficacy against C. violaceum, proposing its use as a surface coating agent to prevent biofilm formation on medical devices, thereby offering a promising strategy to combat bacterial infections., Competing Interests: Declarations. Conflict of interest: The authors declare that they have no conflict of interest in the publication. Ethical approval: The research does not include experiments involving animals or human participants., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Vector mosquito control is an integral part of malaria control. The global emergence of insecticide resistance in malaria-transmitting Anophelines has become an impediment and has created an urgent need for novel mosquito control approaches. Here, we show that a biopesticide derived from the soil-dwelling bacterium Chromobacterium sp. Panama ( Csp_P ) kills insecticide-resistant Anopheles mosquitoes, regardless of their resistance mechanisms. In addition, sublethal dose of Csp_P acts as a synergist to now used chemical insecticides across multiple classes. Moreover, Csp_P reduces host-seeking behavior and malaria parasite infection in vector mosquitoes in ways that further decrease transmission. Mosquito glutathione S -transferases are essential for Csp_P 's mosquito-killing mechanism. Enclosed field trials in Burkina Faso, conducted in diverse ecological settings and supported by a mathematical model, have now demonstrated its potential for malaria control in settings with widespread insecticide resistance.

A total of 52 Pasteurella multocida strains of capsular serogroups (A, B and D) were screened for anti-quorum sensing activity against Chromobacterium violaceum. Of which, 12 strains of serogroups A were found to possess anti-quorum sensing activity. Inhibition activity was highest for strain NIVEDIPm9 and lowest for strain NIVEDIPm30 based on zone of pigment inhibition. Further, cell free extract of NIVEDIPm9 strain showed highest anti-biofilm activity in reference E. coli strain and concentration dependent degradation activity of C6-AHL molecule. In whole genome sequence annotation of NIVEDIPm9 strain predicted the presence of four metallo-β-lactamases (MBL) fold metallo-hydrolase proteins. In docking studies, MBL1 and MBL3 proteins showed high binding affinity with autoinduce signalling molecules AHL compound of OH-C10, binding energy value were -6.3 and -6.2 kcal/mol. Interaction study of VAF and quorum sensing molecules showed that OmpA and HgbA proteins were stimulated by all the ten molecules (C4-AHLs, C6-AHLs, C10-AHLs, C14-AHLs, 3-oxo-C10-AHLs, 3OH-C10-HSL, C8-HSL, C10-HSL, C12-HSL, C14-HSL), while toxA gene was stimulated by OH-C10-AHL molecule, sodC gene was stimulated by none. In conclusion, we described the anti-quorum sensing activities of diverse P. multocida strains causing Pasteurellosis in livestock., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Sathish Bhadravati Shivachandra reports financial support was provided by ICAR-National Institute of Veterinary Epidemiology and Disease Informatics (NIVEDI). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Purpose: Chromobacterium violaceum(C. violaceum) is a gram-negative bacterium that rarely infects humans, especially children. However, the mortality rate is high and there are no clear guidelines for treatment. The aim of this paper is to increase clinicians' awareness of diseases caused by C. violaceum infections in children, to diagnose and treat them in a timely manner, to improve patient survival and to reduce mortality., Results: We analysed the latest paediatric-related English language literature over the last 10 years and summarised the latest mechanisms of injury, susceptibility factors, adverse prognostic and mortality predictors, mortality rates, methods to reduce mortality, clinical manifestations, new diagnostic methods, therapeutic agents and directions for future drug development for C. violaceum., Conclusions: Based on the available data, we conclude that the possibility of C. violaceum infection should be considered and diagnosed when cellulitis, septicaemia and visceral abscesses develop in children with a history of skin injury and exposure to stagnant water or soil. When clinicians strongly suspect that a child is infected with this bacterium, the recommended medication is ciprofloxacin if the child presents with severe illness. If the child has a non-severe condition, medications with relatively fewer side effects for children can be chosen, such as gentamicin, trimethoprim/ sulfamethoxazole, imipenem, and other drugs. The physician can then adjust the antimicrobial regimen based on the antimicrobial spectrum after obtaining the drug sensitivity results., Competing Interests: Declarations. Consent for publication: Informed consent was obtained from the patient’s relative for publication purposes. Competing interests: The authors declare no competing interests. Conflict of interest: The authors declare that they have no conflicts of interest. Ethical approval: Ethical approval was waived by the local Ethics Committee (ShaoXing KeQiao Women And Children’s Hospital Ethics Committee) in view of the retrospective chart review of patient records and all the procedures being performed were part of the routine care. Consent to participate: Informed consent obtained from the patient’s relative. Rights and permissions: Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law., (© 2024. The Author(s).)

Objectives: Food products are often contaminated by pathogens and spoilage bacteria. Most of them can form biofilms, a community of cells embedded in protective extracellular matrix layers resistant to harsh conditions, including antibiotics. Therefore, alternative antibiofilm agents are required to overcome biofilm formation. This study aims to determine and quantify the antibiofilm activity of supernatants from plant-associated bacteria against biofilms of foodborne pathogen and food spoilage bacterium, namely Bacillus cereus and Bacillus subtilis., Results: Plant-associated bacteria (PAB) have shown promising antibiofilm activities against biofilm-forming pathogens in previous studies. Thirteen PAB isolated from Ternate, Indonesia were used in this study. Supernatants of PAB were subjected to antimicrobial activity and quorum quenching detection, both using the well diffusion method. Four supernatants inhibited the growth of B. subtilis, but none affected the growth of B. cereus. Eight supernatants were able to disrupt the quorum sensing system of an indicator bacterium, wild-type Chromobacterium violaceum. Biofilm inhibition and destruction were quantified using 96-well microplates. The highest biofilm inhibition and destruction activities of PAB supernatants against each of B. cereus and B. subtilis biofilms were > 76%, and were later confirmed by light microscope and scanning electron microscope. Brine shrimp lethality assay (BSLA) was conducted and revealed that the selected PAB supernatants were non-toxic. The 16S rRNA gene of PAB were sequenced and they showed similarities to Bacillus, Priestia, and Chryseobacterium. Compounds in the supernatants were determined by GC-MS which revealed contents of fatty acids, ethyl esters, and diketopiperazines. Therefore, PAB supernatants have potential as antibiofilm agents against biofilm formed by Bacillus cereus and Bacillus subtilis., Competing Interests: Declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

The natural product FR900359 (FR) has generated significant attention lately, due to its characteristics as potent and selective inhibitor of G q/11 mediated signal transduction of associated G protein-coupled receptors (GPCRs). This makes FR both a widely used pharmacological tool compound and a lead molecule for targeted cancer therapy. The exploration of structure-activity-relationship (SAR) of the scaffold by total synthesis has been complicated by its structural complexity and its incompatibility with standard approaches of solid-phase peptide synthesis. Options for late-stage functionalization of FR are limited due to a lack of tractable functional groups. Here we present a mixed approach combining (i) genetic engineering of the FR-assembly line in Chromobacterium vaccinii, to obtain a novel FR analog featuring a primary amine, with (ii) its subsequent synthetic modification and biological profiling for further SAR exploration of the FR scaffold., (© 2024 Wiley-VCH GmbH.)

Objectives: This research aimed to identify and quantify the antibiofilm activity of bioactive compounds from bacteria isolated from rhizosphere and nodule butterfly pea (Clitoria ternatea), rhizosphere clove afo 3 (Syzygium aromaticum), nodule mimosa (Mimosa pudica L.), and soil from gold mining land which were recovered from Ternate, Tidore, Obi Island, and Marotai Island, Eastern part of Indonesia., Results: Eight supernatants from soil and plant-associated bacteria were found to have quorum quenching activity against Chromobacterium violaceum. All supernatants exhibited antibiofilm activity against biofilm formed by Aeromonas hydrophila and Vibrio harveyi. The supernatant of FT5 showed the highest activity in disrupting (66.59%) and inhibiting (85.63%) the biofilm of A. hydrophila. For V. harveyi, the supernatant of PTM3 showed the highest disruption activity (72.61%), whileRCA7 showed the highest inhibition activity(75.68%). The Gas Chromatography-Mass Spectrometry (GC-MS) identified fatty acids, ester, and diketopiperazine as the compounds related to the antibiofilm activity. Molecular identification revealed that the isolates belong to the genera Bacillus, Priestia, and Chryseobacterium., (© 2024. The Author(s).)

