Exploiting quorum sensing to confuse bacterial pathogens

Exploring Phenolic Compounds as Quorum Sensing Inhibitors in Foodborne Bacteria

The emergence of multidrug-resistant bacteria stimulates the search for new substitutes to traditional antimicrobial agents, especially molecules with antivirulence properties, such as those that interfere with quorum sensing (QS). This study aimed to evaluate the potential of phenolic compounds for QS inhibition in a QS biosensor strain (Chromobacterium violaceum) and three foodborne bacterial species (Aeromonas hydrophila, Salmonella enterica serovar Montevideo, and Serratia marcescens). Initially, an in silico molecular docking study was performed to select the compounds with the greatest potential for QS inhibition, using structural variants of the CviR QS regulator of C. violaceum as target. Curcumin, capsaicin, resveratrol, gallic acid, and phloridizin presented good affinity to at least four CviR structural variants. These phenolic compounds were tested for antimicrobial activity, inhibition of biofilm formation, and anti-QS activity. The antimicrobial activity when combined with kanamycin was also assessed. Curcumin, capsaicin, and resveratrol inhibited up to 50% of violacein production by C. violaceum. Biofilm formation was inhibited by resveratrol up to 80% in A. hydrophila, by capsaicin and curcumin up to 40% in S. Montevideo and by resveratrol and capsaicin up to 60% in S. marcescens. Curcumin completely inhibited swarming motility in S. marcescens. Additionally, curcumin and resveratrol increased the sensitivity of the tested bacteria to kanamycin. These results indicate that curcumin and resveratrol at concentrations as low as 6μM are potential quorum sensing inhibitors besides having antimicrobial properties at higher concentrations, encouraging applications in the food and pharmaceutical industries.

Mitigation of Pseudomonas syringae virulence by signal inactivation

Pseudomonas syringae is an important plant pathogen of many valuable crops worldwide, with more than 60 identified pathovars. The phytotoxins produced by these organisms were related to the severity of the damage caused to the plant. An emerging strategy to treat bacterial infections relies on interference with their signaling systems. In this study, we investigated P. syringae pv. syringae, which produces the virulence factor mangotoxin that causes bacterial apical necrosis on mango leaves. A previously unknown signaling molecule named leudiazen was identified, determined to be unstable and volatile, and responsible for mangotoxin production. A strategy using potassium permanganate, compatible with organic farming, was developed to degrade leudiazen and thus to attenuate the pathogenicity of P. syringae pv. syringae.

Characterization of Pseudomonas aeruginosa Quorum Sensing Inhibitors from the Endophyte Lasiodiplodia venezuelensis and Evaluation of Their Antivirulence Effects by Metabolomics

The opportunistic pathogen Pseudomonas aeruginosa is one of the "critical priority pathogens" due to its multidrug resistance to a wide range of antibiotics. Its ability to invade and damage host tissues is due to the use of quorum sensing (QS) to collectively produce a plethora of virulence factors. Inhibition of QS is an attractive strategy for new antimicrobial agents because it disrupts the initial events of infection without killing the pathogen. Highly diverse microorganisms as endophytes represent an under-explored source of bioactive natural products, offering opportunities for the discovery of novel QS inhibitors (QSI). In the present work, the objective was to explore selective QSIs within a unique collection of fungal endophytes isolated from the tropical palm Astrocaryum sciophilum. The fungi were cultured, extracted, and screened for their antibacterial and specific anti-QS activities against P. aeruginosa. The endophytic strain Lasiodiplodia venezuelensis was prioritized for scaled-up fractionation for its selective activity, leading to the isolation of eight compounds in a single step. Among them, two pyran-derivatives were found to be responsible for the QSI activity, with an effect on some QS-regulated virulence factors. Additional non-targeted metabolomic studies on P. aeruginosa documented their effects on the production of various virulence-related metabolites.

Interkingdom Signaling Interference: The Effect of Plant-Derived Small Molecules on Quorum Sensing in Plant-Pathogenic Bacteria

In the battle between bacteria and plants, bacteria often use a population density-dependent regulatory system known as quorum sensing (QS) to coordinate virulence gene expression. In response, plants use innate and induced defense mechanisms that include low-molecular-weight compounds, some of which serve as antivirulence agents by interfering with the QS machinery. The best-characterized QS system is driven by the autoinducer N-acyl-homoserine lactone (AHL), which is produced by AHL synthases (LuxI homologs) and perceived by response regulators (LuxR homologs). Several plant compounds have been shown to directly inhibit LuxI or LuxR. Gaining atomic-level insight into their mode of action and how they interfere with QS enzymes supports the identification and design of novel QS inhibitors.Such information can be gained by combining experimental work with molecular modeling and docking simulations. The summary of these findings shows that plant-derived compounds act as interkingdom cues and that these allomones specifically target bacterial communication systems.

Quorum-sensing regulation of virulence factors in bacterial biofilm

Chronic polymicrobial wound infections are often characterized by the presence of bacterial biofilms. They show considerable structural and functional heterogeneity, which influences the choice of antimicrobial therapy and wound healing dynamics. The hallmarks of biofilm-associated bacterial infections include elevated antibiotic resistance and extreme pathogenicity. Biofilm helps bacteria to evade the host defense mechanisms and persist longer in the host. Quorum-sensing (QS)-mediated cell signaling primarily regulates biofilm formation in chronic infections and plays a major role in eliciting virulence. This review focuses on the QS mechanisms of two major bacterial pathogens, Staphylococcus aureus and Pseudomonas aeruginosa and explains how they interact in the wound microenvironment to regulate biofilm development and virulence. The review also provides an insight into the treatment modalities aimed at eradicating polymicrobial biofilms. This information will help us develop better diagnostic modalities and devise effective treatment regimens to successfully manage and overcome severe life-threatening bacterial infections.

Nanotargeting of Resistant Infections with a Special Emphasis on the Biofilm Landscape

Bacterial resistance to antimicrobial compounds is a growing concern in medical and public health circles. Overcoming the adaptable and duplicative resistance mechanisms of bacteria requires chemistry-based approaches. Engineered nanoparticles (NPs) now offer unique advantages toward this effort. However, most in situ infections (in humans) occur as attached biofilms enveloped in a protective surrounding matrix of extracellular polymers, where survival of microbial cells is enhanced. This presents special considerations in the design and deployment of antimicrobials. Here, we review recent efforts to combat resistant bacterial strains using NPs and, then, explore how NP surfaces may be specifically engineered to enhance the potency and delivery of antimicrobial compounds. Special NP-engineering challenges in the design of NPs must be overcome to penetrate the inherent protective barriers of the biofilm and to successfully deliver antimicrobials to bacterial cells. Future challenges are discussed in the development of new antibiotics and their mechanisms of action and targeted delivery via NPs.

Can Eucalyptol Replace Antibiotics?

