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

Dual bioresponsive antibiotic and quorum sensing inhibitor combination nanoparticles for treatment of Pseudomonas aeruginosa biofilms in vitro and ex vivo

Many debilitating infections result from persistent microbial biofilms that do not respond to conventional antibiotic regimens. A potential method to treat such chronic infections is to combine agents which interfere with bacterial biofilm development together with an antibiotic in a single formulation. Here, we explore the use of a new bioresponsive polymer formulation derived from specifically modified alginate nanoparticles (NPs) in order to deliver ciprofloxacin (CIP) in combination with the quorum sensing inhibitor (QSI) 3-amino-7-chloro-2-nonylquinazolin-4(3H)-one (ACNQ) to mature Pseudomonas aeruginosa biofilms. The alginate NPs were engineered to incorporate a pH-responsive linker between the polysaccharide backbone and the QSI, and to encapsulate CIP via charge-charge interactions of the positively-charged drug with the carboxyl residues of the alginate matrix. In this way, a dual-action release of antibiotic and QSI was designed for the low-pH regions of a biofilm, involving cleavage of the QSI-linker to the alginate matrix and reduced charge-charge interactions between CIP and the polysaccharide as the alginate carboxyl side-chains protonated. When tested in a biofilm model the concomitant release of CIP + QSI from the pH-responsive nanoparticles significantly reduced the viability of the biofilm compared with CIP treatment alone. In addition, the alginate NPs were shown to penetrate deeply into P. aeruginosa biofilms, which we attribute in part to the charges of the NPs and the release of the QSI agent. Finally, we tested the formulation in both a 2D keratinocyte and a 3D ex vivo skin infection model. The dual-action bio-responsive QSI and CIP release nanoparticles effectively cleared the infection in the latter, suggesting considerable promise for combination therapeutics which prevent biofilm formation as well as effectively killing mature P. aeruginosa biofilms.

Advances in Research on the Bioactivity of Alginate Oligosaccharides

Alginate is a natural polysaccharide present in various marine brown seaweeds. Alginate oligosaccharide (AOS) is a degradation product of alginate, which has received increasing attention due to its low molecular weight and promising biological activity. The wide-ranging biological activity of AOS is closely related to the diversity of their structures. AOS with a specific structure and distinct applications can be obtained by different methods of alginate degradation. This review focuses on recent advances in the biological activity of alginate and its derivatives, including their anti-tumor, anti-oxidative, immunoregulatory, anti-inflammatory, neuroprotective, antibacterial, hypolipidemic, antihypertensive, and hypoglycemic properties, as well as the ability to suppress obesity and promote cell proliferation and regulate plant growth. We hope that this review will provide theoretical basis and inspiration for the high-value research developments and utilization of AOS-related products.

Alginate Lyase Guided Silver Nanocomposites for Eradicating Pseudomonas aeruginosa from Lungs

Pseudomonas aeruginosa (P. aeruginosa) infections lead to a high mortality rate for cystic fibrosis or immunocompromised patients. The alginate of the biofilm was believed to be the key factor disabling immune therapy and antibiotic treatments. A silver nanocomposite consisting of silver nanoparticles and a mesoporous organosilica layer was created to deliver two pharmaceutical compounds (alginate lyase and ceftazidime) to degrade the alginate and eradicate P. aeruginosa from the lungs. The introduction of thioether-bridged mesoporous organosilica into the nanocomposites greatly benefited the conjunction of foreign functional molecules such as alginate lyase and increased their hemocompatibility and drug-loading capacity. Silver nanocomposites with a uniform diameter (∼39 nm) exhibited a high dispersity, good biocompatibility, and high ceftazidime-loading capacity (380.96 mg/g). Notably, the silver nanocomposites displayed a low pH-dependent drug release and degradation profiles (pH 6.4), guaranteeing the targeted release of the drugs in the acidic niches of the P. aeruginosa biofilm. Indeed, particles loaded with alginate lyase and ceftazidime exhibited high inhibitory and degradation effects on the biofilm of P. aeruginosa PAO1 based on the specific catalytic activity of the enzyme to the alginate and antibacterial function of their loaded ceftazidime and silver ions. It should be noted that the enzyme-decorated nanocomposites succeeded in eradicating P. aeruginosa PAO1 from the mouse lungs and decreasing the lung injuries. No deaths or serious side effects were observed during the experiments. We believe that the silver nanocomposites with high biocompatibility and organic group-incorporated framework have the potential to be used to deliver multiple functional molecules for antibacterial therapy in clinical application.

