Quorum sensing and bacterial biofilms

Antivirulence and antipathogenic activity of Mayan herbal remedies against Pseudomonas aeruginosa

ETHNOPHARMACOLOGICAL RELEVANCE

The Yucatan Peninsula has a privileged wealth of vascular plants with which various Mayan herbal formulations have been developed. However, studies on their antipathogenic and antivirulence properties are scarce.

AIM OF THE STUDY

Identify antivirulence properties in Mayan herbal remedies and determine their antipathogenic capacity in burn wounds infected with Pseudomonas aeruginosa.

MATERIALS AND METHODS

An ethnobotanical study was conducted in Mayan communities in central and southern Quintana Roo, Mexico. Furthermore, the antipathogenic capacity of three Mayan herbal remedies was analyzed using an animal model of thermal damage and P. aeruginosa infection. Antivirulence properties were determined by inhibiting phenotypes regulated by quorum sensing (pyocyanin, biofilm, and swarming) and by the secretion of the ExoU toxin. The chemical composition of the most active herbal remedy was analyzed using molecular network analysis.

RESULTS

It was found that topical administration of the remedy called "herbal soap" (HS) for eleven days maintained 100% survival of the animals, reduced establishment of the bacteria in the burn and prevented its systemic dispersion. Although no curative effect was recorded on tissue damaged by HS treatment, its herbal composition strongly reduced swarming and ExoU secretion. Through analysis of Molecular Networks, it was possible to carry out a global study of its chemical components, and identify the family of oxindole monoterpenoid alkaloids and carboline and tetrahydropyrididole alkaloids. In addition, flavonols, flavan-3-ols, and quinic acid derivatives were detected.

CONCLUSIONS

The antipathogenic and antivirulence capacity of ancient Mayan remedies makes them a potential resource for developing new antibacterial therapies to treat burns infected by P. aeruginosa.

Applications of Microbial Organophosphate-Degrading Enzymes to Detoxification of Organophosphorous Compounds for Medical Countermeasures against Poisoning and Environmental Remediation

Mining of organophosphorous (OPs)-degrading bacterial enzymes in collections of known bacterial strains and in natural biotopes are important research fields that lead to the isolation of novel OP-degrading enzymes. Then, implementation of strategies and methods of protein engineering and nanobiotechnology allow large-scale production of enzymes, displaying improved catalytic properties for medical uses and protection of the environment. For medical applications, the enzyme formulations must be stable in the bloodstream and upon storage and not susceptible to induce iatrogenic effects. This, in particular, includes the nanoencapsulation of bioscavengers of bacterial origin. In the application field of bioremediation, these enzymes play a crucial role in environmental cleanup by initiating the degradation of OPs, such as pesticides, in contaminated environments. In microbial cell configuration, these enzymes can break down chemical bonds of OPs and usually convert them into less toxic metabolites through a biotransformation process or contribute to their complete mineralization. In their purified state, they exhibit higher pollutant degradation efficiencies and the ability to operate under different environmental conditions. Thus, this review provides a clear overview of the current knowledge about applications of OP-reacting enzymes. It presents research works focusing on the use of these enzymes in various bioremediation strategies to mitigate environmental pollution and in medicine as alternative therapeutic means against OP poisoning.

Phosphate recovery from urban sewage by the biofilm sequencing batch reactor process: Key factors in biofilm formation and related mechanisms

The biofilm sequencing batch reactor (BSBR) technique has been deployed in the laboratory to enrich phosphorus from simulated wastewater, but it is still not clear what its performance will be when real world sewage is used. In this work, the effluent from the multi-stage anoxic-oxic (AO) activated sludge process at a sewage plant was used as the feed water for a BSBR pilot system, which had three reactors operating at different levels of dissolved oxygen (DO). The phosphorus adsorption and release, the biofilm growth, and the extracellular polymeric substances (EPS) components and contents were examined. The microbial communities and the signaling molecules N-acyl-l-homoserine lactones (AHLs) were also analyzed. Gratifyingly, the BSBR process successfully processed the treated sewage, and the biofilm developed phosphorus accumulation capability within 40 days. After entering stable operation, the system concentrated phosphate from 2.59 ± 0.77 mg/L in the influent to as much as 81.64 mg/L in the recovery liquid. Sludge discharge had profound impacts on all aspects of BSBR, and it was carried out successfully when the phosphorus absorption capacity of the biofilm alone was comparable to that of the reactor containing the activated sludge. Shortly after the sludge discharge, the phosphate concentration of the recovery liquid surged from 50 to 140 mg/L, the biofilm thickness grew from 20.56 to 67.32 μm, and the diversity of the microbial population plunged. Sludge discharge stimulated Candidatus competibacter to produce a large amount of AHLs, which was key in culturing the biofilm. Among the AHLs, both C10-HSL and 3OC12-HSL were significantly positively correlated with EPS and the abundance of Candidatus competibacter. The current results demonstrated BSBR as a viable option to enrich phosphorus from real world sewage with low phosphorus content and fluctuating chemistry. The mechanistic explorations also provided theoretical guidance for cultivating phosphorus-accumulating biofilms.

Development of a Quorum Sensing-Mediated Bacterial Autolytic System in Escherichia coli for Automatic Release of Intracellular Products

Escherichia coli, one of the most efficient expression hosts for recombinant proteins, is widely used in chemical, medical, food, and other industries. De novo engineering of gene regulation circuits and cell density-controlled E. coli cell lysis are promising directions for the release of intracellular bioproducts. Here, we developed an E. coli autolytic system, named the quorum sensing-mediated bacterial autolytic (QS-BA) system, by incorporating an acyl-homoserine lactone (AHL)-based YasI/YasR-type quorum sensing circuit from Pseudoalteromonas into E. coli cells. The results showed that the E. coli QS-BA system can release the intracellular bioproducts into the cell culture medium in terms of E. coli cell density, which offers an environmentally-friendly, economical, efficient, and flexible E. coli lysis platform for production of recombinant proteins. The QS-BA system has the potential to serve as an integrated system for the large-scale production of target products in E. coli for medical and industrial applications.

A systematic review of antibiotics and antibiotic resistance genes (ARGs) in mariculture wastewater: Antibiotics removal by microalgal-bacterial symbiotic system (MBSS), ARGs characterization on the metagenomic

Antibiotic residues in mariculture wastewater seriously affect the aquatic environment. Antibiotic Resistance Genes (ARGs) produced under antibiotic stress flow through the environment and eventually enter the human body, seriously affecting human health. Microalgal-bacterial symbiotic system (MBSS) can remove antibiotics from mariculture and reduce the flow of ARGs into the environment. This review encapsulates the present scenario of mariculture wastewater, the removal mechanism of MBSS for antibiotics, and the biomolecular information under metagenomic assay. When confronted with antibiotics, there was a notable augmentation in the extracellular polymeric substances (EPS) content within MBSS, along with a concurrent elevation in the proportion of protein (PN) constituents within the EPS, which limits the entry of antibiotics into the cellular interior. Quorum sensing stimulates the microorganisms to produce biological responses (DNA synthesis - for adhesion) through signaling. Oxidative stress promotes gene expression (coupling, conjugation) to enhance horizontal gene transfer (HGT) in MBSS. The microbial community under metagenomic detection is dominated by aerobic bacteria in the bacterial-microalgal system. Compared to aerobic bacteria, anaerobic bacteria had the significant advantage of decreasing the distribution of ARGs. Overall, MBSS exhibits remarkable efficacy in mitigating the challenges posed by antibiotics and resistant genes from mariculture wastewater.

