SILVER NANOCOMPOSITES: A GLIMPSE INTO THEIR GAME-CHANGING ROLES IN ANTIBACTERIAL THERAPY

This study is aimed to prepare and investigate the optical, electrical and antibacterial activity of the environmentally friendly (green) chitosan (Cs)/silver nanocomposites. TEM demonstrated that AgNPs have a spherical shape with particle size ranged from 3 nm to 25 nm. UV analysis spectra of Cs and Cs/Ag nanocomposites showed that, increasing the content of AgNPs led to a noticeable increase in the values of Urbach energy (E U ) and a dramatic decrease in both the indirect (E ig ) and direct (E dg ) optical bandgap energies. It is found that (E ig ) and (E dg ) are decreased from (4.72/5.31 eV) to (2.47/4.19 eV). The formation of the AgNPs is verified by the existence of surface plasmon resonance (SPR) peak at ∼ (421–450) nm. Wemple-DiDomenico and Sellmeier oscillator models are employed and displayed a clear enrichment in the dispersion energy (E d ) and oscillator energy (E 0) as well as the linear and nonlinear optical parameters of Cs. It is observed that the linear (χ(1)) and nonlinear (χ(3) and n2) parameters are enhanced from 0.083, 0.868 × 10−14 and 1.584 × 10−12 to 0.153, 9.762 × 10−14 and 4.088 × 10−12. The novel results in our study nominate Cs/Ag nanocomposites for applications in linear/nonlinear optical devices. AC conductivity behavior of Cs and Cs/Ag nanocomposites is analyzed based on Jonscher’s law and the analysis showed that the overlapping large polaron tunneling (OLPT) is the dominant conduction mechanism for our samples. It is clear that the values of dielectric constant (ε′) of Cs and Cs/Ag nanocomposites are higher confirming the presence of interface polarization (IP) relaxation. Moreover, it is found that the antibacterial activity of Cs against Gram-negative (P. aeruginosa) and Gram-positive (B. thuringiensis) bacteria is found to be enhanced with increasing the content of Ag NPs. These results suggested that Cs/Ag nanocomposites will be good source for preparing bio-nanocomposites for use in many biomedical and industrial applications.

The 3 human salivary cystatins S, SA and SN are multifunctional proteins that possess a cysteine protease inhibitory property, but their ability to act as such is very different (SN > SA >> S). One form, S, also appears to possess antibacterial properties towards the bacterium Porphyromonas gingivalis, often associated with periodontal diseases. In this study we measured the total cystatin inhibitory activity and the levels of each salivary cystatin in the whole saliva of 8 periodontally diseased patients and 2 groups of control subjects (n = 6 and n = 10). The total cystatin inhibitory activity and the total salivary cystatin concentration in the periodontally diseased patients were found to be lower than the controls (p < or = 0.005). The concentration of S was depleted to levels that would not allow it to be an effective antibacterial agent, and the concentration of SA, although depleted in some cases, was still present at sufficient levels to allow it to act as an effective physiological inhibitor of cathepsin L. The concentration of cystatin SN was also depleted in the periodontally diseased patients, but was still present in sufficient quantities to act as an effective physiological cysteine protease inhibitor of cathepsins H and L. In comparison, the concentration of all 3 salivary cystatins in the control subjects were sufficient to enable these proteins to be both effective physiological cysteine protease inhibitors and antibacterial agents.

Microbial pathogens and bulk amounts of industrial toxic wastes in water are an alarming situation to humans and a continuous threat to aquatic life. In this study, multifunctional silver and graphene nanocomposites (Ag)1−x(GNPs)x [25% (x = 0.25), 50% (x = 0.50) and 75% (x = 0.75) of GNPs] were synthesized via ex situ approach. Further, the synthesized nanocomposites were explored for their physicochemical characteristics, such as vibrational modes (Raman spectroscopic analysis), optical properties (UV visible spectroscopic analysis), antibacterial and photocatalytic applications. We investigated the antimicrobial activity of silver and graphene nanocomposites (Ag-GNPs), and the results showed that Ag-GNPs nanocomposites exhibit remarkably improved antimicrobial activity (28.78% (E. coli), 31.34% (S. aureus) and 30.31% (P. aeruginosa) growth inhibition, which might be due to increase in surface area of silver nanoparticles (AgNPs)). Furthermore, we investigated the photocatalytic activity of silver (AgNPs) and graphene (GNPs) nanocomposites in varying ratios. Interestingly, the Ag-GNPs nanocomposites show improved photocatalytic activity (78.55% degradation) as compared to AgNPs (54.35%), which can be an effective candidate for removing the toxicity of dyes. Hence, it is emphatically concluded that Ag-GNPs hold very active behavior towards the decolorization of dyes and could be a potential candidate for the treatment of wastewater and possible pathogenic control over microbes. In the future, we also recommend different other in vitro biological and environmental applications of silver and graphene nanocomposites.

