Insights into the mode of action of chitosan as an antibacterial compound

Proteomic Analyses Reveal New Insights on the Antimicrobial Mechanisms of Chitosan Biopolymers and Their Nanosized Particles against Escherichia coli

The well-known antimicrobial effects of chitosan (CS) polymers make them a promising adjuvant in enhancing antibiotic effectiveness against human pathogens. However, molecular CS antimicrobial mechanisms remain unclear, despite the insights presented in the literature. Thus, the aim of the present study was to depict the molecular effects implicated in the interaction of low or medium molecular mass CS polymers and their nanoparticle-counterparts against Escherichia coli. The differential E. coli proteomes sensitized to either CS polymers or nanoparticles were investigated by nano liquid chromatography–mass spectrometry (micro-LC-MS/MS). A total of 127 proteins differentially expressed in CS-sensitized bacteria were predominantly involved in (i) structural functions associated to the stability of outer membrane, (ii) increment of protein biosynthesis due to high abundance of ribosomal proteins and (iii) activation of biosynthesis of amino acid and purine metabolism pathways. Antibacterial activity of CS polymers/nanoparticles seems to be triggered by the outer bacterial membrane disassembly, leading to increased protein biosynthesis by diverting the metabolic flux to amino acid and purine nucleotides supply. Understanding CS-antibacterial molecular effects can be valuable to optimize the use of CS-based nanomaterials in food decontamination, and may represent a breakthrough on CS nanocapsules-drug delivery devices for novel antibiotics, as the chitosan-disassembly of bacteria cell membranes can potentialize antibiotic effects.

Obtaining and Characterization of the PLA/Chitosan Foams with Antimicrobial Properties Achieved by the Emulsification Combined with the Dissolution of Chitosan by CO2 Saturation

A new method of obtaining functional foam material has been proposed. The materials were created by mixing the poly lactic acid (PLA) solution in chloroform, chitosan (CS) dissolved in water saturated with CO₂ and polyethylene glycol (PEG), and freeze-dried for removal of the solvents. The composite foams were characterized for their structural (SEM, FT-IR, density, porosity), thermal (DSC), functional (hardness, elasticity, swelling capacity, solubility), and biological (antimicrobial and cytotoxic) properties. Chitosan in the composites was a component for obtaining their foamed form with 7.4 to 22.7 times lower density compared to the neat PLA and high porosity also confirmed by the SEM. The foams had a hardness in the range of 70-440 kPa. The FT-IR analysis confirmed no new chemical bonds between the sponge ingredients. Other results showed low sorption capacity (2.5-7.2 g/g) and solubility of materials (less than 0.2%). The obtained foams had the lower T_g value and improved ability of crystallization compared to neat PLA. The addition of chitosan provides the bacteriostatic and bactericidal properties against Escherichia coli and Staphylococcus aureus. Biocompatibility studies have shown that the materials obtained are not cytotoxic to the L929 cell line.

Antifungal activity of different molecular weight chitosans against planktonic cells and biofilm of Sporothrix brasiliensis

Sporotrichosis, caused by Sporothrix schenckii complex species, is the most prevalent subcutaneous mycosis in many areas of Latin America. Chitosan has been used as an antifungal agent; however the effects of the molecular weight (MW) of chitosan (i.e. high (HMW), medium (MMW) and low (LMW) molecular weight chitosan) on S. brasiliensis has not been well described, particularly on biofilms. Effects on the planktonic form activity of S. brasiliensis were quantified by broth microdilution, while anti-biofilm activity was quantified by measuring metabolic activity via XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide and biomass formation (crystal violet). The molecular weight of chitosan modulated its effect on the planktonic form of S. brasiliensis, presenting lower MIC values for LMW chitosan. With regards both the adhesive and mature phases of biofilm, the LMW chitosan reduced biomass and metabolic activity most effectively. This study confirms the effects of the molecular weight and deacetylation degree of chitosan on its antifungal properties for potentially pathogenic fungi.

Chitosan as a Wound Dressing Starting Material: Antimicrobial Properties and Mode of Action

Fighting bacterial resistance is one of the concerns in modern days, as antibiotics remain the main resource of bacterial control. Data shows that for every antibiotic developed, there is a microorganism that becomes resistant to it. Natural polymers, as the source of antibacterial agents, offer a new way to fight bacterial infection. The advantage over conventional synthetic antibiotics is that natural antimicrobial agents are biocompatible, non-toxic, and inexpensive. Chitosan is one of the natural polymers that represent a very promising source for the development of antimicrobial agents. In addition, chitosan is biodegradable, non-toxic, and most importantly, promotes wound healing, features that makes it suitable as a starting material for wound dressings. This paper reviews the antimicrobial properties of chitosan and describes the mechanisms of action toward microbial cells as well as the interactions with mammalian cells in terms of wound healing process. Finally, the applications of chitosan as a wound-dressing material are discussed along with the current status of chitosan-based wound dressings existing on the market.

