High variability in quorum quenching and growth inhibition by furanone C-30 in Pseudomonas aeruginosa clinical isolates from cystic fibrosis patients

Disrupting the bacterial language: quorum quenching and its applications

Quorum sensing (QS) is a bacterial communication method closely linked with population density and regulates biofilm formation and the secretion of virulence factors through the release, recognition, and prompt response to small molecule signals. At low cell density, each bacterium produces a low concentration of QS signals that diffuse or are actively transported into the external environment. The accumulated QS signals in the external environment reach a threshold concentration when the bacterial population attains a certain density, enabling effective recognition and interaction of bacterial QS signals with their receptors. This leads to coordinated gene expression and various biological activities across the bacterial population. Targeting the QS system presents a promising strategy to hinder biofilm formation and virulence factor secretion, providing a potential approach to control bacterial growth and reproduction. This study aims to analyze the intercellular mechanisms of quorum quenching (QQ), which focuses on disrupting bacterial signal molecules to keep their concentration below the threshold and preventing the expression of specific pathogenic factors. The applications of QQ in different fields are also reviewed, underscoring its potential as a novel treatment for bacterial infections.

Emerging strategies to target virulence in Pseudomonas aeruginosa respiratory infections

Pseudomonas aeruginosa is an opportunistic pathogen that is responsible for infections in people living with chronic respiratory conditions, such as cystic fibrosis (CF) and non-CF bronchiectasis (NCFB). Traditionally, in people with chronic respiratory disorders, P. aeruginosa infection has been managed with a combination of inhaled and intravenous antibiotic therapies. However, due in part to the prolonged use of antibiotics in these people, the emergence of multi-drug resistant P. aeruginosa strains is a growing concern. The development of anti-virulence therapeutics may provide a new means of treating P. aeruginosa lung infections whilst also combatting the AMR crisis, as these agents are presumed to exert reduced pressure for the emergence of drug resistance as compared to antibiotics. However, the pipeline for developing anti-virulence therapeutics is poorly defined, and it is currently unclear as to whether in vivo and in vitro models effectively replicate the complex pulmonary environment sufficiently to enable development and testing of such therapies for future clinical use. Here, we discuss potential targets for P. aeruginosa anti-virulence therapeutics and the effectiveness of the current models used to study them. Focus is given to the difficulty of replicating the virulence gene expression patterns of P. aeruginosa in the CF and NCFB lung under laboratory conditions and to the challenges this poses for anti-virulence therapeutic development.

Recent developments in preventing catheter-related infections based on biofilms: A comprehensive review

Urinary and vascular catheters are among the most commonly used medical devices. However, infections caused by biofilm formation on the surface of catheters are a major cause of healthcare-associated infections. Traditional methods, such as using antimicrobials to prevent such infections, generally have short-term effects, and treatment is challenging owing to the emergence of antimicrobial-resistant bacteria. This review aims to evaluate the limitations of conventional catheter-related infection prevention efficacy, such as currently used antimicrobials, and analyze the efficacy and limitations of potential alternatives to prevent catheter-related infections that have not yet been commercialized, classified by the transition stages of biofilm formation. We intend to provide profound insights into the ideal technologies for preventing catheter-associated tract infections and present perspectives on future directions in this field.

Pathogen-associated gene discovery workflows for novel antivirulence therapeutic development

Novel therapeutics to manage bacterial infections are urgently needed as the impact and prevalence of antimicrobial resistance (AMR) grows. Antivirulence therapeutics are an alternative approach to antibiotics that aim to attenuate virulence rather than target bacterial essential functions, while minimizing microbiota perturbation and the risk of AMR development. Beyond known virulence factors, pathogen-associated genes (PAGs; genes found only in pathogens to date) may play an important role in virulence or host association. Many identified PAGs encode uncharacterized hypothetical proteins and represent an untapped wealth of novel drug targets. Here, we review current advances in antivirulence drug research and development, including PAG identification, and provide a comprehensive workflow from the discovery of antivirulence drug targets to drug discovery. We highlight the importance of integrating bioinformatic/genomic-based methods for novel virulence factor discovery, coupled with experimental characterization, into existing drug screening platforms to develop novel and effective antivirulence drugs.

Adaptation of Pseudomonas aeruginosa biofilms to tobramycin and the quorum sensing inhibitor C-30 during experimental evolution requires multiple genotypic and phenotypic changes

In the present study we evaluated the fitness, antimicrobial susceptibility, metabolic activity, gene expression, in vitro production of virulence factors and in vivo virulence of experimentally evolved Pseudomonas aeruginosa PAO1. These strains were previously evolved in the presence of tobramycin and the quorum sensing inhibitor furanone C-30 (C-30) and carried mutations in mexT and fusA1. Compared to the wild-type (WT), the evolved strains show a different growth rate and different metabolic activity, suggesting they have an altered fitness. mexT mutants were less susceptible to C-30 than WT strains; they also show reduced susceptibility to chloramphenicol and ciprofloxacin, two substrates of the MexEF-OprN efflux pump. fusA1 mutants had a decreased susceptibility to aminoglycoside antibiotics, and an increased susceptibility to chloramphenicol. The decreased antimicrobial susceptibility and decreased susceptibility to C-30 was accompanied by a changed metabolic activity profile during treatment. The expression of mexE was significantly increased in mexT mutants and induced by C-30, suggesting that MexEF-OprN exports C-30 out of the bacterial cell. The in vitro production of virulence factors as well as virulence in two in vivo models of the strains evolved in the presence of C-30 was unchanged compared to the virulence of the WT. Finally, the evolved strains were less susceptible towards tobramycin (alone and combined with C-30) in an in vivo mouse model. In conclusion, this study shows that mutations acquired during experimental evolution of P. aeruginosa biofilms in the presence of tobramycin and C-30, are accompanied by an altered fitness, metabolism, mexE expression and in vitro and in vivo antimicrobial susceptibility.

The implications of quorum sensing inhibition in bacterial antibiotic resistance- with a special focus on aquaculture

The aquaculture industry is an expanding and demanding industry and due to an increase in urbanization, with rise in income of developing countries population, it offers to provide a sustainable food supply. However, the industry is facing a number of challenges, out of which few needs to be tackled immediately to maximise the productivity. An upcoming problem is the emergence of antibiotic resistant pathogens due to the unchecked use of antibiotics in aquaculture and human clinical practices. A wide variety of aquatic pathogens such as Edwardsiella, Vibrio, and Aeromonas spp. use quorum sensing (QS) systems, a regulatory process involving cell communication via signalling molecules for the collective function of pathogens which regulates the genes expression including virulent genes. Quorum sensing results in bacterial biofilms formation, which leads to their reduced susceptibility towards antimicrobial agents. The usage of quorum sensing inhibitors (QSIs) has been proposed as an attractive strategy to tackle this problem. Due to the modulation of virulence genes expression, QSIs can be used as novel and viable approach to overcome antibiotic resistance in aquaculture. In this review, we direct our attention to the quorum sensing phenomenon and its viability as a target pathway for tackling the ever-growing problem of antimicrobial resistance in aquaculture. This review also provides a concise compilation of the currently available QSIs and investigates possible natural sources for quorum quenching.