Small-Molecule Inhibition of Bacterial Biofilm

Antibiotic resistance is a massive and serious threat to human welfare and healthcare. Apart from being genetically resistant to antibiotics, the other important mechanism by which bacteria can evade antibiotics is multidrug tolerance. Here cells enter into a transiently nongrowing phase, and as a result, latent infection remains inside the host, causing disease recurrence. Biofilm-derived antibiotic tolerance and persister formation of the pathogenic bacteria inside the host remain a serious issue of treatment failure and recurrent chronic infection in the case of all major pathogens. As a result, new chemotherapeutic agents are sought that specifically inhibit biofilm formation or maturation as well as cause the dispersion of mature biofilms, thus allowing the conventional drugs to kill sensitive cells residing inside. This mini-review attempts to analyze different small-molecule-based chemical approaches that have been used to enable bacterial biofilm inhibition at different steps of maturation.

Metal ions weaken the hydrophobicity and antibiotic resistance of Bacillus subtilis NCIB 3610 biofilms

Surface superhydrophobicity makes bacterial biofilms very difficult to fight, and it is a combination of their matrix composition and complex surface roughness which synergistically protects these biomaterials from wetting. Although trying to eradicate biofilms with aqueous (antibiotic) solutions is common practice, this can be a futile approach if the biofilms have superhydrophobic properties. To date, there are not many options available to reduce the liquid repellency of biofilms or to prevent this material property from developing. Here, we present a solution to this challenge. We demonstrate how the addition of metal ions such as copper and zinc during or after biofilm formation can render the surface of otherwise superhydrophobic B. subtilis NCIB 3610 biofilms completely wettable. As a result of this procedure, these smoother, hydrophilic biofilms are more susceptible to aqueous antibiotics solutions. Our strategy proposes a scalable and widely applicable step in a multi-faceted approach to eradicate biofilms.

Spatiochemically Profiling Microbial Interactions with Membrane Scaffolded Desorption Electrospray Ionization-Ion Mobility-Imaging Mass Spectrometry and Unsupervised Segmentation

Imaging the inventory of microbial small molecule interactions provides important insights into microbial chemical ecology and human medicine. Herein we demonstrate a new method for enhanced detection and analysis of metabolites present in interspecies interactions of microorganisms on surfaces. We demonstrate that desorption electrospray ionization-imaging mass spectrometry (DESI-IMS) using microporous membrane scaffolds (MMS) enables enhanced spatiochemical analyses of interacting microbes among tested sample preparation techniques. Membrane scaffolded DESI-IMS has inherent advantages compared to matrix-assisted laser desorption ionization (MALDI) and other IMS methods through direct IMS analyses of microbial chemistry in situ. This rapid imaging method yields sensitive MS analyses with unique m/z measurements when compared to liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) via unmediated sampling by MMS DESI-IMS. Unsupervised segmentation imaging analysis of acquired DESI-IMS data reveals distinct chemical regions corresponding to intermicrobial phenomenon such as predation and communication. We validate the method by linking Myxovirescin A and DKxanthene-560 to their known biological roles of predation and phase variation, respectively. In addition to providing the first topographic locations of known natural products, we prioritize 54 unknown features using segmentation within the region of predation. Thus, DESI-IMS and unsupervised segmentation spatially annotates the known biology of myxobacteria and provides functional exploration of newly uncharacterized small molecules.