Biological Effects of Chitosan-Based Dressing on Hemostasis Mechanism

There have been numerous recent advances in wound care management. Nevertheless, the assessment of hemostatic dressing is essential to enable surgeons and other physicians and healthcare professionals to make the correct decisions regarding the disposition of severe hemorrhage. Here, we investigated the relative efficacies of chitosan-based and conventional gauze dressings in a rat model of femoral artery hemorrhage and in patients with surgical wounds. Dressing effectiveness was evaluated based on hemostatic profiles, biocompatibility, antimicrobial activity, and blood factor responses in coagulation. Relative to standard gauze dressing, the chitosan fiber (CF) dressing treatment significantly shortened the time to hemostasis in injured rats. Moreover, the CF dressing significantly prolonged partial thromboplastin time, enhanced blood absorption, and reduced antithrombin production without altering the prothrombin ratio. Unlike regular gauze bandages, the CF dressing demonstrated remarkable antibacterial activity. The results of this study indicate the effectiveness of chitosan as a hemostatic dressing and elucidate its underlying mechanism. It is possible that chitosan surgical dressings could serve as first-line intervention in hospital emergency care for uncontrolled hemorrhage.

Food Safety through Natural Antimicrobials

Microbial pathogens are the cause of many foodborne diseases after the ingestion of contaminated food. Several preservation methods have been developed to assure microbial food safety, as well as nutritional values and sensory characteristics of food. However, the demand for natural antimicrobial agents is increasing due to consumers' concern on health issues. Moreover, the use of antibiotics is leading to multidrug resistant microorganisms reinforcing the focus of researchers and the food industry on natural antimicrobials. Natural antimicrobial compounds from plants, animals, bacteria, viruses, algae and mushrooms are covered. Finally, new perspectives from researchers in the field and the interest of the food industry in innovations are reviewed. These new approaches should be useful for controlling foodborne bacterial pathogens; furthermore, the shelf-life of food would be extended.

Natural products with preservative properties for enhancing the microbiological safety and extending the shelf-life of seafood: A review

Seafood is highly perishable, presenting a rapid loss of its quality soon after capture. Temperature is the critical parameter that impacts on seafood shelf-life reduction, allowing the growth of foodborne pathogens and spoilage microorganisms. In recent years, the search by additional methods of preserving seafood has increased, able to ensure quality and safety. Several natural preservatives have highlighted and gained considerable attention from the scientific community, consumers, industry, and health sectors as a method with broad action antimicrobial and generally economical. Natural preservatives, from different sources, have been widely studied, such as chitosan from animal sources, essential oils, and plant extracts from a plant source, lactic acid bacteria, and bacteriocins from microbiological sources and organic acid from different sources, all with great potential for use in seafood systems. This review focuses on the natural preservatives studied in seafood matrices, their forms of application, concentrations usually employed, their mechanisms of action, factors that interfere in their use and the synergistic effect of the interactions among the natural preservatives, with a focus for maintenance of quality and ensure of food safety.

Synthesis, Characterisation and Biological Evaluation of Ampicillin-Chitosan-Polyanion Nanoparticles Produced by Ionic Gelation and Polyelectrolyte Complexation Assisted by High-Intensity Sonication

Recently, one of the promising strategies to fight sensitive and resistant bacteria, and decrease the morbidity and mortality rates due to non-nosocomial infections, is to use antibiotic-loaded nanoparticles. In this study, ampicillin-loaded chitosan-polyanion nanoparticles were produced through the techniques of ionic gelation and polyelectrolyte complexation assisted by high-intensity sonication, using several crosslinking agents, including phytic acid (non-polymeric polyanion), sodium and potassium salts of poly(maleic acid-alt-ethylene) and poly(maleic acid-alt-octadecene) (polymeric polyanions). These nanoparticles were analysed and characterised in terms of particle size, polydispersity index, zeta potential and encapsulation efficiency. The stability of these nanosystems was carried out at temperatures of 4 and 40 °C, and the antimicrobial effect was determined by the broth microdilution method using sensitive and resistant Staphylococcus aureus strains. The results reveal that most of the nanosystems have sizes <220 nm, positive zeta potential values and a monodisperse population, except for the nanoparticles crosslinked with PAM-18 polyanions. The nanometric systems exhibited adequate stability preventing aggregation and revealed a two-fold increase in antimicrobial activity when compared with free ampicillin. This study demonstrates the potential application of synthesised nanoparticles in the field of medicine, especially for treating infections caused by pathogenic S. aureus strains.