A Brominated Furanone Inhibits Pseudomonas aeruginosa Quorum Sensing and Type III Secretion, Attenuating Its Virulence in a Murine Cutaneous Abscess Model

Quorum sensing (QS) and type III secretion systems (T3SSs) are among the most attractive anti-virulence targets for combating multidrug-resistant pathogenic bacteria. Some halogenated furanones reduce QS-associated virulence, but their role in T3SS inhibition remains unclear. This study aimed to assess the inhibition of these two systems on Pseudomonas aeruginosa virulence. The halogenated furanones (Z)-4-bromo-5-(bromomethylene)-2(5H) (C-30) and 5-(dibromomethylene)-2(5H) (named hereafter GBr) were synthesized, and their ability to inhibit the secretion of type III exoenzymes and QS-controlled virulence factors was analyzed in P. aeruginosa PA14 and two clinical isolates. Furthermore, their ability to prevent bacterial establishment was determined in a murine cutaneous abscess model. The GBr furanone reduced pyocyanin production, biofilm formation, and swarming motility in the same manner or more effectively than C-30. Moreover, both furanones inhibited the secretion of ExoS, ExoT, or ExoU effectors in all tested strains. The administration of GBr (25 and 50 µM) to CD1 mice infected with the PA14 strain significantly decreased necrosis formation in the inoculation zone and the systemic spread of bacteria more efficiently than C-30 (50 µM). Molecular docking analysis suggested that the gem position of bromine in GBr increases its affinity for the active site of the QS LasR regulator. Overall, our findings showed that the GBr furanone displayed efficient multi-target properties that may favor the development of more effective anti-virulence therapies.

Actinomycin D: a novel Pseudomonas aeruginosa quorum sensing inhibitor from the endophyte Streptomyces cyaneochromogenes RC1

The infections caused by Pseudomonas aeruginosa are difficult to treat due to its multidrug resistance. A promising strategy for controlling P. aeruginosa infection is targeting the quorum sensing (QS) system. Actinomycin D isolated from the metabolite of endophyte Streptomyces cyaneochromogenes RC1 exhibited good anti-QS activity against P. aeruginosa PAO1. Actinomycin D (50, 100, and 200 μg/mL) significantly inhibited the motility as well as reduced the production of multiple virulence factors including pyocyanin, protease, rhamnolipid, and siderophores. The images of confocal laser scanning microscopy and scanning electron microscopy revealed that the treatment of actinomycin D resulted in a looser and flatter biofilm structure. Real-time quantitative PCR analysis showed that the expression of QS-related genes lasI, rhlI, rhlR, pqsR, pslA, and pilA were downregulated dramatically. The production of QS signaling molecules N-(3-oxododecanoyl)-L-homoserine lactone and N-butanoyl-L-homoserine lactone were also decreased by actinomycin D. These findings suggest that actinomycin D, a potent in vitro anti-virulence agent, is a promising candidate to treat P. aeruginosa infection by interfering with the QS systems.

The Specific Capsule Depolymerase of Phage PMK34 Sensitizes Acinetobacter baumannii to Serum Killing

The rising antimicrobial resistance is particularly alarming for Acinetobacter baumannii, calling for the discovery and evaluation of alternatives to treat A. baumannii infections. Some bacteriophages produce a structural protein that depolymerizes capsular exopolysaccharide. Such purified depolymerases are considered as novel antivirulence compounds. We identified and characterized a depolymerase (DpoMK34) from Acinetobacter phage vB_AbaP_PMK34 active against the clinical isolate A. baumannii MK34. In silico analysis reveals a modular protein displaying a conserved N-terminal domain for anchoring to the phage tail, and variable central and C-terminal domains for enzymatic activity and specificity. AlphaFold-Multimer predicts a trimeric protein adopting an elongated structure due to a long α-helix, an enzymatic β-helix domain and a hypervariable 4 amino acid hotspot in the most ultimate loop of the C-terminal domain. In contrast to the tail fiber of phage T3, this hypervariable hotspot appears unrelated with the primary receptor. The functional characterization of DpoMK34 revealed a mesophilic enzyme active up to 50 °C across a wide pH range (4 to 11) and specific for the capsule of A. baumannii MK34. Enzymatic degradation of the A. baumannii MK34 capsule causes a significant drop in phage adsorption from 95% to 9% after 5 min. Although lacking intrinsic antibacterial activity, DpoMK34 renders A. baumannii MK34 fully susceptible to serum killing in a serum concentration dependent manner. Unlike phage PMK34, DpoMK34 does not easily select for resistant mutants either against PMK34 or itself. In sum, DpoMK34 is a potential antivirulence compound that can be included in a depolymerase cocktail to control difficult to treat A. baumannii infections.

In vitro Activity of Antivirulence Drugs Targeting the las or pqs Quorum Sensing Against Cystic Fibrosis Pseudomonas aeruginosa Isolates

The chronic lung infection caused by Pseudomonas aeruginosa is a major cause of morbidity and mortality in cystic fibrosis (CF) patients. Antivirulence drugs targeting P. aeruginosa quorum sensing (QS) systems are intensively studied as antibiotics substitutes or adjuvants. Previous studies, carried out in non-CF P. aeruginosa reference strains, showed that the old drugs niclosamide and clofoctol could be successfully repurposed as antivirulence drugs targeting the las and pqs QS systems, respectively. However, frequent emergence of QS-defective mutants in the CF lung undermines the use of QS inhibitors in CF therapy. Here, QS signal production and susceptibility to niclosamide and clofoctol have been investigated in 100 P. aeruginosa CF isolates, with the aim of broadening current knowledge on the potential of anti-QS compounds in CF therapy. Results showed that 85, 78, and 69% of the CF isolates from our collection were proficient for the pqs, rhl, and las QS systems, respectively. The ability of both niclosamide and clofoctol to inhibit QS and virulence in vitro was highly variable and strain-dependent. Niclosamide showed an overall low range of activity and its negative effect on las signal production did not correlate with a decreased production of virulence factors. On the other hand, clofoctol displayed a broader QS inhibitory effect in CF isolates, with consequent reduction of the pqs-controlled virulence factor pyocyanin. Overall, this study highlights the importance of testing new antivirulence drugs against large panels of P. aeruginosa CF clinical isolates before proceeding to further pre-clinical studies and corroborates previous evidence that strains naturally resistant to QS inhibitors occur among CF isolates. However, it is also shown that resistance to pqs inhibitors is less frequent than resistance to las inhibitors, thus supporting the development of pqs inhibitors for antivirulence therapy in CF.