Nanoantibiotics: A Novel Rational Approach to Antibiotic Resistant Infections

Background:

The main drawbacks for using conventional antimicrobial agents are the development of multiple drug resistance due to the use of high concentrations of antibiotics for extended periods. This vicious cycle often generates complications of persistent infections, and intolerable antibiotic toxicity. The problem is that while all new discovered antimicrobials are effective and promising, they remain as only short-term solutions to the overall challenge of drug-resistant bacteria.

Objective:

Recently, nanoantibiotics (nAbts) have been of tremendous interest in overcoming the drug resistance developed by several pathogenic microorganisms against most of the commonly used antibiotics. Compared with free antibiotic at the same concentration, drug delivered via a nanoparticle carrier has a much more prominent inhibitory effect on bacterial growth, and drug toxicity, along with prolonged drug release. Additionally, multiple drugs or antimicrobials can be packaged within the same smart polymer which can be designed with stimuli-responsive linkers. These stimuli-responsive nAbts open up the possibility of creating multipurpose and targeted antimicrobials. Biofilm formation still remains the leading cause of conventional antibiotic treatment failure. In contrast to conventional antibiotics nAbts easily penetrate into the biofilm, and selectively target biofilm matrix constituents through the introduction of bacteria specific ligands. In this context, various nanoparticles can be stabilized and functionalized with conventional antibiotics. These composites have a largely enhanced bactericidal efficiency compared to the free antibiotic.

Conclusion:

Nanoparticle-based carriers deliver antibiotics with better biofilm penetration and lower toxicity, thus combating bacterial resistance. However, the successful adaptation of nanoformulations to clinical practice involves a detailed assessment of their safety profiles and potential immunotoxicity.

Antibiofilm Efficacy of Nitric Oxide-Releasing Alginates against Cystic Fibrosis Bacterial Pathogens

Colonization of the lungs by biofilm-forming pathogens is a major cause of mortality in cystic fibrosis (CF). In CF patients, these pathogens are difficult to treat due to the additional protection provided by both the biofilm exopolysaccharide matrix and thick, viscous mucus. The antibiofilm efficacy of nitric oxide (NO)-releasing alginates was evaluated against Pseudomonas aeruginosa, Burkholderia cepacia, Staphylococcus aureus, and methicillin-resistant S. aureus biofilms in both aerobic and anaerobic environments. Varying the amine precursor grafted onto alginate oligosaccharides imparted tunable NO storage (∼0.1-0.3 μmol/mg) and release kinetics (∼4-40 min half-lives) in the artificial sputum media used for biofilm testing. The NO-releasing alginates were highly antibacterial against the four CF-relevant pathogens, achieving a 5-log reduction in biofilm viability after 24 h of treatment, with biocidal efficacy dependent on NO-release kinetics. Aerobic biofilms required greater starting NO doses to achieve killing relative to the anaerobic biofilms. Relative to tobramycin (the minimum concentration of antibacterial agent required to achieve a 5-log reduction in viability after 24 h, MBEC24h, of ≥2000 μg/mL) and vancomycin (MBEC24h ≥ 1000 μg/mL), the NO-releasing alginates proved to be more effective (NO dose ≤ 520 μg/mL) regardless of growth conditions.

Testing Anti-Biofilm Polymeric Surfaces: Where to Start?

Present day awareness of biofilm colonization on polymeric surfaces has prompted the scientific community to develop an ever-increasing number of new materials with anti-biofilm features. However, compared to the large amount of work put into discovering potent biofilm inhibitors, only a small number of papers deal with their validation, a critical step in the translation of research into practical applications. This is due to the lack of standardized testing methods and/or of well-controlled in vivo studies that show biofilm prevention on polymeric surfaces; furthermore, there has been little correlation with the reduced incidence of material deterioration. Here an overview of the most common methods for studying biofilms and for testing the anti-biofilm properties of new surfaces is provided.

