Microbial quorum sensing: a tool or a target for antimicrobial therapy?

Role of bacterial quorum sensing in plant growth promotion

Quorum sensing (QS) also known as bacterial cell-cell communication or bacterial crosstalk is a phenomenon regulating various bacterial traits that can affect plant growth and defence. Similarities in the structure of root exudates and bacterial signalling molecules have tremendous implications governing the plant heath. The rhizosphere ecosystem being an excellent example of plant-microbe and microbe-microbe interactions harbours a variety of microorganisms exhibiting quorum sensing. Phytochemicals present in plant root exudates and QS signal molecules as well as volatile organic compounds (VOCs) produced by microorganisms work in coordination to establish intra- and inter-species communications. Interestingly, a number of plant growth promoting rhziobacterial (PGPR) activities like effective/enhanced root colonization, nutrient uptake, nodulation, nitrogen fixation, production of plant hormones, antimicrobial compounds and induction of plant defences can be attributed directly or indirectly to their quorum sensing and quenching abilities. Although not completely understood, root development, stress tolerance and defence against phytopathogens are some of the implications of such abilities which might prove beneficial for sustainable agriculture. Deciphering the mechanism of these interactions would be instrumental in improving crop health. Plant beneficial microorganisms employing QS and QS inhibition (QSI) strategies have been discussed in this review.

Nanomaterials Regulate Bacterial Quorum Sensing: Applications, Mechanisms, and Optimization Strategies

Anti-virulence therapy that interferes with bacterial communication, known as "quorum sensing (QS)", is a promising strategy for circumventing bacterial resistance. Using nanomaterials to regulate bacterial QS in anti-virulence therapy has attracted much attention, which is mainly attributed to unique physicochemical properties and excellent designability of nanomaterials. However, bacterial QS is a dynamic and multistep process, and there are significant differences in the specific regulatory mechanisms and related influencing factors of nanomaterials in different steps of the QS process. An in-depth understanding of the specific regulatory mechanisms and related influencing factors of nanomaterials in each step can significantly optimize QS regulatory activity and enhance the development of novel nanomaterials with better comprehensive performance. Therefore, this review focuses on the mechanisms by which nanomaterials regulate bacterial QS in the signal supply (including signal synthesis, secretion, and accumulation) and signal transduction cascade (including signal perception and response) processes. Moreover, based on the two key influencing factors (i.e., the nanomaterial itself and the environment), optimization strategies to enhance the QS regulatory activity are comprehensively summarized. Collectively, applying nanomaterials to regulate bacterial QS is a promising strategy for anti-virulence therapy. This review provides reference and inspiration for further research on the anti-virulence application of nanomaterials.

Anti-quorum sensing effects of SidA protein on Escherichia coli receptors: in silico analysis

Quorum sensing enables cell-cell communication in bacteria and regulates biofilm formation. Biofilm production promotes pathogenicity of Escherichia coli and causes infections. However, antibiotic resistance limits conventional treatment efficacy against biofilm infections. Quorum quenching offers an alternative by disrupting quorum sensing signals. Allicin, extracted from garlic, possesses antimicrobial and anti-quorum sensing properties. This study employed molecular docking and dynamics simulations to investigate allicin's interaction with the E. coli quorum sensing system, specifically targeting the cytoplasmic SidA receptor protein. SidA binds to N-acyl-homoserine lactone ligands and regulates quorum sensing in E. coli. The crystal structure of SidA was obtained from the PDB. Molecular docking revealed that allicin competitively binds to the ligand-binding pocket of SidA. Simulations analyzed the effects of allicin binding on SidA stability and affinity for N-acyl-homoserine lactones over 200 ns. Parameters like RMSD, RMSF, and hydrogen bonding indicated SidA was more stable when bound to allicin compared to unbound. Binding free energies suggested allicin reduced SidA's affinity for native ligands. Therefore, allicin binding to SidA alters its conformation and inhibits interaction with N-acyl-homoserine lactones, disrupting quorum sensing signaling and biofilm production in E. coli.

Paraoxonase-1: How a xenobiotic detoxifying enzyme has become an actor in the pathophysiology of infectious diseases and cancer

Both infectious and non-infectious diseases can share common molecular mechanisms, including oxidative stress and inflammation. External factors, such as bacterial or viral infections, excessive calorie intake, inadequate nutrients, or environmental factors, can cause metabolic disorders, resulting in an imbalance between free radical production and natural antioxidant systems. These factors may lead to the production of free radicals that can oxidize lipids, proteins, and nucleic acids, causing metabolic alterations that influence the pathogenesis of the disease. The relationship between oxidation and inflammation is crucial, as they both contribute to the development of cellular pathology. Paraoxonase 1 (PON1) is a vital enzyme in regulating these processes. PON1 is an enzyme that is bound to high-density lipoproteins and protects the organism against oxidative stress and toxic substances. It breaks down lipid peroxides in lipoproteins and cells, enhances the protection of high-density lipoproteins against different infectious agents, and is a critical component of the innate immune system. Impaired PON1 function can affect cellular homeostasis pathways and cause metabolically driven chronic inflammatory states. Therefore, understanding these relationships can help to improve treatments and identify new therapeutic targets. This review also examines the advantages and disadvantages of measuring serum PON1 levels in clinical settings, providing insight into the potential clinical use of this enzyme.

Protective effect of Chromobacterium violaceum and violacein against bone resorption by periodontitis

OBJECTIVES

The aim of this study was to evaluate the potential protective effect of Chromobacterium violaceum and violacein against periodontitis, in experimental models.