Simultaneous deacetylation and degradation of chitin hydrogel by electrical discharge plasma using low sodium hydroxide concentrations

Electrical discharge plasma occurring in a liquid phase, so called solution plasma, can generate highly active species, e.g. free radicals, which can involve in various chemical reactions, leading to less chemical uses. In this study, solution plasma was applied to deacetylation of chitin aiming to reduce the use of alkali. It was found that solution plasma could induce deacetylation of chitin hydrogels that were dispersed in MeOH/water solutions containing low NaOH concentrations (1-12%). Due to the action of free radicals, some extent of chain session of the polymer occurred during the plasma treatment. The degree of deacetylation and molecular weight of the obtained chitosan were 78% and 220 kDa, respectively, after the plasma treatment for five cycles (1 h/cycle) by using 90% MeOH/water solution containing 12% NaOH. The obtained chitosan could completely dissolve in 2% acetic acid solution and had antibacterial activities against S. aureus and E. coli.

Chitosan-laponite nanocomposite scaffolds for wound dressing application

The pivotal issue of skin regeneration research is the development of effective biomaterials that exhibit biological activities as fungicide and bactericide, combining simple and low cost manufacturing technologies. In this context, nanocomposite scaffolds based on chitosan (Ch)/Laponite (Lap) were produced by using different concentrations of Lap via freeze-drying process for potential application in skin regeneration. The influence of Lap concentration on the scaffold properties was evaluated. The prepared scaffolds were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), porosity, swelling capacity, and mechanical analyses. The results revealed that the scaffolds exhibited a porous architecture, besides the increase in the clay content, leads to an increase in the porosity, an improvement of mechanical strength, and a decrease of swelling capacity. In vitro tests were also carried out to evaluate the biocompatibility of the materials, such as bioadhesion, antibacterial activity, viability, and cell adhesion. Viability and cell adhesion demonstrated that all scaffolds were not cytotoxic and the fibroblast cells readily attached on the surface of the scaffolds. Thereby, the results suggested that the nanocomposite scaffolds are biomaterials potentially useful as wound dressings.

Synthesis of chitosan coated metal organic frameworks (MOFs) for increasing vancomycin bactericidal potentials against resistant S. aureus strain

Multiple drug resistant (MDR) has become a major issue in developing countries. MDR bacterial infections lead to significant increase in morbidity, mortality and cost of prolonged treatments. Therefore, designing of strategies for improving the antimicrobial potential of the therapeutic agents are highly required. Metal organic frameworks (MOFs) are highly tunable hybrid material, consist of metal ions linked together by organic bridging ligands have been used as an efficient drug delivery carrier because of their biodegradability, low toxicity and structure integrity upon loading and functionalizing process. Current study was based on the synthesis of chitosan coated MOFs with enhanced contact with S. aureus cell surface. Chitosan is deacetylated derivative of chitin and capable for non-bonding interaction with negatively charged bacterial cell leading to enhanced contact of MOFs with S. aureus. Chitosan coated MOFs were characterized with various techniques such as atomic force microscopy, scanning electron microscopy, DLS, FT-IR, TGA, DSC and Powder X-ray diffraction. They were also studied for their efficacy on resistant S. aureus, results revealed that Vancomycin bactericidal activity significantly increased upon loading in chitosan coated MOFs and caused increased inhibition of resistant S. aureus. AFM analysis of S. aureus strains clearly revealed complete distortion of morphology by treating with chitosan modified drug loaded MOFs. Findings of the current study suggest the potential of chitosan coated MOFs for reversing bacterial resistance against Vancomycin and provide new perspectives for improved antibiotic therapy of infections associated with MDR.

