Chitosan and their derivatives: Antibiofilm drugs against pathogenic bacteria

Chitosan-based smart hybrid materials: a physico-chemical perspective

Chitosan is one of the most studied cationic polysaccharides. Due to its unique characteristics of being water soluble, biocompatible, biodegradable, and non-toxic, this macromolecule is highly attractive for a broad range of applications. In addition, its complex behavior and the number of ways it interacts with different components in a system result in an astonishing variety of chitosan-based materials. Herein, we present recent advances in the field of chitosan-based materials from a physico-chemical perspective, with focus on aqueous mixtures with oppositely charged colloids, chitosan-based thin films, and nanocomposite systems. In this review, we focus our attention on the physico-chemical properties of chitosan-based materials, including solubility, mechanical resistance, barrier properties, and thermal behaviour, and provide a link to the chemical peculiarities of chitosan, such as its intrinsic low solubility, high rigidity, large charge separation, and strong tendency to form intra- and inter-molecular hydrogen bonds.

Caffeic Acid and Its Derivatives: Antimicrobial Drugs toward Microbial Pathogens

Caffeic acid is a plant-derived compound that is classified as hydroxycinnamic acid which contains both phenolic and acrylic functional groups. Caffeic acid has been greatly employed as an alternative strategy to combat microbial pathogenesis and chronic infection induced by microbes such as bacteria, fungi, and viruses. Similarly, several derivatives of caffeic acid such as sugar esters, organic esters, glycosides, and amides have been chemically synthesized or naturally isolated as potential antimicrobial agents. To overcome the issue of water insolubility and poor stability, caffeic acid and its derivative have been utilized either in conjugation with other bioactive molecules or in nanoformulation. Besides, caffeic acid and its derivatives have also been applied in combination with antibiotics or photoirradiation to achieve a synergistic mode of action. The present review describes the antimicrobial roles of caffeic acid and its derivatives exploited either in free form or in combination or in nanoformulation to kill a diverse range of microbial pathogens along with their mode of action. The chemistry employed for the synthesis of the caffeic acid derivatives has been discussed in detail as well.

Combination therapy of biogenic C-dots and lysozyme for enhanced antibacterial and antibiofilm activity

Nearly 80% of human chronic infections are caused due to bacterial biofilm formation. The increased resistance against the conventional antimicrobial agents makes it difficult to treat the biofilm-related infections. The antibiotics resistance developed by planktonic cells has also become a major threat for human. Therefore, we have attempted here to develop an effective alternative strategy to overcome the issues of antibiotics resistance of bacteria. Upon synthesis, biogenic C-dots were combined with lysozymes which were further encapsulated into chitosan nanocarrier to form C-dots carrier (CDC). The as-synthesized C-dots were found irregular shaped and the average size of C-dots and CDC were 8 ± 2 nm and 450 ± 50 nm, respectively. To ensure secure and targeted delivery of C-dots and lysozyme we have employed chitosan, a biodegradable and natural biopolymer, as a delivery system. The study of time-dependent bacterial growth and flow cytometry analysis demonstrated that CDC can exhibit a synergistic bactericidal activity against the antibiotics resistant recombinant E. coli cells. Further, we have shown that the CDC could be a potent agent for both prevention of biofilm formation and eradication of preformed biofilm. In addition, we have observed that our drug delivery system is hemocompatible in nature making it suitable for in vivo applications. Therefore, we believe that the combination therapy of C-dots and lysozyme may be used as an excellent antibacterial and antibiofilm strategy.

