Role of alginate and its O acetylation in formation of Pseudomonas aeruginosa microcolonies and biofilms

Antimicrobial resistance and carbapenemase dissemination in Pseudomonas aeruginosa isolates from Libyan hospitals: a call for surveillance and intervention

Pseudomonas aeruginosa is a multidrug-resistant bacterium capable of forming biofilms. This study aimed to assess resistance of clinical isolates from Libyan hospitals to antipseudomonal antibiotics, the prevalence of selected extended-spectrum β-lactamases and carbapenemase genes among these isolates, and the microorganisms' capacity for alginate and biofilm production. Forty-five isolates were collected from four hospitals in Benghazi and Derna, Libya. Antimicrobial susceptibility was determined using agar disc diffusion. The presence of resistance genes (blaCTXM, blaTEM, blaSHV-1, blaGES-1, blaKPC, and blaNDM) was screened using PCR. Biofilm formation was quantified via the crystal violet assay, while alginate production was measured spectrophotometrically. Resistance to antipseudomonal antibiotics ranged from 48.9% to 75.6%. The most prevalent resistance gene was blaNDM (26.7%), followed by blaGES-1 (17.8%). Moreover, all isolates demonstrated varying degrees of biofilm-forming ability and alginate production. No statistically significant correlation was found between biofilm formation and alginate production. The dissemination of resistant genes in P. aeruginosa, particularly carbapenemases, is of great concern. This issue is compounded by the bacteria's biofilm-forming capability. Urgent intervention and continuous surveillance are imperative to prevent further deterioration and the catastrophic spread of resistance among these formidable bacteria.

Evolution and host-specific adaptation of Pseudomonas aeruginosa

The major human bacterial pathogen Pseudomonas aeruginosa causes multidrug-resistant infections in people with underlying immunodeficiencies or structural lung diseases such as cystic fibrosis (CF). We show that a few environmental isolates, driven by horizontal gene acquisition, have become dominant epidemic clones that have sequentially emerged and spread through global transmission networks over the past 200 years. These clones demonstrate varying intrinsic propensities for infecting CF or non-CF individuals (linked to specific transcriptional changes enabling survival within macrophages); have undergone multiple rounds of convergent, host-specific adaptation; and have eventually lost their ability to transmit between different patient groups. Our findings thus explain the pathogenic evolution of P. aeruginosa and highlight the importance of global surveillance and cross-infection prevention in averting the emergence of future epidemic clones.

Rational design of PspAlgL to improve its thermostability and anti-biofilm activity against Pseudomonas aeruginosa

Pseudomonas aeruginosa biofilm enhances tolerance to antimicrobials and immune system defenses. Alginate is an important component of biofilm and a virulence factor of P. aeruginosa. The degradation of alginate by alginate lyases has come to serve as an adjunctive therapeutic strategy against P. aeruginosa biofilm, but poor stability of the enzyme limited this application. Thus, PspAlgL, an alginate lyase, can degrade acetylated alginate but has poor thermostability. The 3D structure of PspAlgL was predicted, and the thermostability of PspAlgL was rationally designed by GRAPE strategy, resulting in two variants with better stability. These variants, PspAlgLS270F/E311P and PspAlgLG291S/E311P, effectively degraded the alginate in biofilm. In addition, compared with PspAlgL, these variants were more efficient in inhibiting biofilm formation and degrading the established biofilm of P. aeruginosa PAO1, and they were also able to destroy the biofilm attached to catheters and to increase the sensitivity of P. aeruginosa to the antibiotic amikacin. This study provides one potential anti-biofilm agent for P. aeruginosa infection.

Genomic insights into the evolution, pathogenicity, and extensively drug-resistance of emerging pathogens Kluyvera and Phytobacter

Introduction

Kluyvera is a Gram-negative, flagellated, motile bacillus within the Enterobacteriaceae. The case reports of clinical infections shed light on the importance of this organism as an emerging opportunistic pathogen. The genus Phytobacter, which often be misidentified with Kluyvera, is also an important clinically relevant member of the Enterobacteriaceae. However, the identification of Kluyvera and Phytobacter is problematic, and their phylogenetic relationship remains unclear.

Methods

Here, 81 strains of Kluyvera and 16 strains of Phytobacter were collected. A series of comparative genomics approaches were applied to the phylogenetic relationship reconstruction, virulence related genes profiles description, and antibiotic resistance genes prediction.

Results

Using average nucleotide identity (ANI) and in silico DNA-DNA hybridization (isDDH), we offered reliable species designations of 97 strains, in which 40 (41.24%) strains were incorrectly labeled. A new Phytobacter genomospecies-1 were defined. Phytobacter and Kluyvera show great genome plasticity and inclusiveness, which may be related to their diverse ecological niches. An intergenomic distances threshold of 0.15875 was used for taxonomy reassignments at the phylogenomic-group level. Further principal coordinates analysis (PCoA) revealed 11 core genes of Kluyvera (pelX, mdtL, bglC, pcak-1, uhpB, ddpA-2, pdxY, oppD-1, cptA, yidZ, csbX) that could be served as potential identification targets. Meanwhile, the Phytobacter specific virulence genes clbS, csgA-C, fliS, hsiB1_vipA and hsiC1_vipB, were found to differentiate from Kluyvera. We concluded that the evolution rate of Kluyvera was 5.25E-6, approximately three times higher than that of Phytobacter. Additionally, the co-existence of ESBLs and carbapenem resistance genes were present in approximately 40% strains, suggesting the potential development of extensively drug-resistant or even fully drug-resistant strains.

Discussion

This work provided a better understanding of the differences between closely related species Kluyvera and Phytobacter. Their genomes exhibited great genome plasticity and inclusiveness. They not only possess a potential pathogenicity threat, but also a risk of multi-drug resistance. The emerging pathogens Kluyvera and Phytobacter warrant close attention.

Polyproline peptide targets Klebsiella pneumoniae polysaccharides to collapse biofilms

Hypervirulent Klebsiella pneumoniae is known for its increased extracellular polysaccharide production. Biofilm matrices of hypervirulent K. pneumoniae have increased polysaccharide abundance and are uniquely susceptible to disruption by peptide bactenecin 7 (bac7 (1-35)). Here, using confocal microscopy, we show that polysaccharides within the biofilm matrix collapse following bac7 (1-35) treatment. This collapse led to the release of cells from the biofilm, which were then killed by the peptide. Characterization of truncated peptide analogs revealed that their interactions with polysaccharide were responsible for the biofilm matrix changes that accompany bac7 (1-35) treatment. Ultraviolet photodissociation mass spectrometry with the parental peptide or a truncated analog bac7 (10-35) reveal the important regions for bac7 (1-35) complexing with polysaccharides. Finally, we tested bac7 (1-35) using a murine skin abscess model and observed a significant decrease in the bacterial burden. These findings unveil the potential of bac7 (1-35) polysaccharide interactions to collapse K. pneumoniae biofilms.