A critical review of characteristics of domestic wastewater and key treatment techniques in Chinese villages

As of 2022, China's rural sewage treatment rate is only approximately 31 %. Rapid rural development has led to higher demand. However, China's rural areas are complex and face many problems, such as uneven economic development, population distribution, and water availability. Long-lasting and low-cost wastewater treatment measures are needed for application in rural areas. The quantity and quality of rural domestic wastewater in China were characterized first. Next, the hot topic of domestic wastewater in Chinese villages was confirmed via bibliometric analysis using CiteSpace, and the treatment technologies for rural domestic wastewater were compared. Specifically, the technical status and challenges of the most common technology in rural domestic wastewater treatment, constructed wetlands, were summarized.

Development of an analytical method to quantify N-acyl-homoserine lactones in bacterial cultures, river water, and treated wastewater

N-Acyl-homoserine lactones (AHL) play a major role in the communication of Gram-negative bacteria. They influence processes such as biofilm formation, swarming motility, and bioluminescence in the aquatic environment. A comprehensive analytical method was developed to elucidate the "chemical communication" in pure bacterial cultures as well as in the aquatic environment and engineered environments with biofilms. Due to the high diversity of AHLs and their low concentrations in water, a sensitive and selective LC-ESI-MS/MS method combined with solid-phase extraction was developed for 34 AHLs, optimized and validated to quantify AHLs in bacterial conditioned medium, river water, and treated wastewater. Furthermore, the developed method was optimized in terms of enrichment volume, internal standards, limits of detection, and limits of quantification in several matrices. An unanticipated variety of AHLs was detected in the culture media of Pseudomonas aeruginosa (in total 8 AHLs), Phaeobacter gallaeciensis (in total 6 AHLs), and Methylobacterium mesophilicum (in total 15 AHLs), which to our knowledge have not been described for these bacterial cultures so far. Furthermore, AHLs were detected in river water (in total 5 AHLs) and treated wastewater (in total 3 AHLs). Several detected AHLs were quantified (in total 24) using a standard addition method up to 7.3±1.0 µg/L 3-Oxo-C12-AHL (culture media of P. aeruginosa).

AHL-Based Quorum Sensing Regulates the Biosynthesis of a Variety of Bioactive Molecules in Bacteria

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia, Serratia, Pseudomonas, Chromobacterium, and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

Disruption of Communication: Recent Advances in Antibiofilm Materials with Anti-Quorum Sensing Properties

Biofilm contamination presents a significant threat to public health, the food industry, and aquatic/marine-related applications. In recent decades, although various methods have emerged to combat biofilm contamination, the intricate and persistent nature of biofilms makes complete eradication challenging. Therefore, innovative alternative solutions are imperative for addressing biofilm formation. Instead of solely focusing on the eradication of mature biofilms, strategically advantageous measures involve the delay or prevention of biofilm formation on surfaces. Quorum sensing, a communication system enabling bacteria to coordinate their behavior based on population density, plays a pivotal role in biofilm formation for numerous microbial species. Materials possessing antibiofilm properties that target quorum sensing have gained considerable attention for their potential to prevent biofilm formation. This Review consolidates recent research progress on the utilization of materials with antiquorum sensing properties for combating biofilm formation. These materials can be categorized into three distinct types: (i) antibiofilm nanomaterials, (ii) antibiofilm surfaces, and (iii) antibiofilm hydrogels with antiquorum sensing capabilities. Finally, the Review concludes with a brief discussion of current challenges and outlines potential avenues for future research.

Inhibition of quorum sensing serves as an effective strategy to mitigate the risks of human bacterial pathogens in soil

The coexistence of antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and virulence factor genes (VFGs) in human bacterial pathogens (HBPs) increases their risks to ecological security and human health and no effective strategy is available. Herein, we demonstrated two typical quorum sensing (QS) interfering agents, 4-nitropyridine-N-oxide (4-NPO, a QS inhibitor) and Acylase Ⅰ (a quorum quenching (QQ) enzyme), effectively decreased the abundance of HBPs by 48.30% and 72.54%, respectively, which was accompanied by the reduction of VFGs, ARGs, and MGEs. The decrease in QS signals mediated by QS interfering agents disturbed bacterial communication and inhibited biofilm formation. More importantly, QS interfering agents reduced the intra-species and inter-species conjugation frequencies among bacteria, considerably inhibiting the dissemination of ARGs and VFGs via horizontal gene transfer. Furthermore, the QS interfering agents did not significantly affect the metabolic function of other nonpathogenic microorganisms in the soil. Collectively, our study provides an effective and eco-friendly strategy to mitigate the risks of HBPs in soil.

Rethinking the control of Streptococcus suis infection: Biofilm formation

Streptococcus suis is an emerging zoonotic pathogen that is widespread in swine populations. The control of S. suis infection and its associated diseases is a daunting challenge worldwide. Biofilm formation appears to be the main reason for the persistence of S. suis. In this review we gather existing knowledge on S. suis biofilm, describing the role of biofilm formation in S. suis virulence and drug resistance, the regulatory factors of S. suis biofilm formation, and the research progress of inhibiting S. suis biofilm formation, with the aim of providing guidance for future studies related to the field of S. suis biofilms.

Real-Time Spatiotemporal Measurement of Extracellular Signaling Molecules Using an Aptamer Switch-Conjugated Hydrogel Matrix

Cells rely on secreted signaling molecules to coordinate essential biological functions including development, metabolism, and immunity. Unfortunately, such signaling processes remain difficult to measure with sufficient chemical specificity and temporal resolution. To address this need, an aptamer-conjugated hydrogel matrix that enables continuous fluorescent measurement of specific secreted analytes - in two dimensions, in real-time is developed. As a proof of concept, real-time imaging of inter-cellular cyclic adenosine 3',5'-monophosphate (cAMP) signals in Dictyostelium discoideum amoeba cells is performed. A set of aptamer switches that generate a rapid and reversible change in fluorescence in response to cAMP signals is engineered. By combining multiple switches with different dynamic ranges, measure cAMP concentrations spanning three orders of magnitude in a single experiment can be measured. These sensors are embedded within a biocompatible hydrogel on which cells are cultured and their cAMP secretions can be imaged using fluorescent microscopy. Using this aptamer-hydrogel material system, the first direct measurements of oscillatory cAMP signaling that correlate closely with previous indirect measurements are achieved. Using different aptamer switches, this approach can be generalized for measuring other secreted molecules to directly visualize diverse extracellular signaling processes and the biological effects that they trigger in recipient cells.