Repurposing α-Adrenoreceptor Blockers as Promising Anti-Virulence Agents in Gram-Negative Bacteria

Antimicrobial resistance is among the world’s most urgent public health problems. Diminishing of the virulence of bacteria is a promising approach to decrease the development of bacterial resistance. Quorum sensing (QS) systems orchestrate the bacterial virulence in inducer–receptors manner. Bacteria can spy on the cells of the host by sensing adrenergic hormones and other neurotransmitters, and in turn, these neurotransmitters can induce bacterial pathogenesis. In this direction, α-adrenergic blockers were proposed as an anti-virulence agents through inhibiting the bacterial espionage. The current study aimed to explore the α-blockers’ anti-QS activities. Within comprehensive in silico investigation, the binding affinities of seven α-adrenoreceptor blockers were evaluated towards structurally different QS receptors. From the best docked α-blockers into QS receptors, terazosin was nominated to be subjected for further in vivo and in vitro anti-QS and anti-virulence activities against Chromobacterium violaceum and Pseudomonas aeruginosa. Terazosin showed a significant ability to diminish the QS-controlled pigment production in C. violaceum. Moreover, Terazosin decreased the P. aeruginosa biofilm formation and down-regulated its QS-encoding genes. Terazosin protected mice from the P. aeruginosa pathogenesis. In conclusion, α-adrenergic blockers are proposed as promising anti-virulence agents as they hinder QS receptors and inhibit bacterial espionage.

Anti-Pathogenic Properties of the Combination of a T3SS Inhibitory Halogenated Pyrrolidone with C-30 Furanone

Antimicrobial resistance is one of the current public health challenges to be solved. The World Health Organization (WHO) has urgently called for the development of strategies to expand the increasingly limited antimicrobial arsenal. The development of anti-virulence therapies is a viable option to counteract bacterial infections with the possibility of reducing the generation of resistance. Here we report on the chemical structures of pyrrolidones DEXT 1–4 (previously identified as furan derivatives) and their anti-virulence activity on Pseudomonas aeruginosa strains. DEXT 1–4 were shown to inhibit biofilm formation, swarming motility, and secretion of ExoU and ExoT effector proteins. Also, the anti-pathogenic property of DEXT-3 alone or in combination with furanone C-30 (quorum sensing inhibitor) or MBX-1641 (type III secretion system inhibitor) was analyzed in a model of necrosis induced by P. aeruginosa PA14. All treatments reduced necrosis; however, only the combination of C-30 50 µM with DEXT-3 100 µM showed significant inhibition of bacterial growth in the inoculation area and systemic dispersion. In conclusion, pyrrolidones DEXT 1–4 are chemical structures capable of reducing the pathogenicity of P. aeruginosa and with the potential for the development of anti-virulence combination therapies.

In silico analysis of AhyI protein and AI-1 inhibition using N-cis-octadec-9z-enoyl-l-homoserine lactone inhibitor in Aeromonas hydrophila

AhyI is homologous to the protein LuxI and is conserved throughout bacterial species including Aeromonas hydrophila. A. hydrophila causes opportunistic infections in fish and other aquatic organisms. Furthermore, this pathogennot only poses a great risk for the aquaculture industry, but also for human public health. AhyI (expressing acylhomoserine lactone) is responsible for the biosynthesis of autoinducer-1 (AI-1), commonly referred to as a quorum sensing (QS) signaling molecule, which plays an essential role in bacterial communication. Studying protein structure is essential for understanding molecular mechanisms of pathogenicity in microbes. Here, we have deduced a predicted structure of AhyI protein and characterized its function using in silico methods to aid the development of new treatments for controlling A.hydrophila infections. In addition to modeling AhyI, an appropriate inhibitor molecule was identified via high throughput virtual screening (HTVS) using mcule drug-like databases.The AhyI-inhibitor N-cis-octadec-9Z-enoyl-l-Homoserine lactone was selected withthe best drug score. In order to understand the pocket sites (ligand binding sites) and their interaction with the selected inhibitor, docking (predicted protein binding complex) servers were used and the selected ligand was docked with the predicted AhyI protein model. Remarkably, N-cis-octadec-9Z-enoyl-l-Homoserine lactone established interfaces with the protein via16 residues (V24, R27, F28, R31, W34, V36, D45, M77, F82, T101, R102, L103, 104, V143, S145, and V168), which are involved with regulating mechanisms of inhibition. These proposed predictions suggest that this inhibitor molecule may be used as a novel drug candidate for the inhibition of auto-inducer-1 (AI-1) activity.The N-cis-octadec-9Z-enoyl-l-Homoserine lactone inhibitor molecule was studied on cultured bacteria to validate its potency against AI-1 production. At a concentration of 40 μM, optimal inhibition efficiency of AI-1 was observedin bacterial culture media.These results suggest that the inhibitor molecule N-cis-octadec-9Z-enoyl-l-Homoserine lactone is a competitive inhibitor of AI-1 biosynthesis.

The Quorum-Sensing Inhibitor Furanone C-30 Rapidly Loses Its Tobramycin-Potentiating Activity against Pseudomonas aeruginosa Biofilms during Experimental Evolution

The use of quorum-sensing inhibitors (QSI) has been proposed as an alternative strategy to combat antibiotic resistance. QSI reduce the virulence of a pathogen without killing it and it is claimed that resistance to such compounds is less likely to develop, although there is a lack of experimental data supporting this hypothesis. Additionally, such studies are often carried out in conditions that do not mimic the in vivo situation. In the present study, we evaluated whether a combination of the QSI furanone C-30 and the aminoglycoside antibiotic tobramycin would be "evolution-proof" when used to eradicate Pseudomonas aeruginosa biofilms grown in a synthetic cystic fibrosis sputum medium. We found that the biofilm-eradicating activity of the tobramycin/furanone C-30 combination already decreased after 5 treatment cycles. The antimicrobial susceptibility of P. aeruginosa to tobramycin decreased 8-fold after 16 cycles of treatment with the tobramycin/furanone C-30 combination. Furthermore, microcalorimetry revealed changes in the metabolic activity of P. aeruginosa exposed to furanone C-30, tobramycin, and the combination. Whole-genome sequencing analysis of the evolved strains exposed to the combination identified mutations in mexT, fusA1, and parS, genes known to be involved in antibiotic resistance. In P. aeruginosa treated with furanone C-30 alone, a deletion in mexT was also observed. Our data indicate that furanone C-30 is not "evolution-proof" and quickly becomes ineffective as a tobramycin potentiator.

