Linoleic acid inhibits Pseudomonas aeruginosa biofilm formation by activating diffusible signal factor-mediated quorum sensing

Falcaria vulgaris extract: A mixture of quorum sensing inhibitors for controlling Pectobacterium carotovorum subsp. carotovorum

A promising strategy to control bacterial diseases involves using Quorum Sensing Inhibitor (QSI) compounds. This study aimed to evaluate the potential of Falcaria vulgaris plant extract to combat the phytopathogenic Pectobacterium carotovorum subsp. carotovorum (Pcc) via its QSI activity. Using biosensors and Minimum Inhibitory Concentration (MIC) assays, the QSI and antimicrobial aspects of the extract were assessed. Furthermore, the effect of the extract on the reduction of tuber maceration in potatoes was examined. Subsequently, homology modeling based on LasR was conducted to analyze interactions between ligand 3-oxo-C8-AHL, and ExpR2 protein. Docking studies were performed on all extract compounds identified via Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The extract effectively reduced maceration at sub-MIC concentrations across various pathogenic strains. Furthermore, Cyclopentadecanone, 2-hydroxy, showed more negative docking energy than the native ligand. Z,E-2,13-Octadecadien-1-ol showed energy equivalence to the native ligand. Additionally, this plant included certain compounds or their analogs that had previously been discovered as QSI compounds. These compounds included oleic acid, n-Hexadecanoic acid, cytidine, and linoleic acid, and they had energies that were comparable to that of the native ligand. In conclusion, the remarkable QSI property showed by this plant is likely attributed to a combination of compounds possessing this characteristic.

Inhibitory effect of natural compounds on quorum sensing system in Pseudomonas aeruginosa: a helpful promise for managing biofilm community

Pseudomonas aeruginosa biofilm is a community of bacteria that adhere to live or non-living surfaces and are encapsulated by an extracellular polymeric substance. Unlike individual planktonic cells, biofilms possess a notable inherent resistance to sanitizers and antibiotics. Overcoming this resistance is a substantial barrier in the medical and food industries. Hence, while antibiotics are ineffective in eradicating P. aeruginosa biofilm, scientists have explored alternate strategies, including the utilization of natural compounds as a novel treatment option. To this end, curcumin, carvacrol, thymol, eugenol, cinnamaldehyde, coumarin, catechin, terpinene-4-ol, linalool, pinene, linoleic acid, saponin, and geraniol are the major natural compounds extensively utilized for the management of the P. aeruginosa biofilm community. Noteworthy, the exact interaction of natural compounds and the biofilm of this bacterium is not elucidated yet; however, the interference with the quorum sensing system and the inhibition of autoinducer production in P. aeruginosa are the main possible mechanisms. Noteworthy, the use of different drug platforms can overcome some drawbacks of natural compounds, such as insolubility in water, limited oral bioavailability, fast metabolism, and degradation. Additionally, drug platforms can deliver different antibiofilm agents simultaneously, which enhances the antibiofilm potential of natural compounds. This article explores many facets of utilizing natural compounds to inhibit and eradicate P. aeruginosa biofilms. It also examines the techniques and protocols employed to enhance the effectiveness of these compounds.

Regulation of extracellular polymers based on quorum sensing in wastewater biological treatment from mechanisms to applications: A critical review

Extracellular polymeric substances (EPS) regulated by quorum sensing (QS) could directly mediate adhesion between microorganisms and form tight microbial aggregates. Besides, EPS have redox properties, which can facilitate electron transfer for promoting electroactive bacteria. Currently, the applications research on improving wastewater biological treatment performance based on QS regulated EPS have been widely reported, but reviews on the level of QS regulated EPS to enhance EPS function in microbial systems are still lacking. This work proposes the potential mechanisms of EPS synthesis by QS regulation from the viewpoint of material metabolism and energy metabolism, and summarizes the effects of QS on EPS synthesis. By synthesizing the role of QS in EPS regulation, we further point out the applications of QS-regulated EPS in wastewater biological treatment, which involve a series of aspects such as strengthening microbial colonization, mitigating membrane biofouling, improving the shock resistance of microbial metabolic systems, and strengthening the electron transfer capacity of microbial metabolic systems. According to this comprehensive review, future research on QS-regulated EPS should focus on the exploration of the micro-mechanisms, and economic regulation strategies for QS-regulated EPS should be developed, while the stability of QS-regulated EPS in long-term production experimental research should be further demonstrated.