Isolation of a quorum quenching bacterium effective to various acyl-homoserine lactones: Its quorum quenching mechanism and application to a membrane bioreactor

Biofouling, caused by microbial biofilm formation on the membrane surface and in pores, is a major operational problem in membrane bioreactors (MBR). Many quorum quenching (QQ) bacteria have been isolated and applied to MBR to reduce biofouling. However, for more effective MBR biofouling control, novel approaches for isolating QQ bacteria and applying them in MBR are needed. Therefore, Listeria grayi (HEMM-2) was isolated using a mixture of different N-acyl homoserine lactones (AHLs). HEMM-2 degraded various AHLs, regardless of the length and oxo group in the carbon chain, with quorum sensing (QS) inhibition ratios of 47-61%. This QQ activity was attributed to extracellular substances in HEMM-2 cell-free supernatant (CFS). Furthermore, the HEMM-2 CFS negatively regulated QS-related gene expression, inhibiting Pseudomonas aeruginosa and activated sludge-biofilm formation by 53-75%. Surprisingly, when the HEMM-2 CFS was directly injected into a laboratory-scale MBR system, biofouling was not significantly affected. Biofouling was only controlled by cell suspension (CS) of HEMM-2, indicating the importance of QQ bacteria in MBR. The HEMM-2 CS increased operation time to reach 0.4 bar, a threshold transmembrane pressure for complete biofouling, from 315 h to 371 h. Taken together, HEMM-2, which is effective in the degradation of various AHLs, and its applicable method to MBR may be considered a potent approach for controlling biofouling and understanding the behavior of QQ bacteria in MBR systems.

Bromination of Quorum Sensing Molecules: Vanadium Bromoperoxidase and Cerium Dioxide Nanocrystals via Free Active Bromine Transform Bacterial Communication

The halogenation of quorum sensing molecules (QSMs) is known to be catalyzed by enzymes such as haloperoxidase (HPO) as well as cerium dioxide nanocrystals (NC), which mimic enzymes. Those enzymes and mimics can influence biological processes such as biofilm formation, where bacteria use QSMs for the "chemical" communication between each other and the coordination of surface colonization. However, not much is known about the degradation behavior of a broad spectrum of QSMs, especially for HPO and its mimics. Therefore, in this study, the degradation of three QSMs with different molecule moieties was elucidated. For this purpose, different batch experiments were carried out with HPOs, NCs and free active bromine (FAB). For N-β-ketocaproyl-homoserine lactone (3-Oxo-C6-AHL), N-cis-tetradec-9Z-enoyl-homoserine lactone (C14:1-AHL) and 2-heptyl-4-quinolone (HHQ) a fast degradation and moiety-specific transformations were observed. The HPO vanadium bromoperoxidase as well as cerium dioxide NCs catalyzed the formation of the same brominated transformation products (TPs). Since the same TPs are formed in batch experiments with FAB it is very likely that FAB is playing a major role in the catalytical reaction mechanism leading to the transformation of QSMs. In this study in total 17 TPs could be identified in different levels of confidence and the catalytic degradation processes for two QS groups (unsaturated AHLs and alkyl quinolones) with cerium dioxide NCs and vanadium bromoperoxidase were expanded.

Bacteria and microalgae associations in periphyton-mechanisms and biotechnological opportunities

Phototrophic and heterotrophic microorganisms coexist in complex and dynamic structures called periphyton. These structures shape the biogeochemistry and biodiversity of aquatic ecosystems. In particular, microalgae-bacteria interactions are a prominent focus of study by microbial ecologists and can provide biotechnological opportunities for numerous applications (i.e. microalgal bloom control, aquaculture, biorefinery, and wastewater bioremediation). In this review, we analyze the species dynamics (i.e. periphyton formation and factors determining the prevalence of one species over another), coexisting communities, exchange of resources, and communication mechanisms of periphytic microalgae and bacteria. We extend periphyton mathematical modelling as a tool to comprehend complex interactions. This review is expected to boost the applicability of microalgae-bacteria consortia, by drawing out knowledge from natural periphyton.

Combinations of Photodynamic Therapy with Other Minimally Invasive Therapeutic Technologies against Cancer and Microbial Infections

The rapid rise in research and development following the discovery of photodynamic therapy to establish novel photosensitizers and overcome the limitations of the technology soon after its clinical translation has given rise to a few significant milestones. These include several novel generations of photosensitizers, the widening of the scope of applications, leveraging of the offerings of nanotechnology for greater efficacy, selectivity for the disease over host tissue and cells, the advent of combination therapies with other similarly minimally invasive therapeutic technologies, the use of stimulus-responsive delivery and disease targeting, and greater penetration depth of the activation energy. Brought together, all these milestones have contributed to the significant enhancement of what is still arguably a novel technology. Yet the major applications of photodynamic therapy still remain firmly located in neoplasms, from where most of the new innovations appear to launch to other areas, such as microbial, fungal, viral, acne, wet age-related macular degeneration, atherosclerosis, psoriasis, environmental sanitization, pest control, and dermatology. Three main value propositions of combinations of photodynamic therapy include the synergistic and additive enhancement of efficacy, the relatively low emergence of resistance and its rapid development as a targeted and high-precision therapy. Combinations with established methods such as chemotherapy and radiotherapy and demonstrated applications in mop-up surgery promise to enhance these top three clinical tools. From published in vitro and preclinical studies, clinical trials and applications, and postclinical case studies, seven combinations with photodynamic therapy have become prominent research interests because they are potentially easily applied, showing enhanced efficacy, and are rapidly translating to the clinic. These include combinations with chemotherapy, photothermal therapy, magnetic hyperthermia, cold plasma therapy, sonodynamic therapy, immunotherapy, and radiotherapy. Photochemical internalization is a critical mechanism for some combinations.

A FadR-Type Regulator Activates the Biodegradation of Polycyclic Aromatic Hydrocarbons by Mediating Quorum Sensing in Croceicoccus naphthovorans Strain PQ-2

Bacteria employ multiple transcriptional regulators to orchestrate cellular responses to adapt to constantly varying environments. The bacterial biodegradation of polycyclic aromatic hydrocarbons (PAHs) has been extensively described, and yet, the PAH-related transcriptional regulators remain elusive. In this report, we identified an FadR-type transcriptional regulator that controls phenanthrene biodegradation in Croceicoccus naphthovorans strain PQ-2. The expression of fadR in C. naphthovorans PQ-2 was induced by phenanthrene, and its deletion significantly impaired both the biodegradation of phenanthrene and the synthesis of acyl-homoserine lactones (AHLs). In the fadR deletion strain, the biodegradation of phenanthrene could be recovered by supplying either AHLs or fatty acids. Notably, FadR simultaneously activated the fatty acid biosynthesis pathway and repressed the fatty acid degradation pathway. As intracellular AHLs are synthesized with fatty acids as substrates, boosting the fatty acid supply could enhance AHL synthesis. Collectively, these findings demonstrate that FadR in C. naphthovorans PQ-2 positively regulates PAH biodegradation by controlling the formation of AHLs, which is mediated by the metabolism of fatty acids. IMPORTANCE Master transcriptional regulation of carbon catabolites is extremely important for the survival of bacteria that face changes in carbon sources. Polycyclic aromatic hydrocarbons (PAHs) can be utilized as carbon sources by some bacteria. FadR is a well-known transcriptional regulator involved in fatty acid metabolism; however, the connection between FadR regulation and PAH utilization in bacteria remains unknown. This study revealed that a FadR-type regulator in Croceicoccus naphthovorans PQ-2 stimulated PAH biodegradation by controlling the biosynthesis of the acyl-homoserine lactone quorum-sensing signals that belong to fatty acid-derived compounds. These results provide a unique perspective for understanding bacterial adaptation to PAH-containing environments.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Comparison of cell viability assessment and visualization of Aspergillus niger biofilm with two fluorescent probe staining methods