Antivirulence Properties of a Low-Molecular-Weight Quaternized Chitosan Derivative against Pseudomonas aeruginosa

The co-occurrence of increasing rates of resistance to current antibiotics and the paucity of novel antibiotics pose major challenges for the treatment of bacterial infections. In this scenario, treatments targeting bacterial virulence have gained considerable interest as they are expected to exert a weaker selection for resistance than conventional antibiotics. In a previous study, we demonstrated that a low-molecular-weight quaternized chitosan derivative, named QAL, displays antibiofilm activity against the major pathogen Pseudomonas aeruginosa at subinhibitory concentrations. The aim of this study was to investigate whether QAL was able to inhibit the production of relevant virulence factors of P. aeruginosa. When tested in vitro at subinhibiting concentrations (0.31-0.62 mg/mL), QAL markedly reduced the production of pyocyanin, pyoverdin, proteases, and LasA, as well as inhibited the swarming motility of three out of four P. aeruginosa strains tested. Furthermore, quantitative reverse transcription PCR (qRT-PCR) analyses demonstrated that expression of lasI and rhlI, two QS-related genes, was highly downregulated in a representative P. aeruginosa strain. Confocal scanning laser microscopy analysis suggested that FITC-labelled QAL accumulates intracellularly following incubation with P. aeruginosa. In contrast, the reduced production of virulence factors was not evidenced when QAL was used as the main polymeric component of polyelectrolyte-based nanoparticles. Additionally, combination of sub-MIC concentrations of QAL and tobramycin significantly reduced biofilm formation of P. aeruginosa, likely due to a synergistic activity towards planktonic bacteria. Overall, the results obtained demonstrated an antivirulence activity of QAL, possibly due to polymer intracellular localization and QS-inhibition, and its ability to inhibit P. aeruginosa growth synergizing with tobramycin.

Exacerbation of antimicrobial resistance: another casualty of the COVID-19 pandemic?

Introduction: The widespread use of antimicrobial drugs during the ongoing coronavirus disease 2019 (COVID-19) pandemic and the likely emergence of antibiotic-resistant microorganisms is a global health concern. Even before the COVID-19 pandemic, several antimicrobial drugs have lost their efficacy and are no longer useful to treat life-threatening infections. Since the exacerbation of antimicrobial resistance is likely to be another casualty of the COVID-19 pandemic, there is a pressing need to develop innovative strategies to minimize the risk of antimicrobial resistance.Areas covered: Focusing on the COVID-19 pandemic, I have briefly summarized the current knowledge and challenges in our understanding of antimicrobial resistance, emphasizing quorum sensing and quorum quenching. Our understanding of bacterial communication by quorum sensing to acquire virulence has paved the way to reduce bacterial pathogenicity through quorum quenching. Availability of clinically viable quorum quenching agents would likely to diminish bacterial virulence to create a microenvironment for the host phagocytic cells to reduce bacterial infection.Expert opinion: Future studies that aim to generate clinically useful quorum quenching agents need to be considered. An important benefit of such agents may be a diminished risk of antimicrobial resistance.

Quorum sensing: a new prospect for the management of antimicrobial-resistant infectious diseases

INTRODUCTION

Quorum-sensing (QS) is a microbial cell-to-cell communication system that utilizes small signaling molecules to mediates interactions between cross-kingdom microorganisms, including Gram-positive and -negative microbes. QS molecules include N-acyl-homoserine-lactones (AHLs), furanosyl borate, hydroxyl-palmitic acid methylester, and methyl-dodecanoic acid. These signaling molecules maintain the symbiotic relationship between a host and the healthy microbial flora and also control various microbial virulence factors. This manuscript has been developed based on published scientific papers.

AREAS COVERED

Furanones, glycosylated chemicals, heavy metals, and nanomaterials are considered QS inhibitors (QSIs) and are therefore capable of inhibiting the microbial QS system. QSIs are currently being considered as antimicrobial therapeutic options. Currently, the low speed at which new antimicrobial agents are being developed impairs the treatment of drug-resistant infections. Therefore, QSIs are currently being studied as potential interventions targeting QS-signaling molecules and quorum quenching (QQ) enzymes to reduce microbial virulence.

EXPERT OPINION

QSIs represent a novel opportunity to combat antimicrobial resistance (AMR). However, no clinical trials have been conducted thus far assessing their efficacy. With the recent advancements in technology and the development of well-designed clinical trials aimed at targeting various components of the, QS system, these agents will undoubtedly provide a useful alternative to treat infectious diseases.

Quorum quenching enzymes and their effects on virulence, biofilm, and microbiomes: a review of recent advances

INTRODUCTION

Numerous bacterial behaviors are regulated by a cell-density dependent mechanism known as Quorum Sensing (QS). QS relies on communication between bacterial cells using diffusible signaling molecules known as autoinducers. QS regulates physiological processes such as metabolism, virulence, and biofilm formation. Quorum Quenching (QQ) is the inhibition of QS using chemical or enzymatic means to counteract behaviors regulated by QS.

AREAS COVERED

We examine the main, diverse QS mechanisms present in bacterial species, with a special emphasis on AHL-mediated QS. We also discuss key in vitro and in vivo systems in which interference in QS was investigated. Additionally, we highlight promising developments, such as the substrate preference of the used enzymatic quencher, in the application of interference in QS to counter bacterial virulence.

EXPERT OPINION

Enabled via the recent isolation of highly stable quorum quenching enzymes and/or molecular engineering efforts, the effects of the interference in QS were recently evaluated outside of the traditional model of single species culture. Signal disruption in complex microbial communities was shown to result in the disruption of complex microbial behaviors, and changes in population structures. These new findings, and future studies, may result in significant changes in the traditional views about QS.

Characterization of Actinobacillus seminis biofilm formation

Actinobacillus seminis is an autochthonous gram-negative bacterium that affects reproductive organs, causing epididymitis, low fertility, and occasional abortions in ovine and goats. The virulence factors and the pathogenicity mechanisms of A. seminis have not been clearly elucidated yet. In this work, biofilm production by A. seminis in in vitro assays is described and characterized. After 48-h incubation at 37 °C in trypticase soy broth, A. seminis formed biofilms containing an extracellular matrix comprised mainly of fibrillar material. Microaerophilia or the presence of calcium diminished biofilm formation in approximately 50% and 70%, respectively, but low iron concentrations increased it 40%. Through enzymatic digestion, it was found that proteins were the main component of these biofilms. Structural observations through scanning electron microscopy indicated the presence of a high amount of fibrillar material in which bacteria were immersed. Antibodies against different bacterial surface proteins, such as anti-biofilm matrix and anti-adhesin, diminished biofilm formation in 70% and 25%, respectively; whereas furanone C-30 and LED-209, compounds described as quorum-sensing inhibitors, completely inhibited biofilm formation. In conclusion, environmental conditions can influence strongly biofilm formation in A. seminis, and this could be an advantageous strategy that allows bacteria to persist inside a host.

