Structure-Activity Relationships of Low Molecular Weight Alginate Oligosaccharide Therapy against Pseudomonas aeruginosa.

Low molecular weight alginate oligosaccharides have been shown to exhibit anti-microbial activity against a range of multi-drug resistant bacteria, including Pseudomonas aeruginosa. Previous studies suggested that the disruption of calcium (Ca2+)-DNA binding within bacterial biofilms and dysregulation of quorum sensing (QS) were key factors in these observed effects. To further investigate the contribution of Ca2+ binding, G-block (OligoG) and M-block alginate oligosaccharides (OligoM) with comparable average size DPn 19 but contrasting Ca2+ binding properties were prepared. Fourier-transform infrared spectroscopy demonstrated prolonged binding of alginate oligosaccharides to the pseudomonal cell membrane even after hydrodynamic shear treatment. Molecular dynamics simulations and isothermal titration calorimetry revealed that OligoG exhibited stronger interactions with bacterial LPS than OligoM, although this difference was not mirrored by differential reductions in bacterial growth. While confocal laser scanning microscopy showed that both agents demonstrated similar dose-dependent reductions in biofilm formation, OligoG exhibited a stronger QS inhibitory effect and increased potentiation of the antibiotic azithromycin in minimum inhibitory concentration and biofilm assays. This study demonstrates that the anti-microbial effects of alginate oligosaccharides are not purely influenced by Ca2+-dependent processes but also by electrostatic interactions that are common to both G-block and M-block structures.

Defining in vitro topical antimicrobial and antibiofilm activity of epoxy-tigliane structures against oral pathogens.

Background: Peri-implantitis has become an inexorable clinical challenge in implantology. Topical immunomodulatory epoxy-tiglianes (EBCs), derived from the Queensland blushwood tree, which induce remodeling and resolve dermal infection via induction of the inflammasome and biofilm disruption, may offer a novel therapeutic approach. Design: In vitro antimicrobial activity of EBC structures (EBC-46, EBC-1013 and EBC-147) against Streptococcus mutans, Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis in minimum inhibitory concentration, growth curve and permeabilization assays were determined. Antibiofilm activity was assessed using minimum biofilm eradication concentration (MBEC) experiments. Biofilm formation and disruption assays were analyzed using confocal laser scanning microscopy, scanning electron microscopy and direct plate counting. Results: The observed antimicrobial efficacy of the tested compounds (EBC-1013 > EBC-46 > EBC-147) was directly related to significant membrane permeabilization and growth inhibition (p < 0.05) against planktonic S. mutans and P. gingivalis. Antibiofilm activity was evident in MBEC assays, with S. mutans biofilm formation assays revealing significantly lower biomass volume and increased DEAD:LIVE cell ratio observed for EBC-1013 (p < 0.05). Furthermore, biofilm disruption assays on titanium discs induced significant biofilm disruption in S. mutans and P. gingivalis (p < 0.05). Conclusions: EBC-1013 is a safe, semi-synthetic, compound, demonstrating clear antimicrobial biofilm disruption potential in peri-implantitis.

Bromodomain inhibitor i-BET858 triggers a unique transcriptional response coupled to enhanced DNA damage, cell cycle arrest and apoptosis in high-grade ovarian carcinoma cells.

BACKGROUND: Ovarian cancer has a specific unmet clinical need, with a persistently poor 5-year survival rate observed in women with advanced stage disease warranting continued efforts to develop new treatment options. The amplification of BRD4 in a significant subset of high-grade serous ovarian carcinomas (HGSC) has led to the development of BET inhibitors (BETi) as promising antitumour agents that have subsequently been evaluated in phase I/II clinical trials. Here, we describe the molecular effects and ex vivo preclinical activities of i-BET858, a bivalent pan-BET inhibitor with proven in vivo BRD inhibitory activity. RESULTS: i-BET858 demonstrates enhanced cytotoxic activity compared with earlier generation BETis both in cell lines and primary cells derived from clinical samples of HGSC. At molecular level, i-BET858 triggered a bipartite transcriptional response, comprised of a 'core' network of genes commonly associated with BET inhibition in solid tumours, together with a unique i-BET858 gene signature. Mechanistically, i-BET858 elicited enhanced DNA damage, cell cycle arrest and apoptotic cell death compared to its predecessor i-BET151. CONCLUSIONS: Overall, our ex vivo and in vitro studies indicate that i-BET858 represents an optimal candidate to pursue further clinical validation for the treatment of HGSC.