One of the primary reasons for the search for new antimicrobial agents is the increasing and spreading resistance of microorganisms to previously used drugs. This is particularly important in the case of rapidly progressing infections that require the rapid administration of an appropriately selected antibiotic. However, along with the administration of antibiotics, complications in the disease-weakened body may arise in the form of systemic mycoses, viral infections, and protozoan infections. Therefore, there is an increasing interest among researchers focusing on the use of naturally occurring terpenic compounds in stand-alone or combined therapies with antibiotics. In this publication, the aim of our work is to present the results of a literature review on the antimicrobial activity of eucalyptol.

Biocontrol of Biofilm Formation: Jamming of Sessile-Associated Rhizobial Communication by Rhodococcal Quorum-Quenching

Biofilms are complex structures formed by a community of microbes adhering to a surface and/or to each other through the secretion of an adhesive and protective matrix. The establishment of these structures requires a coordination of action between microorganisms through powerful communication systems such as quorum-sensing. Therefore, auxiliary bacteria capable of interfering with these means of communication could be used to prevent biofilm formation and development. The phytopathogen Rhizobium rhizogenes, which causes hairy root disease and forms large biofilms in hydroponic crops, and the biocontrol agent Rhodococcus erythropolis R138 were used for this study. Changes in biofilm biovolume and structure, as well as interactions between rhizobia and rhodococci, were monitored by confocal laser scanning microscopy with appropriate fluorescent biosensors. We obtained direct visual evidence of an exchange of signals between rhizobia and the jamming of this communication by Rhodococcus within the biofilm. Signaling molecules were characterized as long chain (C₁₄) N-acyl-homoserine lactones. The role of the Qsd quorum-quenching pathway in biofilm alteration was confirmed with an R. erythropolis mutant unable to produce the QsdA lactonase, and by expression of the qsdA gene in a heterologous host, Escherichia coli. Finally, Rhizobium biofilm formation was similarly inhibited by a purified extract of QsdA enzyme.

Novel Bifunctional Acylase from Actinoplanes utahensis: A Versatile Enzyme to Synthesize Antimicrobial Compounds and Use in Quorum Quenching Processes

Many intercellular communication processes, known as quorum sensing (QS), are regulated by the autoinducers N-acyl-l-homoserine lactones (AHLs) in Gram-negative bacteria. The inactivation of these QS processes using different quorum quenching (QQ) strategies, such as enzymatic degradation of the autoinducers or the receptor blocking with non-active analogs, could be the basis for the development of new antimicrobials. This study details the heterologous expression, purification, and characterization of a novel N-acylhomoserine lactone acylase from Actinoplanes utahensis NRRL 12052 (AuAHLA), which can hydrolyze different natural penicillins and N-acyl-homoserine lactones (with or without 3-oxo substitution), as well as synthesize them. Kinetic parameters for the hydrolysis of a broad range of substrates have shown that AuAHLA prefers penicillin V, followed by C₁₂-HSL. In addition, AuAHLA inhibits the production of violacein by Chromobacterium violaceum CV026, confirming its potential use as a QQ agent. Noteworthy, AuAHLA is also able to efficiently synthesize penicillin V, besides natural AHLs and phenoxyacetyl-homoserine lactone (POHL), a non-natural analog of AHLs that could be used to block QS receptors and inhibit signal of autoinducers, being the first reported AHL acylase capable of synthesizing AHLs.

Charting the landscape of RNA polymerases to unleash their potential in strain improvement

One major mission of microbial cell factory is overproduction of desired chemicals. To this end, it is necessary to orchestrate enzymes that affect metabolic fluxes. However, only modification of a small number of enzymes in most cases cannot maximize desired metabolites, and global regulation is required. Of myriad enzymes influencing global regulation, RNA polymerase (RNAP) may be the most versatile enzyme in biological realm because it not only serves as the workhorse of central dogma but also participates in a plethora of biochemical events. In fact, recent years have witnessed extensive exploitation of RNAPs for phenotypic engineering. While a few impressive reviews showcase the structures and functionalities of RNAPs, this review not only summarizes the state-of-the-art advance in the structures of RNAPs but also points out their enormous potentials in metabolic engineering and synthetic biology. This review aims to provide valuable insights for strain improvement.

Invasion of Serratia proteamaculans is regulated by the sprI gene encoding AHL synthase

Quorum Sensing (QS) system regulates gene expression in response to a change in the density of the bacterial population. Facultative pathogen Serratia proteamaculans 94 has a LuxI/LuxR type QS system consisting of regulatory protein SprR and AHL synthase SprI. Invasive activity of these bacteria appears at the stationary growth phase corresponding to a maximal density of the bacterial population in vitro. To evaluate the contribution of QS system of S. proteamaculans 94 to the regulation of invasive activity, in this work, S. proteamaculans SprI(-) mutant carrying the inactivated AHL synthase gene was used. Inactivation of the AHL synthase sprI gene resulted in a more than fourfold increase in the invasive activity of S. proteamaculans preceded by the increased adhesion of bacteria to the cell surface. This effect correlated with the increased expression of the outer membrane protein ompX gene and the decrease in the activity of intrabacterial protease protealysin, whose substrate is OmpX. The inverse correlation between activity of protealysin and bacterial invasion was also observed in the model experiments under the iron-limiting culture conditions. These results show that QS system regulates the S. proteamaculans invasion. This regulation can involve changes both in the protealysin activity and in the level of the ompX gene transcription.

Epigallocatechin gallate and Lactobacillus plantarum culture supernatants exert bactericidal activity and reduce biofilm formation in Clostridium perfringens

Clostridium perfringens forms biofilms and spores that are a source of food contamination. In this study, the antibacterial activities of Lactobacillus plantarum culture supernatants (LP-S), LP-S fractions, and the plant-derived compound epigallocatechin gallate (EG) were evaluated. Specifically, their effects on the viability and biofilm-forming ability of C. perfringens were assessed. Moreover, the expression of quorum sensing-regulated genes associated with the pathogenesis of this microorganism and that of genes involved in biofilm formation was also investigated. The results showed that both EG and the LP-S exerted bactericidal activity against all C. perfringens strains tested. The minimal bactericidal concentration (MBC) of EG was 75 µg/mL for all strains but ranged from 61 to 121 µg of total protein per mL for LP-S. EG exerted only minor effects on biofilm formation, whereas LP-S, particularly its 10 and 30 K fractions, significantly reduced the biofilm-forming ability of all the strains. The antibiofilm activity of LP-S was lost following preincubation with proteases, suggesting that it was mediated by a proteinaceous molecule. The treatment of C. perfringens with either EG or LP-S did not change the transcript levels of two CpAL (C. perfringens quorum-sensing Agr-like system)-related genes, agrB and agrD, which are known to be involved in the regulation of biofilms, suggesting that LP-S exerted its biofilm inhibitory activity downstream of CpAL signaling. In summary, we demonstrated the bactericidal activity of EG and LP-S against C. perfringens and antibiofilm activity of LP-S at a subinhibitory dose. Our results suggested that these compounds can be further explored for food safety applications to control agents such as C. perfringens.