Quorum sensing (QS) is pivotal in coordinating virulence factors and biofilm formation in various pathogenic bacteria, making it a prime target for disrupting bacterial communication. Pseudomonas aeruginosa is a member of the "ESKAPE" group of bacterial pathogens known for their association with antimicrobial resistance and biofilm formation. The current antibiotic arsenal falls short of addressing biofilm-related infections effectively, highlighting the urgent need for novel therapeutic agents. In this study, we explored the anti-QS and anti-biofilm properties of theophylline against two significant pathogens, Chromobacterium violaceum and P. aeruginosa. The production of violacein, pyocyanin, rhamnolipid, and protease was carried out, along with the evaluation of biofilm formation through methods including crystal violet staining, triphenyl tetrazolium chloride assay, and fluorescence microscopy. Furthermore, computational analyses were conducted to predict the targets of theophylline in the QS pathways of P. aeruginosa and C. violaceum. Our study demonstrated that theophylline effectively inhibits QS activity and biofilm formation in C. violaceum and P. aeruginosa. In P. aeruginosa, theophylline inhibited the production of key virulence factors, including pyocyanin, rhamnolipid, protease, and biofilm formation. The computational analyses suggest that theophylline exhibits robust binding affinity to CviR in C. violaceum and RhlR in P. aeruginosa, key participants in the QS-mediated biofilm pathways. Furthermore, theophylline also displays promising interactions with LasR and QscR in P. aeruginosa. Our study highlights theophylline as a versatile anti-QS agent and offers a promising avenue for future research to develop novel therapeutic strategies against biofilm-associated infections., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The leaves of Piper betle L., known as betel leaf, have immense medicinal properties. It possesses potent antimicrobial efficacies and can be a valuable tool to combat drug-resistant microorganisms. Quorum sensing (QS) inhibition is one of the best strategies to combat drug resistance. The present study investigates the anti-quorum sensing and biofilm inhibitory potential of Piper betle L. leaf extract against two bacterial strains, Chromobacterium violaceum and Pseudomonas aeruginosa. The extract produced substantial QS-inhibition zones in a biosensor strain of C. violaceum (CV026), indicating interference with quorum-sensing signals. The Results demonstrated significant inhibition in biofilm formation and different QS-regulated virulence factors (violacein, exopolysaccharides, pyocyanin, pyoverdine, elastase) in both C. violaceum and P. aeruginosa at sub-MIC concentrations of the extract and tetracycline, an antibiotic with known anti-QS activity. The quantitative real-time PCR (qRT-PCR) revealed decreased gene expression in different QS-related genes in C. violaceum (cviI, cviR, and vioA) and P. aeruginosa (lasI, lasR, lasB, rhlI, rhlR, and rhlA) strains after treatment. Gas Chromatography-Mass Spectrometry (GC-MS) analysis identified the significant phytocompounds, mainly derivatives of chavicol and eugenol, in the extract. Of these compounds, chavicol acetate (affinity: -7.00 kcal/mol) and acetoxy chavicol acetate (affinity: -7.87 kcal/mol) showed the highest potential to bind with the CviR and LasR protein, respectively, as evident from the in-silico molecular docking experiment. The findings of this endeavour highlight the promising role of Piper betle L. as a source of natural compounds with anti-quorum sensing properties against pathogenic bacteria, opening avenues for developing novel therapeutic agents to combat bacterial infections., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Bratati Sikdar reports financial support was provided by University Grants Commission. Sourav Mukherjee reports financial support was provided by University Grants Commission. Adarsha Raj reports financial support was provided by University Grants Commission. Debarati Banerjee reports financial support was provided by University Grants Commission. All the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

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).

Chemotherapy resistance is one of the main challenges in melanoma treatment. Violacein, a natural pigment produced by Chromobacterium violaceum , induces apoptosis in a variety of tumours, including melanoma. Here, we used BRAF-mutated melanoma spheroids to test the potential of violacein as a sensitizer of cellular viability and levels of the proteins p62 and fatty acid synthase (FASN). Importantly, violacein in combination with vemurafenib (ViVe) was able to interfere with spheroid survival at subtoxic concentrations. The results demonstrated that the ViVe protocol triggered cell death assessed by calcein and ethidium homodimer dyes. Accordingly, melanoma cells in 2D systems also showed a higher apoptosis rate when treated with ViVe. In the current study, we show evidence that ViVe downregulates crucial mediators like FASN, which partially explains how it acts as a sensitizer and ultimately improves the effectiveness of vemurafenib against melanoma cells.

Inter-cellular signaling, referred to as quorum sensing (QS), regulates the production of virulence factors in numerous gram-negative bacteria, such as the human pathogens Pseudomonas aeruginosa and Chromobacterium violaceum. QS inhibition may provide an opportunity for the treatment of bacterial infections. This represents the initial study to examine the antibiofilm and antivirulence capabilities of rose absolute and its primary component, phenylethyl alcohol. QS inhibition was assessed by examining extracellular exopolysaccharide synthesis, biofilm development, and swarming motility in P. aeruginosa PAO1, along with violacein production in C. violaceum ATCC 12472. Molecular docking analysis was conducted to explore the mechanism by which PEA inhibits QS. Our results indicate that rose absolute and PEA caused decrease in EPS production (60.5-33.5%), swarming motility (94.7-64.5%), and biofilm formation (98.53-55.5%) in the human pathogen P. aeruginosa PAO1. Violacein production decreased by 98.1% and 62.5% with an absolute (0.5 v/v %) and PEA (2 mM). Moreover, the molecular docking analysis revealed a promising competitive interaction between PEA and AHLs. Consequently, this study offers valuable insights into the potential of rose absolute and PEA as inhibitors of QS in P. aeruginosa and C. violaceum., (© 2024. The Author(s).)

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.