Alginate oligosaccharides enhance the antifungal activity of nystatin against candidal biofilms.

Background: The increasing prevalence of invasive fungal infections in immuno-compromised patients is a considerable cause of morbidity and mortality. With the rapid emergence of antifungal resistance and an inadequate pipeline of new therapies, novel treatment strategies are now urgently required. Methods: The antifungal activity of the alginate oligosaccharide OligoG in conjunction with nystatin was tested against a range of Candida spp. (C. albicans, C. glabrata, C. parapsilosis, C. auris, C. tropicalis and C. dubliniensis), in both planktonic and biofilm assays, to determine its potential clinical utility to enhance the treatment of candidal infections. The effect of OligoG (0-6%) ± nystatin on Candida spp. was examined in minimum inhibitory concentration (MIC) and growth curve assays. Antifungal effects of OligoG and nystatin treatment on biofilm formation and disruption were characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and ATP cellular viability assays. Effects on the cell membrane were determined using permeability assays and transmission electron microscopy (TEM). Results: MIC and growth curve assays demonstrated the synergistic effects of OligoG (0-6%) with nystatin, resulting in an up to 32-fold reduction in MIC, and a significant reduction in the growth of C. parapsilosis and C. auris (minimum significant difference = 0.2 and 0.12 respectively). CLSM and SEM imaging demonstrated that the combination treatment of OligoG (4%) with nystatin (1 µg/ml) resulted in significant inhibition of candidal biofilm formation on glass and clinical grade silicone surfaces (p < 0.001), with increased cell death (p < 0.0001). The ATP biofilm disruption assay demonstrated a significant reduction in cell viability with OligoG (4%) alone and the combined OligoG/nystatin (MIC value) treatment (p < 0.04) for all Candida strains tested. TEM studies revealed the combined OligoG/nystatin treatment induced structural reorganization of the Candida cell membrane, with increased permeability when compared to the untreated control (p < 0.001). Conclusions: Antimicrobial synergy between OligoG and nystatin against Candida spp. highlights the potential utility of this combination therapy in the prevention and topical treatment of candidal biofilm infections, to overcome the inherent tolerance of biofilm structures to antifungal agents.

Topical, immunomodulatory epoxy-tiglianes induce biofilm disruption and healing in acute and chronic skin wounds.

The management of antibiotic-resistant, bacterial biofilm infections in chronic skin wounds is an increasing clinical challenge. Despite advances in diagnosis, many patients do not derive benefit from current anti-infective/antibiotic therapies. Here, we report a novel class of naturally occurring and semisynthetic epoxy-tiglianes, derived from the Queensland blushwood tree (Fontainea picrosperma), and demonstrate their antimicrobial activity (modifying bacterial growth and inducing biofilm disruption), with structure/activity relationships established against important human pathogens. In vitro, the lead candidate EBC-1013 stimulated protein kinase C (PKC)-dependent neutrophil reactive oxygen species (ROS) induction and NETosis and increased expression of wound healing-associated cytokines, chemokines, and antimicrobial peptides in keratinocytes and fibroblasts. In vivo, topical EBC-1013 induced rapid resolution of infection with increased matrix remodeling in acute thermal injuries in calves. In chronically infected diabetic mouse wounds, treatment induced cytokine/chemokine production, inflammatory cell recruitment, and complete healing (in six of seven wounds) with ordered keratinocyte differentiation. These results highlight a nonantibiotic approach involving contrasting, orthogonal mechanisms of action combining targeted biofilm disruption and innate immune induction in the treatment of chronic wounds.

Jellyfish Collagen: A Biocompatible Collagen Source for 3D Scaffold Fabrication and Enhanced Chondrogenicity.