Gram-Negative Bacteria Holding Together in a Biofilm: The Acinetobacter baumannii Way

Bacterial biofilms are a serious public-health problem worldwide. In recent years, the rates of antibiotic-resistant Gram-negative bacteria associated with biofilm-forming activity have increased worrisomely, particularly among healthcare-associated pathogens. Acinetobacter baumannii is a critically opportunistic pathogen, due to the high rates of antibiotic resistant strains causing healthcare-acquired infections (HAIs). The clinical isolates of A. baumannii can form biofilms on both biotic and abiotic surfaces; hospital settings and medical devices are the ideal environments for A. baumannii biofilms, thereby representing the main source of patient infections. However, the paucity of therapeutic options poses major concerns for human health infections caused by A. baumannii strains. The increasing number of multidrug-resistant A. baumannii biofilm-forming isolates in association with the limited number of biofilm-eradicating treatments intensify the need for effective antibiofilm approaches. This review discusses the mechanisms used by this opportunistic pathogen to form biofilms, describes their clinical impact, and summarizes the current and emerging treatment options available, both to prevent their formation and to disrupt preformed A. baumannii biofilms.

Streptococcus pyogenes ("Group A Streptococcus"), a Highly Adapted Human Pathogen-Potential Implications of Its Virulence Regulation for Epidemiology and Disease Management

Streptococcus pyogenes (group A streptococci; GAS) is an exclusively human pathogen. It causes a variety of suppurative and non-suppurative diseases in people of all ages worldwide. Not all can be successfully treated with antibiotics. A licensed vaccine, in spite of its global importance, is not yet available. GAS express an arsenal of virulence factors responsible for pathological immune reactions. The transcription of all these virulence factors is under the control of three types of virulence-related regulators: (i) two-component systems (TCS), (ii) stand-alone regulators, and (iii) non-coding RNAs. This review summarizes major TCS and stand-alone transcriptional regulatory systems, which are directly associated with virulence control. It is suggested that this treasure of knowledge on the genetics of virulence regulation should be better harnessed for new therapies and prevention methods for GAS infections, thereby changing its global epidemiology for the better.

Approaches for the inhibition and elimination of microbial biofilms using macromolecular agents

Biofilms are complex three-dimensional structures formed at interfaces by the vast majority of bacteria and fungi. These robust communities have an important detrimental impact on a wide range of industries and other facets of our daily lives, yet their removal is challenging owing to the high tolerance of biofilms towards conventional antimicrobial agents. This key issue has driven an urgent search for new innovative antibiofilm materials. Amongst these emerging approaches are highly promising materials that employ aqueous-soluble macromolecules, including peptides, proteins, synthetic polymers, and nanomaterials thereof, which exhibit a range of functionalities that can inhibit biofilm formation or detach and destroy organisms residing within established biofilms. In this Review, we outline the progress made in inhibiting and removing biofilms using macromolecular approaches, including a spotlight on cutting-edge materials that respond to environmental stimuli for "on-demand" antibiofilm activity, as well as synergistic multi-action antibiofilm materials. We also highlight materials that imitate and harness naturally derived species to achieve new and improved biomimetic and biohybrid antibiofilm materials. Finally, we share some speculative insights into possible future directions for this exciting and highly significant field of research.

Trans-Cinnamaldehyde Attenuates Enterococcus faecalis Virulence and Inhibits Biofilm Formation

Enterococcus faecalis as an important nosocomial pathogen is critically implicated in the pathogenesis of endocarditis, urinary tract, and persistent root canal infections. Its major virulence attributes (biofilm formation, production of proteases, and hemolytic toxins) enable it to cause extensive host tissue damage. With the alarming increase in enterococcal resistance to antibiotics, novel therapeutics are required to inhibit E. faecalis biofilm formation and virulence. Trans-cinnamaldehyde (TC), the main phytochemical in cinnamon essential oils, has demonstrated promising activity against a wide range of pathogens. Here, we comprehensively investigated the effect of TC on planktonic growth, biofilm formation, proteolytic and hemolytic activities, as well as gene regulation in E. faecalis. Our findings revealed that sub-inhibitory concentrations of TC reduced biofilm formation, biofilm exopolysaccharides, as well as its proteolytic and hemolytic activities. Mechanistic studies revealed significant downregulation of the quorum sensing fsr locus and downstream gelE, which are major virulence regulators in E. faecalis. Taken together, our study highlights the potential of TC to inhibit E. faecalis biofilm formation and its virulence.

Discovery of novel β-turn mimetic-based peptides as novel quorum sensing inhibitors of gram-negative bacteria

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

Friends or Foes-Microbial Interactions in Nature

Simple Summary

Microorganisms like bacteria, archaea, fungi, microalgae, and viruses mostly form complex interactive networks within the ecosystem rather than existing as single planktonic cells. Interactions among microorganisms occur between the same species, with different species, or even among entirely different genera, families, or even domains. These interactions occur after environmental sensing, followed by converting those signals to molecular and genetic information, including many mechanisms and classes of molecules. Comprehensive studies on microbial interactions disclose key strategies of microbes to colonize and establish in a variety of different environments. Knowledge of the mechanisms involved in the microbial interactions is essential to understand the ecological impact of microbes and the development of dysbioses. It might be the key to exploit strategies and specific agents against different facing challenges, such as chronic and infectious diseases, hunger crisis, pollution, and sustainability.

Abstract

Microorganisms are present in nearly every niche on Earth and mainly do not exist solely but form communities of single or mixed species. Within such microbial populations and between the microbes and a eukaryotic host, various microbial interactions take place in an ever-changing environment. Those microbial interactions are crucial for a successful establishment and maintenance of a microbial population. The basic unit of interaction is the gene expression of each organism in this community in response to biotic or abiotic stimuli. Differential gene expression is responsible for producing exchangeable molecules involved in the interactions, ultimately leading to community behavior. Cooperative and competitive interactions within bacterial communities and between the associated bacteria and the host are the focus of this review, emphasizing microbial cell–cell communication (quorum sensing). Further, metagenomics is discussed as a helpful tool to analyze the complex genomic information of microbial communities and the functional role of different microbes within a community and to identify novel biomolecules for biotechnological applications.

Nitrate- and Nitrite-Sensing Histidine Kinases: Function, Structure, and Natural Diversity

Under anaerobic conditions, bacteria may utilize nitrates and nitrites as electron acceptors. Sensitivity to nitrous compounds is achieved via several mechanisms, some of which rely on sensor histidine kinases (HKs). The best studied nitrate- and nitrite-sensing HKs (NSHKs) are NarQ and NarX from Escherichia coli. Here, we review the function of NSHKs, analyze their natural diversity, and describe the available structural information. In particular, we show that around 6000 different NSHK sequences forming several distinct clusters may now be found in genomic databases, comprising mostly the genes from Beta- and Gammaproteobacteria as well as from Bacteroidetes and Chloroflexi, including those from anaerobic ammonia oxidation (annamox) communities. We show that the architecture of NSHKs is mostly conserved, although proteins from Bacteroidetes lack the HAMP and GAF-like domains yet sometimes have PAS. We reconcile the variation of NSHK sequences with atomistic models and pinpoint the structural elements important for signal transduction from the sensor domain to the catalytic module over the transmembrane and cytoplasmic regions spanning more than 200 Å.