Tracking the genome of four Pseudomonas aeruginosa isolates that have a defective Las quorum-sensing system, but are still virulent

In this work we analysed the whole genome extended multilocus sequence typing (wgMLST) of four Pseudomonas aeruginosa strains that are characterized by being virulent despite having a defective Las quorum-sensing (QS) system, and compare them with the wgMLST of the PAO1 and PA14 type strains. This comparison was done to determine whether there was a genomic characteristic that was common to the strains with an atypical QS response. The analysed strains include two environmental isolates (ID 4365 isolated from the Indian Ocean, and M66 isolated from the Churince water system in Cuatro Ciénegas Coahuila, México), one veterinary isolate (strain 148 isolated from the stomach of a dolphin) and a clinical strain (INP43 that is a cystic fibrosis pediatric isolate). We determine that the six analysed strains have a core genome of 4689 loci that was used to construct a wgMLST-phylogeny tree. Using the cano-wgMLST_BacCompare software we found that there was no common genomic characteristic to the strains with an atypical QS-response and we identify ten loci that are highly discriminatory of the six strains’ phylogeny so that their MLST can reconstruct the wgMLST-phylogeny tree of these strains. We discuss here the nature of these ten highly discriminatory genes in the context of P. aeruginosa virulence and evolution.

Effects of Signal Disruption Depends on the Substrate Preference of the Lactonase

Many bacteria produce and use extracellular signaling molecules such as acyl homoserine lactones (AHLs) to communicate and coordinate behavior in a cell-density dependent manner, via a communication system called quorum sensing (QS). This system regulates behaviors including but not limited to virulence and biofilm formation. We focused on Pseudomonas aeruginosa, a human opportunistic pathogen that is involved in acute and chronic lung infections and which disproportionately affects people with cystic fibrosis. P. aeruginosa infections are becoming increasingly challenging to treat with the spread of antibiotic resistance. Therefore, QS disruption approaches, known as quorum quenching, are appealing due to their potential to control the virulence of resistant strains. Interestingly, P. aeruginosa is known to simultaneously utilize two main QS circuits, one based on C4-AHL, the other with 3-oxo-C12-AHL. Here, we evaluated the effects of signal disruption on 39 cystic fibrosis clinical isolates of P. aeruginosa, including drug resistant strains. We used two enzymes capable of degrading AHLs, known as lactonases, with distinct substrate preference: one degrading 3-oxo-C12-AHL, the other degrading both C4-AHL and 3-oxo-C12-AHL. Two lactonases were used to determine the effects of signal disruption on the clinical isolates, and to evaluate the importance of the QS circuits by measuring effects on virulence factors (elastase, protease, and pyocyanin) and biofilm formation. Signal disruption results in at least one of these factors being inhibited for most isolates (92%). Virulence factor activity or production were inhibited by up to 100% and biofilm was inhibited by an average of 2.3 fold. Remarkably, the treatments led to distinct inhibition profiles of the isolates; the treatment with the lactonase degrading both signaling molecules resulted in a higher fraction of inhibited isolates (77% vs. 67%), and the simultaneous inhibition of more virulence factors per strain (2 vs. 1.5). This finding suggests that the lactonase AHL preference is key to its inhibitory spectrum and is an essential parameter to improve quorum quenching strategies.

AiiM Lactonase Strongly Reduces Quorum Sensing Controlled Virulence Factors in Clinical Strains of Pseudomonas aeruginosa Isolated From Burned Patients

Pseudomonas aeruginosa is an opportunistic bacterium associated with healthcare infections in intensive care units (ICUs), ventilator-associated pneumonia (VAP), surgical site infections, and burns. This bacterium causes 75% of death in burned patients, since it can develop a persistent biofilm associated with infections, express several virulence factors, and antibiotic-resistance mechanisms. Some of these virulence factors are proteases such as elastase and alkaline protease, or toxic metabolites such as pyocyanin and is one of the few microorganisms able to produce cyanide, which inhibits the cytochrome oxidase of host cells. These virulence factors are controlled by quorum sensing (QS). In this work, 30 P. aeruginosa clinical strains isolated from burned patients from a tertiary hospital in Mexico City were studied. Antibiotic susceptibility tests were done, and virulence factors (elastase, alkaline protease, HCN, and pyocyanin) were determined in presence of an N-acylhomoserine lactonase, AiiM able to hydrolyze a wide range of acyl homoserine lactones. The treatment reduced significantly the activities of elastase and alkaline protease, and the production of pyocyanin and HCN in all producer strains but not the secretion of toxins through the type III secretion system. Our work suggests that AiiM treatment may be an effective therapy to combat P. aeruginosa infection in burn patients.

Recent Advances in Anti-virulence Therapeutic Strategies With a Focus on Dismantling Bacterial Membrane Microdomains, Toxin Neutralization, Quorum-Sensing Interference and Biofilm Inhibition

Antimicrobial resistance constitutes one of the major challenges facing humanity in the Twenty-First century. The spread of resistant pathogens has been such that the possibility of returning to a pre-antibiotic era is real. In this scenario, innovative therapeutic strategies must be employed to restrict resistance. Among the innovative proposed strategies, anti-virulence therapy has been envisioned as a promising alternative for effective control of the emergence and spread of resistant pathogens. This review presents some of the anti-virulence strategies that are currently being developed, it will cover strategies focused on quench pathogen quorum sensing (QS) systems, disassemble of bacterial functional membrane microdomains (FMMs), disruption of biofilm formation and bacterial toxin neutralization.

Interference With Quorum-Sensing Signal Biosynthesis as a Promising Therapeutic Strategy Against Multidrug-Resistant Pathogens

Faced with the global health threat of increasing resistance to antibiotics, researchers are exploring interventions that target bacterial virulence factors. Quorum sensing is a particularly attractive target because several bacterial virulence factors are controlled by this mechanism. Furthermore, attacking the quorum-sensing signaling network is less likely to select for resistant strains than using conventional antibiotics. Strategies that focus on the inhibition of quorum-sensing signal production are especially attractive because the enzymes involved are expressed in bacterial cells but are not present in their mammalian counterparts. We review here various approaches that are being taken to interfere with quorum-sensing signal production via the inhibition of autoinducer-2 synthesis, PQS synthesis, peptide autoinducer synthesis, and N-acyl-homoserine lactone synthesis. We expect these approaches will lead to the discovery of new quorum-sensing inhibitors that can help to stem the tide of antibiotic resistance.