Antimicrobial Activity of Trigonelline Hydrochloride Against Pseudomonas aeruginosa and Its Quorum-Sensing Regulated Molecular Mechanisms on Biofilm Formation and Virulence

Pseudomonas aeruginosa, a vivid biofilm-producing bacterium, is considered a dreadful opportunistic pathogen, and thus, management of biofilm-associated infections due to multidrug resistant strains by traditional drugs currently is of great concern. This study was aimed to assess the impact of trigonelline hydrochloride, a pyridine alkaloid, on P. aeruginosa PAO1, in search of an alternative therapeutant. The effect of trigonelline on colony morphology and motility was studied along with its role on biofilm and expression virulence factors. Trigonelline influenced the colony structure, motility, biofilm architecture, and the production of virulence factors in a dose-dependent manner. Alterations in quorum sending (QS)-regulated gene expression after treatment and molecular docking analysis for certain regulator proteins confirmed its effect on the QS-system network by affecting Las, Rhl, and Pqs signaling pathways and as possible molecular targets. Thus, trigonelline might be considered as a potential chemical lead to manage biofilm-associated pathogenesis or to develop other analogues with enhanced pharmacokinetic actions.

Synthesis and application of bacterial exopolysaccharides

Exopolysaccharides are produced and excreted by bacteria in the generation of biofilms to provide a protective environment. These polysaccharides are generally generated as heterogeneous polymers of varying length, featuring diverse substitution patterns. To obtain well-defined fragments of these polysaccharides, organic synthesis often is the method of choice, as it allows for full control over chain length and the installation of a pre-determined substitution pattern. This review presents several recent syntheses of exopolysaccharide fragments of Pseudomonas aeruginosa and Staphylococcus aureus and illustrates how these have been used to study biosynthesis enzymes and generate synthetic glycoconjugate vaccines.

Role of extracellular matrix components in biofilm formation and adaptation of Pseudomonas ogarae F113 to the rhizosphere environment

Regulating the transition of bacteria from motile to sessile lifestyles is crucial for their ability to compete effectively in the rhizosphere environment. Pseudomonas are known to rely on extracellular matrix (ECM) components for microcolony and biofilm formation, allowing them to adapt to a sessile lifestyle. Pseudomonas ogarae F113 possesses eight gene clusters responsible for the production of ECM components. These gene clusters are tightly regulated by AmrZ, a major transcriptional regulator that influences the cellular levels of c-di-GMP. The AmrZ-mediated transcriptional regulation of ECM components is primarily mediated by the signaling molecule c-di-GMP and the flagella master regulator FleQ. To investigate the functional role of these ECM components in P. ogarae F113, we performed phenotypic analyses using mutants in genes encoding these ECM components. These analyses included assessments of colony morphology, dye-staining, static attachment to abiotic surfaces, dynamic biofilm formation on abiotic surfaces, swimming motility, and competitive colonization assays of the rhizosphere. Our results revealed that alginate and PNAG polysaccharides, along with PsmE and the fimbrial low molecular weight protein/tight adherence (Flp/Tad) pilus, are the major ECM components contributing to biofilm formation. Additionally, we found that the majority of these components and MapA are needed for a competitive colonization of the rhizosphere in P. ogarae F113.

In vitro inhibition of Pseudomonas aeruginosa PAO1 biofilm formation by DZ2002 through regulation of extracellular DNA and alginate production

Introduction

Pseudomonas aeruginosa (P. aeruginosa) is a common pathogen associated with biofilm infections, which can lead to persistent infections. Therefore, there is an urgent need to develop new anti-biofilm drugs. DZ2002 is a reversible inhibitor that targets S-adenosylhomocysteine hydrolase and possesses anti-inflammatory and immune-regulatory activities. However, its anti-biofilm activity has not been reported yet.

Methods and results

Therefore, we investigated the effect of DZ2002 on P. aeruginosa PAO1 biofilm formation by crystal violet staining (CV), real-time quantitative polymerase chain reaction (RT-qPCR) and confocal laser scanning microscopy (CLSM). The results indicated that although DZ2002 didn't affect the growth of planktonic PAO1, it could significantly inhibit the formation of mature biofilms. During the inhibition of biofilm formation by DZ2002, there was a parallel decrease in the synthesis of alginate and the expression level of alginate genes, along with a weakening of swarming motility. However, these results were unrelated to the expression of lasI, lasR, rhII, rhIR. Additionally, we also found that after treatment with DZ2002, the biofilms and extracellular DNA content of PAO1 were significantly reduced. Molecular docking results further confirmed that DZ2002 had a strong binding affinity with the active site of S-adenosylhomocysteine hydrolase (SahH) of PAO1.

Discussion

In summary, our results indicated that DZ2002 may interact with SahH in PAO1, inhibiting the formation of mature biofilms by downregulating alginate synthesis, extracellular DNA production and swarming motility. These findings demonstrate the potential value of DZ2002 in treating biofilm infections associated with P. aeruginosa.

Bacterial synergies and antagonisms affecting Pseudomonas aeruginosa virulence in the human lung, skin and intestine

Pseudomonas aeruginosa requires a significant breach in the host defense to cause an infection. While its virulence factors are well studied, its tropism cannot be explained only by studying its interaction with the host. Why are P. aeruginosa infections so rare in the intestine compared with the lung and skin? There is not enough evidence to claim specificity in virulence factors deployed by P. aeruginosa in each anatomical site, and host physiology differences between the lung and the intestine cannot easily explain the observed differences in virulence. This perspective highlights a relatively overlooked parameter in P. aeruginosa virulence, namely, potential synergies with bacteria found in the human skin and lung, as well as antagonisms with bacteria of the human intestine.

Investigating the chemical pathway to the formation of a single biofilm using infrared spectroscopy

Diagnosing biofilm infections has remained a constant challenge for the last 50 years. Existing diagnostic methods struggle to identify the biofilm phenotype. Moreover, most methods of biofilm analysis destroy the biofilm making the resultant data interpretation difficult. In this study we introduce Fourier Transform Infra-Red (FTIR) spectroscopy as a label-free, non-destructive approach to monitoring biofilm progression. We have utilised FTIR in a novel application to evaluate the chemical composition of bacterial biofilms without disrupting the biofilm architecture. S. epidermidis (RP62A) was grown onto calcium fluoride slides for periods of 30 min-96 h, before semi-drying samples for analysis. We report the discovery of a chemical marker to distinguish between planktonic and biofilm samples. The appearance of new proteins in biofilm samples of varying maturity is exemplified in the spectroscopic data, highlighting the potential of FTIR for identifying the presence and developmental stage of a single biofilm.

Ceragenins exhibit bactericidal properties that are independent of the ionic strength in the environment mimicking cystic fibrosis sputum

The purpose of the work was to investigate the impact of sodium chloride (NaCl) on the antimicrobial efficacy of ceragenins (CSAs) and antimicrobial peptides (AMPs) against bacterial and fungal pathogens associated with cystic fibrosis (CF) lung infections. CF-associated bacterial (Pseudomonas aeruginosa, Ochrobactrum spp., and Staphylococcus aureus), and fungal pathogens (Candida albicans, and Candida tropicalis) were used as target organisms for ceragenins (CSA-13 and CSA-131) and AMPs (LL-37 and omiganan). Susceptibility to the tested compounds was assessed using minimal inhibitory concentrations (MICs) and bactericidal concentrations (MBCs), as well as by colony counting assays in CF sputum samples supplemented with various concentrations of NaCl. Our results demonstrated that ceragenins exhibit potent antimicrobial activity in CF sputum regardless of the NaCl concentration when compared to LL-37 and omiganan. Given the broad-spectrum antimicrobial activity of ceragenins in the microenvironments mimicking the airways of CF patients, ceragenins might be promising agents in managing CF disease.