MATERIALS AND METHODS

A double-blind experimental study on the exposure to C. violaceum or violacein in experimentally ligature-induced periodontitis, as preventive factors against alveolar bone loss by periodontitis. Bone resorption was assessed by morphometry. Antibacterial potential of violacein was assessed in an in vitro assay. Its cytotoxicity and genotoxicity were evaluated using the Ames test and SOS Chromotest assay, respectively.

RESULTS

The potential of C. violaceum to prevent/limit bone resorption by periodontitis was confirmed. Daily exposure to 106 cells/ml in water intake since birth and only during the first 30 days of life significantly reduced bone loss from periodontitis in teeth with ligature. Violacein extracted from C. violaceum was efficient in inhibiting or limiting bone resorption and had a bactericidal effect against Porphyromonas gingivalis in the in vitro assay.

CONCLUSIONS

We conclude that C. violaceum and violacein have the potential to prevent or limit the progression of periodontal diseases, in an experimental model.

CLINICAL RELEVANCE

The effect of an environmental microorganism with potential action against bone loss in animal models with ligature-induced periodontitis represents the possibility of understanding the etiopathogenesis of periodontal diseases in populations exposed to C. violaceum and the possibility of new probiotics and antimicrobials. This would imply new preventive and therapeutic possibilities.

Photoinduced micropatterning on biodegradable aliphatic polyester surfaces for anchoring dual brushes and its application in bacteria and cell patterning

In view of intrinsic challenges encountered in surface patterning on actual biomaterials such as the ones based on biodegradable polymers, we have demonstrated an innovative strategy to create micro-patterns on the surface of tartaric acid based aliphatic polyester P (poly(hexamethylene 2,3-O-isoprpylidentartarate)) without significant loss of its molecular weight. Around 10 wt% PAG (photoacid generator, 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine) was purposefully encapsulated in a polyester matrix comprising of P and PLA (polylactide) at a ratio of 5 : 95. With the help of a photomask, selective areas of the matrix were exposed to UV radiation at 395 nm for 25 min to trigger the acid release from PAG entrapped unmasked areas for generating hydroxyl functionality that was later converted to an ATRP (atom transfer radical polymerization) initiating moiety on the irradiated domain of P. In subsequent steps, spatio-selective surface modification by surface initiated ATRP was carried out to generate an alternate pattern of polyPEGMA (poly(ethylene glycol)methyl ether methacrylate) and polyDMAPS (poly(3-dimethyl-(methacryloyloxyethyl)ammonium propane sulfonate)) brushes on the matrix. The patterned surface modified with dual brushes was found to be antifouling in nature (rejection of >97% of proteins). Strikingly, an alternate pattern of live bacterial cells (E. coli and S. aureus) was evident and a relatively high population of bacteria was found on the polyPEGMA brush modified domain. However, a complete reverse pattern was visible in the case of L929 mouse fibroblast cells, i.e., cells were found to predominantly adhere to and proliferate on the zwitterionic brush modified surface. An attempt was made to discuss a plausible mechanism of selective cell adhesion on the zwitterionic brush domain. This novel strategy employed on the biodegradable polymer surface provides an easy and straightforward way to micro-pattern various cells, bacteria, etc. on biodegradable substrates which hold great potential to function as biochips, diagnostics, bacteria/cell microarrays, etc.

Antibiotic-free antimicrobial poly (methyl methacrylate) bone cements: A state-of-the-art review

Prosthetic joint infection (PJI) is the most serious complication following total joint arthroplasty, this being because it is associated with, among other things, high morbidity and low quality of life, is difficult to prevent, and is very challenging to treat/manage. The many shortcomings of antibiotic-loaded poly (methyl methacrylate) (PMMA) bone cement (ALBC) as an agent for preventing and treating/managing PJI are well-known. One is that microorganisms responsible for most PJI cases, such as methicillin-resistant S. aureus, have developed or are developing resistance to gentamicin sulfate, which is the antibiotic in the vast majority of approved ALBC brands. This has led to many research efforts to develop cements that do not contain gentamicin (or, for that matter, any antibiotic) but demonstrate excellent antimicrobial efficacy. There is a sizeable body of literature on these so-called "antibiotic-free antimicrobial" PMMA bone cements (AFAMBCs). The present work is a comprehensive and critical review of this body. In addition to summaries of key trends in results of characterization studies of AFAMBCs, the attractive features and shortcomings of the literature are highlighted. Shortcomings provide motivation for future work, with some ideas being formulation of a new generation of AFAMBCs by, example, adding a nanostructured material and/or an extract from a natural product to the powder and/or liquid of the basis cement, respectively.

Quorum sensing inhibition of hordenine analogs on Pseudomonas aeruginosa and Serratia marcescens

Quorum sensing (QS) plays an essential role in virulence factor production, biofilm formation, and antimicrobial resistance. As a potent QS inhibitor, hordenine can inhibit both QS and biofilm formation in Pseudomonas aeruginosa and Serratia marcescens. In this work, we tested the QS inhibitory potential of 27 hordenine analogs against QS and biofilm formation in P. aeruginosa and S. marcescens. Among the tested analogs, seven (12, 28, 27, 26, 2, 23, and 7) exhibited strong QS inhibitory activity against P. aeruginosa, five of which (12, 28, 27, 26, and 2) showed better inhibitory activity than hordenine. In addition, seven analogs (28, 12, 23, 7, 26, 2, and 27) exhibited better biofilm inhibition against P. aeruginosa than hordenine. Four analogs (7, 28, 2, and 12) showed QS inhibitory activity against S. marcescens, two of which (7 and 28) demonstrated better inhibitory activity than hordenine. Furthermore, analog 7 showed similar biofilm inhibition against S. marcescens as hordenine. Structure-activity relationship (SAR) analysis indicated that the inhibitory activities of the analogs were related to four factors, i.e., carbon chain length, presence or absence of an α,β-C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]>C bond, amino group with/without lipophilic group, such as methyl group, and hydroxyl group in benzene ring.