Functionalization of Polyethylene (PE) and Polypropylene (PP) Material Using Chitosan Nanoparticles with Incorporated Resveratrol as Potential Active Packaging

The present paper reports a novel method to improve the properties of polyethylene (PE) and polypropylene (PP) polymer foils suitable for applications in food packaging. It relates to the adsorption of chitosan-colloidal systems onto untreated and oxygen plasma-treated foil surfaces. It is hypothesized that the first coated layer of chitosan macromolecular solution enables excellent antibacterial properties, while the second (uppermost) layer contains a network of polyphenol resveratrol, embedded into chitosan nanoparticles, which enables antioxidant and antimicrobial properties simultaneously. X-ray photon spectroscopy (XPS) and infrared spectroscopy (FTIR) showed successful binding of both coatings onto foils as confirmed by gravimetric method. In addition, both attached layers (chitosan macromolecular solution and dispersion of chitosan nanoparticles with incorporated resveratrol) onto foils reduced oxygen permeability and wetting contact angle of foils; the latter indicates good anti-fog foil properties. Reduction of both oxygen permeability and wetting contact angle is more pronounced when foils are previously activated by O2 plasma. Moreover, oxygen plasma treatment improves stability and adhesion of chitosan structured adsorbates onto PP and PE foils. Foils also exhibit over 90% reduction of Staphylococcus aureus and over 77% reduction of Escherichia coli as compared to untreated foils and increase antioxidant activity for over a factor of 10. The present method may be useful in different packaging applications such as food (meat, vegetables, dairy, and bakery products) and pharmaceutical packaging, where such properties of foils are desired.

Chitosan-based (Nano)materials for Novel Biomedical Applications

Chitosan-based nanomaterials have attracted significant attention in the biomedical field because of their unique biodegradable, biocompatible, non-toxic, and antimicrobial nature. Multiple perspectives of the proposed antibacterial effect and mode of action of chitosan-based nanomaterials are reviewed. Chitosan is presented as an ideal biomaterial for antimicrobial wound dressings that can either be fabricated alone in its native form or upgraded and incorporated with antibiotics, metallic antimicrobial particles, natural compounds and extracts in order to increase the antimicrobial effect. Since chitosan and its derivatives can enhance drug permeability across the blood-brain barrier, they can be also used as effective brain drug delivery carriers. Some of the recent chitosan formulations for brain uptake of various drugs are presented. The use of chitosan and its derivatives in other biomedical applications is also briefly discussed.

Daylight Bactericidal Titania Textiles: A Contribution to Nosocomial Infections Control

: Daylight bactericidal cotton (100% cotton) textiles are presented and proposed for future hospital use. Amorphous titania (a-TiO2) and amorphous titania/chitosan complexes (a-TiO2//CS) were the selected bactericidal agents. Nanoparticles (NPs) and films were the two paths designed. Cotton textiles were impregnated with a-TiO2-based NPs or coated with a-TiO2 films. Industrial impregnation/coating will be implemented during the textile finishing treatments. A novel (room temperature and base-catalyzed), green (hydrothermal water as a catalyst), time-saving, and easy scale-up sol-gel process was established to produce the a-TiO2-based NPs. Amorphous-TiO2 films were produced by a dip-in (acid catalyzed) sol-gel solution. The daylight bactericidal performance (without the need of an external ultraviolet light source) of a-TiO2 NPs, films, and impregnated/coated textiles was proven according to AATCC 100 and ASTM E2149, using Staphylococcus aureus (ATCC®6538TM) as the bacterial indicator strain. A bacterial reduction of 99.97% was achieved for the a-TiO2 films and of 99.97% for the a-TiO2/CS NPs. Regarding the impregnated textiles, a bacterial reduction of 91.66% was achieved with a-TiO2/CS NPs, and 99.97% for cotton textiles coated with an a-TiO2 film.

Effect of Chitosan Dispersion and Microparticles on Older Streptococcus mutans Biofilms

(1) Background: The effectiveness of chitosan to improve the action of antimicrobial compounds against planktonic bacteria and young biofilms has been widely investigated in Dentistry, where the biofilm lifecycle is a determining factor for the success of antibacterial treatment. In the present study, mature Streptococcus mutans biofilms were treated with chitosan dispersion (CD) or chitosan microparticles (CM). (2) Methods: CD at 0.25% and 1% were characterized by texture analysis, while CD at 2% was spray-dried to form CM, which were characterized with respect to particle size distribution, zeta potential, and morphology. After determining the minimum inhibitory and bactericidal concentrations, S. mutans biofilms were grown on glass slides exposed 8×/day to 10% sucrose and 2×/day to CD or CM at 0.25% and 1%. Biofilm viability and acidogenicity were determined, using appropriate control groups for each experiment. (3) Results: CD had high viscosity and CM were spherical, with narrow size distribution and positive zeta potential. CM affected bacterial viability and acidogenicity in mature S. mutans biofilms more strongly than CD, especially at 1%. (4) Conclusions: Both chitosan forms exerted antimicrobial effect against mature S. mutans biofilms. CM at 1% can reduce bacterial viability and acidogenicity more effectively than CD at 1%, and thereby be more effective to control the growth of mature biofilms in vitro.