Pseudomonas aeruginosa biofilm exopolysaccharides: assembly, function, and degradation

The biofilm matrix is a fortress; sheltering bacteria in a protective and nourishing barrier that allows for growth and adaptation to various surroundings. A variety of different components are found within the matrix including water, lipids, proteins, extracellular DNA, RNA, membrane vesicles, phages, and exopolysaccharides. As part of its biofilm matrix, Pseudomonas aeruginosa is genetically capable of producing three chemically distinct exopolysaccharides - alginate, Pel, and Psl - each of which has a distinct role in biofilm formation and immune evasion during infection. The polymers are produced by highly conserved mechanisms of secretion, involving many proteins that span both the inner and outer bacterial membranes. Experimentally determined structures, predictive modelling of proteins whose structures are yet to be solved, and structural homology comparisons give us insight into the molecular mechanisms of these secretion systems, from polymer synthesis to modification and export. Here, we review recent advances that enhance our understanding of P. aeruginosa multiprotein exopolysaccharide biosynthetic complexes, and how the glycoside hydrolases/lyases within these systems have been commandeered for antimicrobial applications.

Pseudomonas aeruginosa AlgF is a protein-protein interaction mediator required for acetylation of the alginate exopolysaccharide

Enzymatic modifications of bacterial exopolysaccharides enhance immune evasion and persistence during infection. In the Gram-negative opportunistic pathogen Pseudomonas aeruginosa, acetylation of alginate reduces opsonic killing by phagocytes and improves reactive oxygen species scavenging. Although it is well known that alginate acetylation in P. aeruginosa requires AlgI, AlgJ, AlgF, and AlgX, how these proteins coordinate polymer modification at a molecular level remains unclear. Here, we describe the structural characterization of AlgF and its protein interaction network. We characterize direct interactions between AlgF and both AlgJ and AlgX in vitro and demonstrate an association between AlgF and AlgX, as well as AlgJ and AlgI, in P. aeruginosa. We determine that AlgF does not exhibit acetylesterase activity and is unable to bind to polymannuronate in vitro. Therefore, we propose that AlgF functions to mediate protein-protein interactions between alginate acetylation enzymes, forming the periplasmic AlgJFXK (AlgJ-AlgF-AlgX-AlgK) acetylation and export complex required for robust biofilm formation.

Challenges and current advances in in vitro biofilm characterization

Biofilms are structured communities of bacterial cells encased in a self-produced polymeric matrix, which develop over time and exhibit temporal responses to stimuli from internal biological processes or external environmental changes. They can be detrimental, threatening public health and causing economic loss, while they also play beneficial roles in ecosystem health, biotechnology processes, and industrial settings. Biofilms express extreme heterogeneity in their physical properties and structural composition, resulting in critical challenges in understanding them comprehensively. The lack of detailed knowledge of biofilms and their phenotypes has deterred significant progress in developing strategies to control their negative impacts and take advantage of their beneficial applications. A range of in vitro models and characterization tools have been developed and used to study biofilm growth and, specifically, to investigate the impact of environmental and growth factors on their development. This review article discusses the existing knowledge of biofilm properties and explains how external factors, such as flow condition, surface, interface, and host factor, may impact biofilm growth. The limitations of current tools, techniques, and in vitro models that are currently used for biofilms are also presented.

Comparative genomics of Stutzerimonas balearica (Pseudomonas balearica): diversity, habitats, and biodegradation of aromatic compounds

Stutzerimonas balearica (Pseudomonas balearica) has been found principally in oil-polluted environments. The capability of S. balearica to thrive from the degradation of pollutant compounds makes it a species of interest for potential bioremediation applications. However, little has been reported about the diversity of S. balearica. In this study, genome sequences of S. balearica strains from different origins were analyzed, revealing that it is a diverse species with an open pan-genome that will continue revealing new genes and functionalities as the genomes of more strains are sequenced. The nucleotide signatures and intra- and inter-species variation of the 16S rRNA genes of S. balearica were reevaluated. A strategy of screening 16S rRNA gene sequences in public databases enabled the detection of 158 additional strains, of which only 23% were described as S. balearica. The species was detected from a wide range of environments, although mostly from aquatic and polluted environments, predominantly related to petroleum oil. Genomic and phenotypic analyses confirmed that S. balearica possesses varied inherent capabilities for aromatic compounds degradation. This study increases the knowledge of the biology and diversity of S. balearica and will serve as a basis for future work with the species.

Development of the Pseudomonas syringae pv. morsprunorum Biofilm Monitored in Real Time Using Attenuated Total Reflection Fourier Transform Infrared Measurements in a Flow Cell Chamber

Biofilms of sessile Pseudomonas syringae cells formed on top of plant host's leaves or fruits allow surviving harsh environmental conditions (desiccation) and improve their resistance to antibacterial treatments of crops. A better understanding of these biofilms can help minimize their effect on harvests. In the present study, infrared attenuated total reflection spectroscopy coupled with optical and confocal laser scanning microscopy has been applied for the first time to analyze Pseudomonas syringae pathovar morsprunorum biofilm development in real time. The biofilm development was observed within a spectral window 4000-800 cm^-1 under constant flow conditions for 72 h. The kinetics of representative integrated band areas (nucleic acids with polysaccharides at 1141-1006 cm^-1, amino acid side chains with free fatty acids at 1420-1380 cm^-1, proteins at 1580-1490 cm^-1, and lipids with proteins at 2935-2915 cm^-1) were analyzed with regard to the observed biofilm structure and the following P. syringae biofilm developmental stages were attributed: The inoculation phase, washing of weakly attached bacteria closely followed by recolonization of the vacated surface, the restructuration phase, and finally the maturation phase.

Mechanism of resistance to phagocytosis and pulmonary persistence in mucoid Pseudomonas aeruginosa

Introduction

Pseudomonas aeruginosa is known for its ability to form biofilms, which are dependent on the production of exopolysaccharides. During chronic colonization of the airway and biofilm formation, P. aeruginosa converts to a mucoid phenotype, indicating production of the exopolysaccharide alginate. The mucoid phenotype promotes resistance to phagocytic killing, but the mechanism has not been established.

Methods and Results

To better understand the mechanism of phagocytic evasion conferred by alginate production, Human (THP-1) and murine (MH-S) macrophage cell lines were used to determine the effects of alginate production on macrophage binding, signaling and phagocytosis. Phagocytosis assays using mucoid clinical isolate FRD1 and its non-mucoid algD mutant showed that alginate production inhibited opsonic and non-opsonic phagocytosis, but exogenous alginate was not protective. Alginate caused a decrease in binding to murine macrophages. Blocking antibodies to CD11b and CD14 showed that these receptors were important for phagocytosis and were blocked by alginate. Furthermore, alginate production decreased the activation of signaling pathways required for phagocytosis. Mucoid and non-mucoid bacteria induced similar levels of MIP-2 from murine macrophages.

Discussion

This study demonstrated for the first time that alginate on the bacterial surface inhibits receptor-ligand interactions important for phagocytosis. Our data suggest that there is a selection for alginate conversion that blocks the earliest steps in phagocytosis, leading to persistence during chronic pulmonary infections.

A review on the synthesis and development of alginate hydrogels for wound therapy

Convenient and low-cost dressings can reduce the difficulty of wound treatment. Alginate gel dressings have the advantages of low cost and safe usage, and they have obvious potential for development in biomedical materials. Alginate gel dressings are currently a research area of great interest owing to their versatility, intelligent, and their application attempts in treating complex wounds. We present a detailed summary of the preparation of alginate hydrogels and a study of their performance improvement. Herein, we summarize the various applications of alginate hydrogels. The research focuses in this area mainly include designing multifunctional dressings for the treatment of various wounds and fabricating specialized dressings to assist physicians in the treatment of complex wounds (TOC). This review gives an outlook for future directions in the field of alginate hydrogel dressings. We hope to attract more research interest and studies in alginate hydrogel dressings, thus contributing to the creation of low-cost and highly effective wound treatment materials.