Plant compounds and nonsteroidal anti-inflammatory drugs interfere with quorum sensing in Chromobacterium violaceum

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.

Thai herbal formulation 'Ya-Pit-Samut-Noi': Its antibacterial activities, effects on bacterial virulence factors and in vivo acute toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

A Thai herbal formulation 'Ya-Pit-Samut-Noi' containing Nigella sativa (seed), Piper retrofractum (fruit), Punica granatum (pericarp), and Quercus infectoria (nutgall) has long been traditionally used to treat diarrhea or bloody mucous diarrhea. Scientific information is very important to support its therapeutic effects and traditional drug development.

AIM OF THE STUDY

This study aimed to evaluate the antibacterial activities of Ya-Pit-Samut-Noi against diarrhea-causing bacteria and determine its effects on bacterial virulence factors and in vivo acute toxicity.

MATERIALS AND METHODS

Ethanol and water extracts of Ya-Pit-Samut-Noi and its plant components were prepared. The agar diffusion method was used for preliminary screening of antibacterial activity of the extracts against diarrhea-causing bacteria including Staphylococcus aureus, Vibrio cholerae, and Vibrio parahaemolyticus. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were assessed using broth microdilution method. The effects on bactericidal activity, bacterial cell wall, and cell membrane were examined by time-kill, lysis, and leakage assays, respectively. The effects on bacterial virulence factors including quorum-sensing system, biofilm production, and swarming motility were determined. Phytochemical screening was carried out to identify the group of chemical compounds present in the formulation extracts. Acute toxicity study was conducted by a single oral dose of 2000 mg/kg body weight in Wistar albino rats.

RESULTS

Ethanol and water extracts of Ya-Pit-Samut-Noi and Quercus infectoria demonstrated antibacterial efficacy against all bacterial strains as revealed by zones of inhibition ranging from 7.0 to 24.5 mm. The ethanol and water extracts of Ya-Pit-Samut-Noi and Quercus infectoria produced strong bacteriostatic activity against V. parahaemolyticus (n = 11) with an MIC range of 7.81-250 μg/ml. Only the ethanol extract of Ya-Pit-Samut-Noi produced MBC values less than or equal to 1000 μg/ml against all V. parahaemolyticus. Based on time-kill study, no surviving V. parahaemolyticus (ATCC 17802 and 5268) cells were detected within 6-12 h after treatment with the ethanol extract of Ya-Pit-Samut-Noi at MBC-4MBC concentrations. Vibrioparahaemolyticus ATCC 17802 cells treated with the ethanol extract of Ya-Pit-Samut-Noi demonstrated no lysis or leakage through the bacterial membrane was not observed. At low concentrations (0.125-0.25 μg/ml) the ethanol extract of Ya-Pit-Samut-Noi inhibited violacein production by Chromobacterium violaceum DMST 21761 without affecting the bacterial growth. The ethanol (31.25-62.5 μg/ml) and water (31.25-250 μg/ml) extracts of Ya-Pit-Samut-Noi inhibited biofilm production by S. aureus. The ethanol and water extracts of Ya-Pit-Samut-Noi at 1000 μg/ml reduced the swarming motility of Escherichia coli O157: H7 by 74.98% and 52.65%, respectively. Tannins and terpenoids were detected in both the ethanol and water extracts. Flavonoids were present only in the ethanol extract. Alkaloids and antraquinones were not noticed in either extract. In the acute toxicity study, there were no significant changes in hematological and biochemical parameters nor were adverse effects on mortality, general behaviors, body weight, or organ weights detected.

CONCLUSIONS

The scientific evidence from this study supported the therapeutic effects and safety of the traditional Thai herbal formulation 'Ya-Pit-Samut-Noi' which has been used as an alternative treatment for gastrointestinal infections in Thailand.

Effect of kitasamycin and nitrofurantoin at subinhibitory concentrations on quorum sensing regulated traits of Chromobacterium violaceum

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.

Down-regulatory effects of green coffee extract on las I and las R virulence-associated genes in Pseudomonas aeruginosa

BACKGROUND

Antibiotic resistant strains of Pseudomonas aeruginosa are the cause of Gram negative nosocomial infections especially among the immunosuppressed patients. The bacteria contains las I and las R genes that play very important roles in the pathogenesis and mechanisms of aggression. These genes can be influenced by the quorum sensing (QS) system and such mechanism is becoming clinically important worldwide. This study aimed to investigate the preventive effects of green coffee extract (GCE) on the expression of pathogenesis-related genes, las I and las R in P. aeruginosa.

METHODS

A total of fifty four P. aeruginosa strains were isolated out of 100 clinical samples collected from the infectious wards in different hospitals (Tehran province) using conventional microscopic and biochemical methods. Susceptibility of the isolates to different antibiotics, GCE and chlorogenic acid were elucidated. Multiplex polymerase chain reaction (PCR) and real-time PCR were performed to detect and quantify the expression levels of las I and las R genes. The presence of chlorogenic acid in GCE was confirmed by HPLC.

RESULTS

Antibiotic susceptibility tests revealed multidrug resistance among the clinical isolates of those 40 strains were resistant to ciprofloxacin (74.07%), 43 to ceftazidime (79.26%), 29 to amikacin (53.7%), 42 to ampicillin (77.77%), 17 to colistin (31.48%), 40 to gentamicin (74.77%), and 50 to piperacillin (92.59%). PCR outcomes exhibited that the frequency of las I and las R genes were 100% in resistant and sensitive strains isolated from clinical and standard strains of P. aeruginosa (ATCC 15449). Real-time PCR analyses revealed that GCE significantly prevented the expression of las I and las R genes in P. aeruginosa. GCE at concentration level as low as 2.5 mg/mL could prevent the expression of lasI and lasR genes in P. aeruginosa clinical isolates.

