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      Natural quorum sensing inhibitors effectively downregulate gene expression of Pseudomonas aeruginosa virulence factors

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          Abstract

          At present, anti-virulence drugs are being considered as potential therapeutic alternatives and/or adjuvants to currently failing antibiotics. These drugs do not kill bacteria but inhibit virulence factors essential for establishing infection and pathogenesis through targeting non-essential metabolic pathways reducing the selective pressure to develop resistance. We investigated the effect of naturally isolated plant compounds on the repression of the quorum sensing (QS) system which is linked to virulence/pathogenicity in Pseudomonas aeruginosa. Our results show that trans-cinnamaldehyde (CA) and salicylic acid (SA) significantly inhibit expression of QS regulatory and virulence genes in P. aeruginosa PAO1 at sub-inhibitory levels without any bactericidal effect. CA effectively downregulated both the las and rhl QS systems with lasI and lasR levels inhibited by 13- and 7-fold respectively compared to 3- and 2-fold reductions with SA treatment, during the stationary growth phase. The QS inhibitors (QSI) also reduced the production of extracellular virulence factors with CA reducing protease, elastase and pyocyanin by 65%, 22% and 32%, respectively. The QSIs significantly reduced biofilm formation and concomitantly with repressed rhamnolipid gene expression, only trace amount of extracellular rhamnolipids were detected. The QSIs did not completely inhibit virulence factor expression and production but their administration significantly lowered the virulence phenotypes at both the transcriptional and extracellular levels. This study shows the significant inhibitory effect of natural plant-derived compounds on the repression of QS systems in P. aeruginosa.

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          Most cited references36

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          The hierarchy quorum sensing network in Pseudomonas aeruginosa

          Pseudomonas aeruginosa causes severe and persistent infections in immune compromised individuals and cystic fibrosis sufferers. The infection is hard to eradicate as P. aeruginosa has developed strong resistance to most conventional antibiotics. The problem is further compounded by the ability of the pathogen to form biofilm matrix, which provides bacterial cells a protected environment withstanding various stresses including antibiotics. Quorum sensing (QS), a cell density-based intercellular communication system, which plays a key role in regulation of the bacterial virulence and biofilm formation, could be a promising target for developing new strategies against P. aeruginosa infection. The QS network of P. aeruginosa is organized in a multi-layered hierarchy consisting of at least four interconnected signaling mechanisms. Evidence is accumulating that the QS regulatory network not only responds to bacterial population changes but also could react to environmental stress cues. This plasticity should be taken into consideration during exploration and development of anti-QS therapeutics.
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            Identification and characterization of genes for a second anthranilate synthase in Pseudomonas aeruginosa: interchangeability of the two anthranilate synthases and evolutionary implications.

            Two anthranilate synthase gene pairs have been identified in Pseudomonas aeruginosa. They were cloned, sequenced, inactivated in vitro by insertion of an antibiotic resistance gene, and returned to P. aeruginosa, replacing the wild-type gene. One anthranilate synthase enzyme participates in tryptophan synthesis; its genes are designated trpE and trpG. The other anthranilate synthase enzyme, encoded by phnA and phnB, participates in the synthesis of pyocyanin, the characteristic phenazine pigment of the organism. trpE and trpG are independently transcribed; homologous genes have been cloned from Pseudomonas putida. The phenazine pathway genes phnA and phnB are cotranscribed. The cloned phnA phnB gene pair complements trpE and trpE(G) mutants of Escherichia coli. Homologous genes were not found in P. putida PPG1, a non-phenazine producer. Surprisingly, PhnA and PhnB are more closely related to E. coli TrpE and TrpG than to Pseudomonas TrpE and TrpG, whereas Pseudomonas TrpE and TrpG are more closely related to E. coli PabB and PabA than to E. coli TrpE and TrpG. We replaced the wild-type trpE on the P. aeruginosa chromosome with a mutant form having a considerable portion of its coding sequence deleted and replaced by a tetracycline resistance gene cassette. This resulted in tryptophan auxotrophy; however, spontaneous tryptophan-independent revertants appeared at a frequency of 10(-5) to 10(6). The anthranilate synthase of these revertants is not feedback inhibited by tryptophan, suggesting that it arises from PhnAB. phnA mutants retain a low level of pyocyanin production. Introduction of an inactivated trpE gene into a phnA mutant abolished residual pyocyanin production, suggesting that the trpE trpG gene products are capable of providing some anthranilate for pyocyanin synthesis.
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              Quorum sensing inhibitors: an overview.

              Excessive and indiscriminate use of antibiotics to treat bacterial infections has lead to the emergence of multiple drug resistant strains. Most infectious diseases are caused by bacteria which proliferate within quorum sensing (QS) mediated biofilms. Efforts to disrupt biofilms have enabled the identification of bioactive molecules produced by prokaryotes and eukaryotes. These molecules act primarily by quenching the QS system. The phenomenon is also termed as quorum quenching (QQ). In addition, synthetic compounds have also been found to be effective in QQ. This review focuses primarily on natural and synthetic quorum sensing inhibitors (QSIs) with the potential for treating bacterial infections. It has been opined that the most versatile prokaryotes to produce QSI are likely to be those, which are generally regarded as safe. Among the eukaryotes, certain legumes and traditional medicinal plants are likely to act as QSIs. Such findings are likely to lead to efficient treatments with much lower doses of drugs especially antibiotics than required at present. Copyright © 2012 Elsevier Inc. All rights reserved.
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                Author and article information

                Contributors
                jsg.dooley@ulster.ac.uk
                Journal
                Appl Microbiol Biotechnol
                Appl. Microbiol. Biotechnol
                Applied Microbiology and Biotechnology
                Springer Berlin Heidelberg (Berlin/Heidelberg )
                0175-7598
                1432-0614
                9 March 2019
                9 March 2019
                2019
                : 103
                : 8
                : 3521-3535
                Affiliations
                [1 ]ISNI 0000000105519715, GRID grid.12641.30, School of Biomedical Sciences, , Ulster University, ; Coleraine, BT52 1SA UK
                [2 ]ISNI 0000 0004 1936 9668, GRID grid.5685.e, Department of Biology, , University of York, ; Wentworth, York, YO10 5DD UK
                [3 ]ISNI 0000 0004 0488 2696, GRID grid.418998.5, School of Science, , Institute of Technology Sligo, ; Sligo, Ireland
                Author information
                http://orcid.org/0000-0002-9459-5572
                Article
                9618
                10.1007/s00253-019-09618-0
                6449319
                30852658
                200c4935-b7f1-4782-a623-05d2678a0b83
                © The Author(s) 2019

                Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

                History
                : 12 October 2018
                : 2 January 2019
                : 4 January 2019
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/501100001632, Ulster University;
                Award ID: Vice Chancellors Research Award
                Award Recipient :
                Categories
                Genomics, Transcriptomics, Proteomics
                Custom metadata
                © Springer-Verlag GmbH Germany, part of Springer Nature 2019

                Biotechnology
                trans-cinnamaldehyde,salicylic acid,quorum sensing,quorum sensing inhibitor,pseudomonas aeruginosa

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