Fructooligosaccharides and mannose affect Clostridium difficile adhesion and biofilm formation in a concentration-dependent manner

The aim of this study was to investigate the effects that prebiotic and candidates for prebiotics on Clostridium difficile strains to adhere to various human epithelial cell lines and to compare the adhesive properties of specific C. difficile strains. We also sought to examine the effect of different concentrations of fructooligosaccharides and mannose on the formation of biofilms by C. difficile strains. The influence of cellobiose, fructooligosaccharides, inulin, mannose, and raffinose on the adherence properties of various C. difficile strains, including motile 630, non-motile M120, and 10 clinical motile ribotype 027 strains, to non-mucous secreting HT-29, mucous secreting HT-29 MXT, and CCD 841 CoN cells lines. The most effective prebiotics were used in biofilm formation assays. We demonstrated that all C. difficile strains adhered to all cell lines. However, the C. difficile M120 non-motile strain was statistically more likely to adhere to all three cell lines (CFU median, 40) compared to the motile strains (CFU median, 3; p < 0.001). Furthermore, among the carbohydrates examined, only fructooligosaccharides and mannose were found to significantly decrease adhesion (p < 0.001) of C. difficile strains. Alternatively, using a biofilm assay, we observed, via confocal laser scanning microscopy, that sub-inhibitory concentrations (1%) of fructooligosaccharides and mannose functioned to increase biofilm formation by C. difficile. We demonstrated that specific prebiotics and candidate prebiotics exhibit varying anti-adhesive properties towards C. difficile in vitro and that treatment with sub-inhibitory concentrations of prebiotics can cause an increase in biofilm formation by C. difficile.

Biofilms: The Microbial "Protective Clothing" in Extreme Environments

Microbial biofilms are communities of aggregated microbial cells embedded in a self-produced matrix of extracellular polymeric substances (EPS). Biofilms are recalcitrant to extreme environments, and can protect microorganisms from ultraviolet (UV) radiation, extreme temperature, extreme pH, high salinity, high pressure, poor nutrients, antibiotics, etc., by acting as "protective clothing". In recent years, research works on biofilms have been mainly focused on biofilm-associated infections and strategies for combating microbial biofilms. In this review, we focus instead on the contemporary perspectives of biofilm formation in extreme environments, and describe the fundamental roles of biofilm in protecting microbial exposure to extreme environmental stresses and the regulatory factors involved in biofilm formation. Understanding the mechanisms of biofilm formation in extreme environments is essential for the employment of beneficial microorganisms and prevention of harmful microorganisms.

10-undecynoic acid is a new anti-adherent agent killing biofilm of oral Streptococcus spp

In the search for novel agents against oral pathogens in their planktonic and biofilm form, we have focused our attention on 10-undecynoic acid as the representative of the acetylenic fatty acids. Using macro-broth susceptibility testing method we first established MIC value. Next, the MBC value was determined from a broth dilution minimum inhibitory concentration test by sub-culturing it to BHI agar plates that did not contain the test agent. Anti-biofilm efficacy was tested in 96-well plates coated with saliva using BHI broth supplemented with 1% sucrose as a standard approach. Based on obtained results, MIC value for 10-undecynoic acid was established to be 2.5 mg/ml and the MBC value to be 5 mg/ml. The MBIC₉₀ showed to be 2.5 mg/ml, however completed inhibition of biofilm formation was achieved at 5.0 mg/ml. MBBC concentration revealed to be the same as MBC value, causing approximately 30% reduction at the same time in biomass of pre-existing biofilm, whereas application of 7.0 mg/ml of 10-undecynoic acid crossed the 50% eradication mark. Strong anti-adherent effect was observed upon 10-undecynoic acid application at sub-MBC concentrations as well, complemented with suppression of acidogenicity and aciduricity. Thus, we concluded that 10-undecynoic acid might play an important role in the development of alternative or adjunctive antibacterial and anti-biofilm preventive and/or therapeutic approaches.