CONCLUSION

The presence and expression levels of las I and las R genes in P. aeruginosa isolates were investigated when the bacteria was exposed to GCE. Our results tend to suggest that genes involved in pathogenesis of:Pseudomonas aeruginosa are down regulated by quorum sensing effect of chlorogenic acid and therefore GCE could be useful as an adjuvant in combating multidrug resistance strains of Pseudomonas aeruginosa.

Exploring anti-quorum sensing and anti-virulence based strategies to fight Candida albicans infections: an in silico approach

The complex virulence attributes of Candida albicans are an attractive target to exploit in the development of new antifungals and anti-virulence strategies to combat C. albicans infections. Particularly, quorum sensing (QS) has been reported as critical for virulence regulation in C. albicans. This work presents two knowledge networks with up-to-date information about QS regulation and experimentally tested anti-QS and anti-virulence agents for C. albicans. A semi-automatic bioinformatics workflow that combines literature mining and expert curation was used to retrieve otherwise scattered information from the scientific literature. The network representation offers an innovative and continuously updatable means for the Candida research community to query QS and virulence data systematically and in a user-friendly way. Notably, the reconstructed networks show the complexity of QS regulation and the impact that some molecules have on the inhibition of virulence mechanisms responsible for infection establishment (e.g. hyphal development) and perseverance (e.g. biofilm formation). In the future, the compiled knowledge may be used to build decision-making models that help infer new knowledge of practical significance. The knowledge networks are publicly available at http://pcquorum.org/. This Web platform enables the exploration of fungal virulence cues as well as reported inhibitors in a user-friendly fashion.

Analogues ofPseudomonas aeruginosasignalling molecules to tackle infections

The emergence of antibiotic resistance coupled with the lack of investment by pharmaceutical companies necessitates a new look at how we tackle bacterial infections.

Paraoxonases and infectious diseases

The paraoxonases (PON1, PON2 and PON3) are an enzyme family with a high structural homology. All of them have lactonase activity and degrade lipid peroxides in lipoproteins and cells. As such, they play a role in protection against oxidation and inflammation. Infectious diseases are often associated with oxidative stress and an inflammatory response. Infection and inflammation trigger a cascade of reactions in the host, known as the acute-phase response. This response is associated with dramatic changes in serum proteins and lipoproteins, including a decrease in serum PON1 activity. These alterations have clinical consequences for the infected patient, including an increased risk for cardiovascular diseases, and an impaired protection against the formation of antibiotic-resistant bacterial biofilms. Several studies have investigated the value of serum PON1 measurement as a biomarker of the infection process. Low serum PON1 activities are associated with poor survival in patients with severe sepsis. In addition, preliminary studies suggest that serum PON1 concentration and/or enzyme activity may be useful as markers of acute concomitant infection in patients with an indwelling central venous catheter. Investigating the associations between paraoxonases and infectious diseases is a recent, and productive, line of research.

Engineering Soluble Human Paraoxonase 2 for Quorum Quenching

Many pathogenic bacteria utilize quorum sensing (QS) systems to regulate the expression of their virulence genes and promote the formation of biofilm, which renders pathogens with extreme resistance to conventional antibiotic treatments. As a novel approach for attenuating antibiotic resistance and in turn fighting chronic infections, enzymatic inactivation of QS signaling molecules, such as N-acyl homoserine lactones (AHLs), holds great promises. Instead of using bacterial lactonases that can evoke immune response when administered, we focus on the human paraoxonase 2 (huPON2). However, insolubility when heterologously overexpressed hinders its application as anti-infection therapeutics. In this study, huPON2 was engineered for soluble expression with minimal introduction of foreign sequences. On the basis of structure modeling, degenerate linkers were exploited for the removal of hydrophobic helices of huPON2 without disrupting its folding structure and thus retaining its enzymatic function. High soluble expression levels were achieved with a yield of 76 mg of fully human PON2 variants per liter of culture media. Particularly, two clones, D2 and E3, showed significant quorum quenching (QQ) bioactivities and effectively impeded Pseudomonas aeruginosa swimming and swarming motilities, signs of an early stage of biofilm formation. In addition, by correlating QQ with luminescence signal readouts, quantitative analysis of QQ toward natural or non-natural AHL-regulator combinations suggested that D2 and E3 exhibited strong lactone hydrolysis activities toward five AHLs of different side chain lengths and modifications widely utilized by a variety of biomedically important pathogens.

Tannin-Rich Fraction from Pomegranate Rind Inhibits Quorum Sensing in Chromobacterium violaceum and Biofilm Formation in Escherichia coli

Pomegranate rind has been found to inhibit numerous pathogens, mostly attributed to its tannin fraction. The present study was conducted to investigate the quorum sensing (QS) inhibition effect of tannin-rich fraction from pomegranate rind (TFPR) by using an indicator strain Chromobacterium violaceum. Meanwhile, its effect on biofilm formation and motility of Escherichia coli was evaluated. It was shown that TFPR inhibited QS-regulated violacein pigment production. Biofilm formation and motility of E. coli were also hindered by TFPR. Transcriptional analysis further showed that TFPR repressed expressions of curli genes (csgB and csgD) and various motility genes (fimA, fimH, flhD, motB, qseB, and qseC). Our findings indicated that TFPR has potential application for controlling E. coli contaminations or biofilms in the food industry.