Proactive Release of Antimicrobial Essential Oil from a “Smart” Cotton Fabric

Two temperature and pH responsive submicron hydrogels based on poly(N- methylenebisacrylamide), chitosan and β-cyclodextrines (PNCS/CD hydrogel) with varying poly(N-isopropylacrylamide) to chitosan ratios were synthesized according to a simplified procedure, reflecting improved stimuli responsive properties and excellent bio-barrier properties, granted by incorporated chitosan. Hydrogels were applied to cotton-cellulose fabric as active coatings. Subsequently, antimicrobially active savory essential oil (EO) was embedded into the hydrogels in order to develop temperature- and pH-responsive cotton-cellulose fabric with double antimicrobial activity, i.e., bio-barrier formation of chitosan along with the proactive release of savory EO at predetermined conditions. The influence of the hydrogels chemical composition on stimuli responsive and antibacterial properties were assessed. Both PNCS/CD hydrogels showed stimuli responsiveness along with controlled release of savory EO. The chemical composition of the hydrogels strongly influenced the size of the hydrogel particles, their temperature and pH responsiveness, and the bio-barrier forming activity. The increased concentration of chitosan resulted in superior overall stimuli responsiveness and excellent synergy between the antimicrobial activities of the hydrogel and released savory EO.

Antibacterial effect of chitosan from squid pens against Porphyromonas gingivalis bacteria

BACKGROUND AND OBJECTIVES

Chitosan, a polysaccharide derived from squid pens - the squid waste, is gaining considerable interests in biomedical engineering due to the biodegradability, biocompatibility, nontoxicity, and antibacterial activity. It is necessary to eradicate the bacteria from root canal in endodontic treatment, including Porphyromonas gingivalis. P. gingivalis is one of the most prevalently found bacteria in root canals and its presence can cause endodontic treatment failure. This study was conducted to find the antibacterial effect of chitosan from squid pen against P. gingivalis at a certain concentration.

MATERIALS AND METHODS

Chitosan 1.5% (w/v) was diluted in several tubes. The lowest concentration with no bacterial growth was considered to have antibacterial activity against P. gingivalis.

RESULTS

There was no bacterial growth in nutrient agar media at the concentration of 10.75%.

CONCLUSION

Chitosan that was made from squid pens has antibacterial activity against P. gingivalis.

Influence of Antimicrobial Agents on the Thermal Sensitivity of Foodborne Pathogens: A Review

HIGHLIGHTS

Consumers are demanding more natural and organic foods and ingredients. Many additives alone are insufficient to inactivate pathogens or prevent growth. Mild heat combined with antimicrobial agents synergistically inactivate pathogens. Here we review studies using thermally assisted antimicrobial inactivation. Many opportunities exist for the application of this hurdle technology in foods.

Modification of Chitosan for the Generation of Functional Derivatives

Today, chitosan (CS) is probably considered as a biofunctional polysaccharide with the most notable growth and potential for applications in various fields. The progress in chitin chemistry and the need to replace additives and non-natural polymers with functional natural-based polymers have opened many new opportunities for CS and its derivatives. Thanks to the specific reactive groups of CS and easy chemical modifications, a wide range of physico-chemical and biological properties can be obtained from this ubiquitous polysaccharide that is composed of β-(1,4)-2-acetamido-2-deoxy-d-glucose repeating units. This review is presented to share insights into multiple native/modified CSs and chitooligosaccharides (COS) associated with their functional properties. An overview will be given on bioadhesive applications, antimicrobial activities, adsorption, and chelation in the wine industry, as well as developments in medical fields or biodegradability.