Exopolysaccharides as Antimicrobial Agents: Mechanism and Spectrum of Activity

Exopolysaccharides (EPSs) are metabolites synthesized and excreted by a variety of microorganisms, including lactic acid bacteria (LAB). EPS serve several biological functions such as interactions between bacteria and their environments, protection against hostile conditions including dehydration, the alleviation of the action of toxic compounds (bile salts, hydrolyzing enzymes, lysozyme, gastric, and pancreatic enzymes, metal ions, antibiotics), and stresses (changing pH, osmolarity), and evasion of the immune response and phage attack. Bacterial EPSs are considered valuable by the food, pharmaceutical, and nutraceutical industries, owing to their health-promoting benefits and rheological impacts. Numerous studies have reported the unusual antimicrobial activities of various EPS against a wide variety of pathogenic microbes (bacteria, virus, and fungi). This review aims to provide a comprehensive examination of the in vitro and in vivo antimicrobial activities of different EPSs, mainly against foodborne bacterial, fungal, and viral pathogens. The mechanism of EPS action against these pathogens as well as the methods used to measure antimicrobial activities are critically reviewed.

Vertical and horizontal quorum-sensing-based multicellular communications

Quorum sensing (QS) plays an important role in both natural and synthetic microbial systems. The complexity of QS entails multilayer controls, biomolecular crosstalk, and population-based interactions. In this review, we divide complex QS-based interactions into vertical and horizontal interactions. With respect to the former, we discuss QS-based interactions among phages, bacteria, and hosts in natural microbial systems, which are based on various QS signals and hormones. With regard to the latter, we highlight manipulations of QS-based interactions for multicomponent synthetic microbial consortia. We further present the recent and emerging applications of manipulating these interactions (collectively referred to as 'QS communication networks') in natural and synthetic microbiota. Finally, we identify key challenges in engineering diverse QS communication networks for various future applications.

Effects of Gentamicin-Loaded Chitosan-ZnO Nanocomposite on Quorum-Sensing Regulation of Pseudomonas Aeruginosa

Cell density-based intercellular signaling mechanism is known as Quorum sensing (QS); it serves a significant role in regulating the pathogenic factors. The objective of the present study was to assess the influence of chitosan-zinc oxide nanocomposite (CH-ZnO nanocomposite), alone and in combination with gentamicin, on the sensitivity to hydrogen peroxide (H₂O₂), the production of pathogenic factors and QS-regulated genes of Pseudomonas aeruginosa. The efficacy of the minimum inhibitory concentration (MIC) and 1/4 MIC of the CH-ZnO nanocomposite, alone and in combination with gentamicin, on the sensitivity to H₂O₂, pyocyanin secretion, swarming and twitching motilities was evaluated. In addition, the expression of some QS-regulated genes including rhlI, rhlR, lasI and lasR genes was measured by Real-time quantitative PCR (RT-qPCR) following exposure to the nanocomposite. The results demonstrated that at MIC concentrations, the gentamicin-loaded CH-ZnO nanocomposite significantly inhibited QS-regulated phenotypes such as pyocyanin secretion (82.4%), swarming (76%) and twitching (73.6%) motilities; further it increased the inhibition growth zone (134.5%), as well as, at 1/4 MIC concentration decreased the expression of lasI (72%), lasR (78%), rhlI (76%) and rhlR (82%) genes; as compared to untreated P. aeruginosa PAO1 (P < 0.05). Our results also demonstrated that the CH-ZnO nanocomposite combined with gentamicin could be a potential innovative candidate, which could be broadly applied in the treatment of P. aeruginosa infections.

Quorum quenching activity of Andrographis paniculata (Burm f.) Nees andrographolide compounds on metallo-β-lactamase-producing clinical isolates of Pseudomonas aeruginosa PA22 and PA247 and their effect on lasR gene expression

Andrographis paniculata (Burm f.) Nees is a tropical plant native to Southeast Asia that has been used as an effective remedy for a wide variety of illnesses in traditional Chinese and Ayurvedic medicine. The antimicrobial activity of its crude extract had been shown to be due to its quorum quenching activity. The study determined the effect of purified extracted compounds from the leaf of A. paniculata, namely: andrographolide, 14-deoxyandrographolide, 14-deoxy-12-hydroxyandrographolide and neoandrographolide on quorum sensing-mediated virulence mechanisms in clinical isolates of metallo-β-lactamase (MβL)-producing Pseudomonas aeruginosa. Their effect on the expression of the lasR gene, which codes for LasR, a transcription activator protein of the quorum sensing system in P. aeruginosa was also determined using RT-qPCR. All the pure compounds significantly decreased the biofilm formation, protease production and swarming motility of the P. aeruginosa isolates compared to the untreated controls (p < 0.05). Results of the RT-qPCR assay showed that all compounds significantly downregulated the expression of lasR compared to the untreated control (p < 0.05), supporting the position that the lower virulence activities of the treated group were due to quorum quenching activity of the pure compounds. Multiple comparisons using Tukey's HSD analysis revealed that the means of the relative expression of lasR of the isolates treated with the different compounds were not significantly different from each other (p > 0.05), suggesting equal potencies. Results show the potential of the isolated pure compounds from A. paniculata for use as antimicrobial agents as a result of their quorum quenching activities.

The impact of quorum sensing on the modulation of phage-host interactions

Bacteriophages are the most diverse and abundant biological entities on the Earth and require host bacteria to replicate. Because of this obligate relationship, in addition to the challenging conditions of surrounding environments, phages must integrate information about extrinsic and intrinsic factors when infecting their host. This integration helps to determine whether the infection becomes lytic or lysogenic, which likely influences phage spreading and long-term survival. Although a variety of environmental and physiological clues are known to modulate lysis-lysogeny decisions, the social interplay among phages and host populations has been overlooked until recently. A growing body of evidence indicates that cell-cell communication in bacteria and, more recently, peptide-based communication among phage-phage populations, affect phage-host interactions by controlling phage lysis-lysogeny decisions and phage counter-defensive strategies in bacteria. Here, we explore and discuss the role of signal molecules as well as quorum sensing and quenching factors that mediate phage-host interactions. Our aim is to provide an overview of population-dependent mechanisms that influence phage replication, and how social communication may affect the dynamics and evolution of microbial communities, including their implications in phage therapy.

The New Antibacterial Properties of the Plants: Quo vadis Studies of Anti-virulence Phytochemicals?

The recent increase in bacterial resistance to antibiotics has motivated the resurgence of the study of natural antimicrobial products. For centuries, plants have been recognized for their bactericidal properties. However, in the last two decades, it has been reported that several plant derived metabolites at growth subinhibitory concentrations also tend to have anti-virulence properties, since they reduce the expression of factors that cause damage and the establishment of pathogenic bacteria. In this area of study, plants have been positioned as one of the main natural sources of anti-virulence molecules, but only a small portion of the plant species that exist have been investigated. Also, anti-virulence studies have been primarily focused on analyzing the ability of extracts and compounds to inhibit quorum sensing and biofilms formation in vitro. This mini-review discusses the current panorama, the trends in the study of anti-virulence phytochemicals, as well as their potential for the development of antibacterial therapies.