Metabolomics responses and tolerance of Pseudomonas aeruginosa under acoustic vibration stress

Sound has been shown to impact microbial behaviors. However, our understanding of the chemical and molecular mechanisms underlying these microbial responses to acoustic vibration is limited. In this study, we used untargeted metabolomics analysis to investigate the effects of 100-Hz acoustic vibration on the intra- and extracellular hydrophobic metabolites of P. aeruginosa PAO1. Our findings revealed increased levels of fatty acids and their derivatives, quinolones, and N-acylethanolamines upon sound exposure, while rhamnolipids (RLs) showed decreased levels. Further quantitative real-time polymerase chain reaction experiments showed slight downregulation of the rhlA gene (1.3-fold) and upregulation of fabY (1.5-fold), fadE (1.7-fold), and pqsA (1.4-fold) genes, which are associated with RL, fatty acid, and quinolone biosynthesis. However, no alterations in the genes related to the rpoS regulators or quorum-sensing networks were observed. Supplementing sodium oleate to P. aeruginosa cultures to simulate the effects of sound resulted in increased tolerance of P. aeruginosa in the presence of sound at 48 h, suggesting a potential novel response-tolerance correlation. In contrast, adding RL, which went against the response direction, did not affect its growth. Overall, these findings provide potential implications for the control and manipulation of virulence and bacterial characteristics for medical and industrial applications.

Targeting microbial quorum sensing: the next frontier to hinder bacterial driven gastrointestinal infections

Bacteria synchronize social behaviors via a cell-cell communication and interaction mechanism termed as quorum sensing (QS). QS has been extensively studied in monocultures and proved to be intensively involved in bacterial virulence and infection. Despite the role QS plays in pathogens during laboratory engineered infections has been proved, the potential functions of QS related to pathogenesis in context of microbial consortia remain poorly understood. In this review, we summarize the basic molecular mechanisms of QS, primarily focusing on pathogenic microbes driving gastrointestinal (GI) infections. We further discuss how GI pathogens disequilibrate the homeostasis of the indigenous microbial consortia, rebuild a realm dominated by pathogens, and interact with host under worsening infectious conditions via pathogen-biased QS signaling. Additionally, we present recent applications and main challenges of manipulating QS network in microbial consortia with the goal of better understanding GI bacterial sociality and facilitating novel therapies targeting bacterial infections.

Unveiling the Potential of Algal Extracts as Promising Antibacterial and Antibiofilm Agents against Multidrug-Resistant Pseudomonas aeruginosa: In Vitro and In Silico Studies including Molecular Docking

Multidrug-resistant Pseudomonas aeruginosa poses a global challenge due to its virulence and biofilm-forming ability, leading to persistent infections. This study had a dual focus: first, it aimed to investigate the biofilm activity and antibiotic resistance profiles of Pseudomonas aeruginosa isolates obtained from a fish-rearing farm. Second, it explored the potential of algal extracts as effective antibacterial and antibiofilm agents. The study analyzed 23 isolates of P. aeruginosa from the farm, assessing antibiotic resistance and biofilm formation. The antimicrobial and antibiofilm activities of two algal extracts, Arthrospira platensis (cyanobacteria) acetone extract (AAE) and Polysiphonia scopulorum (Rhodophyta) methanol extract (PME), were tested individually and combined (COE). The effects on biofilm-related gene expression were examined. AAE, PME, and COE were evaluated for antimicrobial and antibiofilm properties. Biofilm-related gene expression was measured and the extracts were analyzed for physicochemical properties and toxicity. Most P. aeruginosa isolates (86.9%) were antibiotic-resistant and formed biofilms. AAE, PME, and COE displayed promising antibacterial and antibiofilm effects, with COE being particularly effective. COE reduced a key biofilm-related gene expression. The fatty acid content (56% in AAE and 34% in PME) correlated with the effects. Specific compounds, such as phytol, bromophenol, and dihydroxy benzaldehyde, contributed to the activities. The extracts showed favorable characteristics and interactions with FabZ protein amino acids. This study suggests the potential of algal extracts as antibacterial and antibiofilm agents against drug-resistant infections. Further exploration in clinical applications is warranted.