A Potential Antifungal Effect of Chitosan Against Candida albicans Is Mediated via the Inhibition of SAGA Complex Component Expression and the Subsequent Alteration of Cell Surface Integrity

Due to the high incidence of nosocomial Candida albicans infection, the first-line drugs for C. albicans infection have been heavily used, and the emergence of drug-resistant strains has gradually increased. Thus, a new antifungal drug or therapeutic method is needed. Chitosan, a product of chitin deacetylation, is considered to be potentially therapeutic for fungal infections because of its excellent biocompatibility, biodegradability and low toxicity. The biocidal action of chitosan against C. albicans shows great commercial potential, but the exact mechanisms underlying its antimicrobial activity are unclear. To reveal these mechanisms, mutant library screening was performed. ADA2 gene, which encodes a histone acetylation coactivator in the SAGA complex, was identified. Transmission electronic microscopy images showed that the surface of chitosan-treated ada2Δ cells was substantially disrupted and displayed an irregular morphology. Interestingly, the cell wall of ada2Δ cells was significantly thinner than that of wild-type cells, with a thickness similar to that seen in the chitosan-treated wild-type strain. Although ADA2 is required for chitosan tolerance, expression of ADA2 and several Ada2-mediated cell wall-related genes (ALS2, PGA45, and ACE2) and efflux transporter genes (MDR1 and CDR1) were significantly inhibited by chitosan. Furthermore, GCN5 encoding a SAGA complex catalytic subunit was inhibited by chitosan, and gcn5Δ cells exhibited phenotypes comparable to those of ada2Δ cells in response to chitosan and other cell surface-disrupting agents. This study demonstrated that a potential antifungal mechanism of chitosan against C. albicans operates by inhibiting SAGA complex gene expression, which decreases the protection of the cell surface against chitosan.

Bio-Based Polymers with Antimicrobial Properties towards Sustainable Development

This article concisely reviews the most recent contributions to the development of sustainable bio-based polymers with antimicrobial properties. This is because some of the main problems that humanity faces, nowadays and in the future, are climate change and bacterial multi-resistance. Therefore, scientists are trying to provide solutions to these problems. In an attempt to organize these antimicrobial sustainable materials, we have classified them into the main families; i.e., polysaccharides, proteins/polypeptides, polyesters, and polyurethanes. The review then summarizes the most recent antimicrobial aspects of these sustainable materials with antimicrobial performance considering their main potential applications in the biomedical field and in the food industry. Furthermore, their use in other fields, such as water purification and coating technology, is also described. Finally, some concluding remarks will point out the promise of this theme.

1H NMR characterization of chitin tetrasaccharide in binary H2O:DMSO solution: Evidence for anomeric end-effect propagation

Chitin oligosaccharides, composed of homogeneous β(1 → 4)-linked N-acetyl-D-glucosamine (GlcNAc) sequences, is a well-known elicitor of plant immune defense, and also occur as structural elements of chitosan and nodulation (Nod) factor. Detailed microstructure characterization is required for understanding the function mode of these bioactive molecules. Herein, experimental conditions for detection and elucidation of the ¹H NMR resonances of amide groups in chitin oligosaccharides are presented. The binary mixture of 70% H₂O: 30% DMSO‑d₆ was found to be the optimal solvent for amide proton measurements in homogeneous GlcNAc sequences, facilitating differentiation of the local chemical microenvironments of all four amide groups of the chitin tetrasaccharide. Experimental evidence that anomeric end-effect triggers amide proton resonance differentiation at the adjacent residue has potential to provide important insights into the solution structure of chitin and other amino sugars containing GlcNAc sequences.

Alternative Methods to SO2 for Microbiological Stabilization of Wine

The use of sulfur dioxide (SO₂ ) as wine additive is able to ensure both antioxidant protection and microbiological stability. In spite of these undeniable advantages, in the last two decades the presence of SO₂ in wine has raised concerns about potential adverse clinical effects in sensitive individuals. The winemaking industry has followed the general trend towards the reduction of SO₂ concentrations in food, by expressing at the same time the need for alternative control methods allowing reduction or even elimination of SO_2. In the light of this, research has been strongly oriented toward the study of alternatives to the use of SO₂ in wine. Most of the studies have focused on methods able to replace the antimicrobial activity of SO₂ . This review article gives a comprehensive overview of the current state-of-the-art about the chemical additives and the innovative physical techniques that have been proposed for this purpose. After a focus on the chemistry and properties of SO₂ in wine_, as well as on wine spoilage and on the conventional methods used for the microbiological stabilization of wine, recent advances on alternative methods proposed to replace the antimicrobial activity of SO₂ in winemaking are presented and discussed. Even though many of the alternatives to SO₂ showed good efficacy, nowadays no other physical technique or additive can deliver the efficacy and broad spectrum of action as SO₂ (both antioxidant and antimicrobial), therefore the alternative methods should be considered a complement to SO₂ in low-sulfite winemaking, rather than being seen as its substitutes.