EGCG-Mediated Potential Inhibition of Biofilm Development and Quorum Sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa), one of the dangerous multidrug resistance pathogens, orchestrates virulence factors production through quorum sensing (QS). Since the exploration of QS inhibitors, targeting virulence to circumvent bacterial pathogenesis without causing significant growth inhibition is a promising approach to treat P. aeruginosa infections. The present study has evaluated the anti-QS and anti-infective activity of epigallocatechin-3-gallate (EGCG), a bioactive ingredient of the traditional green tea, against P. aeruginosa. EGCG showed significant inhibitory effects on the development of biofilm, protease, elastase activity, swimming, and swarming motility, which was positively related to the production of C4-AHL. The expression of QS-related and QS-regulated virulence factors genes was also evaluated. Quantitative PCR analysis showed that EGCG significantly reduced the expression of las, rhl, and PQS genes and was highly correlated with the alterations of C4-AHL production. In-vivo experiments demonstrated that EGCG treatment reduced P. aeruginosa pathogenicity in Caenorhabditis elegans (C. elegans). EGCG increased the survival of C. elegans by 23.25%, 30.04%, and 36.35% in a dose-dependent manner. The findings of this study strongly suggest that EGCG could be a potential candidate for QS inhibition as an anti-virulence compound against bacterial infection.

Design, synthesis, and evaluation of transition-state analogs as inhibitors of the bacterial quorum sensing autoinducer synthase CepI

Quorum sensing is a bacterial signaling system that involves the synthesis, secretion and detection of signal molecules called autoinducers. The main autoinducer in Gram-negative bacteria are acylated homoserine lactones, produced by the LuxI family of autoinducer synthases and detected by the LuxR family of autoinducer receptors. Quorum sensing allows for changes in gene expression and bacterial behaviors in a coordinated, cell density dependent manner. Quorum sensing controls the expression of virulence factors in some human pathogens, making quorum sensing an antibacterial drug target. Here we describe the design and synthesis of transition-state analogs of the autoinducer synthase enzymatic reaction and the evaluation of these compounds as inhibitors of the synthase CepI. One such compound potently inhibits CepI and constitutes a new type of inhibitor against this underdeveloped antibacterial target.

Enzyme-Primed Native Chemical Ligation Produces Autoinducing Cyclopeptides in Clostridia

Clostridia coordinate many important processes such as toxin production, infection, and survival by density‐dependent communication (quorum sensing) using autoinducing peptides (AIPs). Although clostridial AIPs have been proposed to be (thio)lactone‐containing peptides, their true structures remain elusive. Here, we report the genome‐guided discovery of an AIP that controls endospore formation in Ruminiclostridium cellulolyticum. Through a combination of chemical synthesis and chemical complementation assays with a mutant strain, we reveal that the genuine chemical mediator is a homodetic cyclopeptide (cAIP). Kinetic analyses indicate that the mature cAIP is produced via a cryptic thiolactone intermediate that undergoes a rapid S→N acyl shift, in a manner similar to intramolecular native chemical ligation (NCL). Finally, by implementing a chemical probe in a targeted screen, we show that this novel enzyme‐primed, intramolecular NCL is a widespread feature of clostridial AIP biosynthesis.

Cross-kingdom inhibition of bacterial virulence and communication by probiotic yeast metabolites

BACKGROUND

Probiotic milk-fermented microorganism mixtures (e.g., yogurt, kefir) are perceived as contributing to human health, and possibly capable of protecting against bacterial infections. Co-existence of probiotic microorganisms are likely maintained via complex biomolecular mechanisms, secreted metabolites mediating cell-cell communication, and other yet-unknown biochemical pathways. In particular, deciphering molecular mechanisms by which probiotic microorganisms inhibit proliferation of pathogenic bacteria would be highly important for understanding both the potential benefits of probiotic foods as well as maintenance of healthy gut microbiome.

RESULTS

The microbiome of a unique milk-fermented microorganism mixture was determined, revealing a predominance of the fungus Kluyveromyces marxianus. We further identified a new fungus-secreted metabolite-tryptophol acetate-which inhibits bacterial communication and virulence. We discovered that tryptophol acetate blocks quorum sensing (QS) of several Gram-negative bacteria, particularly Vibrio cholerae, a prominent gut pathogen. Notably, this is the first report of tryptophol acetate production by a yeast and role of the molecule as a signaling agent. Furthermore, mechanisms underscoring the anti-QS and anti-virulence activities of tryptophol acetate were elucidated, specifically down- or upregulation of distinct genes associated with V. cholerae QS and virulence pathways.

CONCLUSIONS

This study illuminates a yet-unrecognized mechanism for cross-kingdom inhibition of pathogenic bacteria cell-cell communication in a probiotic microorganism mixture. A newly identified fungus-secreted molecule-tryptophol acetate-was shown to disrupt quorum sensing pathways of the human gut pathogen V. cholerae. Cross-kingdom interference in quorum sensing may play important roles in enabling microorganism co-existence in multi-population environments, such as probiotic foods and the gut microbiome. This discovery may account for anti-virulence properties of the human microbiome and could aid elucidating health benefits of probiotic products against bacterially associated diseases. Video Abstract.

Bacterial biofilm-derived antigens: a new strategy for vaccine development against infectious diseases

INTRODUCTION

Microorganisms can develop into a social organization known as biofilms and these communities can be found in virtually all types of environment on earth. In biofilms, cells grow as multicellular communities held together by a self-produced extracellular matrix. Living within a biofilm allows for the emergence of specific properties for these cells that their planktonic counterparts do not have. Furthermore, biofilms are the cause of several infectious diseases and are frequently inhabited by multi-species. These interactions between microbial species are often critical for the biofilm process. Despite the importance of biofilms in disease, vaccine antigens are typically prepared from bacteria grown as planktonic cells under laboratory conditions. Vaccines based on planktonic bacteria may not provide optimal protection against biofilm-driven infections.

AREAS COVERED

In this review, we will present an overview of biofilm formation, what controls this mode of growth, and recent vaccine development targeting biofilms.

EXPERT OPINION

Previous and ongoing research provides evidence that vaccine formulation with antigens derived from biofilms is a promising approach to prevent infectious diseases and can enhance the protective efficacy of existing vaccines. Therefore, research focusing on the identification of biofilm-derived antigens merits further investigations.

Study of quorum-sensing LasR and RhlR genes and their dependent virulence factors in Pseudomonas aeruginosa isolates from infected burn wounds

Background

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic pathogen responsible for burn-wound infection. High incidence, infection severity and increasing resistance characterize P. aeruginosa-induced burn infection.

Purpose

To estimate quorum-sensing (QS)-dependent virulence factors of P. aeruginosa isolates from burn wounds and correlate it to the presence of QS genes.

