Rapid microwave-based method for the preparation of antimicrobial lignin-capped silver nanoparticles active against multidrug-resistant bacteria.

Due to the increasing inability of antibiotics to treat multidrug-resistant (MDR) bacteria, metal and metal oxide nanoparticles have been gaining interest as antimicrobial agents. Among those, silver nanoparticles have been used extensively as broad-spectrum antimicrobial agents. Here, we describe a newly-developed, 10-min (120 °C at 5 bar pressure) microwave-assisted synthesis of silver nanoparticles made from the wood biopolymer lignin as a reducing and capping agent. The resulting lignin-capped silver nanoparticles (AgLNPs) had an average particle diameter of 13.4 ±â€¯2.8 nm. Antimicrobial susceptibility assays against a variety of MDR clinical Gram-positive and Gram-negative pathogens revealed a minimal inhibitory concentration (MIC) of AgLNPs ≤5 µg/mL. AgLNPs (10 µg/mL) showed ≤20% cytotoxicity towards monocytic THP-1 cells and were well tolerated when administered subcutaneously in mice at high concentrations (5 mg at a concentration of 100 mg/mL) with no obvious toxicity. AgLNPs showed efficacy in an in vivo infection (abscess) mouse model against MDR Pseudomonas aeruginosa LESB58 and methicillin-resistant Staphylococcus aureus USA300. A significant decrease in abscess sizes was observed for both strains as well as a reduction in bacterial loads of P. aeruginosa after three days. This demonstrates that microwave-assisted synthesis provides an optimized strategy for the production of AgLNPs while maintaining antimicrobial activity in vitro and in vivo.

Metal nanoparticles: understanding the mechanisms behind antibacterial activity.

As the field of nanomedicine emerges, there is a lag in research surrounding the topic of nanoparticle (NP) toxicity, particularly concerned with mechanisms of action. The continuous emergence of bacterial resistance has challenged the research community to develop novel antibiotic agents. Metal NPs are among the most promising of these because show strong antibacterial activity. This review summarizes and discusses proposed mechanisms of antibacterial action of different metal NPs. These mechanisms of bacterial killing include the production of reactive oxygen species, cation release, biomolecule damages, ATP depletion, and membrane interaction. Finally, a comprehensive analysis of the effects of NPs on the regulation of genes and proteins (transcriptomic and proteomic) profiles is discussed.

Effective Control of Molds Using a Combination of Nanoparticles.

Molds are filamentous fungi able to grow on a variety of surfaces, including constructed surfaces, food, rotten organic matter, and humid places. Mold growth is characterized by having an unpleasant odor in enclosed or non-ventilated places and a non-aesthetic appearance. They represent a health concern because of their ability to produce and release mycotoxins, compounds that are toxic to animals and humans. The aim of this study was to evaluate commercial nanoparticles (NPs) that can be used as an additive in coatings and paints to effectively control the growth of harmful molds. Four different NPs were screened for their antifungal activities against the mycotoxin producing mold strains Aspergillus flavus and A. fumigatus. The minimal inhibitory concentrations of the NPs were determined in broth media, whereas an agar diffusion test was used to assess the antimold activity on acrylic- and water-based paints. The cytotoxic activity and the inflammatory response of the NPs were also evaluated using the established human derived macrophage cell line THP-1. Results showed that a combination of mix metallic- and ZnO-NPs (50:10 µg/mL) effectively inhibited the fungal growth when exposed to fluorescent light. Neither cytotoxic effect nor inflammatory responses were recorded, suggesting that this combination can be safely used in humid or non-ventilated environments without any health concerns.