The Influence of Mg2+ Ions on the In Vitro Efficacy of Chitosan-Titanium Dioxide Nanotubes (CTNTs) Scaffolds

Low mechanical strength and lack of osteoconductive cues are problems associated with chitosan-based scaffolds. This research aimed to fabricate reinforced chitosan-titanium dioxide (TiO2) nanotubes (CTNTs) scaffolds attributed to the enhanced biocompatibility and physical properties of TiO2 nanotubes (TNTs). The incorporation of hydrothermally synthesized TNTs at weight percent of 16 into chitosan was achieved via direct blending and lyophilization. CTNTs scaffolds were further subjected to 24-h adsorption in MgCl2 solutions of 0.5 mM, 1 mM, 2.5 mM, and 5 mM at physiological pH. The adsorption affinity of CTNTs towards Mg2+ ions was high and mainly attributed to the macroporosity of scaffolds and nanocavities of TNTs. The maximum monolayer adsorption capacity of CTNTs for Mg2+ ions was 8.8 mg/g scaffolds. Its adsorption isotherm fitted well with Langmuir isotherm by showing R2 of 0.9995. Fluorescence-based staining, cell viability, and alkaline phosphatase assays indicated that the adsorbed Mg2+ ions onto CTNTs scaffolds aided in promoting higher proliferation and early differentiation of MG63 cells than scaffolds without Mg2+ ions in a concentration-dependent manner. Based on current results, CTNTs scaffolds with Mg2+ ions may be a potential biomaterial for bone regeneration.

Molecular Mechanisms of Chitosan Interactions with Fungi and Plants

Chitosan is a versatile compound with multiple biotechnological applications. This polymer inhibits clinically important human fungal pathogens under the same carbon and nitrogen status as in blood. Chitosan permeabilises their high-fluidity plasma membrane and increases production of intracellular oxygen species (ROS). Conversely, chitosan is compatible with mammalian cell lines as well as with biocontrol fungi (BCF). BCF resistant to chitosan have low-fluidity membranes and high glucan/chitin ratios in their cell walls. Recent studies illustrate molecular and physiological basis of chitosan-root interactions. Chitosan induces auxin accumulation in Arabidopsis roots. This polymer causes overexpression of tryptophan-dependent auxin biosynthesis pathway. It also blocks auxin translocation in roots. Chitosan is a plant defense modulator. Endophytes and fungal pathogens evade plant immunity converting chitin into chitosan. LysM effectors shield chitin and protect fungal cell walls from plant chitinases. These enzymes together with fungal chitin deacetylases, chitosanases and effectors play determinant roles during fungal colonization of plants. This review describes chitosan mode of action (cell and gene targets) in fungi and plants. This knowledge will help to develop chitosan for agrobiotechnological and medical applications.

Antifungal activity of well-defined chito-oligosaccharide preparations against medically relevant yeasts

Due to their antifungal activity, chitosan and its derivatives have potential to be used for treating yeast infections in humans. However, to be considered for use in human medicine, it is necessary to control and know the chemical composition of the compound, which is not always the case for polymeric chitosans. Here, we analyze the antifungal activity of a soluble and well-defined chito-oligosaccharide (CHOS) with an average polymerization degree (DP_n) of 32 and fraction of acetylation (F_A) of 0.15 (C32) on 52 medically relevant yeast strains. Minimal inhibitory concentrations (MIC) varied widely among yeast species, strains and isolates (from > 5000 to < 9.77 μg mL^-1) and inhibition patterns showed a time- and dose-dependencies. The antifungal activity was predominantly fungicidal and was inversely proportional to the pH, being maximal at pH 4.5, the lowest tested pH. Furthermore, antifungal effects of CHOS fractions with varying average molecular weight indicated that those fractions with an intermediate degree of polymerization, i.e. DP 31 and 54, had the strongest inhibitory effects. Confocal imaging showed that C32 adsorbs to the cell surface, with subsequent cell disruption and accumulation of C32 in the cytoplasm. Thus, C32 has potential to be used as a therapy for fungal infections.