Methods

A cross-sectional descriptive study included 50 P. aeruginosa isolates from burn patients in Mansoura University Plastic and Burn Hospital, Egypt. Antibiotic sensitivity tests were done. All isolates were tested for their ability to produce biofilm using a micro-titration assay method. Protease, pyocyanin and rhamnolipid virulence factors were determined using skimmed milk agar, King’s A medium and CTAB agar test, respectively. The identity of QS lasR and rhlR genes was confirmed using PCR.

Results

In total, 86 % of isolates had proteolytic activity. Production of pyocyanin pigment was manifested in 66 % of isolates. Altogether, 76 % of isolates were rhamnolipid producers. Biofilm formation was detected in 96 % of isolates. QS lasR and rhlR genes were harboured by nearly all isolates except three isolates were negative for both lasR and rhlR genes and two isolates were positive for lasR gene and negative for rhlR gene. Forty-nine isolates were considered as extremely QS-proficient strains as they produced QS-dependent virulence factors. In contrast, one isolate was a QS deficient strain.

Conclusions

QS affects P. aeruginosa virulence-factor production and biofilm in burn wounds. Isolates containing lasR and rhlR seem to be a crucial regulator of virulence factors and biofilm formation in P. aeruginosa whereas the lasR gene positively regulates biofilm formation, proteolytic activity, pyocyanin production and rhamnolipid biosurfactant synthesis. The QS regulatory RhlR gene affects protease and rhamnolipid production positively.

Bioaugmentation with immobilized endophytic Penicillium restrictum to improve quorum quenching activity for biofouling control in an aerobic hollow-fiber membrane bioreactor treating antibiotic-containing wastewater

The effects of bioaugmentation with immobilized Penicillium restrictum on the removal efficiency of sulfamethoxazole (SMX), erythromycin (ERY) and tetracycline (TC) antibiotics as well as membrane biofouling was studied using hollow-fiber membrane bioreactor (HF-MBR). Bioaugmentation with P. restrictum led to a significant change in the antibiotic removal efficiency and relative abundance of aerobic microbial community, most probably as a result of its quorum quenching activity. Furthermore, in addition to its role in the increase of SMX and ERY removal efficiencies and the decrease of their sorption on solid phase, bioaugmentation significantly reduced the transmembrane pressure which in turn reduced membrane clogging. The most abundant phyla in sludge and biofilm samples in the presence of P. restrictum were observed to be Proteobacteria, Bacteroidetes and Firmicutes. Differences in bacterial compositions and their specificity in biodegradation of antibiotics in different reactors showed that bacteria were specifically selected under the pressure of antibiotics and growing fungus.

Molecular Mechanisms of Campylobacter Biofilm Formation and Quorum Sensing

Even though Campylobacter spp. are known to be fastidious organisms, they can survive within the natural environment. One mechanism to withstand unfavourable conditions is the formation of biofilms, a multicellular structure composed of different bacterial and other microbial species which are embedded in an extracellular matrix. High oxygen levels, low substrate concentrations and the presence of external DNA stimulate the biofilm formation by C. jejuni. These external factors trigger internal adaptation processes, e.g. via regulating the expression of genes encoding proteins required for surface structure formation, as well as motility, stress response and antimicrobial resistance. Known genes impacting biofilm formation will be summarized in this review. The formation of biofilms as well as the expression of virulence genes is often regulated in a cell density depending manner by quorum sensing, which is mediated via small signalling molecules termed autoinducers. Even though quorum sensing mechanisms of other bacteria are well understood, knowledge on the role of these mechanisms in C. jejuni biofilm formation is still scarce. The LuxS enzyme involved in generation of autoinducer-2 is present in C. jejuni, but autoinducer receptors have not been identified so far. Phenotypes of C. jejuni strains lacking a functional luxS like reduced growth, motility, oxygen stress tolerance, biofilm formation, adhesion, invasion and colonization are also summarized within this chapter. However, these phenotypes are highly variable in distinct C. jejuni strains and depend on the culture conditions applied.

Quorum Sensing Inhibition or Quenching in Acinetobacter baumannii: The Novel Therapeutic Strategies for New Drug Development

Acinetobacter baumannii is a Gram-negative opportunistic nosocomial pathogen, which can cause ventilator-related and blood infection in critically ill patients. The resistance of A. baumannii clinical isolates to common antimicrobials and their tolerance to desiccation have emerged as a serious problem to public health. In the process of pathogenesis, bacteria release signals, which regulate virulence and pathogenicity-related genes. Such bacteria coordinate their virulent behavior in a cell density-dependent phenomenon called quorum sensing (QS). In contrast, the two main approaches of QS interference, quorum sensing inhibitors (QSIs) and quorum quenching (QQ) enzymes, have been developed to reduce the virulence of bacteria, thus reducing the pressure to produce bacterial drug resistance. Therefore, QSIs or QQ enzymes, which interfere with these processes, might potentially inhibit bacterial QS and ultimately biofilm formation. In this review, we aim to describe the state-of-art in the QS process in A. baumannii and elaborate on the use of QSIs or QQ enzymes as antimicrobial drugs in various potential sites of the QS pathway.

Old problems and new solutions: antibiotic alternatives in food animal production

The antimicrobial resistance crisis is a Global Health challenge that impacts humans, animals, and the environment alike. In response to increased demands for animal protein and by-products, there has been a substantial increase in the use of antimicrobial agents in the animal industry. Indeed, they are extensively used to prevent, control, and (or) treat disease in animals. In addition to infection control, in-feed supplementation with antimicrobials became common practice for growth promotion of livestock. Unfortunately, the global overuse of antimicrobials has contributed to the emergence and spread of resistance. As such, many countries have implemented policies and approaches to eliminate the use of antimicrobials as growth promoters in food animals, which necessitates the need for alternate and One Health strategies to maintain animal health and welfare. This review summarizes the antimicrobial resistance crisis from Global Health and One Health perspectives. In addition, we outline examples of potential alternate strategies to circumvent antimicrobial use in animal husbandry practices, including antivirulence agents, bacteriophages, and nutritional measures to control bacterial pathogens. Overall, these alternate strategies require further research and development efforts, including assessment of efficacy and the associated development, manufacturing, and labor costs.

Identification of FDA-approved antivirulence drugs targeting the Pseudomonas aeruginosa quorum sensing effector protein PqsE

The ability of the bacterial pathogen Pseudomonas aeruginosa to cause both chronic and acute infections mainly relies on its capacity to finely modulate the expression of virulence factors through a complex network of regulatory circuits, including the pqs quorum sensing (QS) system. While in most QS systems the signal molecule/receptor complexes act as global regulators that modulate the expression of QS-controlled genes, the main effector protein of the pqs system is PqsE. This protein is involved in the synthesis of the QS signal molecules 2-alkyl-4(1H)-quinolones (AQs), but it also modulates the expression of genes involved in virulence factors production and biofilm formation via AQ-independent pathway(s). P. aeruginosa pqsE mutants disclose attenuated virulence in plant and animal infection models, hence PqsE is considered a good target for the development of antivirulence drugs against P. aeruginosa.