Osteoarthritis (OA) is a multifactorial disease leading to degeneration of articular cartilage, causing morbidity in approximately 8.5 million of the UK population. As the dense extracellular matrix of articular cartilage is primarily composed of collagen, cartilage repair strategies have exploited the biocompatibility and mechanical strength of bovine and porcine collagen to produce robust scaffolds for procedures such as matrix-induced chondrocyte implantation (MACI). However, mammalian sourced collagens pose safety risks such as bovine spongiform encephalopathy, transmissible spongiform encephalopathy and possible transmission of viral vectors. This study characterised a non-mammalian jellyfish (Rhizostoma pulmo) collagen as an alternative, safer source in scaffold production for clinical use. Jellyfish collagen demonstrated comparable scaffold structural properties and stability when compared to mammalian collagen. Jellyfish collagen also displayed comparable immunogenic responses (platelet and leukocyte activation/cell death) and cytokine release profile in comparison to mammalian collagen in vitro. Further histological analysis of jellyfish collagen revealed bovine chondroprogenitor cell invasion and proliferation in the scaffold structures, where the scaffold supported enhanced chondrogenesis in the presence of TGFß1. This study highlights the potential of jellyfish collagen as a safe and biocompatible biomaterial for both OA repair and further regenerative medicine applications.

Highly glycosylated MUC1 mediates high affinity L-selectin binding at the human endometrial surface.

BACKGROUND: Sialyl-Lewis X/L-selectin high affinity binding interactions between transmembrane O-glycosylated mucins proteins and the embryo have been implicated in implantation processes within the human reproductive system. However, the adhesive properties of these mucins at the endometrial cell surface are difficult to resolve due to known discrepancies between in vivo models and the human reproductive system and a lack of sensitivity in current in vitro models. To overcome these limitations, an in vitro model of the human endometrial epithelial was interrogated with single molecule force spectroscopy (SMFS) to delineate the molecular configurations of mucin proteins that mediate the high affinity L-selectin binding required for human embryo implantation. RESULTS: This study reveals that MUC1 contributes to both the intrinsic and extrinsic adhesive properties of the HEC-1 cellular surface. High expression of MUC1 on the cell surface led to a significantly increased intrinsic adhesion force (148 pN vs. 271 pN, p < 0.001), whereas this adhesion force was significantly reduced (271 pN vs. 118 pN, p < 0.001) following siRNA mediated MUC1 ablation. Whilst high expression of MUC1 displaying elevated glycosylation led to strong extrinsic (> 400 pN) L-selectin binding at the cell surface, low expression of MUC1 with reduced glycosylation resulted in significantly less (≤200 pN) binding events. CONCLUSIONS: An optimal level of MUC1 together with highly glycosylated decoration of the protein is critical for high affinity L-selectin binding. This study demonstrates that MUC1 contributes to cellular adhesive properties which may function to facilitate trophoblast binding to the endometrial cell surface through the L-selectin/sialyl-Lewis x adhesion system subsequent to implantation.

Quantifying the effects of antibiotic treatment on the extracellular polymer network of antimicrobial resistant and sensitive biofilms using multiple particle tracking.

Novel therapeutics designed to target the polymeric matrix of biofilms requires innovative techniques to accurately assess their efficacy. Here, multiple particle tracking (MPT) was developed to characterize the physical and mechanical properties of antimicrobial resistant (AMR) bacterial biofilms and to quantify the effects of antibiotic treatment. Studies employed nanoparticles (NPs) of varying charge and size (40-500 nm) in Pseudomonas aeruginosa PAO1 and methicillin-resistant Staphylococcus aureus (MRSA) biofilms and also in polymyxin B (PMB) treated Escherichia coli biofilms of PMB-sensitive (PMBSens) IR57 and PMB-resistant (PMBR) PN47 strains. NP size-dependent and strain-related differences in the diffusion coefficient values of biofilms were evident between PAO1 and MRSA. Dose-dependent treatment effects induced by PMB in PMBSens E. coli biofilms included increases in diffusion and creep compliance (P < 0.05), not evident in PMB treatment of PMBR E. coli biofilms. Our results highlight the ability of MPT to quantify the diffusion and mechanical effects of antibiotic therapies within the AMR biofilm matrix, offering a valuable tool for the pre-clinical screening of anti-biofilm therapies.