Noisy neighbourhoods: quorum sensing in fungal-polymicrobial infections

Quorum sensing was once considered a way in which a species was able to sense its cell density and regulate gene expression accordingly. However, it is now becoming apparent that multiple microbes can sense particular quorum-sensing molecules, enabling them to sense and respond to other microbes in their neighbourhood. Such interactions are significant within the context of polymicrobial disease, in which the competition or cooperation of microbes can alter disease progression. Fungi comprise a small but important component of the human microbiome and are in constant contact with bacteria and viruses. The discovery of quorum-sensing pathways in fungi has led to the characterization of a number of interkingdom quorum-sensing interactions. Here, we review the recent developments in quorum sensing in medically important fungi, and the implications these interactions have on the host's innate immune response.

Thermal Decomposition of 2(3H) and 2(5H) Furanones: Theoretical Aspects

The thermal decomposition reactions of 2(3H) and 2(5H) furanones and their methyl derivatives are explored. Theoretical calculations of the barriers, reaction enthalpies, and the properties of these and intermediate species are reported using the composite model chemistry CBS-QB3 and also the functional M06-2X allied to the 6-311++G(d,p) basis set. Thus, the bond dissociation enthalpies, ionization energies, and unimolecular chemical kinetic rate constants in the high-pressure limit were computed. We show that flow reactor experiments that intimated that heating the 2(3H) furanone converts it to the isomeric 2(5H) furanone occurs via a 1 → 2 H-transfer reaction to an open ring ketenoic aldehyde. The latter can then ring close to the other isomeric structure. The final products acrolein and carbon monoxide are only formed from 2(3H), and acrolein will further decompose to ethylene and CO. Comparable channels explain the interconversion of 5-methyl-2(3H) furanone to its 2(5H) isomer and to the formation of methyl vinyl ketone and CO. The influence of the methyl group at other positions on the ring is hardly of significance except in the case of 5-methyl-2(5H) furanone where a hydrogen atom transfer from the methyl group leads to the formation of a doubly unsaturated carboxylic compound, 2,4-pentadienoic acid. Studies of the UV photolysis of the parent compounds in both low-temperature inert argon matrices and in solution are broadly in accord with the thermal findings insofar as product formation is concerned and with our theoretical calculations. The dominant features of the early decomposition chemistry of these compounds are simple hydrogen transfer and simultaneous ring opening reactions, which do however result in some quite unusual species.

In Vivo Programmed Gene Expression Based on Artificial Quorum Networks

The quorum sensing (QS) system, as a well-functioning population-dependent gene switch, has been widely applied in many gene circuits in synthetic biology. In our work, an efficient cell density-controlled expression system (QS) was established via engineering of the Vibrio fischeri luxI-luxR quorum sensing system. In order to achieve in vivo programmed gene expression, a synthetic binary regulation circuit (araQS) was constructed by assembling multiple genetic components, including the quorum quenching protein AiiA and the arabinose promoter ParaBAD, into the QS system. In vitro expression assays verified that the araQS system was initiated only in the absence of arabinose in the medium at a high cell density. In vivo expression assays confirmed that the araQS system presented an in vivo-triggered and cell density-dependent expression pattern. Furthermore, the araQS system was demonstrated to function well in different bacteria, indicating a wide range of bacterial hosts for use. To explore its potential applications in vivo, the araQS system was used to control the production of a heterologous protective antigen in an attenuated Edwardsiella tarda strain, which successfully evoked efficient immune protection in a fish model. This work suggested that the araQS system could program bacterial expression in vivo and might have potential uses, including, but not limited to, bacterial vector vaccines.

Quorum Sensing Is Accompanied by Global Metabolic Changes in the Opportunistic Human Pathogen Pseudomonas aeruginosa

Pseudomonas aeruginosa uses N-acyl-homoserine lactone (AHL)-dependent quorum sensing (QS) systems to control the expression of secreted effectors. These effectors can be crucial to the ecological fitness of the bacterium, playing roles in nutrient acquisition, microbial competition, and virulence. In this study, we investigated the metabolic consequences of AHL-dependent QS by monitoring the metabolic profile(s) of a lasI rhlI double mutant (unable to make QS signaling molecules) and its wild-type progenitor as they progressed through the growth curve. Analysis of culture supernatants by (1)H-nuclear magnetic resonance ((1)H-NMR) spectroscopy revealed that at the point where AHL concentrations peaked in the wild type, the metabolic footprints (i.e., extracellular metabolites) of the wild-type and lasI rhlI mutant diverged. Subsequent gas chromatography-mass spectrometry (GC-MS)-based analysis of the intracellular metabolome revealed QS-dependent perturbations in around one-third of all identified metabolites, including altered concentrations of tricarboxylic acid (TCA) cycle intermediates, amino acids, and fatty acids. Further targeted fatty acid methyl ester (FAME) GC-MS-based profiling of the cellular total fatty acid pools revealed that QS leads to changes associated with decreased membrane fluidity and higher chemical stability. However, not all of the changes we observed were necessarily a direct consequence of QS; liquid chromatography (LC)-MS analyses revealed that polyamine levels were elevated in the lasI rhlI mutant, perhaps a response to the absence of QS-dependent adaptations. Our data suggest that QS leads to a global readjustment in central metabolism and provide new insight into the metabolic changes associated with QS during stationary-phase adaptation.

IMPORTANCE

Quorum sensing (QS) is a transcriptional regulatory mechanism that allows bacteria to coordinate their gene expression profile with the population cell density. The opportunistic human pathogen Pseudomonas aeruginosa uses QS to control the production of secreted virulence factors. In this study, we show that QS elicits a global "metabolic rewiring" in P. aeruginosa. This metabolic rerouting of fluxes is consistent with a variety of drivers, ranging from altered QS-dependent transcription of "metabolic genes" through to the effect(s) of global "metabolic readjustment" as a consequence of QS-dependent exoproduct synthesis, as well as a general stress response, among others. To our knowledge, this is the first study of its kind to assess the global impact of QS on the metabolome.