In this study, the negative regulation exerted by PqsE on its own transcription has been exploited to develop a screening system for the identification of PqsE inhibitors in a library of FDA-approved drugs. This led to the identification of nitrofurazone and erythromycin estolate, two antibiotic compounds that reduce the expression of PqsE-dependent virulence traits and biofilm formation in the model strain P. aeruginosa PAO1 at concentrations far below those affecting the bacterial growth rate. Notably, both drugs reduce the production of the PqsE-controlled virulence factor pyocyanin also in P. aeruginosa strains isolated from cystic fibrosis patients, and do not antagonize the activity of antibiotics commonly used to treat P. aeruginosa infection.

Diffusible Signaling Factor, a Quorum-Sensing Molecule, Interferes with and Is Toxic Towards Bdellovibrio bacteriovorus 109J

Bdellovibrio bacteriovorus 109J is a predatory bacterium which lives by predating on other Gram-negative bacteria to obtain the nutrients it needs for replication and survival. Here, we evaluated the effects two classes of bacterial signaling molecules (acyl homoserine lactones (AHLs) and diffusible signaling factor (DSF)) have on B. bacteriovorus 109J behavior and viability. While AHLs had a non-significant impact on predation rates, DSF considerably delayed predation and bdelloplast lysis. Subsequent experiments showed that 50 μM DSF also reduced the motility of attack-phase B. bacteriovorus 109J cells by 50% (38.2 ± 14.9 vs. 17 ± 8.9 μm/s). Transcriptomic analyses found that DSF caused genome-wide changes in B. bacteriovorus 109J gene expression patterns during both the attack and intraperiplasmic phases, including the significant downregulation of the flagellum assembly genes and numerous serine protease genes. While the former accounts for the reduced speeds observed, the latter was confirmed experimentally with 50 μM DSF completely blocking protease secretion from attack-phase cells. Additional experiments found that 30% of the total cellular ATP was released into the supernatant when B. bacteriovorus 109J was exposed to 200 μM DSF, implying that this QS molecule negatively impacts membrane integrity.

Tetradecanoic Acids With Anti-Virulence Properties Increase the Pathogenicity of Pseudomonas aeruginosa in a Murine Cutaneous Infection Model

Blocking virulence is a promising alternative to counteract Pseudomonas aeruginosa infections. In this regard, the phenomenon of cell-cell communication by quorum sensing (QS) is an important anti-virulence target. In this field, fatty acids (FA) have gained notoriety for their role as autoinducers, as well as anti-virulence molecules in vitro, like some saturated FA (SAFA). In this study, we analyzed the anti-virulence activity of SAFA with 12 to18 carbon atoms and compared their effect with the putative autoinducer cis-2-decenoic acid (CDA). The effect of SAFA on six QS-regulated virulence factors and on the secretion of the exoenzyme ExoU was evaluated. In addition, a murine cutaneous infection model was used to determine their influence on the establishment and damage caused by P. aeruginosa PA14. Dodecanoic (lauric, C12:0) and tetradecanoic (myristic, C14:0) acids (SAFA C12-14) reduced the production of pyocyanin by 35-58% at 40 and 1,000 µM, while CDA inhibited it 62% at a 3.1 µM concentration. Moreover, the SAFA C12-14 reduced swarming by 90% without affecting biofilm formation. In contrast, CDA reduced the biofilm by 57% at 3 µM but did not affect swarming. Furthermore, lauric and myristic acids abolished ExoU secretion at 100 and 50 µM respectively, while CDA reduced it by ≈ 92% at 100 µM. Remarkably, the coadministration of myristic acid (200 and 1,000 µM) with P. aeruginosa PA14 induced greater damage and reduced survival of the animals up to 50%, whereas CDA to 500 µM reduced the damage without affecting the viability of the PA14 strain. Hence, our results show that SAFA C12-14 and CDA have a role in regulation of P. aeruginosa virulence, although their inhibition/activation molecular mechanisms are different in complex environments such as in vivo systems.

Extracellular Metabolism Sets the Table for Microbial Cross-Feeding

The transfer of nutrients between cells, or cross-feeding, is a ubiquitous feature of microbial communities with emergent properties that influence our health and orchestrate global biogeochemical cycles. Cross-feeding inevitably involves the externalization of molecules. Some of these molecules directly serve as cross-fed nutrients, while others can facilitate cross-feeding. Altogether, externalized molecules that promote cross-feeding are diverse in structure, ranging from small molecules to macromolecules. The functions of these molecules are equally diverse, encompassing waste products, enzymes, toxins, signaling molecules, biofilm components, and nutrients of high value to most microbes, including the producer cell. As diverse as the externalized and transferred molecules are the cross-feeding relationships that can be derived from them. Many cross-feeding relationships can be summarized as cooperative but are also subject to exploitation. Even those relationships that appear to be cooperative exhibit some level of competition between partners. In this review, we summarize the major types of actively secreted, passively excreted, and directly transferred molecules that either form the basis of cross-feeding relationships or facilitate them. Drawing on examples from both natural and synthetic communities, we explore how the interplay between microbial physiology, environmental parameters, and the diverse functional attributes of extracellular molecules can influence cross-feeding dynamics. Though microbial cross-feeding interactions represent a burgeoning field of interest, we may have only begun to scratch the surface.

Disrupting the quorum sensing mediated virulence in soft rot causing Pectobacterium carotovorum by marine sponge associated Bacillus sp. OA10

Strains of genus Pectobacterium are major cause of soft rot diseases in fruits and vegetables worldwide. Traditional control methods have not been very successful in combating the pathogenesis. As a result there has been an emerging need for developing an alternative ecofriendly and economical strategy. The pathogenesis of Pectobacterium sp. is mediated by quorum sensing (QS) and approaches based on inhibition of QS system to shut down the virulence genes without affecting growth of the pathogen may serve the purpose. Bacillus sp. OA10 associated with purple sponge Haliclona sp. was found to possess extracellular quorum quenching activity. The OA10 extract inhibited QS dependent virulence of Pectobacterium carotovorum subsp. carotovorum BR1 (PccBR1) at low concentrations (0.2 mg) as evident from 77.56 ± 6.17% reduction in potato maceration with complete inhibition by 0.8 mg. Inhibition of plant cell wall degrading enzymes (PCWDE) and carbapenem production by PccBR1 in presence of OA10 extract indicated disruption of the two QS pathways ExpI/ExpR and CarI/CarR in PccBR1. Bacillus sp. OA10 was not found to degrade acyl homoserine lactone (AHL), instead exhibited QSI activity by probably inhibiting AHL synthesis in PccBR1. Absence of enzymatic principle in quorum sensing inhibitor (QSI) is beneficial as enzymes may get inhibited by various factors during their application. OA10 extract did not affect growth of PccBR1, thereby reducing the chance of developing resistance against the QSI. Thus, Bacillus sp. OA10 can prove to be a good prospective candidate for QSI based novel biocontrol formulations.