A clash of quorum sensing vs quorum sensing inhibitors: an overview and risk of resistance

Indiscriminate use of antibiotics to treat microbial pathogens has caused emergence of multiple drug resistant strains. Most infectious diseases are caused by microbes that are capable of intercommunication using signaling molecules, which is known as quorum sensing (QS). Such pathogens express their pathogenicity through various QS-regulated virulence factors. Interference of QS could lead to decisive results in controlling such pathogenicity. Hence, QS inhibition has become an attractive new approach for the development of novel drugs. Many quorum sensing inhibitors (QSIs) of diverse origins have been reported. It is imperative that more such anti-QS compounds be found and studied, as they have significant effect on microbial pathogenicity. This review attempts to give a brief account of QS mechanism, its inhibition and describes some compounds with anti-QS potential. Also discussed is the possibility of emergence of quorum sensing resistance.

Polyamines and linear DNA mediate bacterial threat assessment of bacteriophage infection

Monitoring the extracellular environment for danger signals is a critical aspect of cellular survival. However, the danger signals released by dying bacteria and the mechanisms bacteria use for threat assessment remain largely unexplored. Here, we show that lysis of Pseudomonas aeruginosa cells releases polyamines that are subsequently taken up by surviving cells via a mechanism that relies on Gac/Rsm signaling. While intracellular polyamines spike in surviving cells, the duration of this spike varies according to the infection status of the cell. In bacteriophage-infected cells, intracellular polyamines are maintained at high levels, which inhibits replication of the bacteriophage genome. Many bacteriophages package linear DNA genomes and linear DNA is sufficient to trigger intracellular polyamine accumulation, suggesting that linear DNA is sensed as a second danger signal. Collectively, these results demonstrate how polyamines released by dying cells together with linear DNA allow P. aeruginosa to make threat assessments of cellular injury.

Polysaccharides' Structures and Functions in Biofilm Architecture of Antimicrobial-Resistant (AMR) Pathogens

Bacteria and fungi have developed resistance to the existing therapies such as antibiotics and antifungal drugs, and multiple mechanisms are mediating this resistance. Among these, the formation of an extracellular matrix embedding different bacterial cells, called biofilm, is an effective strategy through which bacterial and fungal cells are establishing a relationship in a unique environment. The biofilm provides them the possibility to transfer genes conferring resistance, to prevent them from desiccation and to impede the penetration of antibiotics or antifungal drugs. Biofilms are formed of several constituents including extracellular DNA, proteins and polysaccharides. Depending on the bacteria, different polysaccharides form the biofilm matrix in different microorganisms, some of them involved in the first stage of cells' attachment to surfaces and to each other, and some responsible for giving the biofilm structure resistance and stability. In this review, we describe the structure and the role of different polysaccharides in bacterial and fungal biofilms, we revise the analytical methods to characterize them quantitatively and qualitatively and finally we provide an overview of potential new antimicrobial therapies able to inhibit biofilm formation by targeting exopolysaccharides.

Monitoring biofilm growth and dispersal in real-time with impedance biosensors

Microbial biofilm contamination is a widespread problem that requires precise and prompt detection techniques to effectively control its growth. Microfabricated electrochemical impedance spectroscopy (EIS) biosensors offer promise as a tool for early biofilm detection and monitoring of elimination. This study utilized a custom flow cell system with integrated sensors to make real-time impedance measurements of biofilm growth under flow conditions, which were correlated with confocal laser scanning microscopy (CLSM) imaging. Biofilm growth on EIS biosensors in basic aqueous growth media (tryptic soy broth, TSB) and an oil-water emulsion (metalworking fluid, MWF) attenuated in a sigmoidal decay pattern, which lead to an ∼22-25% decrease in impedance after 24 Hrs. Subsequent treatment of established biofilms increased the impedance by ∼14% and ∼41% in TSB and MWF, respectively. In the presence of furanone C-30, a quorum-sensing inhibitor (QSI), impedance remained unchanged from the initial time point for 18 Hrs in TSB and 72 Hrs in MWF. Biofilm changes enumerated from CLSM imaging corroborated impedance measurements, with treatment significantly reducing biofilm. Overall, these results support the application of microfabricated EIS biosensors for evaluating the growth and dispersal of biofilm in situ and demonstrate potential for use in industrial settings.

ONE-SENTENCE SUMMARY

This study demonstrates the use of microfabricated electrochemical impedance spectroscopy (EIS) biosensors for real-time monitoring and treatment evaluation of biofilm growth, offering valuable insights for biofilm control in industrial settings.

Systems-Wide Dissection of Organic Acid Assimilation in Pseudomonas aeruginosa Reveals a Novel Path To Underground Metabolism

The human pathogen Pseudomonas aeruginosa (Pa) is one of the most frequent and severe causes of nosocomial infection. This organism is also a major cause of airway infections in people with cystic fibrosis (CF). Pa is known to have a remarkable metabolic plasticity, allowing it to thrive under diverse environmental conditions and ecological niches; yet, little is known about the central metabolic pathways that sustain its growth during infection or precisely how these pathways operate. In this work, we used a combination of 'omics approaches (transcriptomics, proteomics, metabolomics, and ¹³C-fluxomics) and reverse genetics to provide systems-level insight into how the infection-relevant organic acids succinate and propionate are metabolized by Pa. Moreover, through structural and kinetic analysis of the 2-methylcitrate synthase (2-MCS; PrpC) and its paralogue citrate (CIT) synthase (GltA), we show how these two crucial enzymatic steps are interconnected in Pa organic acid assimilation. We found that Pa can rapidly adapt to the loss of GltA function by acquiring mutations in a transcriptional repressor, which then derepresses prpC expression. Our findings provide a clear example of how "underground metabolism," facilitated by enzyme substrate promiscuity, "rewires" Pa metabolism, allowing it to overcome the loss of a crucial enzyme. This pathogen-specific knowledge is critical for the advancement of a model-driven framework to target bacterial central metabolism. IMPORTANCE Pseudomonas aeruginosa is an opportunistic human pathogen that, due to its unrivalled resistance to antibiotics, ubiquity in the built environment, and aggressiveness in infection scenarios, has acquired the somewhat dubious accolade of being designated a "critical priority pathogen" by the WHO. In this work, we uncover the pathways and mechanisms used by P. aeruginosa to grow on a substrate that is abundant at many infection sites: propionate. We found that if the organism is prevented from metabolizing propionate, the substrate turns from being a convenient nutrient source into a potent poison, preventing bacterial growth. We further show that one of the enzymes involved in these reactions, 2-methylcitrate synthase (PrpC), is promiscuous and can moonlight for another essential enzyme in the cell (citrate synthase). Indeed, mutations that abolish citrate synthase activity (which would normally prevent the cell from growing) can be readily overcome if the cell acquires additional mutations that increase the expression of PrpC. This is a nice example of the evolutionary utility of so-called "underground metabolism."