Phenotypic and Genotypic Adaptations in Pseudomonas aeruginosa Biofilms following Long-Term Exposure to an Alginate Oligomer Therapy.

Chronic Pseudomonas aeruginosa lung infections in cystic fibrosis (CF) evolve to generate environmentally adapted biofilm communities, leading to increased patient morbidity and mortality. OligoG CF-5/20, a low-molecular-weight inhaled alginate oligomer therapy, is currently in phase IIb/III clinical trials in CF patients. Experimental evolution of P. aeruginosa in response to OligoG CF-5/20 was assessed using a bead biofilm model allowing continuous passage (45 days; ∼245 generations). Mutants isolated after OligoG CF-5/20 treatment typically had a reduced biofilm-forming ability and altered motility profile. Genotypically, OligoG CF-5/20 provided no selective pressure on genomic mutations within morphotypes. Chronic exposure to azithromycin, a commonly prescribed antibiotic in CF patients, with or without OligoG CF-5/20 in the biofilm evolution model also had no effect on rates of resistance acquisition. Interestingly, however, cross-resistance to other antibiotics (e.g., aztreonam) was reduced in the presence of OligoG CF-5/20. Collectively, these findings show no apparent adverse effects from long-term exposure to OligoG CF-5/20, instead resulting in both fewer colonies with multidrug resistance (MDR)-associated phenotypes and improved antibiotic susceptibility of P. aeruginosaIMPORTANCE The emergence of multidrug-resistant (MDR) pathogens within biofilms in the cystic fibrosis lung results in increased morbidity. An inhalation therapy derived from alginate, OligoG CF-5/20, is currently in clinical trials for cystic fibrosis patients. OligoG CF-5/20 has been shown to alter sputum viscoelasticity, disrupt mucin polymer networks, and disrupt MDR pseudomonal biofilms. Long-term exposure to inhaled therapeutics may induce selective evolutionary pressures on bacteria within the lung biofilm. Here, a bead biofilm model with repeated exposure of P. aeruginosa to OligoG CF-5/20 (alone and in combination with azithromycin) was conducted to study these long-term effects and characterize the phenotypic and genotypic adaptations which result. These findings, over 6 weeks, show that long-term use of OligoG CF-5/20 does not lead to extensive mutational changes and may potentially decrease the pathogenicity of the bacterial biofilm and improve the susceptibility of P. aeruginosa to other classes of antibiotics.

Bi-Functional Alginate Oligosaccharide-Polymyxin Conjugates for Improved Treatment of Multidrug-Resistant Gram-Negative Bacterial Infections.

The recent emergence of resistance to colistin, an antibiotic of last resort with dose-limiting toxicity, has highlighted the need for alternative approaches to combat infection. This study aimed to generate and characterise alginate oligosaccharide ("OligoG")-polymyxin (polymyxin B and E (colistin)) conjugates to improve the effectiveness of these antibiotics. OligoG-polymyxin conjugates (amide- or ester-linked), with molecular weights of 5200-12,800 g/mol and antibiotic loading of 6.1-12.9% w/w, were reproducibly synthesised. In vitro inflammatory cytokine production (tumour necrosis factor alpha (TNFα) ELISA) and cytotoxicity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) of colistin (2.2-9.3-fold) and polymyxin B (2.9-27.2-fold) were significantly decreased by OligoG conjugation. Antimicrobial susceptibility tests (minimum inhibitory concentration (MIC), growth curves) demonstrated similar antimicrobial efficacy of ester- and amide-linked conjugates to that of the parent antibiotic but with more sustained inhibition of bacterial growth. OligoG-polymyxin conjugates exhibited improved selectivity for Gram-negative bacteria in comparison to mammalian cells (approximately 2-4-fold). Both OligoG-colistin conjugates caused significant disruption of Pseudomonas aeruginosa biofilm formation and induced bacterial death (confocal laser scanning microscopy). When conjugates were tested in an in vitro "time-to-kill" (TTK) model using Acinetobacter baumannii, only ester-linked conjugates reduced viable bacterial counts (~2-fold) after 4 h. Bi-functional OligoG-polymyxin conjugates have potential therapeutic benefits in the treatment of multidrug-resistant (MDR) Gram-negative bacterial infections, directly reducing toxicity whilst retaining antimicrobial and antibiofilm activities.