Inactivation of the quorum-sensing transcriptional regulators LasR or RhlR does not suppress the expression of virulence factors and the virulence of Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an environmental bacterium but is also an opportunistic pathogen. The aim of this work is to evaluate the contribution of P. aeruginosa LasR and RhlR transcriptional regulators of the quorum-sensing response (QSR) to the production of virulence factors, and to its virulence in a mouse abscess model. The QSR is a complex regulatory network that modulates the expression of several virulence factors, including elastase, pyocyanin and rhamnolipids. LasR, when complexed with the auto-inducer 3-oxo-dodecanoyl lactone (3O-C12-HSL), produced by LasI, is at the top of the QSR regulatory cascade since it activates transcription of some genes encoding virulence factors (such as the gene coding for elastase, lasB) and also transcription of both rhlR and rhlI, encoding the synthase of the auto-inducer butanoyl-homoserine lactone (C4-HSL). In turn RhlR, coupled with C4-HSL, activates the transcription of genes encoding for the enzymes involved in pyocyanin and rhamnolipid production. Several efforts have been made to obtain inhibitors of LasR activity that would suppress the QSR. However, these attempts have used chemical compounds that might not be specific for LasR inactivation. In this work we show that individual inactivation of either lasR or rhlR did not block the QSR, nor did it impair P. aeruginosa virulence, and that even a lasR rhlR double mutant still presented residual virulence, even lacking the production of virulence factors. These results show that the inhibition of either lasR or rhlR is not a straightforward approach to blocking P. aeruginosa virulence, due to the great complexity of the QSR.

In-Silico Prediction and Modeling of the Quorum Sensing LuxS Protein and Inhibition of AI-2 Biosynthesis in Aeromonas hydrophila

luxS is conserved in several bacterial species, including A. hydrophila, which causes infections in prawn, fish, and shrimp, and is consequently a great risk to the aquaculture industry and public health. luxS plays a critical role in the biosynthesis of the autoinducer-2 (AI-2), which performs wide-ranging functions in bacterial communication, and especially in quorum sensing (QS). The prediction of a 3D structure of the QS-associated LuxS protein is thus essential to better understand and control A. hydrophila pathogenecity. Here, we predicted the structure of A. hydrophila LuxS and characterized it structurally and functionally with in silico methods. The predicted structure of LuxS provides a framework to develop more complete structural and functional insights and will aid the mitigation of A. hydrophila infection, and the development of novel drugs to control infections. In addition to modeling, the suitable inhibitor was identified by high through put screening (HTS) against drug like subset of ZINC database and inhibitor ((-)-Dimethyl 2,3-O-isopropylidene-l-tartrate) molecule was selected based on the best drug score. Molecular docking studies were performed to find out the best binding affinity between LuxS homologous or predicted model of LuxS protein for the ligand selection. Remarkably, this inhibitor molecule establishes agreeable interfaces with amino acid residues LYS 23, VAL 35, ILE76, and SER 90, which are found to play an essential role in inhibition mechanism. These predictions were suggesting that the proposed inhibitor molecule may be considered as drug candidates against AI-2 biosynthesis of A. hydrophila. Therefore, (-)-Dimethyl 2,3-O-isopropylidene-l-tartrate inhibitor molecule was studied to confirm its potency of AI-2 biosynthesis inhibition. The results shows that the inhibitor molecule had a better efficacy in AI-2 inhibition at 40 μM concentration, which was further validated using Western blotting at a protein expression level. The AI-2 bioluminescence assay showed that the decreased amount of AI-2 biosynthesis and downregulation of LuxS protein play an important role in the AI-2 inhibition. Lastly, these experiments were conducted with the supplementation of antibiotics via cocktail therapy of AI-2 inhibitor plus OXY antibiotics, in order to determine the possibility of novel cocktail drug treatments of A. hydrophila infection.

Anti-virulence potential of eugenol-rich fraction of Syzygium aromaticum against multidrug resistant uropathogens isolated from catheterized patients

Objective:

Considering the emergence of biofilm-associated pathogens with multidrug resistance, the objective(s) of the present study was to evaluate the anti-virulence property of Syzygium aromaticum extracts/fractions against 2 multidrug-resistant catheter isolates.

Materials and Methods:

Pulverized clove buds were subjected to bioactivity-guided isolation to identify the bioactive extract/fraction(s) with significant anti-virulence property. The clove bud powder was subjected to Soxhlet extraction and all these extracts were investigated in terms of anti-virulent efficacy using initial readout assays. Bioassay-guided partial purification was performed through column and size exclusion chromatography. Detailed testing of the anti-virulence and anti-biofilm activity of sub-minimum inhibitory concentration (sub-MIC) levels of the active fraction, was performed besides the cytotoxicity profiling in RAW 264.7 cells.

Results:

Gas chromatography-mass spectrometry (GC-MS) analysis of the clove bioactive fraction-2 (CBF-2), done after the bioassay-guided fractionation, revealed eugenol as the major bioactive ingredient present in CBF-2. Reduced mRNA levels of virulence factor genes after CBF-2 (700 μg/ml) treatment correlated well with the respective phenotypic assays (p<0.001). Similarly, CBF-2 (700 μg/ml) treatment exhibited significantly low mRNA levels of quorum sensing (QS) receptor genes compared to their cognate synthase genes (p<0.001). Crystal violet staining and scanning electron micrographs of CBF-2-treated biofilms showed lesser macrocolonies with remarkably simplified architecture. Cytotoxic evaluation of CBF-2 suggested a minute reduction in viability even at the highest tested concentration (1600 μg/ml, p<0.05).

Conclusion:

The present study indicated that eugenol-rich CBF-2 has potent anti-virulence and anti-biofilm activity against urinary catheter isolates and can be regarded as an alternative for treatment of catheter-associated urinary tract infections.