Background: In many countries, Salmonella and Shigella species are frequently found to cause gastroenteritis outbreaks. Objectives: We describe nationwide data on infections with Salmonella spp. and Shigella spp. in Iran. Materials and methods: During a two-year period (2012 to 2013), rectal-swab samples were analyzed for the presence of bacteria. Sensitivity of the bacterial isolates to antimicrobial agents was tested according to clinical and laboratory standards institute (CLSI) guidelines. Results: Twenty-nine states reported 249 outbreaks of foodborne illnesses. In total, 1055 patients (604 males and 451 females, age range: < 1 and > 60 years) were enrolled in this study, of whom 18 died. Seventy-four culture-confirmed cases of infection with Salmonella spp. were identified, of which 10.8%, 6.8%, 68.9%, and 13.5% corresponded to Salmonella serotype A, B, C, or D respectively. Similarly, Shigella spp. were responsible for 118 cases of the foodborne illnesses; among them, Shigella sonnei (with 105 cases, 89%) was the leading serovar. Ciprofloxacin (100%) was the most effective antibacterial agent against Salmonella spp. followed by amikacin. Nalidixic acid and gentamycin were the least effective antibacterial agents against Salmonella spp. Similarly, Shigella spp. were also highly sensitive to ciprofloxacin (100%), whereas tetracycline and ampicillin were the least effective antibacterial agents against Shigella spp. Conclusions: These are the first recognized and confirmed outbreaks of foodborne illnesses in Iran. Salmonella and Shigella infections represent a considerable disease burden in our country. Therefore, efforts to reduce transmission of these pathogens via food and other routes must be implemented on a national scale. It is noteworthy that the outbreaks of Shigella and Salmonella infections in our country also pose a threat of antibiotic resistance.

Multifunctional nanocomposites integrated green synthesized amphiphilic chitosan/thyme extract/nanosilver for antimicrobial and anti-biofilm applications

Impairment of the gut health in Danio rerio exposed to triclocarban

Recently inorganic metal nanocomposites especially silver nanocomposites are emerging as the potential candidate for several biomedical applications. From time immemorial silver as a metal has always been used by the human civilization in the form of agriculture, pottery, utensils and even in biology and medicines. Silver nanoparticles as well as nanocomposites have recently been recognized for its usage in the field of medicine such as antifungal, antibacterial and as antioxidants. The silver present within the nanocomposites binds with the biomolecules of the microbial cells which prevents the growth and multiplicity of different bacterial strains. Even though numerous literatures are available focusing on the antibacterial activities of silver nanocomposites, there is not a single comprehensive literature in the form of book chapter or review article that demonstrate the recent development of antibacterial activity and its future challenges. Therefore, the present book chapter highlights the pathogenic strains responsible for the microbial infections, the limitations of the conventional treatment strategies, the emergence of silver nanocomposites as the new treatment strategy. Also various synthesis methods of the silver nanocomposites, its application in the area of antimicrobial activity and its ultimate mechanism of action behind it are discussed. Finally, the chapter concludes with the challenges and future perspectives to be met in order for the silver nanocomposites to act as an excellent antimicrobial agent in the upcoming period of commercial market.KeywordsNanotechnologySilver nanocompositesNanoparticlesAntimicrobialAntibacterialAntifungalBiomedical

Noble metal nanoparticles are important class of nanomaterials which have contributed immensely to the development of nanotechnology. In recent times, the improvement on the properties and applications of the pure noble metal nanoparticles has shifted interest towards the development of their nanocomposites. The noble metals can form composite materials with polymers, cellulose, carbon materials and metal oxides. This chapter will focus on green synthesized nanocomposites of silver, gold and platinum with cellulose, different metal oxides, graphene oxides and polymers. The use of green methods such as plant extracts, microorganism biomolecules and industrial and agricultural wastes are interesting techniques that leads to formation of the nanoparticles with lesser or no toxicity compared to other methods. The different behaviours and applications of the nanocomposites in catalysis, water treatment, sensing and biomedicine would be studied. This work will offer newer perspectives towards the excellent synthesis and applications of the noble metal nanocomposites.

This study reviews the concept, classifications, and techniques involved in the synthesis of nanocomposites. The environmental and health implications of nanoparticles and composite materials were detailed, as well as the applications of nanocomposites in water remediation, antibacterial application, and printed circuit boards. The study gave insights into the challenges of water pollution treatment and provided a broad list of nanocomposites that have been explored for water remediation. Moreover, the emergence of multi-drug resistance to many antibiotics has made current antibiotics inadequate in the treatment of disease. This has engineered the development of alternative strategies in the drug industries for the production of effective therapeutic agents, comprising nanocomposites with antibacterial agents. The new therapeutic agents known as nanoantibiotics are more efficient and have paved the way to handle the challenges of antibiotic resistance. In printed circuit boards, nanocomposites have shown promising applications because of their distinct mechanical, thermal, and electrical characteristics. The uniqueness of the write-up is that it provides a broad explanation of the concept, synthesis, application, toxicity, and harmful effects of nanocomposites. Thus, it will provide all-inclusive awareness to readers to identify research gaps and motivate researchers to synthesize novel nanocomposites for use in various fields.