Synthetic periphyton as a model system to understand species dynamics in complex microbial freshwater communities

Phototrophic biofilms, also known as periphyton, are microbial freshwater communities that drive crucial ecological processes in streams and lakes. Gaining a deep mechanistic understanding of the biological processes occurring in natural periphyton remains challenging due to the high complexity and variability of such communities. To address this challenge, we rationally developed a workflow to construct a synthetic community by co-culturing 26 phototrophic species (i.e., diatoms, green algae, and cyanobacteria) that were inoculated in a successional sequence to create a periphytic biofilm on glass slides. We show that this community is diverse, stable, and highly reproducible in terms of microbial composition, function, and 3D spatial structure of the biofilm. We also demonstrate the ability to monitor microbial dynamics at the single species level during periphyton development and how their abundances are impacted by stressors such as increased temperature and a herbicide, singly and in combination. Overall, such a synthetic periphyton, grown under controlled conditions, can be used as a model system for theory testing through targeted manipulation.

Co-Exposure of Ambient Particulate Matter and Airborne Transmission Pathogens: The Impairment of the Upper Respiratory Systems

Recent evidence has pinpointed the positive relevance between air particulate matter (PM) pollution and epidemic spread. However, there are still significant knowledge gaps in understanding the transmission and infection of pathogens loaded on PMs, for example, the interactions between pathogens and pre-existing atmospheric PM and the health effects of co-exposure on the inhalation systems. Here, we unraveled the interactions between fine particulate matter (FPM) and Pseudomonas aeruginosa (P. aeruginosa) and evaluated the infection and detrimental effects of co-exposure on the upper respiratory systems in both in vitro and in vivo models. We uncovered the higher accessibility and invasive ability of pathogens to epithelial cells after loading on FPMs, compared with the single exposure. Furthermore, we designed a novel laboratory exposure model to simulate a real co-exposure scenario. Intriguingly, the co-exposure induced more serious functional damage and longer inflammatory reactions to the upper respiratory tract, including the nasal cavity and trachea. Collectively, our results provide a new point of view on the transmission and infection of pathogens loaded on FPMs and uncover the in vivo systematic impairments of the inhalation tract under co-exposure through a novel laboratory exposure model. Hence, this study sheds light on further investigations of the detrimental effects of air pollution and epidemic spread.

Shift of Choline/Betaine Pathway in Recombinant Pseudomonas for Cobalamin Biosynthesis and Abiotic Stress Protection

The B12-producing strains Pseudomonas nitroreducens DSM 1650 and Pseudomonas sp. CCUG 2519 (both formerly Pseudomonas denitrificans), with the most distributed pathway among bacteria for exogenous choline/betaine utilization, are promising recombinant hosts for the endogenous production of B12 precursor betaine by direct methylation of bioavailable glycine or non-proteinogenic β-alanine. Two plasmid-based de novo betaine pathways, distinguished by their enzymes, have provided an expression of the genes encoding for N-methyltransferases of the halotolerant cyanobacterium Aphanothece halophytica or plant Limonium latifolium to synthesize the internal glycine betaine or β-alanine betaine, respectively. These betaines equally allowed the recombinant pseudomonads to grow effectively and to synthesize a high level of cobalamin, as well as to increase their protective properties against abiotic stresses to a degree comparable with the supplementation of an exogenous betaine. Both de novo betaine pathways significantly enforced the protection of bacterial cells against lowering temperature to 15 °C and increasing salinity to 400 mM of NaCl. However, the expression of the single plant-derived gene for the β-alanine-specific N-methyltransferase additionally increased the effectiveness of exogenous glycine betaine almost twofold on cobalamin biosynthesis, probably due to the Pseudomonas' ability to use two independent pathways, their own choline/betaine pathway and the plant β-alanine betaine biosynthetic pathway.

Role of Exopolysaccharides of Pseudomonas in Heavy Metal Removal and Other Remediation Strategies

Pseudomonas biofilms have been studied intensively for several decades and research outcomes have been successfully implemented in various medical and agricultural applications. Research on biofilm synthesis and composition has also overlapped with the objectives of environmental sciences, since biofilm components show exceptional physicochemical properties applicable to remediation techniques. Especially, exopolysaccharides (ExPs) have been at the center of scientific interest, indicating their potential in solving the environmental issues of heavy metal land and water contamination via sorptive interactions and flocculation. Since exposure to heavy metal via contaminated water or soil poses an imminent risk to the environment and human health, ExPs provide an interesting and viable solution to this issue, alongside other effective and green remedial techniques (e.g., phytostabilization, implementation of biosolids, and biosorption using agricultural wastes) aiming to restore contaminated sites to their natural, pollution-free state, or to ameliorate the negative impact of heavy metals on the environment. Thus, we discuss the plausible role and performance of Pseudomonas ExPs in remediation techniques, aiming to provide the relevant available and comprehensive information on ExPs’ biosynthesis and their usage in heavy metal remediation or other environmental applications, such as wastewater treatment via bioflocculation and soil remediation.

The SGNH hydrolase family: a template for carbohydrate diversity

The substitution and de-substitution of carbohydrate materials are important steps in the biosynthesis and/or breakdown of a wide variety of biologically important polymers. The SGNH hydrolase superfamily is a group of related and well-studied proteins with a highly conserved catalytic fold and mechanism composed of 16 member families. SGNH hydrolases can be found in vertebrates, plants, fungi, bacteria, and archaea, and play a variety of important biological roles related to biomass conversion, pathogenesis, and cell signaling. The SGNH hydrolase superfamily is chiefly composed of a diverse range of carbohydrate-modifying enzymes, including but not limited to the carbohydrate esterase families 2, 3, 6, 12 and 17 under the carbohydrate-active enzyme classification system and database (CAZy.org). In this review, we summarize the structural and functional features that delineate these subfamilies of SGNH hydrolases, and which generate the wide variety of substrate preferences and enzymatic activities observed of these proteins to date.

Preclinical Evaluation of Recombinant Microbial Glycoside Hydrolases as Antibiofilm Agents in Acute Pulmonary Pseudomonas aeruginosa Infection

The bacterium Pseudomonas aeruginosa can colonize the airways of patients with chronic lung disease. Within the lung, P. aeruginosa forms biofilms that can enhance resistance to antibiotics and immune defenses. P. aeruginosa biofilm formation is dependent on the secretion of matrix exopolysaccharides, including Pel and Psl. In this study, recombinant glycoside hydrolases (GHs) that degrade Pel and Psl were evaluated alone and in combination with antibiotics in a mouse model of P. aeruginosa infection. Intratracheal GH administration was well tolerated by mice. Pharmacokinetic analysis revealed that, although GHs have short half-lives, administration of two GHs in combination resulted in increased GH persistence. Combining GH prophylaxis and treatment with the antibiotic ciprofloxacin resulted in greater reduction in pulmonary bacterial burden than that with either agent alone. This study lays the foundation for further exploration of GH therapy in bacterial infections.

Virulence Factors of Pseudomonas Aeruginosa and Antivirulence Strategies to Combat Its Drug Resistance

Pseudomonas aeruginosa is an opportunistic pathogen causing nosocomial infections in severely ill and immunocompromised patients. Ubiquitously disseminated in the environment, especially in hospitals, it has become a major threat to human health due to the constant emergence of drug-resistant strains. Multiple resistance mechanisms are exploited by P. aeruginosa, which usually result in chronic infections difficult to eradicate. Diverse virulence factors responsible for bacterial adhesion and colonization, host immune suppression, and immune escape, play important roles in the pathogenic process of P. aeruginosa. As such, antivirulence treatment that aims at reducing virulence while sparing the bacterium for its eventual elimination by the immune system, or combination therapies, has significant advantages over traditional antibiotic therapy, as the former imposes minimal selective pressure on P. aeruginosa, thus less likely to induce drug resistance. In this review, we will discuss the virulence factors of P. aeruginosa, their pathogenic roles, and recent advances in antivirulence drug discovery for the treatment of P. aeruginosa infections.