Quorum quenching activity of Syzygium cumini (L.) Skeels and its anthocyanin malvidin against Klebsiella pneumoniae

Many bacterial species use their intercellular signaling mechanism called quorum sensing (QS), which is found to be implicated in various factors including bacterial pathogenicity and food spoilage. Interrupting the bacterial communication is an attractive strategy to develop novel QS-based antibacterial drugs. Present study is aimed to investigate the quorum sensing inhibitory activity of Syzygium cumini and its anti-biofilm property against opportunistic pathogen using a biosensor strain Chromobacterium violaceum CV026. Ethanol extract of S. cumini was investigated for its anti-QS activity, and the possible active component was identified by docking with LasR receptor protein. Based on docking analysis, methanol extract was enriched for its total anthocyanin (STA) and its effect on QS regulated phenotypes was assessed. STA specifically inhibited the violacein production in C. violaceum; biofilm formation and EPS production in Klebsiella pneumoniae up to 82, 79.94 and 64.29% respectively. Synergistic activity of conventional antibiotics with STA enhanced the susceptibility of K. pneumoniae up to 58.45%. Molecular docking analysis of active components attributes the QSI activity of S. cumini to malvidin. Malvidin exhibited highest ligand binding with LasR receptor protein with docking score more than -7. Effect of malvidin to interrupt the QS regulated phenotypes was also assessed, and it was found to reduce the violacein production, biofilm formation and EPS production of K. pneumoniae in a concentration-dependent manner. These findings suggest that S. cumini can be used as novel QS-based antibacterial/anti-biofilm agent to manage food-borne pathogens and to increase food safety.

Patterning of individual Staphylococcus aureus bacteria onto photogenerated polymeric surface structures

This manuscript describes the fabrication of bacterial surface arrays by using photolithographic techniques having in addition some particularly interesting features.

Biomolecular Mechanisms of Pseudomonas aeruginosa and Escherichia coli Biofilm Formation

Pseudomonas aeruginosa and Escherichia coli are the most prevalent Gram-negative biofilm forming medical device associated pathogens, particularly with respect to catheter associated urinary tract infections. In a similar manner to Gram-positive bacteria, Gram-negative biofilm formation is fundamentally determined by a series of steps outlined more fully in this review, namely adhesion, cellular aggregation, and the production of an extracellular polymeric matrix. More specifically this review will explore the biosynthesis and role of pili and flagella in Gram-negative adhesion and accumulation on surfaces in Pseudomonas aeruginosa and Escherichia coli. The process of biofilm maturation is compared and contrasted in both species, namely the production of the exopolysaccharides via the polysaccharide synthesis locus (Psl), pellicle Formation (Pel) and alginic acid synthesis in Pseudomonas aeruginosa, and UDP-4-amino-4-deoxy-l-arabinose and colonic acid synthesis in Escherichia coli. An emphasis is placed on the importance of the LuxR homologue sdiA; the luxS/autoinducer-II; an autoinducer-III/epinephrine/norepinephrine and indole mediated Quorum sensing systems in enabling Gram-negative bacteria to adapt to their environments. The majority of Gram-negative biofilms consist of polysaccharides of a simple sugar structure (either homo- or heteropolysaccharides) that provide an optimum environment for the survival and maturation of bacteria, allowing them to display increased resistance to antibiotics and predation.

Butyrolactone I Quantification from Lovastatin Producing Aspergillus terreus Using Tandem Mass Spectrometry-Evidence of Signalling Functions

Aspergillus terreus is an industrially important filamentous fungus producing a wide spectrum of secondary metabolites, including lovastatin and itaconic acid. It also produces butyrolactone I which has shown potential as an antitumour agent. Additionally, butyrolactone I has been implicated to have a regulating role in the secondary metabolism and morphology of A. terreus. In this study, a quantitative time-course liquid chromatography—electrospray ionisation—tandem mass spectrometry (LC-ESI-MS-MS) analysis of butyrolactone I is reported for the first time in nine-day long submerged cultures of A. terreus. Butyrolactone I was fragmented in the mass analysis producing a reproducible fragmentation pattern of four main daughter ions (m/z 307, 331, 363 and 393) in all the samples tested. Supplementing the cultures with 100 nM butyrolactone I caused a statistically significant increase (up to two-fold) in its production, regardless of the growth stage but was constitutive when butyrolactone I was added at high cell density during the stationary phase. Furthermore, the extracellular butyrolactone I concentration peaked at 48 h post inoculation, showing a similar profile as has been reported for bacterial quorum sensing molecules. Taken together, the results support the idea of butyrolactone I as a quorum sensing molecule in A. terreus.

Quorum sensing-mediated, cell density-dependent regulation of growth and virulence in Cryptococcus neoformans

Quorum sensing (QS) is a cell density-dependent mechanism of communication between microorganisms, characterized by the release of signaling molecules that affect microbial metabolism and gene expression in a synchronized way. In this study, we investigated cell density-dependent behaviors mediated by conditioned medium (CM) in the pathogenic encapsulated fungus Cryptococcus neoformans. CM produced dose-dependent increases in the growth of planktonic and biofilm cells, glucuronoxylomannan release, and melanin synthesis, important virulence attributes of this organism. Mass spectrometry revealed the presence of pantothenic acid (PA) in our samples, and commercial PA was able to increase growth and melanization, although not to the same extent as CM. Additionally, we found four mutants that were either unable to produce active CM or failed to respond with increased growth in the presence of wild-type CM, providing genetic evidence for the existence of intercellular communication in C. neoformans. C. neoformans CM also increased the growth of Cryptococcus albidus, Candida albicans, and Saccharomyces cerevisiae. Conversely, CM from Cryptococcus albidus, C. albicans, S. cerevisiae, and Sporothrix schenckii increased C. neoformans growth. In summary, we report the existence of a new QS system regulating the growth and virulence factor expression of C. neoformans in vitro and, possibly, also able to regulate growth in other fungi.

