Bacteria Exposed to Silver Nanoparticles Synthesized by Laser Ablation in Water: Modelling E. coli Growth and Inactivation

Abstract

This study is aimed to better understand the bactericidal mode of action of silver nanoparticles. Here we present the production and characterization of laser-synthesized silver nanoparticles along with growth curves of bacteria treated at sub-minimal and minimal inhibitory concentrations, obtained by optical density measurements. The main effect of the treatment is the increase of the bacterial apparent lag time, which is very well described by the novel growth model as well as the entire growth curves for different concentrations. The main assumption of the model is that the treated bacteria uptake the nanoparticles and inactivate, which results in the decrease of both the nanoparticles and the bacteria concentrations. The lag assumes infinitive value for the minimal inhibitory concentration treatment. This apparent lag phase is not postponed bacterial growth. It is a dynamic state in which the bacterial growth and death rates are close in value. Our results strongly suggest that the predominant mode of antibacterial action of silver nanoparticles is the penetration inside the membrane.

Probing the Mode of Antibacterial Action of Silver Nanoparticles Synthesized by Laser Ablation in Water: What Fluorescence and AFM Data Tell Us

“…Figure 5 c,d prove that cell growth does not cease immediately upon treatment. This finding is in line with the dynamic nature of the population lag as reported in the model of the AgNP-treated E. coli growth [ 45 ], which assumes that cells that have not been inactivated continue to grow during treatment. A broad minimum in viable-cell number for the ½MIC treatment ( Figure 1 a) is also per the model.…”

“…Similarly, the intensity of the fluorescent light on its path out the sample is reduced by the factor , where and are the constants that for a given sample geometry, depend on the wavelength. The UV-visible absorption spectrum of the LAL-synthesized AgNPs exhibits a typical sharp peak at 404 nm due to nanoparticle’s surface plasmon band absorption [ 45 ]. The absorption of the fluorescence light, emitted by DCF at λ = 523 nm, is about half the maximum but is still strong enough to produce the observed fluorescence signal reduction.…”

“…This could be partially related to the difference in the AgNPs colloid properties which depend on the synthesis method. Recently, based on modeling of the growth of AgNP-treated bacteria, we have shown that the antibacterial action of LAL-synthesized AgNPs is closely related to their penetration into the cell [ 45 ] which should be supported by other complementary experimental methods found in the literature. All the above encouraged us to extend our research of bactericidal effects induced by LAL-synthesized AgNPs, produced in our lab.…”

“…The laser synthesis of AgNPs in water and thorough characterization of the produced colloid is described in [ 45 ]. The nanoparticles were determined to be spherical-like with the mean diameter of 13.1 nm (obtained from the transmission electron microscopy (TEM) measurements).…”

“…Cells were further grown for 1.5 h in the same conditions. The minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) of the produced colloid were determined as previously reported [ 45 ]. These experiments were repeated for each colloid production and are reported in terms of volume shares v of the colloid in the batch culture.…”