Natural products have a long history of success in treating bacterial infections, making them a promising source for novel antibacterial medications. Curcumin, an essential component of turmeric, has shown potential in treating bacterial infections and in this study, we covalently immobilized curcumin (Cur) onto chitosan (CS) using glutaraldehyde and tannic acid (TA), resulting in the fabrication of novel biocomposites with varying CS/Cur/TA ratios. Comprehensive characterization of these ternary biocomposites was conducted using FTIR, SEM, XPS, and XRD to assess their morphology, functional groups, and chemical structures. The inhibitory efficacy of these novel biocomposites (n = 4) against the growth and viability of Pseudomonas aeruginosa (ATCC27853) and Chromobacterium violaceum (ATCC12472) was evaluated and the most promising composite (C3) was investigated for its impact on quorum sensing (QS) and biofilm formation in these bacteria. Remarkably, this biocomposite significantly disrupted QS circuits and effectively curtailed biofilm formation in the tested pathogens without inducing appreciable toxicity. These findings underscore its potential for future in vivo studies, positioning it as a promising candidate for the development of biofilm disrupting antibacterial agents., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Pseudomonas aeruginosa causes life-threatening diseases and is resistant to almost all conventional antibiotics. The quorum sensing (QS) system of P. aeruginosa contributes to many pathogenic factors some of which are pigment production, motility, and biofilm. The disruption of quorum sensing system may be an impactful strategy to deal with infections. The present study investigates the anti-quorum sensing property of a bioactive molecule extracted from marine epibiotic bacteria present on the surface of seaweeds. Among all the isolates tested against monitor strain Chromobacterium violaceum (MTCC 2656), the one with the highest activity was identified as Bacillus zhangzhouensis SK4. The culture supernatant was extracted with chloroform which was then partially purified by TLC and column chromatography. The probable anti-QS compound was identified as 1,2-benzenedicarboxylic acid, bis (2-methylpropyl ester) by GC-MS and NMR analysis. The treatment of P. aeruginosa MCC 3457 with the lead compound resulted in the reduced production of pyocyanin, rhamnolipids, exopolysaccharide, biofilm, and motility. The observations of light and scanning electron microscopy also supported the biofilm inhibition. The lead compound showed synergism with the meropenem antibiotic and significantly reduced MIC. The molecular docking and pharmacokinetics study predicted 1, 2-benzenedicarboxylic acid, bis (2-methylpropyl ester), a phthalate derivative as a good drug candidate. The molecular dynamics study was also performed to check the stability of the lead compound and LasR complex. Further, lead compounds did not exhibit any cytotoxicity when tested on human embryonic kidney cells. As per our knowledge, this is the first report on the anti-QS activity of B. zhangzhouensis SK4, indicating that epibiotic bacteria can be a possible source of novel compounds to deal with the multidrug resistance phenomenon., Competing Interests: Declaration of competing interest There is no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Species of genus Chromobacterium have been isolated from diverse geographical settings, which exhibits significant metabolic flexibility as well as biotechnological and pathogenic properties. This study describes the isolation, characterization, draft assembly, and detailed sequence analysis of Chromobacterium piscinae strain W1B-CG-NIBSM isolated from water samples from multi use community pond. The organism was characterized by biochemical tests, Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI TOF-MS) and partial genome sequencing. The partial genomic data of Chromobacterium pisciane isolate W1B NIBSM strain was submitted to GenBank with Bio project number PRJNA803347 and accession no CP092474. An integrated genome analysis of Chromobacterium piscinae has been accomplished with PATRIC which indicates good quality genome. DNA sequencing using the illumina HiSeq 4000 system generated total length of 4,155,481 bp with 63 contig with G + C content is 62.69%. This partial genome contains 4,126 protein-coding sequences (CDS), 27 repeats region and 78 transfer RNA (tRNA) genes as well as 3 ribosomal RNA (rRNA) genes. The genomic annotation of Chromobacterium W1B depicts 2,925 proteins with functional assignments and 1201 hypothetical proteins. A repertoire of specialty genes implicated in antibiotic resistance (45 genes), drug target (6 genes), Transporter (3 genes) and virulence factor (10 genes). The genomic analysis reveals the adaptability, displays metabolic varied pathways and shows specific structural complex and various virulence factors which makes this strain multi drug resistant. The isolate was found to be highly resistant to β-lactam antibiotics whereas it showed sensitivity towards aminoglycosides and fluoroquinolone antibiotics. Hence, the recovery of Chromobacterium piscinae from community pond evidenced for uncertain hidden source of public health hazard. To the best of authors knowledge this is first report of isolation and genomic description of C. piscinae from India., (© 2024. The Author(s) under exclusive licence to Sociedade Brasileira de Microbiologia.)

Chromobacterium violaceum is a rare but severe and often fatal cause of disease in humans. We present 2 clinical cases of sepsis and skin abscesses / cellulitis caused by C. violaceum seen in a referral hospital for infectious diseases in Vietnam. Both patients survived, but appropriate antibiotic treatment was only installed after culture of the organism. We reviewed and summarised the characteristics of C. violaceum infection and treatment., (© 2024. The Author(s).)

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia , Serratia , Pseudomonas , Chromobacterium , and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

An ethyl acetate extract of a marine actinomycete strain, Nocardiopsis mentallicus SCSIO 53858, isolated from a deep-sea sediment sample in the South China Sea, exhibited anti-quorum-sensing (QS) activity against Chromobacterium violaceum CV026. Guided by the anti-QS activity, a novel active compound was isolated and purified from the extract and was identified as 2,3-dimethoxycinnamic acid (2,3-DCA) through spectral data analysis. At a concentration of 150 μg/mL, 2,3-DCA exhibited robust inhibitory effects on three QS-regulated traits of C . violaceum CV026: violacein production, swarming motility, and biofilm formation, with inhibition rates of 73.9%, 65.9%, and 37.8%, respectively. The quantitative reverse transcription polymerase chain reaction results indicated that 2,3-DCA can disrupt the QS system in C . violaceum CV026 by effectively suppressing the expression of QS-related genes, including cviR , vioA , vioB , and vioE . Molecular docking analysis revealed that 2,3-DCA hinders the QS system by competitively binding to the same binding pocket on the CviR receptor as the natural signal molecule N-hexanoyl-L-homoserine lactone. Collectively, these findings suggest that 2,3-DCA exhibits promising potential as an inhibitor of QS systems, providing a potential solution to the emerging problem of bacterial resistance.

Quorum sensing (QS) can regulate the pathogenicity of bacteria and the production of some virulence factors. It is a promising target for screening to find anti-virulence agents in the coming post-antibiotics era. Cyclo ( L -Trp- L -Ser), one variety of cyclic dipeptides (CDPs), isolated from a marine bacterium Rheinheimera aquimaris , exhibited anti-QS activity against Chromobacterium violaceum CV026 and Pseudomonas aeruginosa PAO1. Unlike the CDPs composed of phenylalanine or tyrosine, the anti-QS activity has been widely studied; however, cyclo ( L -Trp- L -Ser) and derivatives, containing one tryptophan unit and one non-aromatic amino acid, have not been systematically explored. Herein, the cyclo ( L -Trp- L -Ser) and seven derivatives were synthesized and evaluated. All tryptophane-contained CDPs were able to decrease the production of violacein in C. violaceum CV026 and predicted as binding within the same pocket of receptor protein CviR, but in lower binding energy compared with the natural ligand C 6 HSL. As for P. aeruginosa PAO1, owning more complicated QS systems, these CDPs also exhibited inhibitory effects on pyocyanin production, swimming motility, biofilm formation, and adhesion. These investigations suggested a promising way to keep the tryptophan untouched and make modifications on the non-aromatic unit to increase the anti-QS activity and decrease the cytotoxicity, thus developing a novel CDP-based anti-virulence agent.

Pseudomonas aeruginosa is an opportunistic bacterium causing several health problems and having many virulence factors like biofilm formation on different surfaces. There is a significant need to develop new antimicrobials due to the spreading resistance to the commonly used antibiotics, partly attributed to biofilm formation. Consequently, this study aimed to investigate the anti-biofilm and anti-quorum sensing activities of Dioon spinulosum, Dyer Ex Eichler extract (DSE), against Pseudomonas aeruginosa clinical isolates. DSE exhibited a reduction in the biofilm formation by P. aeruginosa isolates both in vitro and in vivo rat models. It also resulted in a decrease in cell surface hydrophobicity and exopolysaccharide quantity of P. aeruginosa isolates. Both bright field and scanning electron microscopes provided evidence for the inhibiting ability of DSE on biofilm formation. Moreover, it reduced violacein production by Chromobacterium violaceum (ATCC 12,472). It decreased the relative expression of 4 quorum sensing genes (lasI, lasR, rhlI, rhlR) and the biofilm gene (ndvB) using qRT-PCR. Furthermore, DSE presented a cytotoxic activity with IC 50 of 4.36 ± 0.52 µg/ml against human skin fibroblast cell lines. For the first time, this study reports that DSE is a promising resource of anti-biofilm and anti-quorum sensing agents., (© 2022. The Author(s).)