The role of the Pseudomonas aeruginosa hypermutator phenotype on the shift from acute to chronic virulence during respiratory infection

Chronic respiratory infection (CRI) with Pseudomonas aeruginosa (Pa) presents many unique challenges that complicate treatment. One notable challenge is the hypermutator phenotype which is present in up to 60% of sampled CRI patient isolates. Hypermutation can be caused by deactivating mutations in DNA mismatch repair (MMR) genes including mutS, mutL, and uvrD. In vitro and in vivo studies have demonstrated hypermutator strains to be less virulent than wild-type Pa. However, patients colonized with hypermutators display poorer lung function and a higher incidence of treatment failure. Hypermutation and MMR-deficiency create increased genetic diversity and population heterogeneity due to elevated mutation rates. MMR-deficient strains demonstrate higher rates of mucoidy, a hallmark virulence determinant of Pa during CRI in cystic fibrosis patients. The mucoid phenotype results from simple sequence repeat mutations in the mucA gene made in the absence of functional MMR. Mutations in Pa are further increased in the absence of MMR, leading to microcolony biofilm formation, further lineage diversification, and population heterogeneity which enhance bacterial persistence and host immune evasion. Hypermutation facilitates the adaptation to the lung microenvironment, enabling survival among nutritional complexity and microaerobic or anaerobic conditions. Mutations in key acute-to-chronic virulence “switch” genes, such as retS, bfmS, and ampR, are also catalyzed by hypermutation. Consequently, strong positive selection for many loss-of-function pathoadaptive mutations is seen in hypermutators and enriched in genes such as lasR. This results in the characteristic loss of Pa acute infection virulence factors, including quorum sensing, flagellar motility, and type III secretion. Further study of the role of hypermutation on Pa chronic infection is needed to better inform treatment regimens against CRI with hypermutator strains.

Natural Biopolymers as Additional Tools for Cell Microencapsulation Applied to Cellular Therapy

One of the limitations in organ, tissue or cellular transplantations is graft rejection. To minimize or prevent this, recipients must make use of immunosuppressive drugs (IS) throughout their entire lives. However, its continuous use generally causes several side effects. Although some IS dose reductions and withdrawal strategies have been employed, many patients do not adapt to these protocols and must return to conventional IS use. Therefore, many studies have been carried out to offer treatments that may avoid IS administration in the long term. A promising strategy is cellular microencapsulation. The possibility of microencapsulating cells originates from the opportunity to use biomaterials that mimic the extracellular matrix. This matrix acts as a support for cell adhesion and the syntheses of new extracellular matrix self-components followed by cell growth and survival. Furthermore, by involving the cells in a polymeric matrix, the matrix acts as an immunoprotective barrier, protecting cells against the recipient’s immune system while still allowing essential cell survival molecules to diffuse bilaterally through the polymer matrix pores. In addition, this matrix can be associated with IS, thus diminishing systemic side effects. In this context, this review will address the natural biomaterials currently in use and their importance in cell therapy.

Design, Synthesis, and Quorum Quenching Potential of Novel Catechol–Zingerone Conjugate to Find an Elixir to Tackle Pseudomonas aeruginosa Through the Trojan Horse Strategy

To address the issue of multidrug resistance in Pseudomonas aeruginosa, a novel catechol–zingerone conjugate (1) linked via a non-hydrolyzable 1,2,3-triazole linker was synthesized and subjected to biological evaluation based on the Trojan horse strategy. To enhance the efficacy, catechol, a xenosiderophore, utilized by P. aeruginosa for iron assimilation, and the dietary phytochemical zingerone, known for its anti-virulent activity against Pseudomonas aeruginosa, were exploited in the present study. Theoretical validation of conjugate (1) was conducted by in silico molecular docking analysis to determine the interaction with outer membrane transport receptor PirA and quorum sensing signal receptors. In addition, nine-fold binding affinity of Conjugate (1) toward PirA (5FP2) in comparison to its natural ligand catechol with D-score −1.13 Å authenticated the designed Trojan horse drug. Conjugate (1) showed stronger anti-virulent activity than zingerone; hence, it exhibited a promising anti-biofilm efficacy as assessed by crystal violet assay and visualized by FESEM toward P. aeruginosa. Encouraging results against P. aeruginosa in terms of quorum sensing regulated virulence factors, motility phenotypes, and biofilm formation with no cell cytotoxicity and could help open hitherto unexplored possibilities of establishing Trojan horse drugs as a successful approach against multidrug resistance in P. aeruginosa.

Microbially-derived cocktail of carbohydrases as an anti-biofouling agents: a 'green approach'

Enzymes, also known as biocatalysts, display vital properties like high substrate specificity, an eco-friendly nature, low energy inputs, and cost-effectiveness. Among their numerous known applications, enzymes that can target biofilms or their components are increasingly being investigated for their anti-biofouling action, particularly in healthcare, food manufacturing units and environmental applications. Enzymes can target biofilms at different levels like during the attachment of microorganisms, formation of exopolymeric substances (EPS), and their disruption thereafter. In this regard, a consortium of carbohydrases that can target heterogeneous polysaccharides present in the EPS matrix may provide an effective alternative to conventional chemical anti-biofouling methods. Further, for complete annihilation of biofilms, enzymes can be used alone or in conjunction with other antimicrobial agents. Enzymes hold the promise to replace the conventional methods with greener, more economical, and more efficient alternatives. The present article explores the potential and future perspectives of using carbohydrases as effective anti-biofilm agents.

Therapeutic stem cell-derived alveolar-like macrophages display bactericidal effects and resolve Pseudomonas aeruginosa-induced lung injury

Bacterial lung infections lead to greater than 4 million deaths per year with antibiotic treatments driving an increase in antibiotic resistance and a need to establish new therapeutic approaches. Recently, we have generated mouse and rat stem cell‐derived alveolar‐like macrophages (ALMs), which like primary alveolar macrophages (1'AMs), phagocytose bacteria and promote airway repair. Our aim was to further characterize ALMs and determine their bactericidal capabilities. The characterization of ALMs showed that they share known 1'AM cell surface markers, but unlike 1'AMs are highly proliferative in vitro. ALMs effectively phagocytose and kill laboratory strains of P. aeruginosa (P.A.), E. coli (E.C.) and S. aureus, and clinical strains of P.A. In vivo, ALMs remain viable, adapt additional features of native 1'AMs, but proliferation is reduced. Mouse ALMs phagocytose P.A. and E.C. and rat ALMs phagocytose and kill P.A. within the lung 24 h post‐instillation. In a pre‐clinical model of P.A.‐induced lung injury, rat ALM administration mitigated weight loss and resolved lung injury observed seven days post‐instillation. Collectively, ALMs attenuate pulmonary bacterial infections and promote airway repair. ALMs could be utilized as an alternative or adjuvant therapy where current treatments are ineffective against antibiotic‐resistant bacteria or to enhance routine antibiotic delivery.