Filamentous fungi are ubiquitous and frequent components of biofilms. A means to visualize them and quantify their viability is essential for understanding their development and disruption. However, quantifying filamentous fungal biofilms poses challenges because, unlike yeasts and bacteria, they are not composed of discrete cells of similar size. This research focused on filamentous fungal biofilms that are representative of those in the built environment. The objective of this study was to develop a rapid method to examine biofilm structure and quantify live (metabolically active/ membrane undamaged) and dead (inactive/ membrane damaged) cells in Aspergillus niger biofilms utilizing a fluorescent probe staining method and confocal laser scanning microscopy (CLSM). For this, we compared two commercially available probe staining kits that have been developed for bacterial and yeast systems. One method utilized the classic cell stain FUN 1 that exhibits orange-red fluorescent intravacuolar structures in metabolically active cells, while dead cells are fluoresced green. The second method utilized a combination of SYTO9 and propidium iodide (PI), and stains cells based on their membrane morphology. SYTO9 is a green fluorescent stain with the capacity to penetrate the living cell walls, and PI is a red fluorescent stain that can only penetrate dead or dying cells with damaged cell membranes. Following staining, the biofilms were imaged using CLSM and biofilm volumes and thickness were quantified using COMSTAT, a computer program that measures biofilm accumulation from digital image stacks. The results were compared to independent measurements of live-dead cell density, as well as a classic cell viability assay-XTT. The data showed that the combination of SYTO9 and PI is optimal for staining filamentous fungal biofilms.

In situ monitoring of Lentilactobacillus parabuchneri biofilm formation via real-time infrared spectroscopy

Foodborne pathogenic microorganisms form biofilms at abiotic surfaces, which is a particular challenge in food processing industries. The complexity of biofilm formation requires a fundamental understanding on the involved molecular mechanisms, which may then lead to efficient prevention strategies. In the present study, biogenic amine producing bacteria, i.e., Lentilactobacillus parabuchneri DSM 5987 strain isolated from cheese were studied in respect with biofilm formation, which is of substantial relevance given their contribution to the presence of histamine in dairy products. While scanning electron microscopy was used to investigate biofilm adhesion at stainless steel surfaces, in situ infrared attenuated total reflection spectroscopy (IR-ATR) using a custom flow-through assembly was used for real-time and non-destructive observations of biofilm formation during a period of several days. The spectral window of 1700-600 cm-1 provides access to vibrational signatures characteristic for identifying and tracking L. parabuchneri biofilm formation and maturation. Especially, the amide I and II bands, lactic acid produced as the biofilm matures, and a pronounced increase of bands characteristic for extracellular polymeric substances (EPS) provide molecular insight into biofilm formation, maturation, and changes in biofilm architecture. Finally, multivariate data evaluation strategies were applied facilitating the unambiguous classification of the observed biofilm changes via IR spectroscopic data.

Recent advances on the regulation of bacterial biofilm formation by herbal medicines

Biofilm formation is a fundamental part of life cycles of bacteria which affects various aspects of bacterial-host interactions including the development of drug resistance and chronic infections. In clinical settings, biofilm-related infections are becoming increasingly difficult to treat due to tolerance to antibiotics. Bacterial biofilm formation is regulated by different external and internal factors, among which quorum sensing (QS) signals and nucleotide-based second messengers play important roles. In recent years, different kinds of anti-biofilm agents have been discovered, among which are the Chinese herbal medicines (CHMs). CHMs or traditional Chinese medicines have long been utilized to combat various diseases around the world and many of them have the ability to inhibit, impair or decrease bacterial biofilm formation either through regulation of bacterial QS system or nucleotide-based second messengers. In this review, we describe the research progresses of different chemical classes of CHMs on the regulation of bacterial biofilm formation. Though the molecular mechanisms on the regulation of bacterial biofilm formation by CHMs have not been fully understood and there are still a lot of work that need to be performed, these studies contribute to the development of effective biofilm inhibitors and will provide a novel treatment strategy to control biofilm-related infections.

Anti-Quorum-Sensing Potential of Ethanolic Extracts of Aromatic Plants from the Flora of Cyprus

Quorum sensing (QS) is a form of intra- and inter-species communication system employed by bacteria to regulate their collective behavior in a cell population-dependent manner. QS has been implicated in the virulence of several pathogenic bacteria. This work aimed to investigate the anti-QS potential of ethanolic extracts of eight aromatic plants of Cyprus, namely, Origanum vulgare subsp. hirtum, Rosmarinus officinalis, Salvia officinalis, Lavendula spp., Calendula officinalis, Melissa officinalis, Sideritis cypria, and Aloysia citriodora. We initially assessed the effects of the extracts on autoinducer 2 (AI-2) signaling activity, using Vibrio harveyi BB170 as a reported strain. We subsequently assessed the effect of the ethanolic extracts on QS-related processes, including biofilm formation and the swarming and swimming motilities of Escherichia coli MG1655. Of the tested ethanolic extracts, those of Origanum vulgare subsp. hirtum, Rosmarinus officinalis, and Salvia officinalis were the most potent AI-2 signaling inhibitors, while the extracts from the other plants exhibited low to moderate inhibitory activity. These three ethanolic extracts also inhibited the biofilm formation (>60%) of E. coli MG1655, as well as its swimming and swarming motilities, in a concentration-dependent manner. These extracts may be considered true anti-QS inhibitors because they disrupt QS-related activities of E. coli MG1655 without affecting bacterial growth. The results suggest that plants from the unexplored flora of Cyprus could serve as a source for identifying novel anti-QS inhibitors to treat infectious diseases caused by pathogens that are resistant to antibiotics.

Noncanonical Functions of Enzyme Cofactors as Building Blocks in Natural Product Biosynthesis

Enzymes involved in secondary metabolite biosynthetic pathways have typically evolutionarily diverged from their counterparts functioning in primary metabolism. They often catalyze diverse and complex chemical transformations and are thus a treasure trove for the discovery of unique enzyme-mediated chemistries. Besides major natural product classes, such as terpenoids, polyketides, and ribosomally or nonribosomally synthesized peptides, biosynthetic investigations of noncanonical natural product biosynthetic pathways often reveal functionally distinct enzyme chemistries. In this Perspective, we aim to highlight challenges and opportunities of biosynthetic investigations on noncanonical natural product pathways that utilize primary metabolites as building blocks, otherwise generally considered as enzyme cofactors. A focus is made on the discovered chemical and enzymological novelties.

Inhibitory Effect of Thymol on Tympanostomy Tube Biofilms of Methicillin-Resistant Staphylococcus aureus and Ciprofloxacin-Resistant Pseudomonas aeruginosa

The formation of antibiotic-resistant strain biofilms in tympanostomy tubes results in persistent and refractory otorrhea. In the present study, we investigated the in vitro antibiofilm activity of thymol against biofilms formed by methicillin-resistant Staphylococcus aureus (MRSA) and ciprofloxacin-resistant Pseudomonas aeruginosa (CRPA), using live and dead bacterial staining and adhesion, biofilm formation, biofilm eradication, and biofilm hydrolytic activity assays. The antibiofilm activity of thymol against tympanostomy tube biofilms formed by MRSA and CRPA strains was examined using a scanning electron microscope. In response to thymol treatment, we detected significant concentration-dependent reductions in the viability and adhesion of MRSA and CRPA. Exposure to thymol also inhibited the formation of both MRSA and CRPA biofilms. Furthermore, thymol was observed to enhance the eradication of preformed mature biofilms produced by MRSA and CRPA and also promoted a reduction in the rates of MRSA and CRPA hydrolysis. Exposure to thymol eradicated extracellular polysaccharide present in the biofilm matrix produced by MRSA and CRPA. Additionally, thymol was observed to significantly eradicate MRSA and CRPA biofilms that had formed on the surface on tympanostomy tubes. Collectively, our findings indicate that thymol is an effective inhibitor of MRSA and CRPA biofilms, and accordingly has potential utility as a therapeutic agent for the treatment of biofilm-associated refractory post-tympanostomy tube otorrhea resulting from MRSA and CRPA infection.