Quorum sensing (QS)-dependent gene regulation in bacteria performs a vital role in synchronization of cell-density-dependent functions. In Chromobacterium violaceum QS-dependent cviI/R regulatory genes are activated during the mid- or late-exponential phase of growth. However, sufficient evidence is lacking on the role of QS inhibitors on gene regulation at different phases of growth. Hence, we report the role of linalool, a natural monoterpenoid on QS mediated gene regulation at different stages of growth in C. violaceum by performing biosensor, growth kinetic and gene expression studies. In vitro and in vivo studies were performed for establishing role of linalool in reducing the virulence and infection by using HEK-293 T cell lines and Caenorhabditis elegans models respectively. C. violaceum CV026 with C 6 -HSL was used as control. The results showed linalool to be a QS inhibitor with an estimated IC 50 of 63 µg/mL for violacein inhibition. At this concentration the cell density difference (delta OD 600 ) of 0.14 from the compound was observed indicating the quorum concentration. The expression of cviI/R was initiated at mid-log phase (~ 18 h) and reached the maximum at 36 h in control whereas in treatment it remained significantly downregulated at all time points. The expression of violacein biosynthetic genes vioA, vioC, vioD and vioE was also downregulated by linalool. Infection studies with linalool showed higher survival rates in HEK-293T cell lines and C. elegans compared to the infection control. Taken together, this study proves linalool to be a QS inhibitor capable of attenuation of QS by controlling the cell density through cviI/R downregulation at the early phase of growth and hence offering scope for its application for controlling infections., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

The skins of frogs of the family Ranidae are particularly rich sources of biologically active peptides, among which antimicrobial peptides (AMPs) constitute the major portion. Some of these have attracted the interest of researchers because they possess both antimicrobial and anticancer activities. In this study, with 'shotgun' cloning and MS/MS fragmentation, three AMPs, homologues of family brevinin-1 (brevinin-1HL), and temporin (temporin-HLa and temporin-HLb), were discovered from the skin secretion of the broad-folded frog, Hylarana latouchii. They exhibited various degrees of antimicrobial and antibiofilm activities against test microorganisms and hemolysis on horse erythrocytes. It was found that they could induce bacteria death through disrupting cell membranes and binding to bacterial DNA. In addition, they also showed different potencies towards human cancer cell lines. The secondary structure and physicochemical properties of each peptide were investigated to preliminarily reveal their structure-activity relationships. Circular dichroism spectrometry showed that they all adopted a canonical α-helical conformation in membrane-mimetic solvents. Notably, the prepropeptide of brevinin-1HL from H. latouchii was highly identical to that of brevinin-1GHd from Hylarana guentheri, indicating a close relationship between these two species. Accordingly, this study provides candidates for the design of novel anti-infective and antineoplastic agents to fight multidrug-resistant bacteria and malignant tumors and also offers additional clues for the taxonomy of ranid frogs., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Chromobacterium violaceum is a Gram-negative, saprophytic bacterium that can infect humans and its virulence may be regulated by quorum sensing via N-acyl homoserine lactones. A virtual screening study with plant compounds and nonsteroidal anti-inflammatory drugs for inhibition of C. violaceum quorum sensing system has been performed. In vitro evaluation was done to validate the in silico results. Molecular docking showed that phytol, margaric acid, palmitic acid, dipyrone, ketoprofen, and phenylbutazone bound to structures of CviR proteins of different C. violaceum strains. Phytol presented higher binding affinities than AHLs and furanones, recognized inducers, and inhibitors of quorum sensing, respectively. When tested in vitro, phytol at a non-inhibitory concentration was the most efficient tested compound to reduce phenotypes regulated by quorum sensing. The results indicate that in silico compound prospection to inhibit quorum sensing may be a good tool for finding alternative lead molecules., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The low stability of anthocyanins is a constraint in the food industry. The present work has been carried out to overcome this low stability by encapsulating fruit concentrate of underutilized plant Carissa spinarum (CS) with polyphenols in microemulsions (CSME) and nanoemulsions (CSNE). Increasing the amount of CS reduced the particle size from 1154 to 70-300 nm whereas addition of Tween 80 reduced it optimally to 5-25 nm. Degradation of anthocyanins in control and ME/NE proceeded with zero- and first-order reaction rates, respectively, at 28 °C (half-life 6, 25 and 40 days, respectively). The degradation kinetics of phenolics-flavonoids were also studied. CSNE exhibited higher anti-quorum sensing (QS) activity than CSME against Chromobacterium violaceum (73.7%); it inhibited biofilm formation by 70.1 and 64.4% in Pseudomonas aeruginosa, and Yersinia enterocolitica, respectively. This is the first report of using the more stable ME/NE to study anti-QS activity, an alternative to conventional antibiotics., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Cell-cell communication is critical for bacterial survival in natural habitats, in which miscellaneous regulatory networks are encompassed. However, elucidating the interaction networks of a microbial community has been hindered by the population complexity. This study reveals that γ-butyrolactone (GBL) molecules from Streptomyces species, the major antibiotic producers, can directly bind to the acyl-homoserine lactone (AHL) receptor of Chromobacterium violaceum and influence violacein production controlled by the quorum sensing (QS) system. Subsequently, the widespread responses of more Gram-negative bacterial AHL receptors to Gram-positive Streptomyces signaling molecules are unveiled. Based on the cross-talk between GBL and AHL signaling systems, combinatorial regulatory circuits (CRC) are designed and proved to be workable in Escherichia coli (E. coli). It is significant that the QS systems of Gram-positive and Gram-negative bacteria can be bridged via native Streptomyces signaling molecules. These findings pave a new path for unlocking the comprehensive cell-cell communications in microbial communities and facilitate the exploitation of innovative regulatory elements for synthetic biology., (© 2021. Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature.)

Quorum sensing (QS) represents a major target for reducing bacterial pathogenicity and antibiotic resistance. This study identifies bergamot and aspidosperma as new potential sources of anti-QS agents. We investigated the anti-QS activity of plant materials on both Chromobacterium violaceum and Pseudomonas aeruginosa. Initially, we determined the minimum inhibitory concentrations (MICs) of plant materials using a broth microdilution method. Subsequently, we tested the effect of sub-MIC concentrations on QS-regulated traits and virulence factors production in test bacteria. Results revealed that bergamot and aspidosperma inhibited the ability of C. violaceum to produce violacein. Other QS-controlled phenotypes of C. violaceum, namely chitinolytic activity, motility, and biofilm formation, were also reduced by both plant materials. Moreover, QS-linked traits of P. aeruginosa were also reduced. Bergamot inhibited swarming but not swimming motility, while aspidosperma diminished both motility types in P. aeruginosa. Both plant materials also demonstrated antibiofilm activity and inhibited the production of protease and pyocyanin in P. aeruginosa. Furthermore, we tested the anti-QS effect of plant materials on the transcriptional level using RT-qPCR. Bergamot dramatically downregulated the C. violaceum autoinducer synthase gene cviI and the vioB gene involved in violacein biosynthesis, confirming the phenotypic observation on its anti-QS activity. Aspidosperma also reduced the expression of cviI and vioB but less drastically than bergamot. In P. aeruginosa, downregulation in the transcripts of the QS genes lasI, lasR, rhlI, and rhlR was also achieved by bergamot and aspidosperma. Therefore, data in the present study suggest the usefulness of bergamot and aspidosperma as sources of antivirulence agents., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The continuous increase in the incidence of infectious diseases and the rapid unchecked rise in multidrug-resistance to conventional antibiotics have led to the search for alternative strategies for treatment and clinical management of microbial infections. Since quorum sensing (QS) regulates numerous virulence determinants and pathogenicity in bacteria, inhibition of QS promises to be an attractive target for development of novel therapeutics. In this study, a series of cinnamic acid analogs and benzalacetone analogs were designed and synthesized, and their QS-inhibitory activities explored. We found that, among the test compounds, 4-methoxybenzalacetone (8) exhibited potent anti-quorum sensing property, as evidenced by inhibition of QS-controlled violacein production of Chromobacterium violaceum ATCC12472. The inhibitory activity of such a compound, which was the methyl keto analog of the corresponding cinnamic acid, was not only stronger than the parent cinnamic acid (1), but also superior to that of furanone, the reference drug. Based on our observations, its mechanism of quorum sensing inhibition is likely to be mediated by interference with N-acyl-homoserine lactones (AHL) synthesis. Moreover, 4-methoxybenzalacetone (8) also suppressed the production of pyocyanin, rhamnolipids and swarming motility of Pseudomonas aeruginosa, suggesting a broad spectrum of anti-QS activities of this compound. In terms of structure-activity relationship, the possible chemical substitutions on the scaffold of cinnamic acid required for QS inhibitory activity are also discussed. Since 4-methoxybenzalacetone (8) showed no toxicity to both bacteria and mammalian cells, our findings therefore indicate the anti-QS potential of this compound as a novel effective QS inhibitor., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

