Quorum Quenching Revisited—From Signal Decays to Signalling Confusion

Division of Genetics and Molecular Biology, Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia.
Sensors (Impact Factor: 2.25). 12/2012; 12(4):4661-96. DOI: 10.3390/s120404661
Source: PubMed


In a polymicrobial community, while some bacteria are communicating with neighboring cells (quorum sensing), others are interrupting the communication (quorum quenching), thus creating a constant arms race between intercellular communication. In the past decade, numerous quorum quenching enzymes have been found and initially thought to inactivate the signalling molecules. Though this is widely accepted, the actual roles of these quorum quenching enzymes are now being uncovered. Recent evidence extends the role of quorum quenching to detoxification or metabolism of signalling molecules as food and energy source; this includes "signalling confusion", a term coined in this paper to refer to the phenomenon of non-destructive modification of signalling molecules. While quorum quenching has been explored as a novel anti-infective therapy targeting, quorum sensing evidence begins to show the development of resistance against quorum quenching.

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Available from: K.W. Hong, Nov 13, 2015
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    • "( Babić et al . , 2010 ; Niu et al . , 2006 ) . In addition to virulence , QS regulates swarming motility , biofilm development , and drug resistance in bacteria ( Wagner and Iglewski , 2008 ; Williams and Camara , 2009 ) . Thus , QS inhibition has become a novel strategy for combating infec - tions , pathogenesis , and bacterial drug resistance ( Hong et al . , 2012 ) . Pseudomonas aeruginosa is a representative bacteria with widespread occurrence and severe virulence , and is regulated by the QS signaling system ( Wagner and Iglewski , 2008 ) . The quorum sensing inhibition activity of N . tetragona was as - sessed in our previous study but was not quantitatively measured ( Hossain et al . , 2014 "
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    ABSTRACT: Ethnopharmacological relevance: Nymphaea tetragona is a widely distributed ornamental species with ethnomedicinal uses in the treatment of diarrhea, dysentery, eruptive fevers, and infections. The anti-infectious activities of this herb have already been assessed to clarify its traditional use as a medicine. Aim of study: In this study, we aimed to verify the inhibitory effects of N. tetragona 50% methanol extract (NTME) on quorum sensing (QS)-controlled virulence factors of bacteria since QS and its virulence factors are novel targets for antimicrobial therapy. Materials and methods: The antibacterial activity of this extract was evaluated against Chromobacterium violaceum and Pseudomonas aeruginosa. The inhibition of the violacein pigment of C. violaceum by NTME was determined qualitative and quantitative using standard methods. The effects of NTME on swarming motility, biofilm viability, pyocyanin production, and LasA protease activity were evaluated using P. aeruginosa. Finally, the in vitro and in vivo cytotoxicity of NTME were verified by MTT assay and oral administration to rats, respectively. Results: The extract had concentration-dependent antibacterial activity against gram-negative bacteria. NTME at 1/2× minimum inhibitory concentration (MIC), 1× MIC and 2× MIC significantly lowered the levels of violacein of C. violaceum compared to that of the control. The swarming motility of P. aeruginosa was inhibited by≥70% by treatment with 1/2× MIC of NTME. There were remarkable reductions in pyocyanin production and LasA protease activity in the overnight culture supernatant of P. aeruginosa supplemented with NTME when compared with that of the untreated control. The confocal micrographs of 24h biofilms of P. aeruginosa exposed to NTME exhibited a lower number of live cells than the control. No toxic effect was observed in in vitro and in vivo cytotoxicity assays of NTME. Conclusions: NTME was demonstrated to have significant concentration-dependent inhibitory effects on quorum sensing-mediated virulence factors of bacteria with non-toxic properties, and could thus be a prospective quorum sensing inhibitor.
    Full-text · Article · Aug 2015 · Journal of ethnopharmacology
    • "Quorum quenching is defined as a process that inhibits quorum sensing signaling across microbial populations by targeting virulence factors (Kusari et al. 2014a; Hosni et al. 2011). The degradation and/or disruption of autoinducers in a variety of bacterial species utilizing quenching enzymes were recently summarized by Hong et al. (2012). Recognition and subsequent disruption of quorum sensing molecules have been demonstrated by plants. "