Genetic engineering of extremely acidophilic Acidithiobacillus species for biomining: Progress and perspectives

With global demands for mineral resources increasing and ore grades decreasing, microorganisms have been increasingly deployed in biomining applications to recover valuable metals particularly from normally considered waste, such as low-grade ores and used consumer electronics. Acidithiobacillus are a genus of chemolithoautotrophic extreme acidophiles that are commonly found in mining process waters and acid mine drainage, which have been reported in several studies to aid in metal recovery from bioremediation of metal-contaminated sites. Compared to conventional mineral processing technologies, biomining is often cited as a more sustainable and environmentally friendly process, but long leaching cycles and low extraction efficiency are main disadvantages that have hampered its industrial applications. Genetic engineering is a powerful technology that can be used to enhance the performance of microorganisms, such as Acidithiobacillus species. In this review, we compile existing data on Acidithiobacillus species' physiological traits and genomic characteristics, progresses in developing genetic tools to engineer them: plasmids, shutter vectors, transformation methods, selection markers, promoters and reporter systems developed, and genome editing techniques. We further propose genetic engineering strategies for enhancing biomining efficiency of Acidithiobacillus species and provide our perspectives on their future applications.

Loss of the Rhodobacter capsulatus Serine Acetyl Transferase Gene, cysE1, Impairs Gene Transfer by Gene Transfer Agents and Biofilm Phenotypes

Biofilms are widespread in the environment, where they allow bacterial species to survive adverse conditions. Cells in biofilms are densely packed, and this proximity is likely to increase the frequency of horizontal gene transfer. Gene transfer agents (GTAs) are domesticated viruses with the potential to spread any gene between bacteria. GTA production is normally restricted to a small subpopulation of bacteria, and regulation of GTA loci is highly coordinated, but the environmental conditions that favor GTA production are poorly understood. Here, we identified a serine acetyltransferase gene, cysE1, in Rhodobacter capsulatus that is required for optimal receipt of GTA DNA, accumulation of extracellular polysaccharide, and biofilm formation. The cysE1 gene is directly downstream of the core Rhodobacter-like GTA (RcGTA) structural gene cluster and upregulated in an RcGTA overproducer strain, although it is expressed on a separate transcript. The data we present suggest that GTA production and biofilm are coregulated, which could have important implications for the study of rapid bacterial evolution and understanding the full impact of GTAs in the environment.

IMPORTANCE Direct exchange of genes between bacteria leads to rapid evolution and is the major factor underlying the spread of antibiotic resistance. Gene transfer agents (GTAs) are an unusual but understudied mechanism for genetic exchange that are capable of transferring any gene from one bacterium to another, and therefore, GTAs are likely to be important factors in genome plasticity in the environment. Despite the potential impact of GTAs, our knowledge of their regulation is incomplete. In this paper, we present evidence that elements of the cysteine biosynthesis pathway are involved in coregulation of various phenotypes required for optimal biofilm formation by Rhodobacter capsulatus and successful infection by the archetypal RcGTA. Establishing the regulatory mechanisms controlling GTA-mediated gene transfer is a key stepping stone to allow a full understanding of their role in the environment and wider impact.

The Cell-Cell Communication Signal Indole Controls the Physiology and Interspecies Communication of Acinetobacter baumannii

Many bacteria utilize quorum sensing (QS) to control group behavior in a cell density-dependent manner. Previous studies have demonstrated that Acinetobacter baumannii employs an N-acyl-L-homoserine lactone (AHL)-based QS system to control biological functions and virulence. Here, we report that indole controls biological functions, virulence and AHL signal production in A. baumannii. The biosynthesis of indole is performed by A1S_3160 (AbiS, Acinetobacter baumannii indole synthase), which is a novel indole synthase annotated as an alpha/beta hydrolase in A. baumannii. Heterologous expression of AbiS in an Escherichia coli indole-deficient mutant also rescued the production of indole by using a distinct biosynthetic pathway from the tryptophanase TnaA, which produces indole directly from tryptophan in E. coli. Moreover, we revealed that indole from A. baumannii reduced the competitive fitness of Pseudomonas aeruginosa by inhibiting its QS systems and type III secretion system (T3SS). As A. baumannii and P. aeruginosa usually coexist in human lungs, our results suggest the crucial roles of indole in both the bacterial physiology and interspecies communication. IMPORTANCE Acinetobacter baumannii is an important human opportunistic pathogen that usually causes high morbidity and mortality. It employs the N-acyl-L-homoserine lactone (AHL)-type quorum sensing (QS) system, AbaI/AbaR, to regulate biological functions and virulence. In this study, we found that A. baumannii utilizes another QS signal, indole, to modulate biological functions and virulence. It was further revealed that indole positively controls the production of AHL signals by regulating abaI expression at the transcriptional levels. Furthermore, indole represses the QS systems and type III secretion system (T3SS) of P. aeruginosa and enhances the competitive ability of A. baumannii. Together, our work describes a QS signaling network where a pathogen uses to control the bacterial physiology and pathogenesis, and the competitive ability in microbial community.

Three lines of defense: A multifunctional coating with anti-adhesion, bacteria-killing and anti-quorum sensing properties for preventing biofilm formation of Pseudomonas aeruginosa

Surfaces of synthetic materials are highly susceptible to pathogenic bacteria colonization and further biofilm formation, leading to device failure in both biomedical and industrial applications. Complete elimination of the mature biofilms formed on the surfaces, however, remains a great challenge due to the complexity of chemical composition and physical structure. Therefore, prevention of biofilm formation becomes a preferred strategy for solving the biofilm-associated problems. Herein, a multifunctional coating showing three lines of defense to prevent biofilm formation of Pseudomonas aeruginosa is fabricated by a simple and versatile method. This coating is composed of multilayers of quaternized chitosan with bactericidal property and acylase with anti-quorum sensing property and a topmost layer of hyaluronic acid with anti-adhesion property. The substrate deposited with this coating could suppress initial adhesion of a majority of bacteria, and then kill the attached bacteria and interfere with their quorum sensing systems related to biofilm formation. The results of short-term antibacterial experiments show that our coating reduced 98 ± 2% of attached live bacteria. In long-term antibiofilm experiments, this "three lines of defense" design endows the coating with enhanced antibiofilm property against the biofilm formation for at least 3 days by reducing 98 ± 1% of bacterial proliferation and 71 ± 2% of biomass production. Benefiting from the natural building blocks with good biocompatibility and the versatile and environmentally friendly preparation method, this coating shows negligible cytotoxicity and broad applicability, providing great potential for a variety of biomedical applications. STATEMENT OF SIGNIFICANCE: Pathogenic biofilms formed on the surfaces of medical devices and materials pose an urgent problem, and it remains challenging to treat and eradicate the established biofilms. Herein, we developed an antibiofilm coating showing three lines of defense to prevent biofilm formation, which could be deposited on diverse substrates via a simple and versatile method. This coating was based on three natural materials with anti-adhesive, bactericidal, and anti-quorum sensing properties and showed different function in a self-adaptive way to target the sequential stages of biofilm formation by preventing initial bacterial adhesion, killing attached bacteria and interfering with their quorum sensing system to inhibit bacterial proliferation and biofilm maturation. This coating with improved antibiofilm performance might provide a simple and reliable solution to the problems associated with biofilm on surfaces.