Quorum sensing is a strategy of communication used by pathogenic microorganisms to coordinate the expression of attributes necessary to cause disease. In this work, we describe a quorum sensing system in Cryptococcus neoformans, a yeast that can cause severe central nervous system infections. Adding conditioned medium—culture medium in which C. neoformans has previously grown—to fresh cultures resulted in faster growth of C. neoformans both as isolated cells and in microbial communities called biofilms. The addition of conditioned medium also increased the secretion of capsule carbohydrates and the formation of melanin pigment, two tools used by this microorganism to thrive in the host. This remarkable example of microbial communication shows that C. neoformans cells can act in unison when expressing attributes necessary to survive in the host, a finding that could point the way to improvements in the treatment of cryptococcosis.

ß-Phenylethylamine as a novel nutrient treatment to reduce bacterial contamination due to Escherichia coli O157:H7 on beef meat

Bacterial infection by Escherichia coli O157:H7 through the consumption of beef meat or meat products is an ongoing problem, in part because bacteria develop resistances towards chemicals aimed at killing them. In an approach that uses bacterial nutrients to manipulate bacteria into behaviors or cellular phenotypes less harmful to humans, we screened a library of 95 carbon and 95 nitrogen sources for their effect on E. coli growth, cell division, and biofilm formation. In the initial screening experiment using the Phenotype MicroArray(TM) technology from BioLog (Hayward, CA), we narrowed the 190 starting nutrients down to eight which were consecutively tested as supplements in liquid beef broth medium. Acetoacetic acid (AAA) and ß-phenylethylamine (PEA) performed best in this experiment. On beef meat pieces, PEA reduced the bacterial cell count by 90% after incubation of the PEA treated and E. coli contaminated meat pieces at 10°C for one week.

Acetate metabolism and Escherichia coli biofilm: new approaches to an old problem

Current antibiotics continue to lose effectiveness for infectious diseases, especially in cases where the bacteria from a biofilm. This review article summarizes control mechanisms for bacterial biofilm, with an emphasis on the modification of signal transduction pathways, such as quorum sensing and two-component signaling, by externally added metabolic intermediates. As a link between central metabolism and signal transduction, we discuss the activation of two-component response regulators by activated acetate intermediates in response to signals from the environment. These signals constitute 'nutrients' for the bacteria in most cases. Depending on the identity of the nutrient, biofilm amounts may be reduced. The nutrient may then be used for the development of both novel prevention and treatment options for biofilm-associated infectious diseases.

Antifungal proteins: More than antimicrobials?

Antimicrobial proteins (AMPs) are widely distributed in nature. In higher eukaryotes, AMPs provide the host with an important defence mechanism against invading pathogens. AMPs of lower eukaryotes and prokaryotes may support successful competition for nutrients with other microorganisms of the same ecological niche. AMPs show a vast variety in structure, function, antimicrobial spectrum and mechanism of action. Most interestingly, there is growing evidence that AMPs also fulfil important biological functions other than antimicrobial activity. The present review focuses on the mechanistic function of small, cationic, cysteine-rich AMPs of mammals, insects, plants and fungi with antifungal activity and specifically aims at summarizing current knowledge concerning additional biological properties which opens novel aspects for their future use in medicine, agriculture and biotechnology.

Applications of small molecule activators and inhibitors of quorum sensing in Gram-negative bacteria

Quorum sensing is a form of intercellular communication used by many species of bacteria that facilitates concerted interactions between the cells comprising a population. The phenotypes regulated by quorum sensing are extremely diverse, with many having a significant impact upon healthcare, agriculture, and the environment. Consequently there has been significant interest in developing methods to manipulate this signalling process and recent years have witnessed significant theoretical and practical developments. A wide range of small molecule modulators of quorum sensing systems has been discovered, providing an expansive chemical toolbox for the study and modulation of this signalling mechanism. In this review, a selection of recent case studies which illustrate the value of both activators and inhibitors of quorum sensing in Gram-negative bacteria are discussed.

Evolution of resistance to quorum quenching in digital organisms

Quorum sensing (QS) is a collective behavior whereby actions of individuals depend on the density of the surrounding population. Bacteria use QS to trigger secretion of digestive enzymes, formation and destruction of biofilms, and, in the case of pathogenic organisms, expression of virulence factors that cause disease. Investigations of mechanisms that prevent or disrupt QS, referred to as quorum quenching, are of interest because they provide a new alternative to antibiotics for treating bacterial infections. Traditional antibiotics either kill bacteria or inhibit their growth, producing selective pressures that promote resistant strains. In contrast, quorum quenching and other so-called anti-infective strategies focus on altering behavior. In this article we evolve QS in populations of digital organisms, a type of self-replicating computer program, and investigate the effects of quorum quenching on these populations. Specifically, we injected the populations with mutant organisms that were impaired in selected ways to disrupt the QS process. The experimental results indicate that the rate at which these mutants are introduced into a population influences both the evolvability of QS and the persistence of an existing QS behavior. Surprisingly, we also observed resistance to quorum quenching. Effectively, populations evolved resistance by reaching quorum at lower cell densities than did the parent strain. Moreover, the level of resistance was highest when the rate of mutant introduction increased over time. These results show that digital organisms can serve as a model to study the evolution and disruption of QS, potentially informing wet-lab studies aimed at identifying targets for anti-infective development.