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    ABSTRACT: Quorum sensing, the cell-to-cell communication system mediated by autoinducers, is responsible for regulation of virulence factors, infections, invasion, colonization, biofilm formation, and antibiotic resistance within bacterial populations. Concomitantly, quorum quenching is a process that involves attenuation of virulence factors by inhibiting or degrading quorum signaling autoinducers. Survival of endophytic microorganisms, commonly known as endophytes, in planta is a continuous mêlée with invading pathogens and pests. In order to survive in their microhabitats inside plants, endophytes have co-evolved to not only utilize an arsenal of biologically active defense compounds but also impede communication between invading pathogens. Such antivirulence strategies prevent pathogens from communicating with or recognizing each other and thus, colonizing plants. The quenching phenomena often involves microbial crosstalk within single or mixed population(s) vis-à-vis gene expression, and production/modulation of quenching enzymes coupled to various antagonistic and synergistic interactions. This concept is particularly interesting because it can be biotechnologically translated in the future to quorum inhibiting antivirulence therapies without triggering resistance in bacteria, which is currently a major problem worldwide that cannot be tackled only with antimicrobial therapies. In this mini-review, we highlight the quorum quenching capacity of endophytes with respect to attenuation of virulence factors and aiding in plant defense response. Further, benefits and potential challenges of using such systems in biotechnology are discussed.
    No preview · Article · May 2015 · Applied Microbiology and Biotechnology
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    • "ble to impact QS more significantly than free β - CD . The larger 50 nm Si - NPs , in contrast , were able to carry a higher dose of β - CD on fewer nanoparticles , and directly influenced QS in V . fischeri . Previous studies have reported the use of QS antagonists and inhibitors to successfully interfere with bacterial QS ( Dong et al . , 2007 ; Hong et al . , 2012 ; Stacy et al . , 2012 ; Welsh et al . , 2015 ) . QS antagonists are often plant - and algal - based compounds that bind to LuxR - type receptors and prevent the complex from initating QS . Alternatively , QS inhibitors include both natural and synthetic compounds that either degrade ( i . e . , enzymes ) or inhibit HSLs . Many propose t"
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    ABSTRACT: The alarming spread of bacterial resistance to traditional antibiotics has warranted the study of alternative antimicrobial agents. Quorum sensing (QS) is a chemical cell-to-cell communication mechanism utilized by bacteria to coordinate group behaviors and establish infections. QS is integral to bacterial survival, and therefore provides a unique target for antimicrobial therapy. In this study, silicon dioxide nanoparticles (Si-NP) were engineered to target the signaling molecules [i.e., acylhomoserine lactones (HSLs)] used for QS in order to halt bacterial communication. Specifically, when Si-NP were surface functionalized with β-cyclodextrin (β-CD), then added to cultures of bacteria (Vibrio fischeri), whose luminous output depends upon HSL-mediated QS, the cell-to-cell communication was dramatically reduced. Reductions in luminescence were further verified by quantitative polymerase chain reaction (qPCR) analyses of luminescence genes. Binding of HSLs to Si-NPs was examined using nuclear magnetic resonance (NMR) spectroscopy. The results indicated that by delivering high concentrations of engineered NPs with associated quenching compounds, the chemical signals were removed from the immediate bacterial environment. In actively-metabolizing cultures, this treatment blocked the ability of bacteria to communicate and regulate QS, effectively silencing and isolating the cells. Si-NPs provide a scaffold and critical stepping-stone for more pointed developments in antimicrobial therapy, especially with regard to QS—a target that will reduce resistance pressures imposed by traditional antibiotics.
    Full-text · Article · Mar 2015 · Frontiers in Microbiology
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