Incubation habitats and aging treatments affect the formation of biofilms on polypropylene microplastics

Microbial colonization and biofilm formation associated with microplastics (MPs) have recently attracted wide attention. However, little is known about the effect of MP aging and different exposed habitats on biofilm formation and associated microbial community characteristics. To obtain a comprehensive understanding, virgin and aged polypropylene MPs were selected as attachment substrates and exposed to different aquatic habitats (marine, estuary, and river). The results showed that the aging process could destroy surface structure and increase oxygen-containing groups of MPs. The total biomass of the biofilms, attached-bacterial OTU numbers, and α diversities increased with exposure time. The biofilms biomass and α diversity of MPs in the river were significantly higher than those in the marine and estuary habitats, and temperature and salinity were primary factors affecting microbial colonization. Bacterial communities in MP-attached biofilms were significantly different from those in surrounding water. Microorganisms tend to adhere to aged MPs, and especially, genes related to human pathogens were significantly expressed on aged MPs, suggesting a potential ecological and health risk of aged MPs in aquatic ecosystems. Our results showed that aged MPs and different habitats have an important influence on microbial colonization, and the weathering process can accelerate biofilm formation on MPs.

Quorum Quenching-Guided Inhibition of Mixed Bacterial Biofilms and Virulence Properties by Protein Derived From Leaves of Carissa carandas

The inhibition/degradation potential of Carissa carandas proteinaceous leaf extract against mixed bacterial biofilm of Staphylococcus aureus MTCC 96, Escherichia coli MTCC 1304, Pseudomonas aeruginosa MTCC 741, and Klebsiella pneumoniae MTCC 109, responsible for nosocomial infections, was evaluated. Distinct inhibition/degradation of mixed bacterial biofilm by the proteinaceous leaf extract of C. carandas was observed under a microscope, and it was found to be 80%. For mono-species biofilm, the maximum degradation of 70% was observed against S. aureus biofilm. The efficiency of aqueous plant extracts to inhibit the mono-species biofilm was observed in terms of minimum inhibitory concentration (MIC), and the best was found against P. aeruginosa (12.5 μg/ml). The presence of flavonoids, phenols, and tannins in the phytochemical analysis of the plant extract suggests the main reason for the antibiofilm property of C. carandas. From the aqueous extract, protein fraction was precipitated using 70% ammonium sulfate and dialyzed. This fraction was purified by ion-exchange chromatography and found to be stable and active at 10°C (pH 7). The purified fraction showed less than 40% cytotoxicity, which suggests that it can be explored for therapeutic purposes after in-depth testing. In order to investigate the mechanistic action of the biofilm inhibition, the plant protein was tested against Chromobacterium violaceum CV026, and its inhibitory effect confirmed its quorum quenching nature. Based on these experimental analyses, it can be speculated that the isolated plant protein might influence the signaling molecule that leads to the inhibition effect of the mixed bacterial biofilm. Further experimental studies are warranted to validate our current findings.

Rapid recovery of mixed culture polyhydroxyalkanoate production system from EPS bulking using azithromycin

The long-term stable operation of the mixed culture polyhydroxyalkanoate (PHA) enrichment stage is the guarantee for the continuous synthesis of PHA, however extracellular polymeric substances (EPS) sludge bulking occurred from time to time may cause the operation fail. In order to solve this problem, as a quencher of signal molecules and antibiotic, azithromycin (AZM) was used in the two systems with different modes to recover the sedimentation capacity of the sludge. The results showed that AZM addition resulted in the reduction of polysaccharide /protein (PS/PN) ratio in EPS and significant improvement of the sedimentation capacity of the sludge. Quorum quenching of AZM or aiiA gene maintained the sedimentation ability of the sludge in a relay mode. By adding AZM, the growth of Thauera and Flavobacterium, which caused sludge bulking, was inhibited. Paracoccus, a strong PHA producer, has been enriched to ensure that the maximum PHA synthesis of the system.

Applications of Antimicrobial Photodynamic Therapy against Bacterial Biofilms

Antimicrobial photodynamic therapy and allied photodynamic antimicrobial chemotherapy have shown remarkable activity against bacterial pathogens in both planktonic and biofilm forms. There has been little or no resistance development against antimicrobial photodynamic therapy. Furthermore, recent developments in therapies that involve antimicrobial photodynamic therapy in combination with photothermal hyperthermia therapy, magnetic hyperthermia therapy, antibiotic chemotherapy and cold atmospheric pressure plasma therapy have shown additive and synergistic enhancement of its efficacy. This paper reviews applications of antimicrobial photodynamic therapy and non-invasive combination therapies often used with it, including sonodynamic therapy and nanozyme enhanced photodynamic therapy. The antimicrobial and antibiofilm mechanisms are discussed. This review proposes that these technologies have a great potential to overcome the bacterial resistance associated with bacterial biofilm formation.

Pathogenic arsenal of Pseudomonas aeruginosa: an update on virulence factors

The emergence of Pseudomonas aeruginosa as a potential threat in persistent infections can be attributed to the plethora of virulence factors expressed by it. This review discusses the various virulence factors that help this pathogen to establish an infection and regulatory systems controlling these virulence factors. Cell-associated virulence factors such as flagella, type IV pili and non-pilus adhesins have been reviewed. Extracellular virulence factors have also been explained. Quorum-sensing systems present in P. aeruginosa play a cardinal role in regulating the expression of virulence factors. The identification of novel virulence factors in hypervirulent strains indicate that the expression of virulence is dynamic and constantly evolving. An understanding of this is critical for the better clinical management of infections.

Asparagopsis Genus: What We Really Know About Its Biological Activities and Chemical Composition

Although the genus Asparagopsis includes only two taxonomically accepted species, the published literature is unanimous about the invasive nature of this genus in different regions of the globe, and about the availability of large amounts of biomass for which it is important to find a commercial application. This review shows that extracts from Asparagospsis species have already been evaluated for antioxidant, antibacterial, antifungal, antiviral, antifouling, cytotoxic, antimethanogenic and enzyme-inhibitory activity. However, the tables presented herein show, with few exceptions, that the activity level displayed is generally low when compared with positive controls. Studies involving pure compounds being identified in Asparagopsis species are rare. The chemical compositions of most of the evaluated extracts are unknown. At best, the families of the compounds present are suggested. This review also shows that the volatile halogenated compounds, fatty acids and sterols that are biosynthesized by the Asparagopsis species are relatively well known. Many other non-volatile metabolites (halogen compounds, flavonoids, other phenolic compounds) seem to be produced by these species, but their chemical structures and properties haven'been investigated. This shows how much remains to be investigated regarding the secondary-metabolite composition of these species, suggesting further studies following more targeted methodologies.