To date, a very limited number of peptides reported as quorum sensing inhibitors. Herein, we report the synthesis and evaluation of a series of β-turn mimetic-based peptides as potent quorum sensing inhibitors and antibiofilm formation. In this series, peptides P1, P4, and P5 showed very promising anti-quorum sensing activity on lasB-gfp reporter strain of Pseudomonas aeruginosa without affecting bacterial growth. Under our condition, these compounds also showed good anti-violacein production of Chromobacterium violaceum. In terms of antibiofilm formation, except P5, two β-turn mimetic-based peptides P1 and P4 showed maximum inhibition of 80% total biomass of Pseudomonas aeruginosa. This report provides the first β-turn mimetic-based scaffold for future drug development., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

We recently and for the first time reported that ethyl acetate extracts isolated from Penicillium chrysogenum DXY-1 exhibited anti-quorum sensing (anti-QS) activity. Herein, another active molecule in the extracts was identified as chrysin by NMR and MS. A 20 μg/mL dose of chrysin inhibited violacein production regulated by QS in C. violaceum CV026 by 31.6%. A 40 μg/mL dose of chrysin suppressed pyocyanin production, elastase activity, proteolytic activity, and biofilm formation regulated by QS in P. aeruginosa PA01 by 41.4%, 13.8%, 8.3%, and 42.4%, respectively. And chrysin could inhibit the swarming activity of P. aeruginosa PA01. Further, molecular docking and CD analysis were used to address the mechanism of chrysin's activity in C. violaceum. Molecular docking results revealed that chrysin suppresses QS system by competing with the natural signal molecule C 6 HSL for binding to the same pocket of CviR receptor. At the same time, CD results also showed that chrysin could change the secondary structure composition of CviR, which greatly prevented the binding of C 6 HSL/CviR, and further playing its role on inhibiting bacterial QS system. All these data demonstate that chrysin may be used as a potential QS inhibitor to tackle increasing drug resistance., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Chromobacterium violaceum (C. violaceum) is a Gram-negative saprophytic bacterium that is widespread in tropical and subtropical environments, and belongs to conditional pathogenic bacteria. Human infection with C. violaceum is rare, and this can be fatal when the diagnosis and treatment are delayed, especially recurrent infection patients. Since clinicians lack the knowledge for C. violaceum, rapid diagnosis and early appropriate antimicrobial treatment remains challenging., Case Presentation: A 15-year-old male student was hospitalized for dark abscess, pustules, severe pain in both legs, and fever for 11 days. There were pustules with gray-white pus and red infiltrating plaques on the back, and the subcutaneous nodules could be touched in front of both tibias, with scab, rupture and necrotic tissue of the lower limb. The patient's condition rapidly progressed. Therefore, next-generation sequencing (NGS), pustular secretion and blood culture were concurrently performed. The final diagnosis for this patient was C. violaceum infection by NGS. However, no bacterial or fungal growth was observed in the pustular secretion and blood culture. After 4 weeks of treatment, the patient was discharged from the hospital without any complications associated with C. violaceum infection., Conclusion: Rapid diagnosis and early appropriate antimicrobial treatment is the key to the successful treatment of C. violaceum infection, especially in patients with sepsis symptoms. This case highlights that NGS is a promising tool for the rapid diagnosis of C. violaceum infection, preventing the delayed diagnosis and misdiagnosis of C. violaceum infection in patients who tested negative for pustular secretion and blood culture.

With an upsurge in multidrug resistant bacteria backed by biofilm defence armours, there is a desperate need of new antibiotics with a non-traditional mechanism of action. Targeting bacteria by misguiding them or halting their communication is a new approach that could offer a new way to combat the multidrug resistance problem. Quorum sensing is considered to be the achilles heel of bacteria that has a lot to offer. Since, both quorum sensing and biofilm formation have been related to drug resistance and pathogenicity, in this study we synthesised new derivatives of citral with antiquorum sensing and biofilm disrupting properties. We previously reported antimicrobial and antiquorum sensing activity of citral and herein we report the synthesis and evaluation of citral and its derivatives (CD1-CD3) for antibacterial, antibiofilm and antiquorum sensing potential against Chromobacterium violaceum using standard methods. Preliminary results revealed that CD1 is the most active of all the derivatives. Qualitative and quantitative evaluation of antiquorum sensing activity at sub-inhibitory concentrations of these compounds also revealed high activity for CD1 followed by CD2, CD3 and citral. These compounds also inhibit biofilm formation at subinhibitory concentrations without causing any bacterial growth inhibition. These results were replicated by RT-qPCR with down regulation of the quorum sensing genes when C. violaceum was treated with these test compounds. Overall, the results are quite encouraging, revealing that biofilm and quorum sensing are interrelated processes and also indicating the potential of these derivatives to impede bacterial communication and biofilm formation.

The essential oil (EO) from the roots of Plectranthus barbatus Andr. (Syn. Coleus forskohlii Briq.) was evaluated for quorum sensing (QS) inhibitory activity. P. barbatus EO was screened for inhibition of QS regulated violacein production in Chromobacterium violaceum (ATCC 12472) wild-type strain. At inhibitory (6.25% v/v) and sub-inhibitory concentrations (3.125% v/v) of the EO, dose-dependent response in the inhibition of violacein production was observed in C. violaceum. Similarly, sub-MIC (6.25% v/v) of P. barbatus EO disrupted QS regulated biofilm formation by 27.87% and inhibited swarming and twitching motility in Pseudomonas aeruginosa PA01 implying its anti-infective and QS modulatory activity. Fluorescence microscopy studies confirmed the disruption of biofilm formation by EO in P. aeruginosa PAO1. Promising antibacterial activity was recorded at concentrations as low as 3.12% v/v for Listeria monocytogenes (ATCC 13932) and at 6.25% v/v for both Salmonella enterica subsp. enterica serovar Typhimurium (ATCC 25241) and Escherichia coli (ATCC 11775). Furthermore, significant dose-dependent inhibition was observed for biofilm formation and motility in all the tested pathogens in different treated concentrations. GC-MS analysis revealed α-pinene, endo-borneol, bornyl acetate, 1-Hexyl-2-Nitrocyclohexane as the major phytoconstituents. P. barbatus EO or its constituent compounds with QS modulatory, antimicrobial and biofilm inhibitory property could be potential new-age dietary source based intervention and preservation technologies.