Bioactive Materials for Soft Tissue Repair

Over the past decades, age-related pathologies have increased abreast the aging population worldwide. The increased age of the population indicates that new tools, such as biomaterials/scaffolds for damaged tissues, which display high efficiency, effectively and in a limited period of time, for the regeneration of the body's tissue are needed. Indeed, scaffolds can be used as templates for three-dimensional tissue growth in order to promote the tissue healing stimulating the body's own regenerative mechanisms. In tissue engineering, several types of biomaterials are employed, such as bioceramics including calcium phosphates, bioactive glasses, and glass-ceramics. These scaffolds seem to have a high potential as biomaterials in regenerative medicine. In addition, in conjunction with other materials, such as polymers, ceramic scaffolds may be used to manufacture composite scaffolds characterized by high biocompatibility, mechanical efficiency and load-bearing capabilities that render these biomaterials suitable for regenerative medicine applications. Usually, bioceramics have been used to repair hard tissues, such as bone and dental defects. More recently, in the field of soft tissue engineering, this form of scaffold has also shown promising applications. Indeed, soft tissues are continuously exposed to damages, such as burns or mechanical traumas, tumors and degenerative pathology, and, thereby, thousands of people need remedial interventions such as biomaterials-based therapies. It is known that scaffolds can affect the ability to bind, proliferate and differentiate cells similar to those of autologous tissues. Therefore, it is important to investigate the interaction between bioceramics and somatic/stem cells derived from soft tissues in order to promote tissue healing. Biomimetic scaffolds are frequently employed as drug-delivery system using several therapeutic molecules to increase their biological performance, leading to ultimate products with innovative functionalities. This review provides an overview of essential requirements for soft tissue engineering biomaterials. Data on recent progresses of porous bioceramics and composites for tissue repair are also presented.

A Potential Quorum-Sensing Inhibitor for Bronchiectasis Therapy: Quercetin-Chitosan Nanoparticle Complex Exhibiting Superior Inhibition of Biofilm Formation and Swimming Motility of Pseudomonas aeruginosa to the Native Quercetin

Quercetin (QUE)—a plant-derived flavonoid, is recently established as an effective quorum sensing (QS) inhibiting agent in Pseudomonas aeruginosa—the main bacterial pathogen in bronchiectasis lungs. Successful clinical application of QUE, however, is hindered by its low solubility in physiological fluids. Herein we developed a solubility enhancement strategy of QUE in the form of a stable amorphous nanoparticle complex (nanoplex) of QUE and chitosan (CHI), which was prepared by electrostatically driven complexation between ionized QUE molecules and oppositely charged CHI. At its optimal preparation condition, the QUE–CHI nanoplex exhibited a size of roughly 150 nm with a 25% QUE payload and 60% complexation efficiency. The complexation with CHI had no adverse effect on the antibacterial and anticancer activities of QUE, signifying the preservation of QUE’s bioactivities in the nanoplex. Compared to the native QUE, the QUE–CHI nanoplex exhibited superior QS inhibition in suppressing the QS-regulated swimming motility and biofilm formation of P. aeruginosa, but not in suppressing the virulence factor production. The superior inhibitions of the biofilm formation and swimming motility afforded by the nanoplex were attributed to (1) its higher kinetic solubility (5-times higher) that led to higher QUE exposures, and (2) the synergistic QS inhibition attributed to its CHI fraction.

Antibacterial Behavior of Chitosan-Sodium Hyaluronate-PEGDE Crosslinked Films

Chitosan is a natural polymer that can sustain not only osteoblast adhesion and proliferation for bone regeneration purposes, but it is also claimed to exhibit antibacterial properties towards several Gram-positive and Gram-negative bacteria. In this study, chitosan was modified with sodium hyaluronate, crosslinked with polyethylene glycol diglycidyl ether (PEGDE) and both osteoblast cytotoxicity and antibacterial behavior studied. The presence of sodium hyaluronate and PEGDE on chitosan was detected by FTIR, XRD, and XPS. Chitosan (CHT) films with sodium hyaluronate crosslinked with PEGDE showed a better thermal stability than pristine hyaluronate. In addition, osteoblast cytocompatibility improved in films containing sodium hyaluronate. However, none of the films exhibit antimicrobial activity against Escherichia coli, Enterococcus faecalis, and Staphylococcus aureus while exhibiting low to mild activity against Salmonella typhimurion.

A comparative study of antimicrobial activity of differently-synthesized chitosan nanoparticles against bovine mastitis pathogens