The importance of a multifaceted approach to characterizing the microbial flora of chronic wounds

Chronic wounds contain complex polymicrobial communities of sessile organisms that have been underappreciated because of limitations of standard culture techniques. The aim of this work was to combine recently developed next-generation investigative techniques to comprehensively describe the microbial characteristics of chronic wounds. Tissue samples were obtained from 15 patients with chronic wounds presenting to the Johns Hopkins Wound Center. Standard bacteriological cultures demonstrated an average of three common bacterial species in wound samples. By contrast, high-throughput pyrosequencing revealed increased bacterial diversity with an average of 17 genera in each wound. Data from microbial community profiling of chronic wounds were compared with published sequenced analyses of bacteria from normal skin. Increased proportions of anaerobes, Gram-negative rods and Gram-positive cocci were found in chronic wounds. In addition, chronic wounds had significantly lower populations of Propionibacterium compared with normal skin. Using epifluorescence microscopy, wound bacteria were visualized in highly organized thick confluent biofilms or as scattered individual bacterial cells. Fluorescent in situ hybridization allowed for the visualization of Staphylococcus aureus cells in a wound sample. Quorum-sensing molecules were measured by bioassay to evaluate signaling patterns among bacteria in the wounds. A range of autoinducer-2 activities was detected in the wound samples. Collectively, these data provide new insights into the identity, organization, and behavior of bacteria in chronic wounds. Such information may provide important clues to effective future strategies in wound healing.

Quorum sensing in fungi--a review

Quorum sensing (QS) is a mechanism of microbial communication dependent on cell density that can regulate several behaviors in bacteria such as secretion of virulence factors, biofilm formation, competence and bioluminescence. The existence of fungal QS systems was revealed ten years ago after the discovery that farnesol controls filamentation in the pathogenic polymorphic fungus Candida albicans. In the past decade, farnesol has been shown to play multiple roles in C. albicans physiology as a signaling molecule and inducing detrimental effects on host cells and other microbes. In addition to farnesol, the aromatic alcohol tyrosol was also found to be a C. albicans QS molecule (QSM) controlling growth, morphogenesis and biofilm formation. In Saccharomyces cerevisiae, two other aromatic alcohols, phenylethanol and tryptophol were found to be QSMs regulating morphogenesis during nitrogen starvation conditions. Additionally, population density-dependent behaviors that resemble QS have been described in several other fungal species. Although fungal QS research is still in its infancy, its discovery has changed our views about the fungal kingdom and could eventually lead to the development of new antifungal therapeutics.

The anisin1 gene encodes a defensin-like protein and supports the fitness of Aspergillus nidulans

In the genome of Aspergillus nidulans, a defensin-like protein, Anisin1, was annotated with high homology to the mosquito defensin AaDefA1. So far, no studies exist on defensins from filamentous ascomycetes. Therefore, we characterized the anisin1 gene in A. nidulans and generated a deletion mutant, which suffered from a defect in mitospore development and produced less conidia at 42°C compared to the reference strain. In surface cultures of A. nidulans wild type, the anisin1 expression correlated with that of the central regulator for asexual development, brlA, and with the major scavanger of H₂O₂ stress, catB, which is indicative for cell differentiation in developing fungi. Interestingly, brlA and anisin1 expressions were deregulated in a ΔsrrA strain that covers a central role in the histidine-to-aspartate (His-Asp) phosphorelay signaling pathway and shows impaired asexual development and H₂O₂ detoxification. In submers cultures of A. nidulans wild type and other mutants of the His-Asp phosphorelay signaling pathway, anisin1 was repressed, but derepressed in a ΔsrrA background, and anisin1 transcription was further increased in this mutant by H₂O₂ addition. We therefore conclude that the secreted protein Anisin1 contributes to the optimal development of A. nidulans and we further propose that it has a sensing/signaling function for elevated H₂O₂ levels.

Anti-quorum sensing activity of essential oils from Colombian plants

Essential oils from Colombian plants were characterised by GC-MS, and assayed for anti-quorum sensing activity in bacteria sensor strains. Two major chemotypes were found for Lippia alba, the limonene-carvone and the citral (geranial-neral). For other species, the main components included α-pinene (Ocotea sp.), β-pinene (Swinglea glutinosa), cineol (Elettaria cardamomun), α-zingiberene (Zingiber officinale) and pulegone (Minthostachys mollis). Several essential oils presented promising inhibitory properties for the short chain AHL quorum sensing (QS) system, in Escherichia coli containing the biosensor plasmid pJBA132, in particular Lippia alba. Moderate activity as anti-QS using the same plasmid, were also found for selected constituents of essential oils studied here, such as citral, carvone and α-pinene, although solely at the highest tested concentration (250 µg mL(-1)). Only citral presented some activity for the long chain AHL QS system, in Pseudomonas putida containing the plasmid pRK-C12. In short, essential oils from Colombian flora have promising properties as QS modulators.

Synthetic polymers for simultaneous bacterial sequestration and quorum sense interference

Double agents: dual-action polymers are able to sequester rapidly the marine organism Vibrio harveyi from suspension, while at the same time quenching bacterial quorum sense (QS) signals. The potency of the polymers is assessed by cell aggregation experiments and competitive binding assays against a QS signal precursor, and their effect on bacterial behavior is shown by means of bioluminescence.

LuxR dependent quorum sensing inhibition by N,N'-disubstituted imidazolium salts

Thirty N,N'-disubstituted imidazolium salts have been synthesized and evaluated as LuxR antagonists. Substitution on one of the imidazolium nitrogen atoms includes benzhydryl, fluorenyl or cyclopentyl substituent, and alkyl chains of various lengths on the second one. Most of these compounds displayed antagonist activity, with IC(50) reaching the micromolar range for the most active ones. The disubstituted imidazolium scaffold is thus shown to be a new pertinent pharmacophore in the field of AHL dependent QS inhibition.