Ethnopharmcological Relevance: Microbial biofilm formation, a quorum sensing (QS) regulated process, is one of the major causes of nosocomial and chronic infections, foodborne diseases, and associated deaths. Various approaches have been used to eradicate the menace of biofilm. Ethnomedicinal plants as potent antibiofilm agents are gaining a lot of interest in an era where the drug resistance is increasing and the availability of potent antibiotics is no longer promised. In this context, the methanol extract of Cuphea carthagenensis (CCMD), an ethno-medicinal and culinary herb, was evaluated as an antibiofilm and anti-QS agent against Pseudomonas aeruginosa., Aim of the Study: The aim of the study is to evaluate the antibiofilm and anti-QS activity of an ethnomedicinal plant against a strong biofilm forming microorganism, P. aeruginosa., Methods: Antibiofilm activity of CCMD was demonstrated at different concentrations by Tissue Culture Plate, Test Tube method and other microscopic techniques. The effect of CCMD on QS and QS-related virulence factors viz. Pyocyanin, exopolymeric substance matrix (EPS), total protease, elastase, pyoverdin and swimming motility in P. aeruginosa were also evaluated. Antioxidant activity (DPPH & FRAP), total phenolic and flavonoid content were also checked. In order to determine the composition of the extract HPLC analysis was also performed., Results: In vitro study demonstrated a significant inhibition of biofilm formation (81.88 ± 2.57%) as well as production of QS-dependent virulence factors in P. aeruginosa. The extract also inhibited violacein production (83.31 ± 2.77%) in Chromobacterium violaceum which correlates with the reduction in QS-mediated virulence factors. The extract showed 64.79% ± 0.83% DPPH scavenging activity and reduction of ferricyanide complex (Fe 3+ ) to the ferrous form (Fe 2+ ) in DPPH and FRAP assay, respectively. Furthermore, the extract showed thermal stability and does not have any growth inhibitory effect on P. aeruginosa. The HPLC analysis demonstrated the presence of ellagic acid, ascorbic acid and hippuric acid in the extract., Conclusion: This work is the first to demonstrate that C. carthagenensis can attenuate biofilm formation and QS-mediated virulence factors of P. aeruginosa. Further investigation is required to use this ethnomedicinal plant (CCMD) as an important source of antibiofilm agents., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Pseudomonas aeruginosa is one of the vulnerable opportunistic pathogens associated with nosocomial infections, cystic fibrosis, burn wounds and surgical site infections. Several studies have reported that quorum sensing (QS) systems are controlled the P. aeruginosa pathogenicity. Hence, the targeting of QS considered as an alternative approach to control P. aeruginosa infections. This study aimed to evaluate the anti-quorum sensing and antibiofilm inhibitory potential of Musa paradisiaca against Chromobacterium violaceum (ATCC 12472) and Pseudomonas aeruginosa. The methanol extract of M. paradisiacsa exhibits that better antibiofilm potential against P. aeruginosa. Then, the crude methanol extract was subjected to purify by column chromatography and collected the fractions. The mass-spectrometric analysis of a methanol extract of M. paradisiaca revealed that 1,8-cineole is the major compounds. 1, 8-cineole significantly inhibited the QS regulated violacein production in C. violaceum. Moreover, 1,8-cineole significantly inhibited the QS mediated virulence production and biofilm formation of P. aeruginosa without affecting their growth. The real-time PCR analysis showed the downregulation of autoinducer synthase and transcriptional regulator genes upon 1,8-cineole treatment. The findings of the present study strongly suggested that metabolite of M. paradisiaca impedes P. aeruginosa QS system and associated virulence productions.

The P2X7 receptor (P2X7R) is an ATP-gated ion channel and potential therapeutic target for new drug development. In this study, we synthesized a series of new 1,4-naphthoquinone (1,4-NQ) derivatives and investigated their antagonistic effects against mouse P2X7R. We explored the ability of the tested substances to block ATP-induced Ca 2+ influx into mouse Neuro-2a cells and selected the four most effective substances: the 1,4-naphthoquinone thioglucosides U-548 and U-557 and their tetracyclic conjugates U-286 and U-556. Biological analysis of these compounds revealed significant in vitro inhibition of murine P2X7R. This inhibition resulted in marked blockade of ethidium bromide (EtBr) and YO-PRO-1 fluorescent dye uptake, pronounced decreases in ROS and NO production and protection of neuronal cell viability against the toxic action of high ATP concentrations. In silico analysis indicated favorable molecular docking results of these 1,4-NQs, pointing to their potential to bind in an allosteric site located in the extracellular region of P2X7R. These findings suggest compounds U-286, U-548, U-556 and U-557 as potential scaffolds for the design of new P2X7R blockers and drugs effective against neuropathic pain and neurodegenerative diseases., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Biofilms can form in many industries, one of them is the food industry. The formation of biofilms in this industry could cause immense economic losses and endanger public health. Biofilms formation is mainly triggered by quorum sensing. Therefore, inhibition of quorum sensing could be an innovative approach to inhibit the formation of biofilms. One way to inhibit quorum sensing is by using anti-quorum sensing compounds. Actinomycetes are a group of bacteria that is acknowledged to produce these compounds., Results: There were eight crude extracts of Actinomycetes isolates that showed promising anti-quorum sensing activity against Chromobacterium violaceum. The concentration of the crude extracts was 20 mg/mL. All the crude extracts showed no antibacterial activity against food spoilage bacteria, except for crude extracts of isolate 18 PM that showed antibacterial activity against Bacillus subtilis. They also showed various antibiofilm activity, both inhibition and destruction. The highest inhibition and destruction activity sequentially was done by crude extracts of isolate 12 AC with 89.60% against Bacillus cereus and crude extracts of isolate SW03 with 93.06% against Shewanella putrefaciens., Conclusions: Actinomycetes isolates that isolated from different regions in Indonesia can be used as potential candidates to overcome biofilms formed by food spoilage bacteria using their ability to produce anti-quorum sensing compounds.

Background: Indonesia is the third largest producer of fish and other aquaculture products in the world, making this industry a major contributor in the economy of Indonesia. However, this industry continually overcome challenges, one of them are bacterial outbreaks. In addition, the emergence of these bacterial outbreaks were worsen due to the biofilm produced by many significant pathogenic bacteria and the impact of increased antibiotic resistance. These issues have become a global concern, because antibiotics are currently one of the main treatments available to overcome this problems. Therefore, studies aimed at finding and characterizing bioactive compounds to combat these issues. In this study actinomycetes isolates were screened and characterized for their bioactive compounds produced which have inhibitory and destructive activity and also QS inhibitors against biofilm structure of aquatic pathogenic bacteria, such as Vibrio harveyi, A. hydrophila, and S. agalactiae., Result: Extracts (20 mg/mL) produced by sixteen Actinomycetes isolates showed anti-quorum sensing activity towards reporter stain Chromobacterium violaceum wild-type. Most of these extracts showed better inhibitory activity on all of the pathogenic bacteria biofilm structure tested than the destructive activity on the preformed of those biofilm structure. Subsequently, we also performed characterization of bioactive compound and found that in this study, polysaccharide is the most common antibiofilm agents, which were responsible to their antibiofilm activity. Finally, we found that the value of LC 50 of all extracts tested were more than 1 mg/mL, thereby all of extracts tested did not show cyto-toxic effect against Artemia salina., Conclusion: All of the extracts of Actinomycetes isolates showed promising inhibitory activity towards biofilm structure of pathogenic bacteria tested. So far, all of the extracts are potential to be QS inhibitors and antibiofilm agents of all pathogenic bacteria tested.

Quorum sensing (QS) is a mechanism of intercellular communication in bacteria that received substantial attention as alternate strategy for combating bacterial resistance and the development of new anti-infective agents. The present investigation reports on the assessment of using subinhibitory concentrations of antibiotics for the inhibition of QS-regulated phenotypes in Chromobacterium violaceum. Primarily, the minimum inhibitory concentrations of a series of antibiotics were determined by a microdilution method. Subsequently, the inhibitory effects of selected antibiotics on QS-regulated traits, namely violacein and chitinase production, biofilm formation and motility were evaluated using C. violaceum CV026 and C. violaceum ATCC 12472. Results revealed that kitasamycin and nitrofurantoin exhibited the highest quorum sensing inhibitory (QSI) activity. The amount of violacein produced by C. violaceum was significantly reduced in the presence of either kitasamycin or nitrofurantoin. Moreover, the chitinolytic activity, biofilm formation, and motility were also impaired in kitasamycin or nitrofurantoin-treated cultures. We further confirmed QSI effects at the molecular level using molecular docking and real-time quantitative polymerase chain reaction (RT-qPCR). Results of molecular docking suggested that both antibiotics can interact with CviR transcriptional regulator of C. violaceum. Furthermore, RT-qPCR revealed the suppressive effect of kitasamycin and nitrofurantoin on five genes under the control of the CviI/CviR system: cviI, cviR, vioB, vioC, and vioD. Giving that kitasamycin and nitrofurantoin are being safely used for decades, this study emphasizes their potential application as antivirulence agents to disarm resistant bacterial strains, making their removal an easier task for the immune system or for another antibacterial agent.