Compensatory mutations modulate the competitiveness and dynamics of plasmid-mediated colistin resistance in Escherichia coli clones.

The emergence of mobile colistin resistance (mcr) threatens to undermine the clinical efficacy of the last antibiotic that can be used to treat serious infections caused by Gram-negative pathogens. Here we measure the fitness cost of a newly discovered MCR-3 using in vitro growth and competition assays. mcr-3 expression confers a lower fitness cost than mcr-1, as determined by competitive ability and cell viability. Consistent with these findings, plasmids carrying mcr-3 have higher stability than mcr-1 plasmids across a range of Escherichia coli strains. Crucially, mcr-3 plasmids can stably persist, even in the absence of colistin. Recent compensatory evolution has helped to offset the cost of mcr-3 expression, as demonstrated by the high fitness of mcr-3.5 as opposed to mcr-3.1. Reconstructing all of the possible evolutionary trajectories from mcr-3.1 to mcr-3.5 reveals a complex fitness landscape shaped by negative epistasis between compensatory and neutral mutations. Our findings highlight the importance of fitness costs and compensatory evolution in driving the dynamics and stability of mobile colistin resistance in bacterial populations, and they highlight the need to understand how processes (other than colistin use) impact mcr dynamics.

Cellulose Nanofibril Formulations Incorporating a Low-Molecular-Weight Alginate Oligosaccharide Modify Bacterial Biofilm Development.

Cellulose nanofibrils (CNFs) from wood pulp are a renewable material possessing advantages for biomedical applications because of their customizable porosity, mechanical strength, translucency, and environmental biodegradability. Here, we investigated the growth of multispecies wound biofilms on CNF formulated as aerogels and films incorporating the low-molecular-weight alginate oligosaccharide OligoG CF-5/20 to evaluate their structural and antimicrobial properties. Overnight microbial cultures were adjusted to 2.8 × 109 colony-forming units (cfu) mL-1 in Mueller Hinton broth and growth rates of Pseudomonas aeruginosa PAO1 and Staphylococcus aureus 1061A monitored for 24 h in CNF dispersions sterilized by γ-irradiation. Two CNF formulations were prepared (20 g m-2) with CNF as air-dried films or freeze-dried aerogels, with or without incorporation of an antimicrobial alginate oligosaccharide (OligoG CF-5/20) as a surface coating or bionanocomposite, respectively. The materials were structurally characterized by scanning electron microscopy (SEM) and laser profilometry (LP). The antimicrobial properties of the formulations were assessed using single- and mixed-species biofilms grown on the materials and analyzed using LIVE/DEAD staining with confocal laser scanning microscopy (CLSM) and COMSTAT software. OligoG-CNF suspensions significantly decreased the growth of both bacterial strains at OligoG concentrations >2.58% (P < 0.05). SEM showed that aerogel-OligoG bionanocomposite formulations had a more open three-dimensional structure, whereas LP showed that film formulations coated with OligoG were significantly smoother than untreated films or films incorporating PEG400 as a plasticizer (P < 0.05). CLSM of biofilms grown on films incorporating OligoG demonstrated altered biofilm architecture, with reduced biomass and decreased cell viability. The OligoG-CNF formulations as aerogels or films both inhibited pyocyanin production (P < 0.05). These novel CNF formulations or bionanocomposites were able to modify bacterial growth, biofilm development, and virulence factor production in vitro. These data support the potential of OligoG and CNF bionanocomposites for use in biomedical applications where prevention of infection or biofilm growth is required.

Polymer Masked-Unmasked Protein Therapy: Identification of the Active Species after Amylase Activation of Dextrin-Colistin Conjugates.