From Biomedical Applications of Alginate towards CVD Implications Linked to COVID-19

In the past year, researchers have focused their attention on developing new strategies for understanding how the coronavirus affects human health and developing novel biomaterials to help patients with cardiovascular disease, which greatly increases the risk of complications from the virus. Natural biopolymers have been investigated, and it has been proven that alginate-based materials have important features. This review presents an overview of alginate-based materials used for developing innovative biomaterial platforms for biomedical applications to mitigate the effects of the coronavirus. As presented in this review, COVID-19 affects the cardiovascular system, not only the lungs. The first part of the review presents an introduction to cardiovascular diseases and describes how they have become an important problem worldwide. In the second part of the review, the origin and unique properties of the alginate biopolymer are presented. Among the properties of alginate, the most important are its biocompatibility, biodegradability, low cost, nontoxicity, unique structure, and interesting features after chemical modification. The third section of the review illustrates some of the functions of alginate in biomedical, pharmaceutical, and drug delivery applications. Researchers are using alginate to develop new devices and materials for repairing heart tissues that have been damaged by the coronavirus. Further, insights regarding how cardiovascular disease affects COVID-19 patients are also discussed. Finally, we conclude the review by presenting a summary of the impacts of COVID-19 on cardiovascular patients, their implications, and several hypothetical alginate-based treatments for infected patients.

N-acyl Homoserine Lactone Mediated Quorum Sensing Exhibiting Plant Growth-promoting and Abiotic Stress Tolerant Bacteria Demonstrates Drought Stress Amelioration

Multiple plant growth-promoting attributes with N-acyl homoserine lactone (AHL)-mediated quorum sensing exhibiting bacterial strains can help plants to withstand varying abiotic and biotic stress conditions for improving the plant health and productivity. In total, 306 bacterial isolates were isolated from diverse locations and sites. In our exploration, bacterial isolates were screened based on AHL production, plant growth-promoting attributes, abiotic stress tolerance, and antagonistic activity against phytopathogenic fungi. Among the screened 306 isolates, 4 (11VPKHP4, 7VP51.8, P51.10, NBRI N7) were selected based on their efficiency in AHL production, biofilm formation, enduring different abiotic stress conditions, exhibiting plant growth-promoting attributes, and antagonistic activity. Based on 16S rRNA gene sequencing analyses of the selected 4 isolates belong to Pseudomonas genera. Selected isolates 11VPKHP4, 7VP51.8, P51.10, and NBRI N7 were also proficient in biosurfactant production, emulsification, suggesting that all isolates fabricate emulsifiers. The plant growth promotion potential of selected 4 bacterial isolates showed significant growth enhancement in all the vegetative parameters of Zea mays under control as well as drought stress condition. Biochemical parameters and defense enzymes under drought stress conditions were also modulated in the PGPR treated plants as compared to their uninoculated respective controls. With quorum sensing, multiple PGPR attributes, stress tolerance, biofilm formation, and EPS production the selected isolates have the potential to facilitate enhanced plant growth, rhizosphere colonization, maintenance of soil moisture content under normal and diverse stresses.

Competitive Biosynthesis of Bacterial Alginate Using Azotobacter vinelandii 12 for Tissue Engineering Applications

This study investigated the effect of various cultivation conditions (sucrose/phosphate concentrations, aeration level) on alginate biosynthesis using the bacterial producing strain Azotobacter vinelandii 12 by the full factorial design (FFD) method and physicochemical properties (e.g., rheological properties) of the produced bacterial alginate. We demonstrated experimentally the applicability of bacterial alginate for tissue engineering (the cytotoxicity testing using mesenchymal stem cells (MSCs)). The isolated synthesis of high molecular weight (M_w) capsular alginate with a high level of acetylation (25%) was achieved by FFD method under a low sucrose concentration, an increased phosphate concentration, and a high aeration level. Testing the viscoelastic properties and cytotoxicity showed that bacterial alginate with a maximal M_w (574 kDa) formed the densest hydrogels (which demonstrated relatively low cytotoxicity for MSCs in contrast to bacterial alginate with low M_w). The obtained data have shown promising prospects in controlled biosynthesis of bacterial alginate with different physicochemical characteristics for various biomedical applications including tissue engineering.

Enhancing the therapeutic use of biofilm-dispersing enzymes with smart drug delivery systems

Biofilm-dispersing enzymes degrade the extracellular polymeric matrix surrounding bacterial biofilms, disperse the microbial community and increase their susceptibility to antibiotics and immune cells. Challenges for the clinical translation of biofilm-dispersing enzymes involve their susceptibility to denaturation, degradation, and clearance upon administration in vivo. Drug delivery systems aim to overcome these limitations through encapsulation, stabilization and protection from the exterior environment, thereby maintaining the enzymatic activity. Smart drug delivery systems offer target specificity, releasing payloads at the site of infection while minimizing unnecessary systemic exposure. This review highlights critical advances of biofilm-dispersing enzymes as a novel therapeutic approach for biofilm-associated infections. We explore how smart, bio-responsive delivery systems overcome the limiting factors of biofilm-dispersing enzymes and summarize the key systems designed. This review will guide future developments, focusing on utilizing selective and specific therapies in a targeted fashion to meet the unmet therapeutic needs of biofilm infections.

Alginate-Based Smart Materials and Their Application: Recent Advances and Perspectives

Nature produces materials using available molecular building blocks following a bottom-up approach. These materials are formed with great precision and flexibility in a controlled manner. This approach offers the inspiration for manufacturing new artificial materials and devices. Synthetic artificial materials can find many important applications ranging from personalized therapeutics to solutions for environmental problems. Among these materials, responsive synthetic materials are capable of changing their structure and/or properties in response to external stimuli, and hence are termed "smart" materials. Herein, this review focuses on alginate-based smart materials and their stimuli-responsive preparation, fragmentation, and applications in diverse fields from drug delivery and tissue engineering to water purification and environmental remediation. In the first part of this report, we review stimuli-induced preparation of alginate-based materials. Stimuli-triggered decomposition of alginate materials in a controlled fashion is documented in the second part, followed by the application of smart alginate materials in diverse fields. Because of their biocompatibility, easy accessibility, and simple techniques of material formation, alginates can provide solutions for several present and future problems of humankind. However, new research is needed for novel alginate-based materials with new functionalities and well-defined properties for targeted applications.

Challenges and solutions in polymer drug delivery for bacterial biofilm treatment: A tissue-by-tissue account

To tackle the emerging antibiotic resistance crisis, novel antimicrobial approaches are urgently needed. Bacterial communities (biofilms) are a particular concern in this context. Biofilms are responsible for most human infections and are inherently less susceptible to antibiotic treatments. Biofilms have been linked with several challenging chronic diseases, including implant-associated osteomyelitis and chronic wounds. The specific local environments present in the infected tissues further contribute to the rise in antibiotic resistance by limiting the efficacy of systemic antibiotic therapies and reducing drug concentrations at the infection site, which can lead to reoccurring infections. To overcome the shortcomings of systemic drug delivery, encapsulation within polymeric carriers has been shown to enhance antimicrobial efficacy, permeation and retention at the infection site. In this Review, we present an overview of current strategies for antimicrobial encapsulation within polymeric carriers, comparing challenges and solutions on a tissue-by-tissue basis. We compare challenges and proposed drug delivery solutions from the perspective of the local environments for biofilms found in oral, wound, gastric, urinary tract, bone, pulmonary, vaginal, ocular and middle/inner ear tissues. We will also discuss future challenges and barriers to clinical translation for these therapeutics. The following Review demonstrates there is a significant imbalance between the research focus being placed on different tissue types, with some targets (oral and wound biofims) being extensively more studied than others (vaginal and otitis media biofilms and endocarditis). Furthermore, the importance of the local tissue environment when selecting target therapies is demonstrated, with some materials being optimal choices for certain sites of bacterial infection, while having limited applicability in others.