Recovery of chitin and chitosan from shrimp waste with microwave technique and versatile application

ABSTRACT: In this study, chitin and chitosan were extracted from Litopenaeus vannamei waste using chemical and microwave methods. Shrimp waste was cleaned, dried and ground sieved to 16, 32 and 60 mesh, and the samples were depigmented, demineralized, and deproteinized. Then, the chitin was submitted to a deacetylation process by 45% NaOH solution under microwave irradiation at 600w, for intermittent 15 min or using 5 pulses of 5 minutes. The study showed that the effectiveness of the particle size of 32 mesh and 6 pulses of 5 min to deacetylation with 92% of degree and chitosan yield (52.2%). The polymer chitosan showed higher antimicrobial activity against to Staphylococcus aureus, Escherichia coli, Salmonella enterica and the yeast Candida sp., respectively. The results indicated the feasibility of the microwave radiation as an attractive method to recover chitin and chitosan from shrimp wastes.

Selective Targeting of 4SO4-N-Acetyl-Galactosamine Functionalized Mycobacterium tuberculosis Protein Loaded Chitosan Nanoparticle to Macrophages: Correlation With Activation of Immune System

In the present study, we investigated potential of chitosan-based nanoparticles (CNPs) to deliver loaded therapeutic molecules to pathogen harboring macrophages. We fabricated stable CNPs employing ionic cross-linking method and evaluated their potential to target RAW 264.7 cells. The physicochemical characterization of as-synthesized CNPs was determined using electron microscopy, infrared microscopy and zeta potential measurement. Next, cellular uptake and intracellular localization studies of CNPs were followed in living RAW264.7 cells using confocal microscopy. We found that both Acr-1 loaded (CNP-A) and 4-SO₄-GalNAc ligand harboring (CNP-L) chitosan nanoparticle experience increased cellular uptake by Mycobacterium smegmatis infected RAW cells. Following cellular digestion in model macrophage cell line (RAW), CNPs provide an increased immune response. Further, 4-SO₄-GalNAc bearing CNP-L exhibits high binding affinity as well as antibacterial efficacy toward M. smegmatis. The data of the present study suggest that CNP-based nanoparticle offer a promising delivery strategy to target infected macrophages for prevention and eradication of intracellular pathogens such as M. smegmatis.

Challenges and opportunities related to the use of chitosan as a food preservative

Chitosan has attracted a growing attention as a food preservative due to its versatility, nontoxicity, biodegradability and biocompatibility. This review aims to provide a critical appraisal of the limitations and opportunities of the use of chitosan as a food preservative. The application of chitosan as a food preservative necessitates insights into mechanisms of chitosan-mediated cell death and injury, factors affecting chitosan activity and effects of chitosan on food safety and quality. Chitosan exerts antimicrobial activity by perturbing the negatively charged cell envelope of micro-organisms with its polycationic structure. Intrinsic characteristics, including molecular weight and degree of deacetylation (DD), and other ambient conditions, including pH, temperature and neighbouring components, affect chitosan activity. Because the antimicrobial activity of chitosan is mainly based on ionic interactions with negatively charged components of the bacterial cell envelope, the food matrix can strongly interfere with the antimicrobial activity of chitosan. Despite its limited antimicrobial efficacy, chitosan demonstrates both bactericidal and bacteriostatic effects in specific food products. Moreover, chitosan can also enhance the efficacy of commercial intervention technologies, such as heat and pressure treatment, and aid the preservation of food quality, including retardation of lipid oxidation, weight loss and deterioration in sensory attributes.

Decoupling the Functional Roles of Cationic and Hydrophobic Groups in the Antimicrobial and Hemolytic Activities of Methacrylate Random Copolymers

In this study, we report the antimicrobial and hemolytic activities of ternary statistical methacrylate copolymers consisting of cationic ammonium (amino-ethyl methacrylate: AEMA), hydrophobic alkyl (ethyl methacrylate: EMA), and neutral hydroxyl (hydroxyethyl methacrylate: HEMA) side chain monomers. The cationic and hydrophobic functionalities of copolymers mimic the cationic amphiphilicity of naturally occurring antimicrobial peptides (AMPs). The HEMA monomer units were used to separately modulate the compositions of cationic and hydrophobic monomers, and we investigated the effect of each component on the antimicrobial and hemolytic activities of copolymers. Our data indicated that increasing the number of cationic groups of the copolymers to be more than 30 mol % did not increase their antimicrobial activity against Escherichia coli. The number of cationic side chains in a polymer chain at this threshold is 5.5-7.7, which is comparable to those of natural antimicrobial peptides such as maginin (+6). The MIC values of copolymers with >30 mol % of AEMA depend on only the mol % of EMA, indicating that the hydrophobic interactions of the copolymers with E. coli cell membranes determine the antimicrobial activity of copolymers. These results suggest that the roles of cationic and hydrophobic groups can be controlled independently by design in the ternary copolymers studied here.