Availability of novel antimicrobial agents is an urgent necessity to combat the growing threat posed by multidrug-resistant bacteria, prompting exploration of marine antimicrobial peptides (AMPs) as potential solutions. Crustacean AMPs are equitably diverse in terms of structure and function, making them consistent templates for novel antimicrobials. From Scylla olivacea gill transcriptome cDNA, a putative Crustin AMP sequence of 333 nucleotides, encoding a 111 amino acid Crustin Type-I isoform was identified. The mature peptide encoding region was cloned and recombinantly expressed in E. coli using Luria Bertani (LB) broth, yielding approximately 0.9 mg/L peptide. This cationic (+6.25) peptide with amphipathic properties (34% hydrophobicity) exhibited antibacterial effects against Gram-positive and Gram-negative strains, with MIC 16 μM against Vibrio spp. The identified modes of actions included disruption of bacterial membranes, membrane potential dissipation, and induction of ROS. Scanning electron microscopy (SEM) analysis revealed bacterial lysis and structural damage. Being non-toxic to mammalian cells (CHO-K1) and non-haemolytic, So-Crustin qualifies to be safe for therapeutic applications. It was quite stable under different physio-chemical/biological conditions, including temperature, pH, NaCl concentrations and proteases like trypsin and proteinase K. This study emphasizes So-Crustin's potential as a safe and effective antibacterial agent.

In this critical review, plant sources used as effective antibacterial agents against Helicobacter pylori infections are carefully described. The main intrinsic bioactive molecules, responsible for the observed effects are also underlined and their corresponding modes of action specifically highlighted. In addition to traditional uses as herbal remedies, in vitro and in vivo studies focusing on plant extracts and isolated bioactive compounds with anti-H. pylori activity are also critically discussed. Lastly, special attention was also given to plant extracts with urease inhibitory effects, with emphasis on involved modes of action.

Small molecule interaction with lipid bilayers: A molecular dynamics study of chlorhexidine

Location of chlorhexidine in DMPC model membranes: a neutron diffraction study

Kojic acid is a wonderful fungal secondary metabolite that has several applications in the food, medical, and agriculture sectors. Many human diseases become resistant to normal antibiotics and normal treatments. We need to search for alternative treatment sources and understand their mode of action. Aspergillus flavus ASU45 (OL314748) was isolated from the caraway rhizosphere as a non-aflatoxin producer and identified genetically using 18S rRNA gene sequencing. After applying the Box-Behnken statistical design to maximize KA production, the production raised from 39.96 to 81.59 g/l utilizing (g/l) glucose 150, yeast extract 5, KH2PO4 1, MgSO4.7H2O 2, and medium pH 3 with a coefficient (R2) of 98.45%. Extracted KA was characterized using FTIR, XRD, and a scanning electron microscope. Crystalized KA was an effective antibacterial agent against six human pathogenic bacteria (Bacillus cereus, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, Serratia marcescens, and Serratia plymuthica). KA achieves high inhibition activity against Bacillus cereus, K. pneumonia, and S. plymuthica at 100 μg/ml concentration by 2.75, 2.85, and 2.85 compared with chloramphenicol which gives inhibition zones 1, 1.1, and 1.6, respectively. Crystalized KA had anticancer activity versus three types of cancer cell lines (Mcf-7, HepG2, and Huh7) and demonstrated high cytotoxic capabilities on HepG-2 cells that propose strong antitumor potent of KA versus hepatocellular carcinoma. The antibacterial and anticancer modes of action were illustrated using the molecular docking technique. Crystalized kojic acid from a biological source represented a promising microbial metabolite that could be utilized as an alternative antibacterial and anticancer agent effectively.

Essential oils (EOs) and plant extracts, rich in beneficial chemical compounds, have diverse applications in medicine, food, cosmetics, and agriculture. This study investigates the antibacterial activity of nine essential oil constituents (EOCs) against Escherichia coli, focusing on the effects of treatment pH and biosynthetic requirements. The impact of EOCs on bacterial inactivation in E. coli strains was examined using both nonselective and selective culture media. Computer-assisted drug design (CADD) methods were employed to identify critical binding sites and predict the main binding modes of ligands to proteins. The EOCs, including citral, α-terpinyl acetate, α-terpineol, and linalool, demonstrated significant bacterial inactivation, particularly under acidic conditions. This study revealed that EOCs have an effect on the presence of sublethal damage to both the cytoplasmic membrane and the outer membrane in Gram-negative bacteria. Adding penicillin G to the repair medium prevents the recovery of sublethal injuries in E. coli treated with α-terpinyl acetate, α-terpineol, linalool, and citral, indicating that peptidoglycan synthesis is essential for recovering from these injuries. However, penicillin G did not hinder the recovery process of most sublethally injured cells treated with the other assessed EOCs. Molecular docking studies revealed the favorable binding interactions of α-terpinyl acetate, α-terpineol, linalool, and citral with the β-lactamase enzyme Toho-1, indicating their potential as effective antibacterial agents. The findings suggest that EOCs could serve as viable alternatives to synthetic preservatives, offering new strategies for combating antibiotic-resistant bacteria.