The greatest concern in dairy farming nowadays is bovine mastitis (BM), which results mainly from bacterial colonization of the mammary gland. Antibiotics are the most widely used strategy for its prevention and treatment, but overuse has led to growing antimicrobial resistance. Pathogens have also developed other mechanisms to persist in the udder, such as biofilm formation and internalization into bovine epithelial cells. New therapies are therefore needed to reduce or replace antibiotic therapies. In a previous study, we found that chitosan nanoparticles (Ch-NPs) have considerable potential for the treatment of BM. The aim of the present study was to evaluate the antimicrobial activity of differently-synthesized Ch-NPs against BM pathogens and their toxicity in bovine cells in vitro, to further explore the attributes of Ch-NPs for the prevention and treatment of intramammary infections. We also looked into their ability to inhibit biofilm formation and prevent the internalization of S. aureus into mammary epithelial cells. Finally, since an interesting approach for BM prevention is to enhance the host's immune response, we studied whether Ch-NPs could promote the release of pro-inflammatory cytokines in mammary epithelial cells. The results reveal that the bactericidal effect of Ch-NPs on BM pathogens and their ability to inhibit biofilm formation are size-dependent, with smaller particles being more efficient. In contrast, their effect on the viability of the cell lines is not size-dependent and all samples tested were non-toxic. The smallest Ch-NPs successfully prevented the internalization of S. aureus into the cells, but did not promote the production of pro-inflammatory cytokines. These findings make it possible to conclude that Ch-NPs are a great bactericidal agent which can prevent the main mechanisms developed by BM pathogens to persist in the udder.

Nanotheranostics: A Possible Solution for Drug-Resistant Staphylococcus aureus and their Biofilms?

Staphylococcus aureus is a notorious pathogen that colonizes implants (orthopedic and breast implants) and wounds with a vicious resistance to antibiotic therapy. Methicillin-resistant S. aureus (MRSA) is a catastrophe mainly restricted to hospitals and emerged to community reservoirs, acquiring resistance and forming biofilms. Treating biofilms is problematic except via implant removal or wound debridement. Nanoparticles (NPs) and nanofibers could combat superbugs and biofilms and rapidly diagnose MRSA. Nanotheranostics combine diagnostics and therapeutics into a single agent. This comprehensive review is interpretative, utilizing mainly recent literature (since 2016) besides the older remarkable studies sourced via Google Scholar and PubMed. We unravel the molecular S. aureus resistance and complex biofilm. The diagnostic properties and detailed antibacterial and antibiofilm NP mechanisms are elucidated in exciting stories. We highlight the challenges of bacterial infections nanotheranostics. Finally, we discuss the literature and provide "three action appraisals". (i) The first appraisal consists of preventive actions (two wings), avoiding unnecessary hospital visits, hand hygiene, and legislations against over-the-counter antibiotics as the general preventive wing. Our second recommended preventive wing includes preventing the adverse side effects of the NPs from resistance and toxicity by establishing standard testing procedures. These standard procedures should provide breakpoints of bacteria's susceptibility to NPs and a thorough toxicological examination of every single batch of synthesized NPs. (ii) The second appraisal includes theranostic actions, using nanotheranostics to diagnose and treat MRSA, such as what we call "multifunctional theranostic nanofibers. (iii) The third action appraisal consists of collaborative actions.

Positive effects of zeolite powder on aerobic granulation: Nitrogen and phosphorus removal and insights into the interaction mechanisms

Aerobic granular sludge is considered one of the most promising biological wastewater treatment technologies of the 21st century. However, the long granulation time and poor treatment effect on N and P have severely limited its popularity and large-scale application. In this study, we systematically examine the strengthening effects of zeolite powder on granulation, N and P removal, and their interaction mechanisms. The addition of zeolite powder decreased sludge granulation time to 18 d, and improved average N and P removal rates by 4.48% and 2.22%, respectively. The multi-pore and nutrient-rich environment of the zeolite powder is beneficial for maintaining microbial activity and granular stability. Moreover, its adsorption to N and P enriches their respective removal strains, improving their removal efficiency.

Tunable Thiol-Ene Photo-Cross-Linked Chitosan-Based Hydrogels for Biomedical Applications

Access to biocompatible hydrogels with tunable properties is of great interest in biomedical applications. Here we report the synthesis and characterization of a series of photo-cross-linked chitosan hydrogels from norbornene-functionalized chitosan (CS-nb) and various thiolated cross-linkers. The resulting materials were characterized by NMR, swelling ratio, rheology, SEM, and small angle neutron scattering (SANS) measurements. The hydrogels exhibited pH- and salt-dependent swelling, while the macro- and microscale properties could be modulated by the choice and degree of cross-linker or the polymer concentration. The materials could be molded in situ and loaded with small molecules that can be released overtime. Moreover, the incorporation of collagen in the hydrogels drastically improved cell adhesion, with excellent viabilities of human dermofibroblast cells on the hydrogels observed for up to 6 days, highlighting the potential use of these materials in the biomedical area.