Polymer masked-unmasked protein therapy (PUMPT) uses conjugation of a biodegradable polymer, such as dextrin, hyaluronic acid, or poly(l-glutamic acid), to mask a protein or peptide's activity; subsequent locally triggered degradation of the polymer at the target site regenerates bioactivity in a controllable fashion. Although the concept of PUMPT is well established, the relationship between protein unmasking and reinstatement of bioactivity is unclear. Here, we used dextrin-colistin conjugates to study the relationship between the molecular structure (degree of unmasking) and biological activity. Size exclusion chromatography was employed to collect fractions of differentially degraded conjugates and ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) employed to characterize the corresponding structures. Antimicrobial activity was studied using a minimum inhibitory concentration (MIC) assay and confocal laser scanning microscopy of LIVE/DEAD-stained biofilms with COMSTAT analysis. In vitro toxicity of the degraded conjugate was assessed using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. UPLC-MS revealed that the fully "unmasked" dextrin-colistin conjugate composed of colistin bound to at least one linker, whereas larger species were composed of colistin with varying lengths of glucose units attached. Increasing the degree of dextrin modification by succinoylation typically led to a greater number of linkers bound to colistin. Greater antimicrobial and antibiofilm activity were observed for the fully "unmasked" conjugate compared to the partially degraded species (MIC = 0.25 and 2-8 µg/mL, respectively), whereas dextrin conjugation reduced colistin's in vitro toxicity toward kidney cells, even after complete unmasking. This study highlights the importance of defining the structure-antimicrobial activity relationship for novel antibiotic derivatives and demonstrates the suitability of LC-MS to aid the design of biodegradable polymer-antibiotic conjugates.

Anti-pseudomonad Activity of Manuka Honey and Antibiotics in a Specialized ex vivo Model Simulating Cystic Fibrosis Lung Infection.

Pseudomonas aeruginosa causes problematic chronic lung infections in those suffering from cystic fibrosis. This is due to its antimicrobial resistance mechanisms and its ability to form robust biofilm communities with increased antimicrobial tolerances. Using novel antimicrobials or repurposing current ones is required in order to overcome these problems. Manuka honey is a natural antimicrobial agent that has been used for many decades in the treatment of chronic surface wounds with great success, particularly those infected with P. aeruginosa. Here we aim to determine whether the antimicrobial activity of manuka honey could potentially be repurposed to inhibit pulmonary P. aeruginosa infections using two ex vivo models. P. aeruginosa isolates (n = 28) from an international panel were tested for their susceptibility to manuka honey and clinically relevant antibiotics (ciprofloxacin, ceftazidime, and tobramycin), alone and in combination, using conventional antimicrobial susceptibility testing (AST). To increase clinical applicability, two ex vivo porcine lung (EVPL) models (using alveolar and bronchiolar tissue) were used to determine the anti-biofilm effects of manuka honey alone and in combination with antibiotics. All P. aeruginosa isolates were susceptible to manuka honey, however, varying incidences of resistance were seen against antibiotics. The combination of sub-inhibitory manuka honey and antibiotics using conventional AST had no effect on activity against the majority of isolates tested. Using the two ex vivo models, 64% (w/v) manuka honey inhibited many of the isolates where abnormally high concentrations of antibiotics could not. Typically, combinations of both manuka honey and antibiotics had increased antimicrobial activity. These results highlight the potential of manuka honey as a future antimicrobial for the treatment of pulmonary P. aeruginosa isolates, clearing potential infection reservoirs within the upper airway.

Controlled release of dextrin-conjugated growth factors to support growth and differentiation of neural stem cells.

An essential aspect of stem cell in vitro culture and in vivo therapy is achieving sustained levels of growth factors to support stem cell survival and expansion, while maintaining their multipotency and differentiation potential. This study investigated the ability of dextrin (~74,000 g/mol; 27.8 mol% succinoylation) conjugated to epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF; or FGF-2) (3.9 and 6.7% w/w protein loading, respectively) to support the expansion and differentiation of stem cells in vitro via sustained, controllable growth factor release. Supplementation of mouse neural stem cells (mNSCs) with dextrin-growth factor conjugates led to greater and prolonged proliferation compared to unbound EGF/bFGF controls, with no detectable apoptosis after 7 days of treatment. Immunocytochemical detection of neural precursor (nestin) and differentiation (Olig2, MAP2, GFAP) markers verified that controlled release of dextrin-conjugated growth factors preserves stem cell properties of mNSCs for up to 7 days. These results show the potential of dextrin-growth factor conjugates for localized delivery of bioactive therapeutic agents to support stem cell expansion and differentiation, and as an adjunct to direct neuronal repair.