Ethnopharmacological Relevance: Coreopsis tinctoria Nutt has various medical and functional properties and its flower is widely used as health-care tea to decrease blood glucose and to lower blood lipids. However, the quorum sensing (QS) inhibition activity of Coreopsis tinctoria Nutt flower remains unclear., Aim of the Study: To assess inhibitory activity against quorum sensing by Chromobacterium violaceum, to identify the chemical composition of the extracts and to disclose the action mechanism of separated compound., Material and Methods: Violacein inhibition assays were performed in 96-wells microplates. The compounds extracted from Coreopsis tinctoria Nutt flower were separated and purified by various chromatography techniques. Respectively, thin layer chromatography (TLC, GF254), mass spectrometer (Agilent 1100 Series LC/MSD Trap SL), Medium-pressure automatic purification system (Buscisepacore C 620, Switzerland), High performance liquid chromatography (HPLC, Shimadzu LC-20AD, Japan), Liquid preparation Chromatography (Waters2545, USA). The chemical structures were identified by nuclear magnetic resonance (NMR, Bruker AV-500, Germany) technique. The inhibitory mechanism of okanin against C. violaceum quorum sensing was detected by quantitative real-time PCR (qRT-PCR)., Results: Quorum sensing regulates production of bacterial virulence factors, thereby making it an intriguing target for attenuating bacterial pathogenicity. In this study, anti-QS activity of Coreopsis tinctoria Nutt methanol fraction (CTM) was investigated against C. violaceum ATCC12472. CTM showed an inhibitory effect on the QS-mediated virulence factors production such as violacein in C. violaceum without effect on growth rate. Also, okanin was isolated from CTM and its potential of anti-QS was confirmed after observing a significant reduction of violacein production in C. violaceum. An attempt was made to assess the effect of okanin on vioABCDE expression in C. violaceum to disclose acting mechanisms., Conclusions: The results of this study contribute to validate an inhibitory effect of Coreopsis tinctoria Nutt flower on quorum sensing by Chromobacterium violaceum and to determine the compound responsible for inhibition. Also, the inhibitory effect was achieved in tandem with the down-regulation of vio operon., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Chromobacterium violaceum is an emerging environmental pathogen that causes life-threatening infection in humans and animals. In October 2017, a Bangladeshi farmer was hospitalized with high-grade fever due to an agricultural injury-related wound infection. Bacteriological and 16S rRNA gene investigation detected C. violaceum in the wound discharge. The patient recovered successfully after a combination treatment with meropenem and ciprofloxacin, followed by prolonged medication to avoid recurrence. We strongly propose to incorporate C. violaceum in the differential diagnosis of wound and skin infections occurring in tropical and subtropical regions, especially when the injury was exposed to soil or sluggish water.

Quorum sensing inhibitors (QSIs) that specifically interfere with bacterial cell-to-cell communication are considered as an alternative approach to conventional antibacterial therapy. In our study, a set of twenty-six fumardiamides with a quinoline head-group were evaluated as potential QSIs. Two strains of Gram-negative Chromobacterium violaceum (violacein-producing strain ATCC31532 and violacein-negative, mini-Tn5 mutant derivative CV026) were used as QS reporters for testing anti-QS and bactericidal activity of various quinoline fumardiamides. The initial screening of eighteen fumardiamides with primaquine, mefloquine and chloroquine scaffolds identified chloroquine derivatives as the most promising QSIs. Tail-group optimization of chloroquine fumardiamides led to the most active compounds 27, 29 and 30 bearing aminoethyl or piperidine moieties. At 400 µM concentration, these compounds inhibited the QS of C. violaceum strains in a manner similar to quercetin (the model QSI), while at the 40 µM concentration their inhibitory effect was twice less than that of quercetin. As none of the compounds displayed a bactericidal effect and that the QS inhibition was specific to the CV026 strain, our findings indicate that the structurally optimized chloroquine derivatives could function as quorum quenching (QQ) agents with a potential to block the signaling without entering the cell. In conclusion, our finding provides an important step toward the further design of agents targeting cell-to-cell communication., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Aim: To determine phenotypically the anti quorum-sensing (QS) activity of 30 volatile organic products (VOPs) through the inhibition of swarming motility and pyoverdine production in Pseudomonas aeruginosa . Materials & methods: Twenty-four essential oils and six small volatile organic compounds randomly selected were screened for their anti-QS activity by violacein inhibition on Chromobacterium violaceum . The VOPs with positive results were subsequently evaluated for swarming motility and pyoverdine production on P. aeruginosa determining the colony diameter and fluorescence under UV light, respectively. Results: Fifty percent of VOPs tested showed strong violacein inhibition, 40% presented anti-swarming activity and 33% inhibited pyoverdine production. Conclusion: Our data demonstrate that VOPs have a great potential to inhibit virulence factors mediated by QS in P. aeruginosa .

The increasing number of Chromobacterium haemolyticum human infection reports, especially in tropical regions and connected with environmental sources, resulted in an urge to better describe this species. This study aimed to characterize the C. haemolyticum resistome, virulence determinants and genetic platforms related with genome plasticity. A comparative genomic analysis was conducted between clinical C. haemolyticum genomes publicly available and the genome of an environmental isolate obtained in this study. The pangenome of C. haemolyticum was calculated and a total of 3378 core genes were predicted in its core genome, corresponding to 51.7% of the pangenome. Genetic determinants putatively encoding resistance to beta-lactams, fosfomycin, aminoglycosides and trimethoprim were predicted in all genomes, possibly constituting the intrinsic resistome of this species. In terms of resistance to beta-lactams, 4 genes were predicted encoding beta-lactamases of classes A, C and D. Moreover, the analysis of Chromobacterium genomes and C. haemolyticum environmental isolates reinforced the role of this genus as progenitor of the bla KPC gene. Putative virulence factors (VFs) were predicted in all genomes, related to adherence, toxins production, colonization and cell invasion. Secretion systems, including type III, were detected. A significant number of transposases and genomic islands were predicted in C. haemolyticum, in some cases above the average reported for Gram-negative bacterial genomes. We conclude that C. haemolyticum strains, including those of environmental origin, present a noteworthy collection of antibiotic resistance genes and VFs. Furthermore, sequences related to gene mobility and genome plasticity suggest high adaptability potential and a possible role as disseminator of antibiotic resistance.

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.)

Chromobacterium violaceum, one free-living Gram-negative bacterium, is abundantly presented in tropics and sub-tropics soil and aquatic environment; it is also an opportunistic human pathogen. Here, two cinnamic acid derivatives, i.e., 4-dimethylaminocinnamic acid (DCA) and 4-methoxycinnamic acid (MCA), were identified as potential quorum sensing (QS) and biofilm inhibitors in C. violaceum ATCC12472. Both DCA (100 μg/mL) and MCA (200 μg/mL) inhibited the levels of N-decanoyl-homoserine lactone (C10-HSL) and reduced the production of certain virulence factors in C. violaceum, including violacein, hemolysin, and chitinase. Metabolomics analysis indicated that QS-related metabolites, such as ethanolamine and L-methionine, were down-regulated after treatment with DCA and MCA. Quantitative real-time polymerase chain reaction (qRT-PCR) demonstrated that DCA and MCA markedly suppressed the expression of two QS-related genes (cviI and cviR). In addition, DCA and MCA also inhibited biofilm formation and enhanced the susceptibility of biofilms to tobramycin, which was evidenced by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Our results indicated that DCA and MCA can serve as QS-based agent for controlling pathogens.Key Points • DCA and MCA inhibited QS and biofilm formation in C. violaceum.• The combination of DCA or MCA and tobramycin removed the preformed biofilm of C. violaceum. • DCA or MCA inhibited virulence factors and expressions of cviI and cviR of C. violaceum.• DCA or MCA are potential antibiotic accelerants for treating C. violaceum infection.

