Biosorption of silver cations onto <i>Lactococcus lactis</i> and <i>Lactobacillus casei</i> isolated from dairy products

<div><p>The current work deals with the phenomenon of silver cations uptake by two kinds of bacteria isolated from dairy products. The mechanism of sorption of silver cations by <i>Lactococcus lactis</i> and <i>Lactobacillus casei</i> bacteria was investigated. Inductively coupled plasma–mass spectrometry (ICP-MS) was used for determination of silver concentration sorbed by bacteria. Analysis of charge distribution was conducted by diffraction light scattering method. Changes in the ultrastructure of <i>Lactococcus lactis</i> and <i>Lactobacillus casei</i> cells after treatment with silver cations were investigated using transmission electron microscopy observation. Molecular spectroscopy methods, namely Fourier transform-infrared spectroscopy (FT-IR) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) were employed for description of the sorption mechanism. Moreover, an analysis of volatile organic compounds (VOCs) extracted from bacterial cells was performed.</p></div

Concentration of Ag in OPTION 1 & 2 measured using ICP-MS.

<p>Concentration of Ag in OPTION 1 & 2 measured using ICP-MS.</p

A spectrum of <i>L</i>. <i>lactis</i> recorded using MALDI-TOF MS technique with the use of DHB (top) and HCCA (bottom) matrix; photos of crystals of the matrices are shown in the corner.

<p>A spectrum of <i>L</i>. <i>lactis</i> recorded using MALDI-TOF MS technique with the use of DHB (top) and HCCA (bottom) matrix; photos of crystals of the matrices are shown in the corner.</p

OD values for the studied strains of bacteria inoculated with different concentrations of silver.

<p>OD values for the studied strains of bacteria inoculated with different concentrations of silver.</p

A spectrum of <i>L</i>. <i>casei</i> recorded using MALDI-TOF MS technique on DHB (top) and HCCA (bottom) matrix; photos of crystals of the matrices are shown in the corner.

<p>A spectrum of <i>L</i>. <i>casei</i> recorded using MALDI-TOF MS technique on DHB (top) and HCCA (bottom) matrix; photos of crystals of the matrices are shown in the corner.</p

Chromatogram of VOCs from <i>L</i>. <i>lactis</i> obtained using HS-SPME-GC/MS, where: (1) acetaldehyde, (2) ethanol, (3) butane, (4) acetone, (5) 2-methylpropanal, (6) ethenyl acetate, (7) 2-butanone, (8) ethyl acetate, (9) hexane, (10) 3-methylbutanal, (11) 1-pentanol, (12) 3-methyl-1-butanol, (13) 2-phenylethyl acetate.

<p>Chromatogram of VOCs from <i>L</i>. <i>lactis</i> obtained using HS-SPME-GC/MS, where: (1) acetaldehyde, (2) ethanol, (3) butane, (4) acetone, (5) 2-methylpropanal, (6) ethenyl acetate, (7) 2-butanone, (8) ethyl acetate, (9) hexane, (10) 3-methylbutanal, (11) 1-pentanol, (12) 3-methyl-1-butanol, (13) 2-phenylethyl acetate.</p

Comparative viability of <i>L</i>. <i>lactis</i> and <i>L</i>. <i>casei</i> cells after the treatment with AgNO₃ (1 ppm) regarding the first (OPTION 1) and the second method (OPTION 2).

<p>Comparative viability of <i>L</i>. <i>lactis</i> and <i>L</i>. <i>casei</i> cells after the treatment with AgNO₃ (1 ppm) regarding the first (OPTION 1) and the second method (OPTION 2).</p

Silver-Lactoferrin Nanocomplexes as a Potent Antimicrobial Agent

The process of silver immobilization onto and/or into bovine lactoferrin (LTF), the physicochemical properties of bovine lactoferrin and obtained silver-lactoferrin complexes, as well as antibacterial activity of silver-lactoferrin complexes were investigated in this work. Kinetic study of the silver immobilization into lactoferrin was carried out using batch sorption techniques. Spectrometric (MALDI-TOF/TOF-MS, ICP-MS), spectroscopic (FTIR, SERS), electron microscopic (TEM) and electrophoretic (I-DE) techniques, as well as zeta potential measurements, were applied for characterization of LTF and binding nature of silver in Ag-LTF complexes. On the basis of the results of the kinetics study, it was established that the silver binding to LTF is a heterogeneous process involving two main stages: (i) internal diffusion and sorption onto external surface of lactoferrin globules; and (ii) internal diffusion and binding into lactoferrin globule structure. Spectroscopic techniques combined with TEM analysis confirmed the binding process. Molecular dynamics (MD) analysis was carried out in order to simulate the mechanism of the binding process, and locate potential binding sites, as well as complement the experimental findings. Quantum mechanics (QM) simulations were performed utilizing density functional theory (DFT) in order to support the reduction mechanism of silver ions to elemental silver. Antimicrobial activity of synthesized lactoferrin complexes against selected clinical bacteria was confirmed using flow cytometry and antibiograms