Effect of photocatalysis (TiO2/UVA) on the inactivation and inhibition of Pseudomonas aeruginosa virulence factors expression

Water disinfection using visible light-active photocatalyst has recently attracted more attention due to its potential to inactivate microbes. In this study, we have investigated the efficiency of photocatalysis (TiO₂/UV_A) on the inactivation of Pseudomonas aeruginosa and the attenuation of its virulence factors. For this aim, the photocatalytic effects of TiO₂/UV_A on the cultivability and viability of P. aeruginosa were investigated. Furthermore, during the photocatalysis, the morphology of the bacterial cells was examined by atomic force microscopy (AFM) while the virulence factors were assessed by protease and lipase activities in addition to the mobility and communication of cells. The results revealed that during the photocatalysis the bacterial cells lost their cultivability and viability on agar under the action of the reactive oxygen species generated by the photocatalytic reaction. In addition, AFM observations have shown a damage of the bacterial membrane and a total disruption of the bacterial cells. Moreover, the major virulence factors such as biofilm, lipase and protease expression have been markedly inhibited by TiO₂/UV_A treatment. In addition, the bacteria lost their ability of communication 'quorum sensing' and mobility with twitching and swarming types after 60 min of photocatalytic treatment. Accordingly, TiO₂/UV_A is an effective method to reduce P. aeruginosa virulence and to prevent biofilm formation.

Intraluminal diamond-like carbon coating with anti-adhesion and anti-biofilm effects for uropathogens: A novel technology applicable to urinary catheters

Objectives

To examine anti‐adhesion and anti‐biofilm effects of a diamond‐like carbon coating deposited via a novel technique on the inner surface of a thin silicon tube.

Methods

Diamond‐like carbon coatings were deposited into the lumen of a silicon tube with inner diameters of 2 mm. The surface of the diamond‐like carbon was evaluated using physicochemical methods. We used three clinical isolates including green fluorescent protein‐expressing Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus. We employed a continuous flow system for evaluation of both bacterial adhesion and biofilm formation. Bacterial adhesion assays consisted of counting the number of colony‐forming units and visualization of adhered bacterial cells by scanning electron microscope to evaluate the diamond‐like carbon‐coated/uncoated samples. The biofilm structure was analyzed by confocal laser scanning microscopy on days 3, 5, 7 and 14 for green fluorescent protein‐expressing Pseudomonas aeruginosa.

Results

The smooth and carbon‐rich structure of the intraluminal diamond‐like carbon film remained unchanged after the experiments. The numbers of colony‐forming units suggested lower adherence of green fluorescent protein‐expressing Pseudomonas aeruginosa and Escherichia coli in the diamond‐like carbon‐coated samples compared with the uncoated samples. The scanning electron microscope images showed adhered green fluorescent protein‐expressing Pseudomonas aeruginosa cells without formation of microcolonies on the diamond‐like carbon‐coated samples. Finally, biofilm formation on the diamond‐like carbon‐coated samples was lower until at least day 14 compared with the uncoated samples.

Conclusions

Intraluminal diamond‐like carbon coating on a silicone tube has anti‐adhesion and anti‐biofilm effects. This technology can be applied to urinary catheters made from various materials.

Bismuth subsalicylate incorporated in polycaprolactone-gelatin membranes by electrospinning to prevent bacterial colonization

Periodontitis is a chronic, multifactorial, inflammatory disease characterized by the progressive destruction of the periodontal tissues. Guided tissue regeneration (GTR), involving the use of barrier membranes, is one of the most successful clinical procedures for periodontal therapy. Nevertheless, rapid degradation of the membranes and membrane-related infections are considered two of the major reasons for GTR clinical failure. Recently, integration of non-antibiotic, antimicrobial materials to the membranes has emerged as a novel strategy to face the bacterial infection challenge, without increasing bacterial resistance. In this sense, bismuth subsalicylate (BSS) is a non-antibiotic, metal-based antimicrobial agent effective against different bacterial strains, that has been long safely used in medical treatments. Thus, the aim of the present work was to fabricate fibrillar, non-rapidly bioresorbable, antibacterial GTR membranes composed of polycaprolactone (PCL), gelatin (Gel), and BSS as the antibacterial agent. PCL-G-BSS membranes with three different BSS concentrations (2 wt./v%, 4 wt./v%, and 6 wt./v%) were developed by electrospinning and their morphology, composition, water wettability, mechanical properties, Bi release and degradation rate were characterized. The Cytotoxicity of the membranes was studiedin vitrousing human osteoblasts (hFOB) and gingival fibroblasts (HGF-1), and their antibacterial activity was tested againstAggregatibacter actinomycetemcomitans, Escherichia coli, Porphyromonas gingivalisandStaphylococcus aureus.The membranes obtained exhibited adequate mechanical properties for clinical application, and appropriate degradation rates for allowing periodontal defects regeneration. The hFOB and HGF-1 cells displayed adequate viability when in contact with the lixiviated products from the membranes, and, in general, displayed antibacterial activity against the four bacteria strains tested. Thus, the PCL-G-BSS membranes showed to be appropriate as potential barrier membranes for periodontal GTR treatments.

Biofilm inhibitory effect of alginate lyases on mucoid P. aeruginosa from a cystic fibrosis patient

Chronic mucoid Pseudomonas aeruginosa infections are a major scourge in cystic fibrosis patients. Mucoid P. aeruginosa displays structured alginate-rich biofilms that are resistant to antibiotics. Here, we have assessed the efficacy of a panel of alginate lyases in combating mucoid P. aeruginosa biofilms in cystic fibrosis. Albeit we could not demonstrate alginate degradation by alginate lyases in sputum, we demonstrate that the endotypic alginate lyases, CaAly (from Cellulophaga algicola) and VspAlyVI (from Vibrio sp. QY101) and the exotypic alginate lyases, FspAlyFRB (from Falsirhodobacterium sp. alg1), and SA1-IV (from Sphingomonas sp. A1), indeed inhibit biofilm formation by a mucoid P. aeruginosa strain isolated from the sputum of a cystic fibrosis patient with comparative effect to that of the glycoside hydrolase PslG, a promising candidate for biofilm treatment. We believe that these enzymes should be explored for in vivo efficacy in future studies.

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A P. aeruginosa strain was isolated from the sputum of a cystic fibrosis patient.

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The anti-biofilm efficacy of endotypic and exotypic alginate lyases was assessed.

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Alginate lyases CaAly, VspAlyVI, FspAlyFRB, and SA1-IV inhibited biofilm formation.

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Similar anti-biofilm effect was observed for the glycoside hydrolase, PslG.

Preparation of Alginate-Based Biomaterials and Their Applications in Biomedicine

Alginates are naturally occurring polysaccharides extracted from brown marine algae and bacteria. Being biocompatible, biodegradable, non-toxic and easy to gel, alginates can be processed into various forms, such as hydrogels, microspheres, fibers and sponges, and have been widely applied in biomedical field. The present review provides an overview of the properties and processing methods of alginates, as well as their applications in wound healing, tissue repair and drug delivery in recent years.