Targeted disruption of the extracellular polymeric network of Pseudomonas aeruginosa biofilms by alginate oligosaccharides.

Acquisition of a mucoid phenotype by Pseudomonas sp. in the lungs of cystic fibrosis (CF) patients, with subsequent over-production of extracellular polymeric substance (EPS), plays an important role in mediating the persistence of multi-drug resistant (MDR) infections. The ability of a low molecular weight (Mn = 3200 g mol-1) alginate oligomer (OligoG CF-5/20) to modify biofilm structure of mucoid Pseudomonas aeruginosa (NH57388A) was studied in vitro using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) with Texas Red (TxRd®)-labelled OligoG and EPS histochemical staining. Structural changes in treated biofilms were quantified using COMSTAT image-analysis software of CLSM z-stack images, and nanoparticle diffusion. Interactions between the oligomers, Ca2+ and DNA were studied using molecular dynamics (MD) simulations, Fourier transform infrared spectroscopy (FTIR) and isothermal titration calorimetry (ITC). Imaging demonstrated that OligoG treatment (≥0.5%) inhibited biofilm formation, revealing a significant reduction in both biomass and biofilm height (P < 0.05). TxRd®-labelled oligomers readily diffused into established (24 h) biofilms. OligoG treatment (≥2%) induced alterations in the EPS of established biofilms; significantly reducing the structural quantities of EPS polysaccharides, and extracellular (e)DNA (P < 0.05) with a corresponding increase in nanoparticle diffusion (P < 0.05) and antibiotic efficacy against established biofilms. ITC demonstrated an absence of rapid complex formation between DNA and OligoG and confirmed the interactions of OligoG with Ca2+ evident in FTIR and MD modelling. The ability of OligoG to diffuse into biofilms, potentiate antibiotic activity, disrupt DNA-Ca2+-DNA bridges and biofilm EPS matrix highlights its potential for the treatment of biofilm-related infections.

Alginate Oligosaccharide-Induced Modification of the lasI-lasR and rhlI-rhlR Quorum-Sensing Systems in Pseudomonas aeruginosa.

Pseudomonas aeruginosa plays a major role in many chronic infections. Its ability to readily form biofilms contributes to its success as an opportunistic pathogen and its resistance/tolerance to antimicrobial/antibiotic therapy. A low-molecular-weight alginate oligomer (OligoG CF-5/20) derived from marine algae has previously been shown to impair motility in P. aeruginosa biofilms and disrupt pseudomonal biofilm assembly. As these bacterial phenotypes are regulated by quorum sensing (QS), we hypothesized that OligoG CF-5/20 may induce alterations in QS signaling in P. aeruginosa QS regulation was studied by using Chromobacterium violaceum CV026 biosensor assays that showed a significant reduction in acyl homoserine lactone (AHL) production following OligoG CF-5/20 treatment (≥2%; P < 0.05). This effect was confirmed by liquid chromatography-mass spectrometry analysis of C4-AHL and 3-oxo-C12-AHL production (≥2%; P < 0.05). Moreover, quantitative PCR showed that reduced expression of both the las and rhl systems was induced following 24 h of treatment with OligoG CF-5/20 (≥0.2%; P < 0.05). Circular dichroism spectroscopy indicated that these alterations were not due to steric interaction between the AHL and OligoG CF-5/20. Confocal laser scanning microscopy (CLSM) and COMSTAT image analysis demonstrated that OligoG CF-5/20-treated biofilms had a dose-dependent decrease in biomass that was associated with inhibition of extracellular DNA synthesis (≥0.5%; P < 0.05). These changes correlated with alterations in the extracellular production of the pseudomonal virulence factors pyocyanin, rhamnolipids, elastase, and total protease (P < 0.05). The ability of OligoG CF-5/20 to modify QS signaling in P. aeruginosa PAO1 may influence critical downstream functions such as virulence factor production and biofilm formation.

Balancing mcr-1 expression and bacterial survival is a delicate equilibrium between essential cellular defence mechanisms.