Coumarin Reduces Virulence and Biofilm Formation in Pseudomonas aeruginosa by Affecting Quorum Sensing, Type III Secretion and C-di-GMP Levels

As one of the major pathogens in wound infections, Pseudomonas aeruginosa produces several virulence factors and forms biofilms; these processes are under the regulation of various quorum sensing (QS) systems. Therefore, QS has been regarded as a promising target to treat P. aeruginosa infections. In the present study, we evaluated the effect of the plant-derived QS inhibitor coumarin on P. aeruginosa biofilms and virulence. Coumarin inhibited QS in the P. aeruginosa QSIS2 biosensor strain, reduced protease and pyocyanin production, and inhibited biofilm formation in microtiter plates in different P. aeruginosa strains. The effects of coumarin in inhibiting biofilm formation in an in vitro wound model and reducing P. aeruginosa virulence in the Lucilia sericata infection model were strain-dependent. Transcriptome analysis revealed that several key genes involved in the las, rhl, Pseudomonas quinolone signal (PQS), and integrated QS (IQS) systems were downregulated in coumarin-treated biofilms of P. aeruginosa PAO1. Coumarin also changed the expression of genes related to type III secretion and cyclic diguanylate (c-di-GMP) metabolism. The cellular c-di-GMP level of P. aeruginosa PAO1 and recent clinical P. aeruginosa strains was significantly reduced by coumarin. These results provide new evidence for the possible application of coumarin as an anti-biofilm and anti-virulence agent against P. aeruginosa in wound infections.

Association of furanone C-30 with biofilm formation & antibiotic resistance in Pseudomonas aeruginosa

Background & objectives

Pseudomonas aeruginosa is an opportunistic pathogen that can cause nosocomial bloodstream infections in humans. This study was aimed to explore the association of furanone C-30 with biofilm formation, quorum sensing (QS) system and antibiotic resistance in P. aeruginosa.

Methods

An in vitro model of P. aeruginosa bacterial biofilm was established using the standard P. aeruginosa strain (PAO-1). After treatment with 2.5 and 5 μg/ml of furanone C-30, the change of biofilm morphology of PAO-1 was observed, and the expression levels of QS-regulated virulence genes (lasB, rhlA and phzA2), QS receptor genes (lasR, rhlR and pqsR) as well as QS signal molecule synthase genes (lasI, rhlI, pqsE and pqsH) were determined. Besides, the AmpC expression was quantified in planktonic and mature biofilm induced by antibiotics.

Results

Furanone C-30 treatment significantly inhibited biofilm formation in a dose-dependent manner. With the increase of furanone C-30 concentration, the expression levels of lasB, rhlA, phzA2, pqsR, lasI, rhlI pqsE and pqsH significantly decreased in mature biofilm bacteria while the expression levels of lasR and rhlR markedly increased. The AmpC expression was significantly decreased in both planktonic and biofilm bacteria induced by imipenem and ceftazidime.

Interpretation & conclusions

Furanone C-30 may inhibit biofilm formation and antibiotic resistance in P. aeruginosa through regulating QS genes. The inhibitory effect of furanone C-30 on las system appeared to be stronger than that on rhl system. Further studies need to be done with different strains of P. aeruginosa to confirm our findings.

Pyocyanin Restricts Social Cheating in Pseudomonas aeruginosa

Quorum sensing (QS) in Pseudomonas aeruginosa coordinates the expression of virulence factors, such as exoproteases and siderophores, that are public goods utilized by the whole population of bacteria, regardless of whether they invested or not in their production. These public goods can be used by QS defective mutants for growth, and since these mutants do not contribute to public goods production, they are considered social cheaters. Pyocyanin is a phenazine that is a toxic, QS-controlled metabolite produced by P. aeruginosa. It is a redox-active compound and promotes the generation of reactive oxygen species; it also possesses antibacterial properties and increases fitness in competition with other bacterial species. Since QS-deficient individuals are less able to tolerate oxidative stress, we hypothesized that the pyocyanin produced by the wild-type population could promote selection of functional QS systems in this bacterium. Here, we demonstrate, using competition experiments and mathematical models, that, indeed, pyocyanin increases the fitness of the cooperative QS-proficient individuals and restricts the appearance of social cheaters. In addition, we also show that pyocyanin is able to select QS in other bacteria such as Acinetobacter baumannii.

Interference in Bacterial Quorum Sensing: A Biopharmaceutical Perspective

Numerous bacteria utilize molecular communication systems referred to as quorum sensing (QS) to synchronize the expression of certain genes regulating, among other aspects, the expression of virulence factors and the synthesis of biofilm. To achieve this process, bacteria use signaling molecules, known as autoinducers (AIs), as chemical messengers to share information. Naturally occurring strategies that interfere with bacterial signaling have been extensively studied in recent years, examining their potential to control bacteria. To interfere with QS, bacteria use quorum sensing inhibitors (QSIs) to block the action of AIs and quorum quenching (QQ) enzymes to degrade signaling molecules. Recent studies have shown that these strategies are promising routes to decrease bacterial pathogenicity and decrease biofilms, potentially enhancing bacterial susceptibility to antimicrobial agents including antibiotics and bacteriophages. The efficacy of QSIs and QQ enzymes has been demonstrated in various animal models and are now considered in the development of new medical devices against bacterial infections, including dressings, and catheters for enlarging the therapeutic arsenal against bacteria.

Glutathione Enhances Antibiotic Efficiency and Effectiveness of DNase I in Disrupting Pseudomonas aeruginosa Biofilms While Also Inhibiting Pyocyanin Activity, Thus Facilitating Restoration of Cell Enzymatic Activity, Confluence and Viability

Pyocyanin secreted by Pseudomonas aeruginosa is a virulence factor that damages epithelial cells during infection through the action of reactive oxygen species, however, little is known about its direct effect on biofilms. We demonstrated that pyocyanin-producing P. aeruginosa strains (PA14WT, DKN370, AES-1R, and AES-2) formed robust biofilms in contrast to the poorly formed biofilms of the pyocyanin mutant PA14ΔphzA-G and the low pyocyanin producer AES-1M. Addition of DNase I and reduced glutathione (GSH) significantly reduced biofilm biomass of pyocyanin-producing strains (P < 0.05) compared to non-pyocyanin producers. Subsequently we showed that a combined treatment comprising: GSH + DNase I + antibiotic, disrupted and reduced biofilm biomass up to 90% in cystic fibrosis isolates AES-1R, AES-2, LESB58, and LES431 and promoted lung epithelial cell (A549) recovery and growth. We also showed that exogenously added GSH restored A549 epithelial cell glutathione reductase activity in the presence of pyocyanin through recycling of GSSG to GSH and consequently increased total intracellular GSH levels, inhibiting oxidative stress, and facilitating cell growth and confluence. These outcomes indicate that GSH has multiple roles in facilitating a return to normal epithelial cell growth after insult by pyocyanin. With increased antibiotic resistance in many bacterial species, there is an urgency to establish novel antimicrobial agents. GSH is able to rapidly and comprehensively destroy P. aeruginosa associated biofilms while at a same time assisting in the recovery of host cells and re-growth of damaged tissue.

