Fabrication of Silver Nanoparticles Against Fungal Pathogens

The use of silver nanoparticles (AgNPs) against various pathogens is now being well recognized in the agriculture and health sector. Nanoparticles have been shown to exhibit various novel properties and these properties, on other hand, rely upon the size, shape, and morphology of these particles. Moreover, these physical characteristics enable them to interact with microbes, plants, and animals. Smaller-sized particles have shown more toxicity than larger-sized nanoparticles. AgNPs have shown growth inhibition of many fungi like Aspergillus fumigates, A. niger, A. flavus, Trichophyton rubrum, Candida albicans, and Penicillium species. According to the current hypothesis, AgNPs act by producing reactive oxygen species and free radicals, which cause protein denaturation, nucleic acid and proton pump damage, lipid peroxidation, and cell wall damage. Therefore, they alter the cell membrane permeability, causing cell death. This mini-review summarizes the use of silver nanoparticles against fungal pathogens and fungal biofilm in the agricultural sector.

Grafting of wool fibers through disulfide bonds: An advanced application of S-protected thiolated starch

The purpose of this study is to develop a potential pathway for grafting polymers onto wool fibers based on thiol-disulfide exchange reactions. S-protected thiolated starch (PTS) was synthesized by coupling 3-(2-pyridyldithio) propanoic acid to starch through esterification, resulting in 417.3 ± 15.1 μmol ligand binding to 1 g of starch. PTS was labelled with fluorescein isothiocyanate (FITC) prior to grafting. Wool fibers were preactivated by raising the amount of thiol groups utilizing mild reducing agents. The highest degree of preactivation on the surface of wool fibers was achieved by a 0.2% (w/v) sodium borohydride and 1.5% (w/v) sodium bisulfite mixture pH 5.0 resulting in 182.6 ± 8.7 μmol thiol groups per gram of fibers. Different incubation times and ratios between FITC-labelled PTS and wool fibers were investigated. A graft yield of 58.5% was achieved at a ratio of 1:1.5 (w/w) between wool fibers and FITC-labelled PTS within 18 h of incubation. Successful coating of PTS on wool fibers was confirmed by confocal imaging, scanning electron microscopy and FT-IR. Mechanical properties of grafted wool fibers were tested regarding elongation and tensile strength. These results provide evidence for the potential of S-protected thiolated starch as a superior coating material for wool fibers.

Antimicrobial and cytotoxic activity of silver nanoparticles synthesized from two haloalkaliphilic actinobacterial strains alone and in combination with antibiotics

AIMS

Presently, the effective antimicrobial agents have been limited by the emergence of microbial strains with multidrug resistance and biofilm formation potential. In the present study, we report remarkable antimicrobial activity of silver nanoparticles (AgNPs) synthesized from Streptomyces calidiresistens IF11 and IF17 strains, including inhibition of biofilm formation and synergistic effect of AgNPs and antibiotics against selected bacteria and yeasts. Cytotoxic effect of AgNPs on mammalian cell lines was also evaluated.

METHODS AND RESULTS

Analysis of biosynthesized AgNPs by Fourier Transform Infrared Spectroscopy and transmission electron microscopy revealed their spherical shape, small size in the range of 5-50 and 5-20 nm, respectively, as well as the presence of capping agents. Study of antimicrobial activity of AgNPs against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Candida albicans and Malassezia furfur evaluated by minimum inhibitory concentration (MIC) and minimum biocidal concentration (MBC) assays revealed that MICs of AgNPs from IF11 and IF17 strains against bacteria and yeasts were found to be in the range of 16-128 and 8-256 μg ml^-1 , while MBCs were in the range of 48-192 and 32-256 μg ml^-1 respectively. AgNPs inhibited biofilm formation of microbial strains, which was tested by using crystal violet stain. The highest synergistic effect determined by fractional inhibitory index of AgNPs with antibiotic (kanamycin or tetracycline) was found against Staph. aureus; while in case of yeasts, M. furfur showed highest sensitivity to AgNPs-ketoconazole combination (FIC = 0·12). The cytotoxic activity of AgNPs towards HeLa and 3T3 cell lines was studied by MTT assay. The IC₅₀ of AgNPs estimated against mouse fibroblasts was found to be 8·3 and 28·3 μg ml^-1 and, against HeLa cell line, 28·5 and 53·8 μg ml^-1 respectively.

CONCLUSIONS

It can be concluded that AgNPs synthesized from S. calidiresistens IF11 and IF17 strains have potential as an effective antimicrobial and cytotoxic agent, especially when used in combination with antibiotics/antifungal agents.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicates potential application of biogenic silver nanoparticles as an antimicrobial agent in nanomedicine.

New technique in starch nanoparticles synthesis

Starch nanoparticles (StNPs) were previously prepared using severe mechanical, physical and/or chemical conditions that takes too long time to produce a little yield of uncontrolled large size of StNP. The current work presents a new technique for the synthesis of StNPs based on the combination between sodium hydroxide and glycerol in aqueous medium during the synthesis process while the precipitation of the StNPs is performed under homogenization at ambient conditions. The new technique is based on three assumptions: 1) the dual impact of sodium hydroxide and glycerol on the swelling and gelatinization of starch as a pre-stage of the synthesis of (StNPs1), 2) the dual impact of glycerol and cooking of starch on the swelling and gelatinization of starch as a pre-stage of the formation of (StNPs2), and 3) the precipitation under homogenization at ambient conditions and its effect on breaking the H- bonds of the starch molecule in both StNPs1 and StNPs2. The importance of this technique arises from the ease of the process, the eco-friendly chemicals and the combination between the mechanical and chemical processes. NS (native starch), StNPs1 and StNPs2 were characterized using FTIR, XRD, TGA and TEM. TEM of StNPs1 showed a well-defined round particles uniformly distributed with size of about 62.5nm. StNPs2 showed a non-specific shape starch particles.

One Step Photopolymerization of N, N-Methylene Diacrylamide and Photocuring of Carboxymethyl Starch-Silver Nanoparticles onto Cotton Fabrics for Durable Antibacterial Finishing

The PI/UV system ((4-trimethyl ammonium methyl) benzophenone chloride/UV) was used to synthesize carboxymethyl starch- (CMS-) stabilized silver nanoparticles (AgNPs). AgNPs so prepared had round shape morphology with size of 1–7 nm. The prepared AgNPs were utilized to impart antibacterial finishing for cotton fabrics. The PI/UV system was further utilized to fix AgNPs onto cotton fabrics by photocrosslinking of AgNPs-CMS composite onto cotton fabrics to impart durable antibacterial properties. Effect of irradiation time and incorporating N, N-methylene diacrylamide (MDA) in different concentrations on antibacterial performance before and after repeated washing cycles was studied. S. aureus and E. coli were used to evaluate the antibacterial performance of finished fabrics. The antibacterial performance was directly proportional to the irradiation time and concentration of MDA but inversely proportional to the number of washing cycles. The inhibition zone of S. aureus and E. coli is the same although they are different in the cell wall structure and mode of action due to the nanosize structure formed.