Tatjana Krivorotova

Impact of pectin esterification on the antimicrobial activity of nisin-loaded pectin particles

The relationship between pectin structure and the antimicrobial activity of nisin‐loaded pectin particles was examined. The antimicrobial activity of five different nisin‐loaded pectin particles, i.e., nisin‐loaded high methoxyl pectin, low methoxyl pectin, pectic acid, dodecyl pectin with 5.4 and 25% degree of substitution were tested in the pH range of 4.0–7.0 by agar‐diffusion assay and agar plate count methods. It was found that the degree of esterification of carboxyl group of galacturonic acid in pectin molecule is important for the antimicrobial activity of nisin‐loaded pectin particles. Nisin‐loaded particles prepared using pectic acid or the pectin with low degree of esterification exhibit higher antimicrobial activity than nisin‐loaded high methoxyl pectin particles. Pectins with free carboxyl groups or of low degree of esterification are the most suitable for particles preparation. Moreover, nisin‐loaded pectin particles were active at close to neutral or neutral pH values. Therefore, they could be effectively applied for food preservation.

Overcoming Antimicrobial Resistance in Bacteria Using Bioactive Magnetic Nanoparticles and Pulsed Electromagnetic Fields

Nisin is a known bacteriocin, which exhibits a wide spectrum of antimicrobial activity, while commonly being inefficient against Gram-negative bacteria. In this work, we present a proof of concept of novel antimicrobial methodology using targeted magnetic nisin-loaded nano-carriers [iron oxide nanoparticles (NPs) (11–13 nm) capped with citric, ascorbic, and gallic acids], which are activated by high pulsed electric and electromagnetic fields allowing to overcome the nisin-resistance of bacteria. As a cell model the Gram-positive bacteria Bacillus subtilis and Gram-negative Escherichia coli were used. We have applied 10 and 30 kV cm-1 electric field pulses (100 μs × 8) separately and in combination with two pulsed magnetic field protocols: (1) high dB/dt 3.3 T × 50 and (2) 10 mT, 100 kHz, 2 min protocol to induce additional permeabilization and local magnetic hyperthermia. We have shown that the high dB/dt pulsed magnetic fields increase the antimicrobial efficiency of nisin NPs similar to electroporation or magnetic hyperthermia methods and a synergistic treatment is also possible. The results of our work are promising for the development of new methods for treatment of the drug-resistant foodborne pathogens to minimize the risks of invasive infections.

Preparation and characterization of iron oxide magnetic nanoparticles functionalized by nisin

Nisin is a known bacteriocin approved as a food additive for food preservation. It exhibits a wide spectrum antimicrobial activity against Gram-positive bacteria. Iron oxide magnetic nanoparticles were synthesized and characterized by X-ray diffraction method. A main part of iron oxide nanoparticles was found to be maghemite though a small quantity of magnetite could also be present. Magnetic nanoparticles were stabilized by citric, ascorbic, gallic or glucuronic acid coating. Stable iron oxide magnetic nanoparticles were functionalized by nisin using a simple and low cost adsorption method. Nisin loading was confirmed by FT-IR spectra, thermogravimetric analysis, dynamic light scattering and atomic force microscopy methods. Nisin-loaded iron oxide magnetic nanoparticles were stable at least six weeks as judged by the measurements of zeta-potential and hydrodynamic diameter. The antimicrobial activity of nisin-loaded iron oxide magnetic nanoparticles was demonstrated toward Gram-positive bacteria. Functionalized nanoparticles could therefore find the application as antimicrobials in innovative and emerging technologies based on the magnetic field.

Double thermoresponsive pentablock copolymers: synthesis by one-pot RAFT polymerization and self-assembly in aqueous solutions

In this study, well-defined hydrophilic pentablock copolymers with iterative blocks of poly(2-hydroxyethyl methacrylate) (pHEMA) and poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) were synthesized by three-step one-pot RAFT polymerization in the presence of difunctional RAFT CTA. Two types of pentablock copolymers with central blocks of either pHEMA or pDMAEMA were synthesized and thermoresponsive self-assembly of these copolymers in aqueous solutions was studied by DLS, SEM, and zeta potential measurements. It was determined that these copolymers are double thermoresponsive, with temperature-induced aggregation at about 26–36 °C and 59–65 °C. Upon heating, these copolymers form micellar aggregates with pHEMA blocks in the core, while above the LCST of pDMAEMA the micellar aggregates gradually lose their previous core–shell form and convert to aggregates with more or less evenly distributed pDMAEMA and pHEMA blocks. Aggregation behaviour of the pentablock copolymers depends on the position of the blocks and content of HEMA units.