Nature to the natural rescue: Silencing microbial chats

Communication is the sole means by which effective networking and co-existence is accomplished amongst living beings. Microbes have their own chit-chats. Science has overheard these microbial gossips and have concluded that these aren't just informal communications, but carefully coordinated signals that plan their effective strategies. Tracking one such signal molecule, N-acyl homoserine lactone (AHL), led to a fundamental understanding to microbial quorum sensing (QS). Furtherance of research sought for ways to cut off communication between these virulent forms, so as to hinder their combinatorial attacks through quorum sensing inhibitors (QSIs). A clear understanding of the inhibitors of these microbial communication systems is vital to destroy their networking and co-working. The current review, consolidates the solutions for QSIs offered from natural sources against these micro components, that are capable of slaughtering even nature's most fit entity-man. The applications of effective out sourcing of this QSI technologies and the need for development are discussed. The importance of silencing this microbial chatter to various aspects of human life and their implications are discussed and elaborated.

Effect of Quorum Quenching Lactonase in Clinical Isolates of Pseudomonas aeruginosa and Comparison with Quorum Sensing Inhibitors

Pseudomonas aeruginosa is a Gram negative pathogenic bacterium involved in many human infections including otitis, keratitis, pneumonia, and diabetic foot ulcers. P. aeruginosa uses a communication system, referred to as quorum sensing (QS), to adopt a group behavior by synchronizing the expression of certain genes. Among the regulated traits, secretion of proteases or siderophores, motility and biofilm formation are mainly involved in the pathogenicity. Many efforts have been dedicated to the development of quorum sensing inhibitors (QSI) and quorum quenching (QQ) agents to disrupt QS. QQ enzymes have been particularly considered as they may act in a catalytic way without entering the cell. Here we focus on the lactonase SsoPox which was previously investigated for its ability to degrade the signaling molecules, acyl-homoserine lactones, in particular on the engineered variant SsoPox-W263I. We highlight the potential of SsoPox-W263I to inhibit the virulence of 51 clinical P. aeruginosa isolates from diabetic foot ulcers by decreasing the secretion of two virulence factors, proteases and pyocyanin, as well as biofilm formation. We further compared the effect of SsoPox-W263I to the comprehensively described QSI, 5-fluorouracil and C-30. We found the lactonase SsoPox-W263I to be significantly more effective than the tested QSI at their respective concentration optimum and to retain its activity after immobilization steps, paving the way for future therapeutic applications.

Is Quorum Sensing Interference a Viable Alternative to Treat Pseudomonas aeruginosa Infections?

Quorum sensing (QS) coordinates the expression of multiple virulence factors in Pseudomonas aeruginosa; hence its inhibition has been postulated as a new alternative to treat its infections. In particular, QS interference approaches claim that they attenuate bacterial virulence without directly decreasing bacterial growth and suggest that in vivo the immune system would control the infections. Moreover, since in vitro experiments performed in rich medium demonstrate that interfering with QS decreases the production of virulence factors without affecting bacterial growth it was assumed than in vivo therapies will minimize the selection of resistant strains. Therefore, the underlying assumptions toward an effective implementation of a successful Quorum sensing interference (QSI) therapy for treating P. aeruginosa infections are that (i) QS only exerts important effects in the regulation of virulence genes but it does not affect metabolic processes linked to growth, (ii) the expression of virulence factors is only positively regulated by QS, (iii) inhibition of virulence factors in vivo do not affect bacterial growth, (iv) the immune system of the infected patients will be able to get rid of the infections, and (v) the therapy will be effective in the strains that are actively producing the infections. Nevertheless, for QSI in P. aeruginosa, substantial experimental evidence against the validity of most of these assumptions has accumulated during the past years, suggesting that a far better understanding of its virulence and its behavior during infections is needed in order to design truly solid QSI therapeutic alternatives to combat this remarkable pathogen.

Quorum Signal Inhibitors and Their Potential Use against Fish Diseases

Quorum sensing (QS) is a process of bacterial communication used to control group behaviors, including bioluminescence, virulence factor production, biofilm formation, and biofilm antimicrobial tolerance. Many aquatic bacterial pathogens such as Aeromonas, Vibrio, and Edwardsiella spp. use QS to regulate virulence factor production. The disruption of QS has been shown to be an effective strategy in the competition between higher organisms and bacteria and more recently between bacterial species. For this reason, QS disruption has been proposed as a strategy to prevent bacterial pathogenicity. In this review, we summarize the current literature and illustrate the value of QS inhibitors in controlling virulence production in aquatic bacterial pathogens. This represents a new, nonantibiotic strategy to combat fish diseases. Received August 11, 2015; accepted January 26, 2016.

DNA-crosslinker cisplatin eradicates bacterial persister cells

For all bacteria, nearly every antimicrobial fails since a subpopulation of the bacteria enter a dormant state known as persistence, in which the antimicrobials are rendered ineffective due to the lack of metabolism. This tolerance to antibiotics makes microbial infections the leading cause of death worldwide and makes treating chronic infections, including those of wounds problematic. Here, we show that the FDA-approved anti-cancer drug cisplatin [cis-diamminodichloroplatinum(II)], which mainly forms intra-strand DNA crosslinks, eradicates Escherichia coli K-12 persister cells through a growth-independent mechanism. Additionally, cisplatin is more effective at killing Pseudomonas aeruginosa persister cells than mitomycin C, which forms inter-strand DNA crosslinks, and cisplatin eradicates the persister cells of several pathogens including enterohemorrhagic E. coli, Staphylococcus aureus, and P. aeruginosa. Cisplatin was also highly effective against clinical isolates of S. aureus and P. aeruginosa. Therefore, cisplatin has broad spectrum activity against persister cells. Biotechnol. Bioeng. 2016;113: 1984-1992. © 2016 Wiley Periodicals, Inc.

Going beyond the Control of Quorum-Sensing to Combat Biofilm Infections

Most bacteria attach to surfaces where they form a biofilm, cells embedded in a complex matrix of polymers. Cells in biofilms are much better protected against noxious agents than free-living cells. As a consequence it is very difficult to control pathogens with antibiotics in biofilm infections and novel targets are urgently needed. One approach aims at the communication between cells to form and to maintain a biofilm, a process called quorum-sensing. Water soluble small-sized molecules mediate this process and a number of antagonists of these compounds have been found. In this review natural compounds and synthetic drugs which do not interfere with the classical quorum-sensing compounds are discussed. For some of these compounds the targets are still not known, but others interfere with the formation of exopolysaccharides, virulence factors, or cell wall synthesis or they start an internal program of biofilm dispersal. Some of their targets are more conserved among pathogens than the receptors for quorum sensing autoinducers mediating quorum-sensing, enabling a broader application of the drug. The broad spectrum of mechanisms, the diversity of bioactive compounds, their activity against several targets, and the conservation of some targets among bacterial pathogens are promising aspects for several clinical applications of this type of biofilm-controlling compound in the future.