New developments in anti-biofilm intervention towards effective management of orthopedic device related infections (ODRI's)

Orthopedic device related infections (ODRI's) represent a difficult to treat situation owing to their biofilm based nature. Biofilm infections once established are difficult to eradicate even with an aggressive treatment regimen due to their recalcitrance towards antibiotics and immune attack. The involvement of antibiotic resistant pathogens as the etiological agent further worsens the overall clinical picture, pressing on the need to look into alternative treatment strategies. The present review highlightes the microbiological challenges associated with treatment of ODRI's due to biofilm formation on the implant surface. Further, it details the newer anti-infective modalities that work either by preventing biofilm formation and/or through effective disruption of the mature biofilms formed on the medical implant. The study, therefore aims to provide a comprehensive insight into the newer anti-biofilm interventions (non-antibiotic approaches) and a better understanding of their mechanism of action essential for improved management of orthopedic implant infections.

Benzo[d]thiazole-2-thiol bearing 2-oxo-2-substituted-phenylethan-1-yl as potent selective lasB quorum sensing inhibitors of Gram-negative bacteria

Quorum sensing is a well-known term for describing bacterial cell–cell communication. Bacteria use quorum sensing pathways to respond to external factors such as nutrient availability, defense mechanisms, and coordinate host toxic behaviors such as biofilm formation, virulence production, and other pathogenesis. Discovery of novel compounds which inhibit quorum sensing without being antibiotic are currently emerging fields. Herein, the library of fifteen benzo[d]thiazole/quinoline-2-thiol bearing 2-oxo-2-substituted-phenylethan-1-yl compounds was designed, synthesized and evaluated to find novel quorum sensing inhibitors. Firstly, compounds were evaluated for their growth inhibitory activities at high concentrations up to 1000 μg mL⁻¹ toward Pseudomonas aeruginosa. Under our conditions, twelve compounds showed moderate growth inhibitory activities in the concentration tested. To our delight, three compounds 3, 6 and 7 do not affect the growth of the bacteria which were chosen for the evaluation of quorum sensing inhibitor activities. In the LasB system, our compounds 3, 6, 7 showed promising quorum-sensing inhibitors with IC₅₀ of 115.2 μg mL⁻¹, 182.2 μg mL⁻¹ and 45.5 μg mL⁻¹, respectively. In the PqsR system, no activity observed suggesting that the selectivity of the compound toward the LasB system. In addition, 7 showed the moderate anti-biofilm formation of Pseudomonas aeruginosa. Docking studies revealed that 3, 6 and 7 binding to the active site of Pseudomonas aeruginosa quorum sensing LasR system with better affinity compared to reference compounds 4-NPO. Finally, computation calculations suggest that compounds are a good template for further drug development.

Benzo[d]thiazole-2-thiol bearing 2-oxo-2-substituted-phenylethan-1-yl as potent selective lasB quorum sensing inhibitors and anti-biofilm formation of Pseudomonas aeruginosa.

Tackling Antimicrobial Resistance with Small Molecules Targeting LsrK: Challenges and Opportunities

Antimicrobial resistance (AMR) is a growing threat with severe health and economic consequences. The available antibiotics are losing efficacy, and the hunt for alternative strategies is a priority. Quorum sensing (QS) controls biofilm and virulence factors production. Thus, the quenching of QS to prevent pathogenicity and to increase bacterial susceptibility to antibiotics is an appealing therapeutic strategy. The phosphorylation of autoinducer-2 (a mediator in QS) by LsrK is a crucial step in triggering the QS cascade. Thus, LsrK represents a valuable target in fighting AMR. Few LsrK inhibitors have been reported so far, allowing ample room for further exploration. This perspective aims to provide a comprehensive analysis of the current knowledge about the structural and biological properties of LsrK and the state-of-the-art technology for LsrK inhibitor design. We elaborate on the challenges in developing novel LsrK inhibitors and point out promising avenues for further research.

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.

Anti-quorum Sensing and Anti-biofilm Activity of Zinc Oxide Nanospikes

This study evaluates the impact of two separate incubation periods (4 and 6 weeks) on the morphology of sol-gel-fabricated ZnO nanospikes (ZNs), that is, ZN1 and ZN2, respectively. We further analyzed the inhibitory effects of ZN1 and ZN2 on quorum sensing (QS) and biofilm formation in Pseudomonas aeruginosa (PAO1) and Chromobacterium violaceum (strains 12472 and CVO26). The size of the synthesized ZNs was in the range of 40-130 nm, and finer nanoparticles were synthesized after an incubation period of 6 weeks. Treatment with ZNs decreased the production of violacein in the pathogen without affecting the bacterial growth, which indicated that ZNs inhibited the QS signaling regulated by N-acyl homoserine lactone. ZN2 had a higher inhibitory action on the virulence factor productivity than ZN1. Furthermore, ZN2-treated cells displayed a substantial decrease in azocasein-degrading protease activity (80%), elastase activity (83%), and pyocyanin production (85%) relative to untreated P. aeruginosa PAO1 cells. Treatment with ZN2 decreased swarming motility and exopolysaccharide production by 89 and 85%, respectively. ZN2 was effective against both the las & pqs systems of P. aeruginosa and exhibited broad-spectrum activity. Additionally, ZN2 was more efficient in inhibiting the biofilm formation at the attachment stage than ZN1. These findings revealed that in P. aeruginosa, ZN2 demonstrated inhibitory effects on QS as well as on the development of biofilms. Thus, ZN2 can be potentially used to treat drug-resistant P. aeruginosa infections.

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 Sensing Inhibition Attenuates the Virulence of the Plant Pathogen Ralstonia solanacearum Species Complex

Strains of Ralstonia solanacearum species complex (RSSC) cause "bacterial wilt" on a wide range of plant species and thus lead to marked economic losses in agriculture. Quorum sensing (QS), a bacterial cell-cell communication mechanism, controls the virulence of RSSC strains by regulating the production of extracellular polysaccharide (EPS) and secondary metabolites, biofilm formation, and cellular motility. R. solanacearum strain OE1-1 employs (R)-methyl 3-hydroxymyristate (3-OH MAME) as a QS signal, which is synthesized by the PhcB methyltransferase and sensed by the PhcS/PhcRQ two-component system. We describe the design, synthesis, and biological evaluation of inhibitors of the phc QS system. Initial screening of a small set of QS signal analogues revealed that methyl 3-hydroxy-8-phenyloctanoate, named, PQI-1 (phc quorum sensing inhibitor-1), inhibited biofilm formation by strain OE1-1. To improve its inhibitory activity, the derivatives of PQI-1 were synthesized, and their QS inhibition activities were evaluated. PQIs-2-5 evolved from PQI-1 more strongly inhibited not only biofilm formation but also the production of ralfuranone and EPS. Furthermore, RNA-Seq analysis revealed that the PQIs effectively inhibited QS-dependent gene expression and repression in strain OE1-1. On the other hand, the PQIs did not affect the canonical QS systems of the representative reporter bacteria. These antagonists, especially PQI-5, reduced wilting symptoms of the tomato plants infected with strain OE1-1. Taken together, we suggest that targeting the phc QS system has potential for the development of chemicals that protect agricultural crops from bacterial wilt disease.