Wsp system oppositely modulates antibacterial activity and biofilm formation via FleQ-FleN complex in Pseudomonas putida

Type VI secretion systems (T6SS) are specific antibacterial weapons employed by diverse bacteria to protect themselves from competitors. Pseudomonas putida KT2440 possesses a functional T6SS (K1-T6SS) and exhibits antibacterial activity towards a broad range of bacteria. Here we found that the Wsp signal transduction system regulated K1-T6SS expression via synthesizing the second messenger cyclic di-GMP (c-di-GMP), thus mediating antibacterial activity in P. putida. High-level c-di-GMP produced by Wsp system repressed the transcription of K1-T6SS genes in structural operon and vgrG1 operon. Transcriptional regulator FleQ and ATPase FleN functioned as repressors in the Wsp system-modulated K1-T6SS transcription. However, FleQ and FleN functioned as activators in biofilm formation, and Wsp system promoted biofilm formation largely in a FleQ/FleN-dependent manner. Furthermore, FleQ-FleN complex bound directly to the promoter of K1-T6SS structural operon in vitro, and c-di-GMP promoted the binding. Besides, P. putida biofilm cells showed higher c-di-GMP levels and lower antibacterial activity than planktonic cells. Overall, our findings reveal a mechanism by which Wsp system oppositely modulates antibacterial activity and biofilm formation via FleQ-FleN, and demonstrate the relationship between plankton/biofilm lifestyles and antibacterial activity in P. putida.

Colonization of biofilm in wastewater treatment: A review

The attachment and colonization process of microorganisms on a carrier is an interdisciplinary research field. Through a series of physical, chemical, and biological actions, the microorganisms can eventually reproduce on the carrier. This article introduces biofilm start-up and its applications, and explores the current issues to look forward to future development directions. Firstly, the mechanism of microbial film formation is analyzed from the microbial community colonization and reproduction process. Secondly, when analyzing the factors influencing microbial membrane formation, the effect of microbial properties (e.g., genes, proteins, lipids) and external conditions (i.e., carrier, operating environment, and regulation mechanism among microbial communities) were discussed in depth. Aimed at exploring the mechanisms and influencing factors of biofilm start-up, this article proposes the application measures to strengthen this process. Finally, the problems encountered and the future development direction of the technology are analyzed and prospected.

Influence of Nisin-Biogel at Subinhibitory Concentrations on Virulence Expression in Staphylococcus aureus Isolates from Diabetic Foot Infections

A new approach to diabetic foot infections (DFIs) has been investigated, using a nisin-biogel combining the antimicrobial peptide (AMP) nisin with the natural polysaccharide guar-gum. Since in in vivo conditions bacteria may be exposed to decreased antimicrobial concentrations, known as subinhibitory concentrations (sub-MICs), effects of nisin-biogel sub-MIC values corresponding to 1/2, 1/4 and 1/8 of nisin's minimum inhibitory concentration (MIC) on virulence expression by six Staphylococcus aureus DFI isolates was evaluated by determining bacteria growth rate; expression of genes encoding for staphylococcal protein A (spA), coagulase (coa), clumping factor A (clfA), autolysin (atl), intracellular adhesin A (icaA), intracellular adhesin D (icaD), and the accessory gene regulator I (agrI); biofilm formation; Coa production; and SpA release. Nisin-biogel sub-MICs decreased bacterial growth in a strain- and dose-dependent manner, decreased agrI, atl and clfA expression, and increased spA, coa, icaA and icaD expression. Biofilm formation increased in the presence of nisin-biogel at 1/4 and 1/8 MIC, whereas 1/2 MIC had no effect. Finally, nisin-biogel at sub-MICs did not affect coagulase production, but decreased SpA production in a dose-dependent manner. Results highlight the importance of optimizing nisin-biogel doses before proceeding to in vivo trials, to reduce the risk of virulence factor's up-regulation due to the presence of inappropriate antimicrobial concentrations.

Pseudomonas aeruginosa Biofilm Formation and Its Control

Microbes are hardly seen as planktonic species and are most commonly found as biofilm communities in cases of chronic infections. Biofilms are regarded as a biological condition, where a large group of microorganisms gets adhered to a biotic or abiotic surface. In this context, Pseudomonas aeruginosa, a Gram-negative nosocomial pathogen is the main causative organism responsible for life-threatening and persistent infections in individuals affected with cystic fibrosis and other lung ailments. The bacteria can form a strong biofilm structure when it adheres to a surface suitable for the development of a biofilm matrix. These bacterial biofilms pose higher natural resistance to conventional antibiotic therapy due to their multiple tolerance mechanisms. This prevailing condition has led to an increasing rate of treatment failures associated with P. aeruginosa biofilm infections. A better understanding of the effect of a diverse group of antibiotics on established biofilms would be necessary to avoid inappropriate treatment strategies. Hence, the search for other alternative strategies as effective biofilm treatment options has become a growing area of research. The current review aims to give an overview of the mechanisms governing biofilm formation and the different strategies employed so far in the control of biofilm infections caused by P. aeruginosa. Moreover, this review can also help researchers to search for new antibiofilm agents to tackle the effect of biofilm infections that are currently imprudent to conventional antibiotics.

The Case against Antibiotics and for Anti-Virulence Therapeutics

Although antibiotics have been indispensable in the advancement of modern medicine, there are downsides to their use. Growing resistance to broad-spectrum antibiotics is leading to an epidemic of infections untreatable by first-line therapies. Resistance is exacerbated by antibiotics used as growth factors in livestock, over-prescribing by doctors, and poor treatment adherence by patients. This generates populations of resistant bacteria that can then spread resistance genes horizontally to other bacterial species, including commensals. Furthermore, even when antibiotics are used appropriately, they harm commensal bacteria leading to increased secondary infection risk. Effective antibiotic treatment can induce bacterial survival tactics, such as toxin release and increasing resistance gene transfer. These problems highlight the need for new approaches to treating bacterial infection. Current solutions include combination therapies, narrow-spectrum therapeutics, and antibiotic stewardship programs. These mediate the issues but do not address their root cause. One emerging solution to these problems is anti-virulence treatment: preventing bacterial pathogenesis instead of using bactericidal agents. In this review, we discuss select examples of potential anti-virulence targets and strategies that could be developed into bacterial infection treatments: the bacterial type III secretion system, quorum sensing, and liposomes.

Surface-Enhanced Raman Spectroscopy of Bacterial Metabolites for Bacterial Growth Monitoring and Diagnosis of Viral Infection

Bacterial metabolites are intermediate products of bacterial metabolism and their production reflects metabolic activity. Herein, we report the use of surface-enhanced Raman spectroscopy (SERS) for detection of both volatile and nonvolatile metabolites and the application of this approach for bacterial growth quantification and diagnosis of viral infection. The time-dependent SERS signal of the volatile metabolite dimethyl disulfide in the headspace above bacteria growing on an agar plate was detected and quantified. In addition, SERS signals arising from the plate reflected nutrient consumption and production of nonvolatile metabolites. The measurement of metabolite accumulation can be used for bacterial quantification. In the presence of bacteriophage virus, bacterial metabolism is suppressed, and the relative decrease in SERS intensity reflects the initial virus concentration. Using multivariate analysis, we detect viral infection with a prediction accuracy of 93%. Our SERS-based approach for metabolite production monitoring provides new insights toward viral infection diagnosis.