Chitosan-Based Biomimetically Mineralized Composite Materials in Human Hard Tissue Repair

Chitosan is a natural, biodegradable cationic polysaccharide, which has a similar chemical structure and similar biological behaviors to the components of the extracellular matrix in the biomineralization process of teeth or bone. Its excellent biocompatibility, biodegradability, and polyelectrolyte action make it a suitable organic template, which, combined with biomimetic mineralization technology, can be used to develop organic-inorganic composite materials for hard tissue repair. In recent years, various chitosan-based biomimetic organic-inorganic composite materials have been applied in the field of bone tissue engineering and enamel or dentin biomimetic repair in different forms (hydrogels, fibers, porous scaffolds, microspheres, etc.), and the inorganic components of the composites are usually biogenic minerals, such as hydroxyapatite, other calcium phosphate phases, or silica. These composites have good mechanical properties, biocompatibility, bioactivity, osteogenic potential, and other biological properties and are thus considered as promising novel materials for repairing the defects of hard tissue. This review is mainly focused on the properties and preparations of biomimetically mineralized composite materials using chitosan as an organic template, and the current application of various chitosan-based biomimetically mineralized composite materials in bone tissue engineering and dental hard tissue repair is summarized.

Novel Colloidal Nanocarrier of Cetylpyridinium Chloride: Antifungal Activities on Candida Species and Cytotoxic Potential on Murine Fibroblasts

Nanocarriers have been used as alternative tools to overcome the resistance of Candida species to conventional treatments. This study prepared a nanocarrier of cetylpyridinium chloride (CPC) using iron oxide nanoparticles (IONPs) conjugated with chitosan (CS), and assessed its antifungal and cytotoxic effects. CPC was immobilized on CS-coated IONPs, and the nanocarrier was physico-chemically characterized. Antifungal effects were determined on planktonic cells of Candida albicans and Candida glabrata (by minimum inhibitory concentration (MIC) assays) and on single- and dual-species biofilms of these strains (by quantification of cultivable cells, total biomass and metabolic activity). Murine fibroblasts were exposed to different concentrations of the nanocarrier, and the cytotoxic effect was evaluated by MTT reduction assay. Characterization methods confirmed the presence of a nanocarrier smaller than 313 nm. IONPs-CS-CPC and free CPC showed the same MIC values (0.78 µg mL⁻¹). CPC-containing nanocarrier at 78 µg mL⁻¹ significantly reduced the number of cultivable cells for all biofilms, surpassing the effect promoted by free CPC. For total biomass, metabolic activity, and cytotoxic effects, the nanocarrier and free CPC produced statistically similar outcomes. In conclusion, the IONPs-CS-CPC nanocarrier was more effective than CPC in reducing the cultivable cells of Candida biofilms without increasing the cytotoxic effects of CPC, and may be a useful tool for the treatment of oral fungal infections.

Antimicrobial and Antibiofilm Capacity of Chitosan Nanoparticles against Wild Type Strain of Pseudomonas sp. Isolated from Milk of Cows Diagnosed with Bovine Mastitis

Bovine mastitis (BM) is the most prevalent bacterial infection in the livestock sector, affecting the dairy industry greatly. The prevention and treatment of this disease is mainly made via antibiotics, but the increasing antimicrobial resistance of pathogens has affected the efficiency of conventional drugs. Pseudomonas sp. is one of the pathogens involved in this infection. The therapeutic rate of cure for this environmental mastitis-causing pathogen is practically zero, regardless of treatment. Biofilm formation has been one of the main virulence mechanisms of Pseudomonas hence presenting resistance to antibiotic therapy. We have manufactured chitosan nanoparticles (NQo) with tripolyphosphate (TPP) using ionotropic gelation. These NQo were confronted against a Pseudomonas sp. strain isolated from milk samples of cows diagnosed with BM, to evaluate their antimicrobial and antibiofilm capacity. The NQo showed great antibacterial effect in the minimum inhibitory concentrations (MIC), minimum bactericidal concentration (MBC) and disk diffusion assays. Using sub lethal concentrations, NQo were tested for inhibition of biofilm formation. The results show that the nanoparticles exhibited biofilm inhibition and were capable of eradicate pre-existing mature biofilm. These findings indicate that the NQo could act as a potential alternative to antibiotic treatment of BM.