Biosurfactants: Secondary Metabolites Involved in the Process of Bioremediation and Biofilm Removal

The search for environmentally friendly methods to remove persistent substances such as organic pollutants and sessile communities such as biofilms that severely affect the environment and human health resulted in biosurfactant discovery. Owing to their low level of toxicity and high biodegradability, biosurfactants are increasingly preferred to be used for removal of pollutants from nature. These amphipathic molecules can be synthesized inexpensively, employing cheap substrates such as agricultural and industrial wastes. Recent progress has been made in identifying various biosurfactants that can be used to remove organic pollutants and harmful microbial aggregates, as well as novel microbial strains that produce these surface-active molecules to survive in a hydrocarbon-rich environment. This review focuses on the identification and understanding the role of biosurfactants and the microorganisms involved in the removal of biofilms and remediation of xenobiotics and various types of hydrocarbons such as crude oil, aromatic hydrocarbons, n-alkanes, aliphatic hydrocarbons, asphaltenes, naphthenes, and other petroleum products. This property of biosurfactant is very important as biofilms are of great concern due to their impact on the environment, public health, and industries worldwide. This work also includes several advanced molecular methods that can be used to enhance the production of biosurfactants by the microorganisms studied.

Inhibiting bacterial biofilm formation by stimulating c-di-GMP regulation using citrus peel extract from Jeju Island

Biofilms consist of single or multiple species of bacteria embedded in extracellular polymeric substances (EPSs), which affect the increase in antibiotic resistance by restricting the transport of antibiotics to the bacterial cells. An alternative approach to treatment with antimicrobial agents is using biofilm inhibitors that regulate biofilm development without inhibiting bacterial growth. In this study, we found that citrus peel extract from Jeju Island (CPEJ) can inhibit bacterial biofilm formation. According to the results, CPEJ concentration-dependently reduces biofilm formation without affecting bacterial growth. Additionally, CPEJ decreased the production of extracellular polymeric substances but increased bacterial swarming motility. These results led to the hypothesis that CPEJ can reduce intracellular bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) concentration. The results showed that CPEJ significantly reduced the c-di-GMP level through increased phosphodiesterase activity. Altogether, these findings suggest that CPEJ as a biofilm inhibitor has new potential for pharmacological (e.g. drug and medication) and industrial applications (e.g. ship hulls, water pipes, and membrane processes biofouling control).

Multifunctional Edible Oil-Impregnated Nanoporous Oxide Layer on AISI 304 Stainless Steel

Slippery liquid-infused porous surface (SLIPS) realized on commercial materials provides various functionalities, such as corrosion resistance, condensation heat transfer, anti-fouling, de/anti-icing, and self-cleaning. In particular, perfluorinated lubricants infused in fluorocarbon-coated porous structures have showed exceptional performances with durability; however, they caused several issues in safety, due to their difficulty in degradation and bio-accumulation. Here, we introduce a new approach to create the multifunctional lubricant-impregnated surface with edible oils and fatty acid, which are also safe to human body and degradable in nature. The edible oil-impregnated anodized nanoporous stainless steel surface shows a significantly low contact angle hysteresis and sliding angle, which is similar with general surface of fluorocarbon lubricant-infused systems. The edible oil impregnated in the hydrophobic nanoporous oxide surface also inhibits the direct contact of external aqueous solution to a solid surface structure. Due to such de-wetting property caused by a lubricating effect of edible oils, the edible oil-impregnated stainless steel surface shows enhanced corrosion resistance, anti-biofouling and condensation heat transfer with reduced ice adhesion.

Mini-Review of Biofilm Interactions with Surface Materials in Industrial Piping System

The growth of biofilm, which is caused by microorganism accumulation and growth on wetted surfaces, may damage industrial piping systems, increase maintenance and cleaning costs for the system sterilization, and even divulge the immune system into high risk. This article systematically analyzes the biofilm interactions with piping surface materials from the perspectives of physical convection, and biological and chemical adhesion. The thermodynamics of the flow, bacterial surface sensing, and bio-communication are the most critical factors for biofilm attachment. Furthermore, experimental analysis methods as well as biofilm control and removal approaches, are also included in this study. Finally, the resistance and growth of biofilm, as well as the practical and advanced methodology to control the biofilm and challenges associated with technology, are also discussed. Moreover, this paper may also offer a significant reference for the practice and strategic applications to address the biofilm resistance issues in industrial piping.