Antibiotics produced by bacteria play important roles in microbial interactions and competition Antibiosis can induce resistance mechanisms in target organisms, and at sublethal doses, antibiotics have been shown to globally alter gene expression patterns. Here, we show that hygromycin A from Streptomyces sp. strain 2AW. induces Chromobacterium violaceum ATCC 31532 to produce the purple antibiotic violacein. Sublethal doses of other antibiotics that similarly target the polypeptide elongation step of translation likewise induced violacein production, unlike antibiotics with different targets. C. violaceum biofilm formation and virulence against Drosophila melanogaster were also induced by translation-inhibiting antibiotics, and we identified an a ntibiotic- i nduced r esponse ( air ) two-component regulatory system that is required for these responses. Genetic analyses indicated a connection between the Air system, quorum-dependent signaling, and the negative regulator VioS, leading us to propose a model for induction of violacein production. This work suggests a novel mechanism of interspecies interaction in which a bacterium produces an antibiotic in response to inhibition by another bacterium and supports the role of antibiotics as signal molecules. IMPORTANCE Secondary metabolites play important roles in microbial communities, but their natural functions are often unknown and may be more complex than appreciated. While compounds with antibiotic activity are often assumed to underlie microbial competition, they may alternatively act as signal molecules. In either scenario, microorganisms might evolve responses to sublethal concentrations of these metabolites, either to protect themselves from inhibition or to change certain behaviors in response to the local abundance of another species. Here, we report that violacein production by C. violaceum ATCC 31532 is induced in response to hygromycin A from Streptomyces sp. 2AW, and we show that this response is dependent on inhibition of translational polypeptide elongation and a previously uncharacterized two-component regulatory system. The breadth of the transcriptional response beyond violacein induction suggests a surprisingly complex metabolite-mediated microbe-microbe interaction and supports the hypothesis that antibiotics evolved as signal molecules. These novel insights will inform predictive models of soil community dynamics and the unintended effects of clinical antibiotic administration., (Copyright © 2020 Lozano et al.)

The increasing incidence of antimicrobial-resistant bacterial pathogens has focused researchers on quorum sensing inhibition strategies instead of those conventional approaches to fight bacterial infections. Anti-quorum sensing (QS) activity of aqueous extract from Forsythia suspense (FSE) was assessed, and its potential QS inhibition mechanisms were also analyzed. The minimal inhibitory concentration (MIC) of FSE to Chromobacterium violaceum 12472 is 0.5 mg mL -1 . Inhibition of QS-regulated violacein production and biofilm formation in C. violaceum 12472 by FSE occurred in a concentration-dependent manner at sub-MIC, with > 70.12 and > 85.31% inhibition at 0.25 mg mL -1 , respectively. N-Acyl homoserine lactones (AHLs) extracted from cultures of C. violaceum 31532 grown in the presence of FSE could not change the violacein production in C. violaceum 026, which indicated that FSE did not inhibit AHL synthesis. We also found that FSE cannot degrade AHLs. Finally, in silico molecular docking was conducted. The computed binding energy data suggested that components of F. suspense have a tendency to inhibit CviR with varying binding affinities and the energy score of Pinoresinol (- 26.02 kcal/mol) is higher than that of C6-HSL (- 16.09 kcal mol -1 ). We concluded that FSE acts as an antagonist of bacterial quorum sensing by competing with AHL receptor binding site.

Lichens are composite organisms, comprising of a fungus (mycobiont) and a blue-green alga (photobiont). Along with the mycobiont, numerous non-obligate microfungi live in lichen thalli. These microfungi are called endolichenic fungi (ELF). In recent years, the ELF are emerging as promising natural sources because of their capability to exert unique drug molecules. The current study aimed to isolate the ELF from the lichen, Usnea longissima Ach., to control of biofilm formation and quorum sensing phenomenon in Pseudomonas aeruginosa PAO1, an opportunistic multidrug resistance pathogen that uses quorum sensing network to produce an array of pathogenic agents. Therefore, inhibiting quorum sensing to manage the infection caused by PAO1 could be the paramount alternative approach to conventional antibiotics. The isolated ELF was identified by amplifying the long subunit region of the fungal genome. The extracted metabolites of ELF (MELE) using the acetone solvent was further investigated for anti-quorum sensing activity using the biomarker strain Chromobacterium violaceum 12472 which exerts violacein pigment via the AHL mediated quorum sensing signalling. Moreover, the effect of MELE was also evaluated on the production of virulence factors and biofilm formation of P. aeruginosa PAO1. The molecular identification revealed that ELF (accession number MN171299) exhibited 100% similarity with Aspergillus quandricinctus strain CBS 135.52. The MELE showed significant anti-quorum sensing activity at the concentration of 4 mg/mL without affecting the bacterial cell viability of P. aeruginosa PAO1. The MELE diminished the production of virulence factors, including pyocyanin, protease, elastase, rhamnolipids, and extracellular polysaccharides of P. aeruginosa PAO1 in a concentration-dependent manner. The MELE also disturbed biofilm formation of P. aeruginosa PAO1. The 3-D analysis of biofilm architecture showed that the thickness and surface area covered by microcolonies was decreased as the concentration of MELE was increased. The GC-MS analysis of MELE exhibited that organic acids and fatty acids are major constituents of the MELE. The present study reports first time that the ELF, A. quandricinctus possesses potential to inhibit quorum sensing and biofilm formation of P. aeruginosa and can be further exploited for hospital and healthcare facilities., Competing Interests: Declaration of competing interest The authors declare no potential conflicts of interest among them., (Copyright © 2019. Published by Elsevier Ltd.)

Introduction: In the context of the global threat of antimicrobial resistance (AMR) among bacterial pathogens against conventional bactericidal antibiotics, investigation on complementary/ alternative approaches to manage bacterial infections is warranted. The present study aimed at investigating the anti-pathogenic potential of Phyllanthus emblica seed extract (PESE) against four different pathogenic bacteria., Methods: Hydroalcoholic extract of P. emblica seeds was tested for its possible in vitro quorummodulatory potential against Chromobacterium violaceum, Serratia marcescens, Pseudomonas aeruginosa, and Staphylococcus aureus through broth dilution assay. In vivo efficacy of PESE was assayed employing Caenorhabditis elegans as the model host for these four pathogens., Results: PESE was found to exert in vitro quorum-modulatory effect on C. violaceum, S. marcescens, P. aeruginosa, and S. aureus at ≥50 μg/mL. This extract could curb the haemolytic activity of all the four test bacteria by 23-65%, inhibit biofilm formation, and was also able to modulate their antibiotic susceptibility (AS) and catalase activity. Susceptibility of P. aeruginosa and S. aureus to lysis by human serum was enhanced under the influence of this extract by 23% and 49%, respectively. Repeated exposure of both these notorious pathogens to PESE did not induce resistance in them. In vivo assay confirmed the anti-virulence effect of this extract in the C. elegans host, wherein the nematode host challenged with the PESE-treated pathogenic bacteria scored better survival. PESE also displayed notable prebiotic potential by promoting the growth of three probiotic strains., Conclusion: To the best of our awareness, this is the first report on the quorum-modulatory potential of P. emblica seed extract, validating its anti-infective potential and prebiotic property., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)