Motility of Vibrio spp.: regulation and controlling strategies

Flagellar motility in bacteria is a highly regulated and complex cellular process that requires high energy investment for movement and host colonization. Motility plays an important role in the lifestyle of Vibrio spp. in the aquatic environment and during host colonization. Flagellar motility in vibrios is associated with several cellular processes, such as movement, colonization, adhesion, biofilm formation, and virulence. The transcription of all flagella-related genes occurs hierarchically and is regulated positively or negatively by several transcription factors and regulatory proteins. The flagellar regulatory hierarchy is well studied in Vibrio cholerae and Vibrio parahaemolyticus. Here, we compared the regulatory cascade and molecules involved in the flagellar motility of V. cholerae and V. parahaemolyticus in detail. The evolutionary relatedness of the master regulator of the polar and lateral flagella in different Vibrio species is also discussed. Although they can form symbiotic associations of some Vibrio species with humans and aquatic organisms can be harmed by several species of Vibrio as a result of surface contact, characterized by flagellar movement. Thus, targeting flagellar motility in pathogenic Vibrio species is considered a promising approach to control Vibrio infections. This approach, along with the strategies for controlling flagellar motility in different species of Vibrio using naturally derived and chemically synthesized compounds, is discussed in this review. KEY POINTS: • Vibrio species are ubiquitous and distributed across the aquatic environments. • The flagellar motility is responsible for the chemotactic movement and initial colonization to the host. • The transition from the motile into the biofilm stage is one of the crucial events in the infection. • Several signaling pathways are involved in the motility and formation of biofilm. • Attenuation of motility by naturally derived or chemically synthesized compounds could be a potential treatment for preventing Vibrio biofilm-associated infections.

Bactericidal Activity of Usnic Acid-Chitosan Nanoparticles against Persister Cells of Biofilm-Forming Pathogenic Bacteria

The present study aimed to prepare usnic acid (UA)-loaded chitosan (CS) nanoparticles (UA-CS NPs) and evaluate its antibacterial activity against biofilm-forming pathogenic bacteria. UA-CS NPs were prepared through simple ionic gelification of UA with CS, and further characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and field-emission transmission electron microscopy. The UA-CS NPs presented a loading capacity (LC) of 5.2%, encapsulation efficiency (EE) of 24%, and a spherical shape and rough surface. The maximum release of UA was higher in pH 1.2 buffer solution as compared to that in pH 6.8 and 7.4 buffer solution. The average size and zeta potential of the UA-CS NPs was 311.5 ± 49.9 nm in diameter and +27.3 ± 0.8 mV, respectively. The newly prepared UA-CS NPs exhibited antibacterial activity against persister cells obtained from the stationary phase in batch culture, mature biofilms, and antibiotic-induced gram-positive and gram-negative pathogenic bacteria. Exposure of sub-inhibitory concentrations of UA-CS NPs to the bacterial cells resulted in a change in morphology. The present study suggests an alternative method for the application of UA into nanoparticles. Furthermore, the anti-persister activity of UA-CS NPs may be another possible strategy for the treatment of infections caused by biofilm-forming pathogenic bacteria.

Inhibition of biofilm and virulence properties of Pseudomonas aeruginosa by sub-inhibitory concentrations of aminoglycosides

Aminoglycosides are a commonly used class of antibiotics; however, their application has been discontinued due to the emergence of multi-drug resistance bacterial strains. In the present study, the subinhibitory concentrations (sub-MIC) of several aminoglycosides were determined and tested as an antibiofilm and for their anti-virulence properties against Pseudomonas aeruginosa PAO1, which is an opportunistic foodborne pathogen. P. aeruginosa PAO1 exhibits multiple mechanisms of resistance, including the formation of biofilm and production of several virulence factors, against aminoglycoside antibiotics. The sub-MIC of these antibiotics exhibited biofilm inhibition of P. aeruginosa in alkaline TSB (pH 7.9). Moreover, various concentrations of these aminoglycosides also eradicate the mature biofilm of P. aeruginosa. In the presence of sub-MIC of aminoglycosides, the morphological changes of P. aeruginosa were found to change from rod-shaped to the filamentous, elongated, and streptococcal forms. Similar growth conditions and sub-MIC of aminoglycosides were also found to attenuate several virulence properties of P. aeruginosa PAO1. Molecular docking studies demonstrate that these aminoglycosides possess strong binding properties with the LasR protein, which is a well-characterized quorum-sensing receptor of P. aeruginosa. The present study suggests a new approach to revitalize aminoglycosides as antibiofilm and antivirulence drugs to treat infections caused by pathogenic bacteria.