Quorum sensing in human gut and food microbiomes: Significance and potential for therapeutic targeting

Human gut and food microbiomes interact during digestion. The outcome of these interactions influences the taxonomical composition and functional capacity of the resident human gut microbiome, with potential consequential impacts on health and disease. Microbe-microbe interactions between the resident and introduced microbiomes, which likely influence host colonisation, are orchestrated by environmental conditions, elements of the food matrix, host-associated factors as well as social cues from other microorganisms. Quorum sensing is one example of a social cue that allows bacterial communities to regulate genetic expression based on their respective population density and has emerged as an attractive target for therapeutic intervention. By interfering with bacterial quorum sensing, for instance, enzymatic degradation of signalling molecules (quorum quenching) or the application of quorum sensing inhibitory compounds, it may be possible to modulate the microbial composition of communities of interest without incurring negative effects associated with traditional antimicrobial approaches. In this review, we summarise and critically discuss the literature relating to quorum sensing from the perspective of the interactions between the food and human gut microbiome, providing a general overview of the current understanding of the prevalence and influence of quorum sensing in this context, and assessing the potential for therapeutic targeting of quorum sensing mechanisms.

Repurposing Dimetridazole and Ribavirin to disarm Pseudomonas aeruginosa virulence by targeting the quorum sensing system

Pseudomonas aeruginosa relies on its complex cellular regulatory network to produce a series of virulence factors and to cause various acute and chronic infections in a wide range of hosts. Compared with traditional antibiotics which frequently accompany with widespread antibiotic resistance, crippling the virulence system of bacteria is expected to be a promising anti-infective strategy. In this study, Dimetridazole and Ribavirin, which had poor antibacterial activities on P. aeruginosa reference isolate PAO1 in nutrient medium but significantly inhibited the growth of P. aeruginosa PAO1 in M9-adenosine, were selected from 40 marketed compounds with similar core structure (furan, benzofuran, or flavonoids) to the acyl-homoserine lactone signals of P. aeruginosa quorum sensing (QS) system. The production of QS-controlled proteases, pyocyanin, and biofilm formation of P. aeruginosa PAO1 and the clinical isolates were significantly decreased by the presence of Dimetridazole or Ribavirin. Correspondingly, the majority of QS-activated genes in P. aeruginosa, including the key regulatory genes lasR, rhlR, and pqsR and their downstream genes, were significantly inhibited by Ribavirin or Dimetridazole, as determined by RNA-sequencing and quantitative PCR. Furthermore, the susceptibilities of drug-resistant P. aeruginosa isolates to polymyxin B, meropenem, and kanamycin were remarkably promoted by the synergistic application of Dimetridazole or Ribavirin. Finally, the treatment of Ribavirin or Dimetridazole effectively protected Caenorhabditis elegans and mice from P. aeruginosa infection. In conclusion, this study reports the antivirulence potentials of Dimetridazole and Ribavirin on P. aeruginosa and provides structural basis and methodological reference for the development of anti-pseudomonal drugs.

The Molecular Architecture of Pseudomonas aeruginosa Quorum-Sensing Inhibitors

The survival selection pressure caused by antibiotic-mediated bactericidal and bacteriostatic activity is one of the important inducements for bacteria to develop drug resistance. Bacteria gain drug resistance through spontaneous mutation so as to achieve the goals of survival and reproduction. Quorum sensing (QS) is an intercellular communication system based on cell density that can regulate bacterial virulence and biofilm formation. The secretion of more than 30 virulence factors of P. aeruginosa is controlled by QS, and the formation and diffusion of biofilm is an important mechanism causing the multidrug resistance of P. aeruginosa, which is also closely related to the QS system. There are three main QS systems in P. aeruginosa: las system, rhl system, and pqs system. Quorum-sensing inhibitors (QSIs) can reduce the toxicity of bacteria without affecting the growth and enhance the sensitivity of bacterial biofilms to antibiotic treatment. These characteristics make QSIs a popular topic for research and development in the field of anti-infection. This paper reviews the research progress of the P. aeruginosa quorum-sensing system and QSIs, targeting three QS systems, which will provide help for the future research and development of novel quorum-sensing inhibitors.

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Antibacterial Activity and Mechanism of Polygonum orientale L. Essential Oil against Pectobacterium carotovorum subsp. carotovorum