A biophysical limit for quorum sensing in biofilms

Bacteria grow on surfaces in complex immobile communities known as biofilms, which are composed of cells embedded in an extracellular matrix. Within biofilms, bacteria often interact with members of their own species and cooperate or compete with members of other species via quorum sensing (QS). QS is a process by which microbes produce, secrete, and subsequently detect small molecules called autoinducers (AIs) to assess their local population density. We explore the competitive advantage of QS through agent-based simulations of a spatial model in which colony expansion via extracellular matrix production provides greater access to a limiting diffusible nutrient. We note a significant difference in results based on whether AI production is constitutive or limited by nutrient availability: If AI production is constitutive, simple QS-based matrix-production strategies can be far superior to any fixed strategy. However, if AI production is limited by nutrient availability, QS-based strategies fail to provide a significant advantage over fixed strategies. To explain this dichotomy, we derive a biophysical limit for the dynamic range of nutrient-limited AI concentrations in biofilms. This range is remarkably small (less than 10-fold) for the realistic case in which a growth-limiting diffusible nutrient is taken up within a narrow active growth layer. This biophysical limit implies that for QS to be most effective in biofilms AI production should be a protected function not directly tied to metabolism.

Micro and nanoemulsions of Carissa spinarum fruit polyphenols, enhances anthocyanin stability and anti-quorum sensing activity: Comparison of degradation kinetics

The low stability of anthocyanins is a constraint in the food industry. The present work has been carried out to overcome this low stability by encapsulating fruit concentrate of underutilized plant Carissa spinarum (CS) with polyphenols in microemulsions (CSME) and nanoemulsions (CSNE). Increasing the amount of CS reduced the particle size from 1154 to 70-300 nm whereas addition of Tween 80 reduced it optimally to 5-25 nm. Degradation of anthocyanins in control and ME/NE proceeded with zero- and first-order reaction rates, respectively, at 28 °C (half-life 6, 25 and 40 days, respectively). The degradation kinetics of phenolics-flavonoids were also studied. CSNE exhibited higher anti-quorum sensing (QS) activity than CSME against Chromobacterium violaceum (73.7%); it inhibited biofilm formation by 70.1 and 64.4% in Pseudomonas aeruginosa, and Yersinia enterocolitica, respectively. This is the first report of using the more stable ME/NE to study anti-QS activity, an alternative to conventional antibiotics.

Singularities of Pyogenic Streptococcal Biofilms - From Formation to Health Implication

Biofilms are generally defined as communities of cells involved in a self-produced extracellular matrix adhered to a surface. In biofilms, the bacteria are less sensitive to host defense mechanisms and antimicrobial agents, due to multiple strategies, that involve modulation of gene expression, controlled metabolic rate, intercellular communication, composition, and 3D architecture of the extracellular matrix. These factors play a key role in streptococci pathogenesis, contributing to therapy failure and promoting persistent infections. The species of the pyogenic group together with Streptococcus pneumoniae are the major pathogens belonging the genus Streptococcus, and its biofilm growth has been investigated, but insights in the genetic origin of biofilm formation are limited. This review summarizes pyogenic streptococci biofilms with details on constitution, formation, and virulence factors associated with formation.

Microfluidic Microbial Bioelectrochemical Systems: An Integrated Investigation Platform for a More Fundamental Understanding of Electroactive Bacterial Biofilms

It is the ambition of many researchers to finally be able to close in on the fundamental, coupled phenomena that occur during the formation and expression of electrocatalytic activity in electroactive biofilms. It is because of this desire to understand that bioelectrochemical systems (BESs) have been miniaturized into microBES by taking advantage of the worldwide development of microfluidics. Microfluidics tools applied to bioelectrochemistry permit even more fundamental studies of interactions and coupled phenomena occurring at the microscale, thanks, in particular, to the concomitant combination of electroanalysis, spectroscopic analytical techniques and real-time microscopy that is now possible. The analytical microsystem is therefore much better suited to the monitoring, not only of electroactive biofilm formation but also of the expression and disentangling of extracellular electron transfer (EET) catalytic mechanisms. This article reviews the details of the configurations of microfluidic BESs designed for selected objectives and their microfabrication techniques. Because the aim is to manipulate microvolumes and due to the high modularity of the experimental systems, the interfacial conditions between electrodes and electrolytes are perfectly controlled in terms of physicochemistry (pH, nutrients, chemical effectors, etc.) and hydrodynamics (shear, material transport, etc.). Most of the theoretical advances have been obtained thanks to work carried out using models of electroactive bacteria monocultures, mainly to simplify biological investigation systems. However, a huge virgin field of investigation still remains to be explored by taking advantage of the capacities of microfluidic BESs regarding the complexity and interactions of mixed electroactive biofilms.

Targeted and untargeted quantification of quorum sensing signalling molecules in bacterial cultures and biological samples via HPLC-TQ MS techniques

Quorum sensing (QS) is the ability of some bacteria to detect and to respond to population density through signalling molecules. QS molecules are involved in motility and cell aggregation mechanisms in diseases such as sepsis. Few biomarkers are currently available to diagnose sepsis, especially in high-risk conditions. The aim of this study was the development of new analytical methods based on liquid chromatography-mass spectrometry for the detection and quantification of QS signalling molecules, including N-acyl homoserine lactones (AHL) and hydroxyquinolones (HQ), in biofluids. Biological samples used in the study were Pseudomonas aeruginosa bacterial cultures and plasma from patients with sepsis. We developed two MS analytical methods, based on neutral loss (NL) and product ion (PI) experiments, to identify and characterize unknown AHL and HQ molecules. We then established a multiple-reaction-monitoring (MRM) method to quantify specific QS compounds. We validated the HPLC-MS-based approaches (MRM-NL-PI), and data were in accord with the validation guidelines. With the NL and PI MS-based methods, we identified and characterized 3 and 13 unknown AHL and HQ compounds, respectively, in biological samples. One of the newly found AHL molecules was C12-AHL, first quantified in Pseudomonas aeruginosa bacterial cultures. The MRM quantitation of analytes in plasma from patients with sepsis confirmed the analytical ability of MRM for the quantification of virulence factors during sepsis.

The Principles, Mechanisms, and Benefits of Unconventional Agents in the Treatment of Biofilm Infection

Today, researchers are looking at new ways to treat severe infections caused by resistance to standard antibiotic therapy. This is quite challenging due to the complex and interdependent relationships involved: the cause of infection-the patient-antimicrobial agents. The sessile biofilm form is essential in research to reduce resistance to very severe infections (such as ESKAPE pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanni, Pseudomonas aeruginosa, and Enterobacter spp). The purpose of this study is to elucidate the mechanisms of the occurrence, maintenance, and suppression of biofilm infections. One form of biofilm suppression is the efficient action of natural antagonists of bacteria-bacteriophages. Bacteriophages effectively penetrate the biofilm's causative cells. They infect those bacterial cells and either destroy them or prevent the infection spreading. In this process, bacteriophages are specific, relatively easy to apply, and harmless to the patient. Antimicrobial peptides (AMPs) support the mechanisms of bacteriophages' action. AMPs could also attack and destroy infectious agents on their own (even on biofilm). AMPs are simple, universal peptide molecules, mainly cationic peptides. Additional AMP research could help develop even more effective treatments of biofilm (bacteriophages, antibiotics, AMPs, nanoparticles). Here, we review recent unconventional agents, such as bacteriophages and AMPs, used for eradication of biofilm, providing an overview of potentially new biofilm treatment strategies.