Nano-Based Drug Delivery or Targeting to Eradicate Bacteria for Infection Mitigation: A Review of Recent Advances

Pathogenic bacteria infection is a major public health problem due to the high morbidity and mortality rates, as well as the increased expenditure on patient management. Although there are several options for antimicrobial therapy, their efficacy is limited because of the occurrence of drug-resistant bacteria. Many conventional antibiotics have failed to show significant amelioration in overall survival of infectious patients. Nanomedicine for delivering antibiotics provides an opportunity to improve the efficiency of the antibacterial regimen. Nanosystems used for antibiotic delivery and targeting to infection sites render some benefits over conventional formulations, including increased solubility, enhanced stability, improved epithelium permeability and bioavailability, prolonged antibiotic half-life, tissue targeting, and minimal adverse effects. The nanocarriers' sophisticated material engineering tailors the controllable physicochemical properties of the nanoparticles for bacterial targeting through passive or active targeting. In this review, we highlight the recent progress on the development of antibacterial nanoparticles loaded with antibiotics. We systematically introduce the concepts and amelioration mechanisms of the nanomedical techniques for bacterial eradication. Passive targeting by modulating the nanoparticle structure and the physicochemical properties is an option for efficient drug delivery to the bacteria. In addition, active targeting, such as magnetic hyperthermia induced by iron oxide nanoparticles, is another efficient way to deliver the drugs to the targeted site. The nanoparticles are also designed to respond to the change in environment pH or enzymes to trigger the release of the antibiotics. This article offers an overview of the benefits of antibacterial nanosystems for treating infectious diseases.

Sequential Delivery of Cryogel Released Growth Factors and Cytokines Accelerates Wound Healing and Improves Tissue Regeneration

Growth factors and cytokines that are secreted by cells play a crucial role in the complex physiological reaction to tissue injury. The ability to spatially and temporally control their actions to maximize regenerative benefits and minimize side effects will help accelerate wound healing and improve tissue regeneration. In this study, the sequential targeted delivery of growth factor/cytokine combinations with regulatory functions on inflammation and tissue regeneration was examined using an internal splint wound healing model. Four examined growth factors and cytokines were effectively incorporated into a novel chitosan-based cryogel, which offered a controlled and sustained release of all factors while maintaining their biological activities. The cryogels incorporated with inflammation modulatory factors (IL-10 and TGF-β) and with wound healing factors (VEGF and FGF) were placed on the wound surface on day 0 and day 3, respectively, after wound initiation. Although wound area gradually decreased in all groups over time, the area in the cryogel group with growth factor/cytokine combinations was significantly reduced starting on day 7 and reached about 10% on day 10, as compared to 60-65% in the control groups. Sequential delivery of inflammation modulatory and wound healing factors enhanced granulation tissue formation, as well as functional neovascularization, leading to regenerative epithelialization. Collectively, the chitosan-based cryogel can serve as a controlled release system for sequential delivery of several growth factors and cytokines to accelerate tissue repair and regeneration.

Synthesis of new Enrofloxacin Derivatives as Potential Antibiofilm Drugs Against Staphylococcus Aureus and Klebsiella Pneumoniae

BACKGROUND

The antimicrobial resistance due to biofilm formation among bacteria is a significant problem in the healthcare and food industries.

OBJECTIVE

The current study describes the synthesis of enrofloxacin derivatives 2-17, and the evaluation of their anti-bacterial and anti-biofilm activities.

METHODS

Compounds 2-17 were synthesized through the acylation of enrofloxacin with thionyl chloride, followed by reaction with different aromatic amines. The new analogues identified among the sixteen compounds were 2-7, 11, 14, and 17.