Infected by Pectobacterium carotovorum subsp. carotovorum (Pcc), the quality of Chinese cabbage could severely decline. Using chemical bactericides to control Pcc could cause food safety problems. Thus, we investigated the optimum extraction conditions, antibacterial activity, chemical compounds and antibacterial mechanism of Polygonum orientale L. essential oil (POEO) against Pcc in order to search a new way to control Pcc. The optimum extraction conditions of POEO (soaking time 2.6 h, extraction time 7.7 h and ratio of liquid to solid 10.3 mL/g) were optimized by response surface methodology. The minimum inhibitory concentration (MIC) of POEO against Pcc was 0.625 mg/mL. The control efficiency of protective activity of POEO against Pcc was 74.67~92.67%, and its curative activity was 76.00~93.00%. Then, 29 compounds were obtained by GC-MS; the prime compounds of POEO were phytol, phytone, n-pentacosane, 1-octen-3-ol and β-ionone. It was verified that, compared with control samples, POEO destroyed cell morphology. It increased surface potential, increased hydrophobicity, damaged cell walls, destroyed the integrity and permeability of cell membrane, reduced membrane potential (MP), and changed membrane protein conformation. It inhibited the activities of pyruvate kinase (PK), succinate dehydrogenase (SDH) and adenosine triphosphatase (ATPase). Briefly, the results of this study demonstrate that POEO showed effective inhibitory activity against Pcc, thus POEO could have potential application in controlling Pcc.

Bacterial signalling mechanism: An innovative microbial intervention with multifaceted applications in microbial electrochemical technologies: A review

Microbial electrochemical technologies (METs) are a set of inventive tools that generate value-added by-products with concomitant wastewater remediation. However, due to the bottlenecks, like higher fabrication cost and inferior yield of resources, these inventive METs are still devoid of successful field-scale implementation. In this regard, application of quorum sensing (QS) mechanism to improve the power generation of the METs has gained adequate attention. The QS is an intercellular signalling mechanism that controls the bacterial social network in its vicinity via the synthesis of diffusible signal molecules labelled as auto inducers, thus ameliorating yield of valuables produced through METs. This state-of-the-art review elucidates different types of QS molecules and their working mechanism with the special focus on the widespread application of QS in the field of METs for their performance enhancement. Thus, this review intends to guide the researchers in rendering scalability to METs by integrating innovative QS mechanisms into them.

Identification of FadT as a Novel Quorum Quenching Enzyme for the Degradation of Diffusible Signal Factor in Cupriavidus pinatubonensis Strain HN-2

Quorum sensing (QS) is a microbial cell–cell communication mechanism and plays an important role in bacterial infections. QS-mediated bacterial infections can be blocked through quorum quenching (QQ), which hampers signal accumulation, recognition, and communication. The pathogenicity of numerous bacteria, including Xanthomonas campestris pv. campestris (Xcc), is regulated by diffusible signal factor (DSF), a well-known fatty acid signaling molecule of QS. Cupriavidus pinatubonensis HN-2 could substantially attenuate the infection of XCC through QQ by degrading DSF. The QQ mechanism in strain HN-2, on the other hand, is yet to be known. To understand the molecular mechanism of QQ in strain HN-2, we used whole-genome sequencing and comparative genomics studies. We discovered that the fadT gene encodes acyl-CoA dehydrogenase as a novel QQ enzyme. The results of site-directed mutagenesis demonstrated the requirement of fadT gene for DSF degradation in strain HN-2. Purified FadT exhibited high enzymatic activity and outstanding stability over a broad pH and temperature range with maximal activity at pH 7.0 and 35 °C. No cofactors were required for FadT enzyme activity. The enzyme showed a strong ability to degrade DSF. Furthermore, the expression of fadT in Xcc results in a significant reduction in the pathogenicity in host plants, such as Chinese cabbage, radish, and pakchoi. Taken together, our results identified a novel DSF-degrading enzyme, FadT, in C. pinatubonensis HN-2, which suggests its potential use in the biological control of DSF-mediated pathogens.

Biological and Physiochemical Methods of Biofilm Adhesion Resistance Control of Medical-Context Surface

The formation of biofilms on medical-context surfaces gives the EPS embedded bacterial community protection and additional advantages that planktonic cells would not have such as increased antibiotic resistance and horizontal gene transfer. Bacterial cells tend to attach to a conditioning layer after overcoming possible electrical barriers and go through two phases of attachments: reversible and irreversible. In the first, bacterial attachment to the surface is reversible and occurs quickly whilst the latter is permanent and takes place over a longer period of time. Upon reaching a certain density in the bacterial community, quorum sensing causes phenotypical changes leading to a loss in motility and the production of EPS. This position paper seeks to address the problem of bacterial adhesion and biofilm formation for the medical surfaces by comparing inhabiting physicochemical interactions and biological mechanisms. Several physiochemical methodologies (e.g. ultrasonication, alternating magnetic field and chemical surface coating) and utilizing biological mechanisms (e.g. quorum quenching and EPS degrading enzymes) were suggested. The possible strategical applications of each category were suggested and evaluated to a balanced position to possibly eliminate the adhesion and formation of biofilms on medical-context surfaces.