Development and Evaluation of qPCR Detection Method and Zn-MgO/Alginate Active Packaging for Controlling Listeria monocytogenes Contamination in Cold-Smoked Salmon.

To answer to food industry requests to monitor the presence of L. monocytogenes in cold-smoked salmon samples and to extend their shelf-life, a qPCR protocol for the detection of L. monocytogenes, and an antibacterial active packaging reinforced with zinc magnesium oxide nanoparticles (Zn-MgO NPs) were developed. The qPCR allowed the sensitive and easy detection of L. monocytogenes in naturally contaminated samples, with specificity in full agreement with the standard methods. The halo diffusion study indicated a high antibacterial efficiency of 1 mg/mL Zn-MgO NPs against L. monocytogenes, while the flow cytometry showed only moderate cytotoxicity of the nanoparticles towards mammalian cells at a concentration above 1 mg/mL. Thus, the novel active packaging was developed by using 1 mg/mL of Zn-MgO NPs to reinforce the alginate film. Cold-smoked salmon samples inoculated with L. monocytogenes and air-packed with the Zn-MgO NPs-alginate nanobiocomposite film showed no bacterial proliferation at 4 °C during 4 days. In the same condition, L. monocytogenes growth in control contaminated samples packed with alginate film alone. Our results suggest that Zn-MgO nanoparticles can extend the shelf-life of cold-smoked salmon samples.

Exploring the impact of Mg-doped ZnO nanoparticles on a model soil microorganism Bacillus subtilis.

The environmental contamination of soil by metal oxide nanomaterials is a growing global concern because of their potential toxicity. We investigated the effects of Mg doped ZnO (Mg-nZnO) nanoparticles on a model soil microorganism Bacillus subtilis. Mg-nZnO exhibited only a moderate toxic effect on B. subtilis vegetative cells but was able to prevent biofilm formation and destroy already formed biofilms. Similarly, Mg-nZnO (≤1 mg/mL) was moderately toxic towards Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella enterica, Saccharomyces cerevisiae and murine macrophages. Engineered Mg-nZnO produced H2O2 and O2•- radicals in solutions of various salt and organic molecule compositions. A quantitative proteomic analysis of B. subtilis membrane proteins showed that Mg-nZnO increased the expression of proteins involved in detoxification of ROS, translation and biofilm formation. Overall, our results suggest that Mg-nZnO released into the environment may hinder the spreading, colonization and biofilm formation by B. subtilis but also induce a mechanism of bacterial adaptation.