RESULTS

Compound 2 appeared to be effective against pathogens S. aureus as well as K. pneumonia, whereas, compound 11 was found active against K. pneumonia only. Compound 2 inhibited >75% biofilm formation of S. aureus at 20 μg/mL and K. pneumonia at 10 μg/mL concentrations. These doses are far below the bactericidal concentration of compound 2, suggesting the anti-virulence mechanism of these compounds. Compound 11 inhibited 60% biofilm formation of K. pneumoniae at 70 μg/mL concentration. Compound 5 inhibited the biofilm of K. pneumoniae at 62 μg/mL concentration but also had bactericidal properties at this concentration. Interestingly, compound 2 eradicated the preformed biofilm of both the pathogens at much lower doses as compared to control drug, gentamycin and substrate, enrofloxacin. Cytotoxicity of compounds 2-17 was checked by a standard method using 3T3 normal cell lines (mouse fibroblast), all compounds were found to be noncytotoxic.

CONCLUSION

These compounds can be used alone or with FDA approved drugs to overcome biofilm related K. pneumoniae and S. aureus infections.

Silver Nanoparticles for the Therapy of Tuberculosis

Rapid emergence of aggressive, multidrug-resistant Mycobacteria strain represents the main cause of the current antimycobacterial-drug crisis and status of tuberculosis (TB) as a major global health problem. The relatively low-output of newly approved antibiotics contributes to the current orientation of research towards alternative antibacterial molecules such as advanced materials. Nanotechnology and nanoparticle research offers several exciting new-concepts and strategies which may prove to be valuable tools in improving the TB therapy. A new paradigm in antituberculous therapy using silver nanoparticles has the potential to overcome the medical limitations imposed in TB treatment by the drug resistance which is commonly reported for most of the current organic antibiotics. There is no doubt that AgNPs are promising future therapeutics for the medication of mycobacterial-induced diseases but the viability of this complementary strategy depends on overcoming several critical therapeutic issues as, poor delivery, variable intramacrophagic antimycobacterial efficiency, and residual toxicity. In this paper, we provide an overview of the pathology of mycobacterial-induced diseases, andhighlight the advantages and limitations of silver nanoparticles (AgNPs) in TB treatment.

Dual responsive linalool capsules with high loading ratio for excellent antioxidant and antibacterial efficiency

Linalool is a main component in different naturally derived essential oils, and widely used in household, personal care, food and therapeutic formulations. However, the application is limited due to its high volatility and low stability. In this study, an effective encapsulation with high loading ratio was built up together with thermal-redox dual responsiveness and controlled release properties. The emulsified linalool droplets were modified with carbon-carbon double bonds, followed by the precipitation polymerization with thermal sensitive monomer, N-vinyl caprolactam. The average size and the loading ratio of the prepared linalool capsules were 1.4 μm and 50.41 wt%. The linalool capsules exhibited thermal-redox dual responsive properties and the antioxidant-antibacterial performance. Especially, responding to the stimuli mimicking practical circumstance, the synthesized capsules presented excellent bacteria inhibiting effect. This work may open a new path for fragrance and essential oil encapsulation, enlarging them as the green biological antibacterial agents in different applications.

Synthesis and Characterization of N,N,N-trimethyl-O-(ureidopyridinium)acetyl Chitosan Derivatives with Antioxidant and Antifungal Activities

Chitosan is an active biopolymer, and the combination of it with other active groups can be a valuable method to improve the potential application of the resultant derivatives in food, cosmetics, packaging materials, and other industries. In this paper, a series of N,N,N-trimethyl-O-(ureidopyridinium)acetyl chitosan derivatives were synthesized. The combination of chitosan with ureidopyridinium group and quaternary ammonium group made it achieve developed water solubility and biological properties. The structures of chitosan and chitosan derivatives were confirmed by FTIR, ¹H NMR spectra, and elemental analysis. The prepared chitosan derivatives were evaluated for antioxidant property by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability, hydroxyl radical scavenging ability, and superoxide radical scavenging ability. The results revealed that the synthesized chitosan derivatives exhibited improved antioxidant activity compared with chitosan. The chitosan derivatives were also investigated for antifungal activity against Phomopsis asparagus as well as Botrytis cinerea, and they showed a significant inhibitory effect on the selected phytopathogen. Meanwhile, CCK-8 assay was used to test the cytotoxicity of chitosan derivatives, and the results showed that most derivatives had low toxicity. These data suggested to develop analogs of chitosan derivatives containing ureidopyridinium group and quaternary ammonium group, which will provide a new kind of promising biomaterials having decreased cytotoxicity as well as excellent antioxidant and antimicrobial activity.