MCR-1 is a lipid A modifying enzyme that confers resistance to the antibiotic colistin. Here, we analyse the impact of MCR-1 expression on E. coli morphology, fitness, competitiveness, immune stimulation and virulence. Increased expression of mcr-1 results in decreased growth rate, cell viability, competitive ability and significant degradation in cell membrane and cytoplasmic structures, compared to expression of catalytically inactive MCR-1 (E246A) or MCR-1 soluble component. Lipopolysaccharide (LPS) extracted from mcr-1 strains induces lower production of IL-6 and TNF, when compared to control LPS. Compared to their parent strains, high-level colistin resistance mutants (HLCRMs) show reduced fitness (relative fitness is 0.41-0.78) and highly attenuated virulence in a Galleria mellonella infection model. Furthermore, HLCRMs are more susceptible to most antibiotics than their respective parent strains. Our results show that the bacterium is challenged to find a delicate equilibrium between expression of MCR-1-mediated colistin resistance and minimalizing toxicity and thus ensuring cell survival.

A Low-Molecular-Weight Alginate Oligosaccharide Disrupts Pseudomonal Microcolony Formation and Enhances Antibiotic Effectiveness.

In chronic respiratory disease, the formation of dense, 3-dimensional "microcolonies" by Pseudomonas aeruginosa within the airway plays an important role in contributing to resistance to treatment. An in vitro biofilm model of pseudomonal microcolony formation using artificial-sputum (AS) medium was established to study the effects of low-molecular-weight alginate oligomers (OligoG CF-5/20) on pseudomonal growth, microcolony formation, and the efficacy of colistin. The studies employed clinical cystic fibrosis (CF) isolates (n = 3) and reference nonmucoid and mucoid multidrug-resistant (MDR) CF isolates (n = 7). Bacterial growth and biofilm development and disruption were studied using cell viability assays and image analysis with scanning electron and confocal laser scanning microscopy. Pseudomonal growth in AS medium was associated with increased ATP production (P < 0.05) and the formation (at 48 h) of discrete (>10-µm) microcolonies. In conventional growth medium, colistin retained an ability to inhibit growth of planktonic bacteria, although the MIC was increased (0.1 to 0.4 µg/ml) in AS medium compared to Mueller-Hinton (MH) medium. In contrast, in an established-biofilm model in AS medium, the efficacy of colistin was decreased. OligoG CF-5/20 (≥2%) treatment, however, induced dose-dependent biofilm disruption (P < 0.05) and led to colistin retaining its antimicrobial activity (P < 0.05). While circular dichroism indicated that OligoG CF-5/20 did not change the orientation of the alginate carboxyl groups, mass spectrometry demonstrated that the oligomers induced dose-dependent (>0.2%; P < 0.05) reductions in pseudomonal quorum-sensing signaling. These findings reinforce the potential clinical significance of microcolony formation in the CF lung and highlight a novel approach to treat MDR pseudomonal infections.

The antimicrobial effects of the alginate oligomer OligoG CF-5/20 are independent of direct bacterial cell membrane disruption.

Concerns about acquisition of antibiotic resistance have led to increasing demand for new antimicrobial therapies. OligoG CF-5/20 is an alginate oligosaccharide previously shown to have antimicrobial and antibiotic potentiating activity. We investigated the structural modification of the bacterial cell wall by OligoG CF-5/20 and its effect on membrane permeability. Binding of OligoG CF-5/20 to the bacterial cell surface was demonstrated in Gram-negative bacteria. Permeability assays revealed that OligoG CF-5/20 had virtually no membrane-perturbing effects. Lipopolysaccharide (LPS) surface charge and aggregation were unaltered in the presence of OligoG CF-5/20. Small angle neutron scattering and circular dichroism spectroscopy showed no substantial change to the structure of LPS in the presence of OligoG CF-5/20, however, isothermal titration calorimetry demonstrated a weak calcium-mediated interaction. Metabolomic analysis confirmed no change in cellular metabolic response to a range of osmolytes when treated with OligoG CF-5/20. This data shows that, although weak interactions occur between LPS and OligoG CF-5/20 in the presence of calcium, the antimicrobial effects of OligoG CF-5/20 are not related to the induction of structural alterations in the LPS or cell permeability. These results suggest a novel mechanism of action that may avoid the common route in acquisition of resistance via LPS structural modification.